this is spectacular explanation of N=1 experiments with lots of insights
so excellent data match with personal needs and intuitions, paying attention to how quality of life during day, sleep, performance, recovery look like in these month, adjusting for different training and... yess I think a bit of effort and courage to test something extremely new
Perdonatemi per questo lungo commento, ma leggere e rileggere il vostro blog e ascoltare i podcast stimola davvero la mia piccola mente appassionata di sport!
- Again, congratulations for your dedication, navigating such diet changes in the pursuit of racing goals is purely amazing
- Was there a gradual cut of carbs before December/January or was it more direct process ?
- It would be nice to have the written percentages on the histograms of your macro distribution
- I would also be interested in knowing your energy expenditure at the pace you take for examples in your oxidation rates
- I see that you’re often very low in carbs (<50g) despite training everyday, that’s quite a challenge to go lower 50g of carbs. I guess you must cut off anything starchy and get your carbs from vegetables to stay this low. I will have to start a new love with broccoli if I go this way…
- I see AC back in 2008 having good results with an athlete with still quite a lot of carbs, of course everyone is different, but his strikes me : « I put this athlete on a diet of 400g of CHO/200g of (lean) Protein and 100g of (good) Fat. This represents 3300kcal/day and 48%/24%/28% macronutrient breakdown. Irrespective of whether the diet is eucaloric or not, I have found these percentages to be ideal in the base phase of training. » I have computed my macros this week and I was 39%/21%/39% and I feel like I have plenty of room in terms of fat oxidation (last time I measured I was 0.6 g/min at FatMax…)
- Also DP seems to have some divergent opinion from BS when writing « Remember that exercise duration is the most potent stimulant for fat oxidation; this is above specific macro-nutrient manipulation. » So my remark is that your ability (dedication and lifestyle) to do super long training might also be a key to drive fat oxidation. Do you have data to support that your workout duration distribution has not changed and that weight loss and macronutrients distribution (+strides) were the drivers of your improvement this year ?
- On your hard workouts days, I feel like you still stay under 250g of carbs, am I right ?
- After the 1st of February I am amazed that you are hovering over 2000 kcal only on lighter days. I know BMR and EE during exercise are hard to « measure » but still, it strucks me…
- Do you plan rest days ? I guess you keep the carbs super low when you do no train ?
- I feel like it’s difficult to get my calories needs if I don’t eat often. Do you think it’s even more ok to eat often when you eat fat and protein as snacks vs carbs ?
- I find super interesting that you keep the fat oxidation abilities when having some carbs before exercising, that’s big news to me.
- About LCHF and "LMHR" people, we have already discussed this... the Keto-CTA study has been quite something on socials (the speed of rising of the plaque is stunning !) and I am highly convinced that the keto crowd is falling into cognitive biais when they don't take actions in front of a big LDL-C or CAC score. Frankly, even just thinking of going on Periodized Nutrition and knowing my ability to produce LDL-C, I would put myself on a statin giving that I would rise drastically saturated fats in my diet. I know you have proven with adding a lot of fibers that we can manage LDL with periodized nutrition but my previous experiments show me that I don't reduce much my LDL with psyllium...
- We all crave for more recipes and menu ;) let’s add a cooking section to the blog ;)
- Eventually graze mille for sharing all your journey with us with such dedication. You add Signal in a noisy world of information.
thank you my friend. My question for you, reading this, is the following: are the things that we like, the ones that make us better? :)
Sometimes they are, or for some people they might be (e.g. eating higher amounts of carbs and training many hours, clearly works for some people), but the fact that it works for them, does it mean that it works for us too? In my case the answer is a clear no. Even the story about volume and long duration exercise overriding dietary choices, as you can imagine I'd love for that to be true, but my data shows the opposite: I train high volume, I stay out entire days, and my fat ox sucks, which is not just "about fat ox" it's about how poorly I perform in long races wrt to the short ones, despite training only for the long ones! I changed because of my interest in improving outcomes that matter (health and performance) not because of a metric, but the metric here was indicative of an issue in my metabolism. Hence something needed to change, and this change, made all the difference, as documented in my long-distance performance (and my health) this year.
If your fat ox is good already, it is unlikely that you need to go through the same, but it is too easy to find someone who speaks to our bias and then take that as the right thing to do :)
Happy to discuss more about all the points above when we chat!
First of all, thank you Marco for sharing such a detailed and transparent account.
It’s rare to see a personal case study so well-documented, with data, reflections, and practical tools.
That said, I’d like to raise a few methodological doubts — as an external reader — and I fully acknowledge that I may have misunderstood some aspects or conditions of your testing protocol.
The reported increase in fat oxidation is one of the most intriguing elements, but it’s difficult to confidently attribute it to a chronic adaptation. The test was performed only once, with no true pre/post comparison using an identical protocol, and in a metabolic state likely influenced by at least 2 days of low-carb intake and possibly slight caloric restriction.
These conditions are known to acutely elevate fat oxidation even in the absence of structural (e.g., mitochondrial) adaptations.
Moreover, the improvements in performance metrics (pace, threshold, running economy) appear largely consistent with the 10 kg weight loss, which alone could explain most of the positive physiological changes.
It’s therefore hard to isolate the specific impact of nutrition periodization, especially given concurrent changes in diet quality, training composition, and overall context.
In short, I consider your self-experiment an excellent starting point and an inspiring framework for further exploration, but I believe more robust conclusions would require controlled studies, with standardized pre/post testing and systematic comparisons against alternative strategies (e.g., consistent high-carb, caloric deficit without periodization, etc.).
Thanks again for your work and for openly sharing this journey — it’s rare to see such a thoughtful balance between data, self-awareness, and curiosity for improvement.
thanks! And of course, I agree with the points brought up, I can only document my process and the data collected.
I would stress that there is no performance improvement wrt when I was the same body composition, for distances up to the half marathon, but I do perform much better where first I was limited by my non-existent fat-oxidation (e.g. 50 km or longer), hence I think we have good indications that the change to periodized nutrition resulted in the expected outcome (very specific to a condition in which carbohydrate stores are running out, which is not the case for shorter distances). Keep in mind that when looking at running economy and metabolic flexibility I am comparing to myself when I was the same body composition as now, and running my best times, hence the comparison is not impacted by weight/body composition.
This being said, as you say, this is just my experience, not something that everyone needs to do, especially if their fat-ox is within normal ranges (mine wasn't, hence I might be benefiting more than others) or if they target shorter events.
I'll do plenty of additional testing in the future as I am setting up a lab with a metabolic cart, and I have many questions still to answer :)
Thank you again — your openness and transparency are always truly valuable.
I still have a few doubts, simply because I believe we’re dealing with a field that is inherently complex to interpret.
That said, I deeply appreciate the fact that you’re continuing to test yourself with more precise and replicable tools — it’s the best way to turn personal experience into something useful for others.
In a way, I even envy you for it.
Congratulations once again on your work and the clarity with which you’re pursuing your journey.
thanks Jeff! During hard workouts I normally have a gel mid-session, e.g. if I'm doing a 4 x 2000m, I'd have one after the first two reps, and similarly for other hard sessions. An alternative could be one after the warmup, but normally I fuel them well also with breakfast, hence I tend to eat only during. This has not changed wrt before periodized nutrition. For long, hard runs, e.g. 30-40 km with segments at marathon or 50 km pace, I do fuel a bit differently, and while before I was trying to get to eat 1 gel every 6 km, now I try to get to 1 every 8-9 km, so lowering a bit the frequency and seeing how I do (this is more experimental).
thanks Adam! The deficit was intentional and unrelated to reducing CHO intake, I just thought I needed to get back where I was 2 years prior to this (I had lost much of the weight already before shifting to lower CHO, simply eating high CHO but with a caloric deficit). Maybe it is easier to lose weight on a certain diet, but in my experience it was a similar process to when I did the same years before (also high CHO but caloric deficit, I lost the same weight in the same time I did this year) - so in my experience both macronutrient distributions led to the same outcome in terms of body composition, and the deficit was the only thing that mattered (again, just in my experience, not in general). Here I documented the weight loss because it was part of the process I went through, but I think the interesting part is the macronutrient change and what that brings in terms of fat oxidation, as only the macronutrient change and periodization of CHO led to a huge change in fat ox (while before, even when losing much weight and reducing body fat, I still had fat ox of "zero", as I was eating high carb, and apparently my body works this way - not everyone that eats lots of carbs has poor fat ox, as genetics is always another key factor). I hope this answers your question!
Sure does, thanks for the quick reply. So if I were to start this and want to maintain weight, I just adjust fats and proteins to match my calorie requirements day to day? Depending on training intensity, etc
yes, it has been a few months now that I've been stable in weight (February to today) and the way I think about it from a practical point of view is to start with protein, and then depending on training, add either more carbs (hard day or long day) or else (easy day). I shared recently 2 podcasts that you can find on my feed, where I tried to discuss a bit more also these more practical aspects, should you be interested.
Hi Marco. Very interesting article and insights...as usual with your post. Any suggestion to make an accurate indirect calorimetry test in Italy? Thanks
thanks a lot Antonello! Unfortunately my 'trusted lab' is in Amsterdam, but in theory any exercise science lab that offers testing should be fine, as long as they provide you with the breath-by-breath VO2 and VCO2 data (something important to check before booking the test). Maybe via some private personal trainer or medical center that offers these services in your area.
Fantastic N=1 study and awesome to hear about improvement in blood biomarkers. I completely agree that, especially for folks with genetic predispositions towards high cholesterol (and associated issues), following a low-carb diet without considerations of saturated fats and fiber intake can yield poor markers. And thank you for linking to Dr. Williden's podcast on the subject- I have found her to be a wealth of knowledge regarding nutrition and metabolic flexibility in general. Really trying to get the athletes I work with to buck the trend of "i'm an athlete so I can eat whatever I want" mentality. Thanks for sharing!
Hey Marco! How do you come up with the amount of calories you need each day? Are you wearing/recommending a certain device for that? True calorie needs obviously can not be measured but only estimated, so I was wondering how you assess them? Especially on rest days you might need much more than your watch etc might say, right? Greetings from Innsbruck!
hi Tobias! no device, during the caloric deficit phase I wasn't tracking anything for weeks (not intake nor expenditure), but going by feel. Similarly now I also go by feel and do not track anything. Once we stop eating just because food is around, and overeating at every meal, it's easy to get in tune with our body as it gives you the right cues (i.e. "hunger"). As you say, intake and expenditure estimates are all very inaccurate and I only used a rough estimate for the period in which I tracked manually, which mostly was to learn more about the macros (hence the input I logged in the excel file for a few weeks) and to collect some data for this report. For that purpose, I simply used estimated calories from training and estimated basal metabolic rates from formulas (for expenditure) and the macros from the food I was logging (as intake). The error can be huge, and I would discourage to attempt to track expenditure (people can get quite obsessive, tracking every step they take, which defeats the purpose of getting more in tune with their bodies... !), but again, on my end I wasn't using this for anything practical, at the end of the day you have a tool you can use to see the outcome metric (i.e. check your weight with a scale), and therefore over weeks it was easy to see if I was in deficit or stable. I wasn't trying to hit a deficit of 1000 kcals at the beginning: I simply knew that to drop the weight I had to be hungry at times, which is what I had done also in the past, and when I did the math weeks later, I saw that I was around that number (based on kg lost / week). Now I have been the same weight from February to May, which I do measure a few times per week, as some feedback is useful to keep us on track, but I have not tracked any of my expenditure or intake in months. I think there is something to manually logging intake, we learn a lot from that, but expenditure tracking is mostly inaccurate and can lead people to focus on the numbers as opposed to the body's cues / becoming more aware, which is what I think matters the most. The same argument can be made for the scale, but I think there is a difference between "getting some feedback / output at certain time intervals" and "tracking every second obsessively", it's the same difference I see between a morning HRV measurement (useful) and continuous HRV tracking (total nonsense). I hope this somewhat answers your question!
Thank you for taking your time to answer my question!
To be completely honest, this is exactly what I was hoping to hear from you. I struggle with disordered eating and want to get away from counting calories, because I know how inaccurate it is and because it really ruined my relationship with food, sports and life in the past...
Listening to the body is definitely a skill that needs to be trained. It is not easy, but I am trying my best to fight the ED and relearn to get in touch with my intuition.
It helps me a lot to know that you agree that it is neither sustainable nor necessary to be counting everything we eat. Focusing on macros and quality nutrition, together with adequately fueling our workouts and listening to our bodies are the things that really matter the most.
Thanks again for your answer!! I actually even started a list with people/athletes who I respect or look up to that don't count calories, and I am glad I can put you up on it as well :D
Marco, this was a thorough, non-dogmatic write up. I’m operating under the assumption that you’re only counting net carbohydrates in the above numbers, correct?
thank you Skyler, much appreciated. In these plots I was only counting carbohydrates (regardless of fiber), hence total carbohydrates are reported. Later I shifted to counting net carbohydrates, but this is not included in the reports above (e.g. if I had beans or farro or chia seeds, I counted the total carbohydrates for those foods and logged them). Does this answer your question?
Yes, thank you. I cycle my carbs but end up with a lot of fiber, hence my question.
My background is largely strength/power/fitness (MS Exercise & Sport Science) but I find it interesting that individuals from that side of the world have long used this approach, specifically individuals like John Bernardo PhD.
While the idea of “needing” carbs around training matters “more” for stage events, putting starchy carbs around higher effort workouts, as is often the case in the S&C world, makes so much sense. If you’re an ultra distance athlete training low intensity most of the time, shouldn’t you be protecting your carbs as a function of your relatively high fat max day to day? What do you need massive carbs for on a recovery day?
Those are rhetorical questions at the end. Thank you again!
I have some experience with periods of caloric deficit in my past, and what I found in most cases was a suppression of lactate values at submax intensity which suggests a better fuel economy (didn’t have the possibility to measure fat ox).
Normally what I see after going back to a normal diet is that the values go back to normal.
How much of your results do you think might be due to the caloric deficit compared to the lower carb approach?
What I understood from the literature on lower carb approaches is that once you go back to normal diets the fat ox tends to go back to normal values again, so you would need to protract the diet up until race day. Wouldn’t it be risky (higher immuno-suppression exc)? If doing so, you think one/two days of higher carbs before race would be enough to top up glycogen levels without compromising the fatox values reached with the dietary intervention?
Yes, diet is key. The change in fat ox is entirely due to the diet in this case (I know this because I went through the exact same in the past, losing the same weight, performing similarly, but eating high-carb - just with a high deficit - and my fat ox was near 0). Metablism shifts because of the macro distribution, not because of the weight loss or caloric deficit.
I agree that I need to keep up the diet, otherwise I would revert back to poor fat ox. That's okay, as I think the periodized approach is better also for health (it's the chronic high carb and sugar intake that causes higher inflammation, etc.).
Regardiing timing of the dietary change, unfortunately typically it takes 6-8 weeks to shift metabolism, hence a few days would not do the job and I do need to keep this up until race day. Just to reiterate, I do eat carbs, I just periodize the intake, so typically I have 2 days or 2 days and a half in a week that are higher carb and about 5 days low carb. The exact amounts will depend on the type of training (intensity and duration).
I'm sure others (like yourself) have a much better fat ox than me even on a high carb diet, but for me unfortunately that is not the case, hence I need to periodize a bit more strictly :)
Thank you again and all the best for your training!
Grazie Marco for the article, great job. I actually been through the same process and I got into the lab last Friday. Results were shockingly good as well. I am long distance triathlete and I ate mainly carbs for 36 years (Italian). After 6 weeks of low carbs adaptation and periodisation, my fat oxidation was 3.5x better. I followed Dan Plews LDT01, but slowly migrated to periodisation. I am still struggling to understand what to eat after a training session. I usually go for a protein + Greek yogurt and, if the session is longer/harder, I go for whole wheat bread with peanut butter. However, I keep reading that even with easy sessions, it’s always good to have some carbs if you have proteins. How do you feel about this? Note: most of my pre-training session breakfast consists of 1/2 banana, and that’s it
grazie Alessio! Great to hear you have experienced consistent changes.
I think it's difficult to assess the impact of smaller factors like the exact macros of a post exercise snack, without frequent testing (and we can't really do frequent testing unless we own a lab with indirect calorimetry). On my end I tried to push fat ox as much as possible, but I do think now that we might get away with a smaller stimulus, maybe 2-3 low days per week, 1-2 high days per week, and the rest more moderate (as opposed to staying low 4-5 days per week, which is what I'm still doing). There's something to say also about high-quality food (e.g. carbs that are glycemic index, etc.), such as the ones you bring up, those are likely beneficial for recovery and performance even if they might not push fat ox as high. At the moment when hungry I go also with greek yogurt, or protein powder + peanut butter or nuts or the usual eggs/avocado. All of these things do have some carbs :) I found it relatively easy during base training to stick to the diet but I might need to add more carbs here and there for heavier training blocks, this is something that requires some trial and error and fine tuning, adjustments based on personal preference, etc - my main point here is that we do need to provide the stimulus via the diet, but there is probably no reason to overdo it (just like with high intensity, or anything else really, a little stimulus with high consistency goes a long way!)
Thanks for sharing your case study Marco! It's amazing to see how flexible the body can be in terms of metabolism depending on choices in diet. Personally I like the example that is shown here that it is not high carb always, but nutrition should be considered as part of a periodisation and be used as a tool to drive specific adaptations as well. Both are qualities to have as an athlete.
And above all a glimmer of hope for the "low fat burners": the body will adapt even if the starting point is relatively low.
I wanted to ask about gut health difficulties you have experienced. Are you talking about problems during training or competition, i.e. not being able to fuel sufficiently during exertion, or are you talking about gut health in general everyday life?
hello Jens, in terms of training I never really had issues apart from when racing 100 km (I had problems both times that I ran that long, but it's really hard there to understand the reason behind the issues, given that I do it only once per year and many factors play a role). No issues normally during training or other races, apart from maybe nausea during marathons, but that's also a bit of a different story when pushing our limits (it would not happen if not racing for a personal best, and it would not happen for the many 3-6 hours runs I did in training over the years)
my concern was more with general everyday life, as I had various problems last summer and then again last autumn, and I wasn't able to link it to anything in particular. I had stomach pain, needed to go way too often to the bathroom, etc. - for weeks at a time - but again, no specific food allergies or else. I was functioning well both in life and training even back then (meaning that I didn't feel tired or fatigued or anything, I didn't feel sick so to speak, but obviously, "not a nice experience", especially when it lasts weeks). The issues are gone now since I changed diet, and everything seems to work the way it should with my gut health. I have to say that the few days that I loaded on lower quality carbs, I still experienced some of those symptoms, hence maybe something there (?). This is also why I am trying now to load with higher quality carbs and see if I can find the right mix of foods for both low carb and high carb days, that would make me not only perform well, but also have none of those issues outside of training.
I see! So, it sounds like the change in diet was motivated by factors beyond just pure performance, meaning it might not apply universally to all athletes.
I’m asking because I want to evaluate whether the benefits are significant enough for me to make a more conscious effort in managing my diet throughout the week. The idea of a "fuel for what you need" approach makes sense, but I still need to research more to determine its overall value for me.
In my case, I see two potential benefits:
- It could help me lose some weight during a training phase.
- It might improve my race performance (5–10 hour ultras) by reducing reliance on exogenous carbs.
thanks Jens, that makes sense to me. There could be also something in terms of reducing inflammation (a likely result of low quality and high carb diets typical of endurance athletes), for recovery and performance long term. All the best!
Thank you for sharing this Marco. It’s extremely interesting to read your case study and the insightful background you have provided. I’ve been following with interest your posts about this for the last few weeks. Your results are very encouraging and I am definitely going to try a more periodised approach. I’ve experimented with low carb in the past and had less GI issues, but not performed as well, feeling more tired than with a higher carb diet. My events are in June and September so hopefully I’ve time to experiment.
thank you Steve, I really appreciate the support. Indeed my gut health and energy levels in general seem much better now, but I do see that loading on (higher quality) carbs is quite essential to execute workouts well (at least for me!). All the best for your training and events
Many thanks Marco. I noted your points about loading with higher quality carbs and I’ve started to do this. Good luck in your training too and for the Passatore
Hey Marco, enormously interesting. I've adopted a "fuel for the work required, otherwise be responsive to hunger" approach to my diet over the past few years, but haven't played around with varying the type of fuel. I certainly will be now.
A couple of questions from me:
- How would you approach fueling a gym session, in which you were doing compound lifts and plyometrics? My instinct would be to eat carbs beforehand
- How would you approach fueling during a "return to training" phase following an injury?
thanks Luke! It sounds like you had a very sensible approach.
Regarding gym sessions, I would be inclined to agree, as you are doing activities that require quick energy, even though maybe it depends also on how much work you are doing (for a few short high intensity efforts we use the phosphocreatine system to generate ATP and therefore do not really need more carbs - this is similar to when I do hill sprints, I go all out for 8-10" and always do these sessions on low-carb days, but it's only 8-10 sprints with a very slow jog of 5 minutes in between, to get the system up and running again). If your volume is higher then probably more carbs would help (just some considerations, this is not my area of expertise after all).
Return to training: the focus should be really on listening to our body and rebuilding load slowly, using nutrition as support (e.g. adequate protein for muscle repair), but we are also unlikely to require many carbs as volume and intensity will be low. I would however in this case be cautious and definitely not go in caloric deficit, hence better to have a little more than a little less than what we need in this case, otherwise we risk to mess it up big time (in my opinion!).
Congrats on your results, Marco! The data is incredibly helpful to drive home the impact. I don’t have a race until August and will be in the base building phase for a few months, so definitely going to give this a go and see how the bike/run power/effort changes
this is spectacular explanation of N=1 experiments with lots of insights
so excellent data match with personal needs and intuitions, paying attention to how quality of life during day, sleep, performance, recovery look like in these month, adjusting for different training and... yess I think a bit of effort and courage to test something extremely new
chapeau @marco :))))))))
Grazie Ilaria! Really appreciate the kind words from you 🙏
I trust in N= 1 experiments with integration of data, intuitions and feelings!!! A must read
Ciao Marco,
Perdonatemi per questo lungo commento, ma leggere e rileggere il vostro blog e ascoltare i podcast stimola davvero la mia piccola mente appassionata di sport!
- Again, congratulations for your dedication, navigating such diet changes in the pursuit of racing goals is purely amazing
- Was there a gradual cut of carbs before December/January or was it more direct process ?
- It would be nice to have the written percentages on the histograms of your macro distribution
- I would also be interested in knowing your energy expenditure at the pace you take for examples in your oxidation rates
- I see that you’re often very low in carbs (<50g) despite training everyday, that’s quite a challenge to go lower 50g of carbs. I guess you must cut off anything starchy and get your carbs from vegetables to stay this low. I will have to start a new love with broccoli if I go this way…
- I see AC back in 2008 having good results with an athlete with still quite a lot of carbs, of course everyone is different, but his strikes me : « I put this athlete on a diet of 400g of CHO/200g of (lean) Protein and 100g of (good) Fat. This represents 3300kcal/day and 48%/24%/28% macronutrient breakdown. Irrespective of whether the diet is eucaloric or not, I have found these percentages to be ideal in the base phase of training. » I have computed my macros this week and I was 39%/21%/39% and I feel like I have plenty of room in terms of fat oxidation (last time I measured I was 0.6 g/min at FatMax…)
- Also DP seems to have some divergent opinion from BS when writing « Remember that exercise duration is the most potent stimulant for fat oxidation; this is above specific macro-nutrient manipulation. » So my remark is that your ability (dedication and lifestyle) to do super long training might also be a key to drive fat oxidation. Do you have data to support that your workout duration distribution has not changed and that weight loss and macronutrients distribution (+strides) were the drivers of your improvement this year ?
- On your hard workouts days, I feel like you still stay under 250g of carbs, am I right ?
- After the 1st of February I am amazed that you are hovering over 2000 kcal only on lighter days. I know BMR and EE during exercise are hard to « measure » but still, it strucks me…
- Do you plan rest days ? I guess you keep the carbs super low when you do no train ?
- I feel like it’s difficult to get my calories needs if I don’t eat often. Do you think it’s even more ok to eat often when you eat fat and protein as snacks vs carbs ?
- I find super interesting that you keep the fat oxidation abilities when having some carbs before exercising, that’s big news to me.
- About LCHF and "LMHR" people, we have already discussed this... the Keto-CTA study has been quite something on socials (the speed of rising of the plaque is stunning !) and I am highly convinced that the keto crowd is falling into cognitive biais when they don't take actions in front of a big LDL-C or CAC score. Frankly, even just thinking of going on Periodized Nutrition and knowing my ability to produce LDL-C, I would put myself on a statin giving that I would rise drastically saturated fats in my diet. I know you have proven with adding a lot of fibers that we can manage LDL with periodized nutrition but my previous experiments show me that I don't reduce much my LDL with psyllium...
- We all crave for more recipes and menu ;) let’s add a cooking section to the blog ;)
- Eventually graze mille for sharing all your journey with us with such dedication. You add Signal in a noisy world of information.
thank you my friend. My question for you, reading this, is the following: are the things that we like, the ones that make us better? :)
Sometimes they are, or for some people they might be (e.g. eating higher amounts of carbs and training many hours, clearly works for some people), but the fact that it works for them, does it mean that it works for us too? In my case the answer is a clear no. Even the story about volume and long duration exercise overriding dietary choices, as you can imagine I'd love for that to be true, but my data shows the opposite: I train high volume, I stay out entire days, and my fat ox sucks, which is not just "about fat ox" it's about how poorly I perform in long races wrt to the short ones, despite training only for the long ones! I changed because of my interest in improving outcomes that matter (health and performance) not because of a metric, but the metric here was indicative of an issue in my metabolism. Hence something needed to change, and this change, made all the difference, as documented in my long-distance performance (and my health) this year.
If your fat ox is good already, it is unlikely that you need to go through the same, but it is too easy to find someone who speaks to our bias and then take that as the right thing to do :)
Happy to discuss more about all the points above when we chat!
So much to explore then…
First of all, thank you Marco for sharing such a detailed and transparent account.
It’s rare to see a personal case study so well-documented, with data, reflections, and practical tools.
That said, I’d like to raise a few methodological doubts — as an external reader — and I fully acknowledge that I may have misunderstood some aspects or conditions of your testing protocol.
The reported increase in fat oxidation is one of the most intriguing elements, but it’s difficult to confidently attribute it to a chronic adaptation. The test was performed only once, with no true pre/post comparison using an identical protocol, and in a metabolic state likely influenced by at least 2 days of low-carb intake and possibly slight caloric restriction.
These conditions are known to acutely elevate fat oxidation even in the absence of structural (e.g., mitochondrial) adaptations.
Moreover, the improvements in performance metrics (pace, threshold, running economy) appear largely consistent with the 10 kg weight loss, which alone could explain most of the positive physiological changes.
It’s therefore hard to isolate the specific impact of nutrition periodization, especially given concurrent changes in diet quality, training composition, and overall context.
In short, I consider your self-experiment an excellent starting point and an inspiring framework for further exploration, but I believe more robust conclusions would require controlled studies, with standardized pre/post testing and systematic comparisons against alternative strategies (e.g., consistent high-carb, caloric deficit without periodization, etc.).
Thanks again for your work and for openly sharing this journey — it’s rare to see such a thoughtful balance between data, self-awareness, and curiosity for improvement.
thanks! And of course, I agree with the points brought up, I can only document my process and the data collected.
I would stress that there is no performance improvement wrt when I was the same body composition, for distances up to the half marathon, but I do perform much better where first I was limited by my non-existent fat-oxidation (e.g. 50 km or longer), hence I think we have good indications that the change to periodized nutrition resulted in the expected outcome (very specific to a condition in which carbohydrate stores are running out, which is not the case for shorter distances). Keep in mind that when looking at running economy and metabolic flexibility I am comparing to myself when I was the same body composition as now, and running my best times, hence the comparison is not impacted by weight/body composition.
This being said, as you say, this is just my experience, not something that everyone needs to do, especially if their fat-ox is within normal ranges (mine wasn't, hence I might be benefiting more than others) or if they target shorter events.
I'll do plenty of additional testing in the future as I am setting up a lab with a metabolic cart, and I have many questions still to answer :)
Thanks again for reading and for your thoughts!
Thank you again — your openness and transparency are always truly valuable.
I still have a few doubts, simply because I believe we’re dealing with a field that is inherently complex to interpret.
That said, I deeply appreciate the fact that you’re continuing to test yourself with more precise and replicable tools — it’s the best way to turn personal experience into something useful for others.
In a way, I even envy you for it.
Congratulations once again on your work and the clarity with which you’re pursuing your journey.
All the best,
Lorenzo
Hey Marco, great article, thank you. Can you talk about how you fuel during workouts that have intensity?
thanks Jeff! During hard workouts I normally have a gel mid-session, e.g. if I'm doing a 4 x 2000m, I'd have one after the first two reps, and similarly for other hard sessions. An alternative could be one after the warmup, but normally I fuel them well also with breakfast, hence I tend to eat only during. This has not changed wrt before periodized nutrition. For long, hard runs, e.g. 30-40 km with segments at marathon or 50 km pace, I do fuel a bit differently, and while before I was trying to get to eat 1 gel every 6 km, now I try to get to 1 every 8-9 km, so lowering a bit the frequency and seeing how I do (this is more experimental).
Was the calorie deficit intentional to lose weight? Or was it a consequence of reducing CHO intake?
This is fascinating and I will be trying this out on myself, as I have access to a full metabolic cart at work.
thanks Adam! The deficit was intentional and unrelated to reducing CHO intake, I just thought I needed to get back where I was 2 years prior to this (I had lost much of the weight already before shifting to lower CHO, simply eating high CHO but with a caloric deficit). Maybe it is easier to lose weight on a certain diet, but in my experience it was a similar process to when I did the same years before (also high CHO but caloric deficit, I lost the same weight in the same time I did this year) - so in my experience both macronutrient distributions led to the same outcome in terms of body composition, and the deficit was the only thing that mattered (again, just in my experience, not in general). Here I documented the weight loss because it was part of the process I went through, but I think the interesting part is the macronutrient change and what that brings in terms of fat oxidation, as only the macronutrient change and periodization of CHO led to a huge change in fat ox (while before, even when losing much weight and reducing body fat, I still had fat ox of "zero", as I was eating high carb, and apparently my body works this way - not everyone that eats lots of carbs has poor fat ox, as genetics is always another key factor). I hope this answers your question!
Thanks again Marco! Much appreciated
Sure does, thanks for the quick reply. So if I were to start this and want to maintain weight, I just adjust fats and proteins to match my calorie requirements day to day? Depending on training intensity, etc
yes, it has been a few months now that I've been stable in weight (February to today) and the way I think about it from a practical point of view is to start with protein, and then depending on training, add either more carbs (hard day or long day) or else (easy day). I shared recently 2 podcasts that you can find on my feed, where I tried to discuss a bit more also these more practical aspects, should you be interested.
Hi Marco. Very interesting article and insights...as usual with your post. Any suggestion to make an accurate indirect calorimetry test in Italy? Thanks
thanks a lot Antonello! Unfortunately my 'trusted lab' is in Amsterdam, but in theory any exercise science lab that offers testing should be fine, as long as they provide you with the breath-by-breath VO2 and VCO2 data (something important to check before booking the test). Maybe via some private personal trainer or medical center that offers these services in your area.
Fantastic N=1 study and awesome to hear about improvement in blood biomarkers. I completely agree that, especially for folks with genetic predispositions towards high cholesterol (and associated issues), following a low-carb diet without considerations of saturated fats and fiber intake can yield poor markers. And thank you for linking to Dr. Williden's podcast on the subject- I have found her to be a wealth of knowledge regarding nutrition and metabolic flexibility in general. Really trying to get the athletes I work with to buck the trend of "i'm an athlete so I can eat whatever I want" mentality. Thanks for sharing!
thank you Mikki!
Hey Marco! How do you come up with the amount of calories you need each day? Are you wearing/recommending a certain device for that? True calorie needs obviously can not be measured but only estimated, so I was wondering how you assess them? Especially on rest days you might need much more than your watch etc might say, right? Greetings from Innsbruck!
hi Tobias! no device, during the caloric deficit phase I wasn't tracking anything for weeks (not intake nor expenditure), but going by feel. Similarly now I also go by feel and do not track anything. Once we stop eating just because food is around, and overeating at every meal, it's easy to get in tune with our body as it gives you the right cues (i.e. "hunger"). As you say, intake and expenditure estimates are all very inaccurate and I only used a rough estimate for the period in which I tracked manually, which mostly was to learn more about the macros (hence the input I logged in the excel file for a few weeks) and to collect some data for this report. For that purpose, I simply used estimated calories from training and estimated basal metabolic rates from formulas (for expenditure) and the macros from the food I was logging (as intake). The error can be huge, and I would discourage to attempt to track expenditure (people can get quite obsessive, tracking every step they take, which defeats the purpose of getting more in tune with their bodies... !), but again, on my end I wasn't using this for anything practical, at the end of the day you have a tool you can use to see the outcome metric (i.e. check your weight with a scale), and therefore over weeks it was easy to see if I was in deficit or stable. I wasn't trying to hit a deficit of 1000 kcals at the beginning: I simply knew that to drop the weight I had to be hungry at times, which is what I had done also in the past, and when I did the math weeks later, I saw that I was around that number (based on kg lost / week). Now I have been the same weight from February to May, which I do measure a few times per week, as some feedback is useful to keep us on track, but I have not tracked any of my expenditure or intake in months. I think there is something to manually logging intake, we learn a lot from that, but expenditure tracking is mostly inaccurate and can lead people to focus on the numbers as opposed to the body's cues / becoming more aware, which is what I think matters the most. The same argument can be made for the scale, but I think there is a difference between "getting some feedback / output at certain time intervals" and "tracking every second obsessively", it's the same difference I see between a morning HRV measurement (useful) and continuous HRV tracking (total nonsense). I hope this somewhat answers your question!
Thank you for taking your time to answer my question!
To be completely honest, this is exactly what I was hoping to hear from you. I struggle with disordered eating and want to get away from counting calories, because I know how inaccurate it is and because it really ruined my relationship with food, sports and life in the past...
Listening to the body is definitely a skill that needs to be trained. It is not easy, but I am trying my best to fight the ED and relearn to get in touch with my intuition.
It helps me a lot to know that you agree that it is neither sustainable nor necessary to be counting everything we eat. Focusing on macros and quality nutrition, together with adequately fueling our workouts and listening to our bodies are the things that really matter the most.
Thanks again for your answer!! I actually even started a list with people/athletes who I respect or look up to that don't count calories, and I am glad I can put you up on it as well :D
thank you Tobias! Wishing you all the best
Marco, this was a thorough, non-dogmatic write up. I’m operating under the assumption that you’re only counting net carbohydrates in the above numbers, correct?
thank you Skyler, much appreciated. In these plots I was only counting carbohydrates (regardless of fiber), hence total carbohydrates are reported. Later I shifted to counting net carbohydrates, but this is not included in the reports above (e.g. if I had beans or farro or chia seeds, I counted the total carbohydrates for those foods and logged them). Does this answer your question?
Yes, thank you. I cycle my carbs but end up with a lot of fiber, hence my question.
My background is largely strength/power/fitness (MS Exercise & Sport Science) but I find it interesting that individuals from that side of the world have long used this approach, specifically individuals like John Bernardo PhD.
While the idea of “needing” carbs around training matters “more” for stage events, putting starchy carbs around higher effort workouts, as is often the case in the S&C world, makes so much sense. If you’re an ultra distance athlete training low intensity most of the time, shouldn’t you be protecting your carbs as a function of your relatively high fat max day to day? What do you need massive carbs for on a recovery day?
Those are rhetorical questions at the end. Thank you again!
Hello Marco, really interesting article.
I have some experience with periods of caloric deficit in my past, and what I found in most cases was a suppression of lactate values at submax intensity which suggests a better fuel economy (didn’t have the possibility to measure fat ox).
Normally what I see after going back to a normal diet is that the values go back to normal.
How much of your results do you think might be due to the caloric deficit compared to the lower carb approach?
What I understood from the literature on lower carb approaches is that once you go back to normal diets the fat ox tends to go back to normal values again, so you would need to protract the diet up until race day. Wouldn’t it be risky (higher immuno-suppression exc)? If doing so, you think one/two days of higher carbs before race would be enough to top up glycogen levels without compromising the fatox values reached with the dietary intervention?
Thanks!
ciao Mattia!
Yes, diet is key. The change in fat ox is entirely due to the diet in this case (I know this because I went through the exact same in the past, losing the same weight, performing similarly, but eating high-carb - just with a high deficit - and my fat ox was near 0). Metablism shifts because of the macro distribution, not because of the weight loss or caloric deficit.
I agree that I need to keep up the diet, otherwise I would revert back to poor fat ox. That's okay, as I think the periodized approach is better also for health (it's the chronic high carb and sugar intake that causes higher inflammation, etc.).
Regardiing timing of the dietary change, unfortunately typically it takes 6-8 weeks to shift metabolism, hence a few days would not do the job and I do need to keep this up until race day. Just to reiterate, I do eat carbs, I just periodize the intake, so typically I have 2 days or 2 days and a half in a week that are higher carb and about 5 days low carb. The exact amounts will depend on the type of training (intensity and duration).
I'm sure others (like yourself) have a much better fat ox than me even on a high carb diet, but for me unfortunately that is not the case, hence I need to periodize a bit more strictly :)
Thank you again and all the best for your training!
Grazie Marco for the article, great job. I actually been through the same process and I got into the lab last Friday. Results were shockingly good as well. I am long distance triathlete and I ate mainly carbs for 36 years (Italian). After 6 weeks of low carbs adaptation and periodisation, my fat oxidation was 3.5x better. I followed Dan Plews LDT01, but slowly migrated to periodisation. I am still struggling to understand what to eat after a training session. I usually go for a protein + Greek yogurt and, if the session is longer/harder, I go for whole wheat bread with peanut butter. However, I keep reading that even with easy sessions, it’s always good to have some carbs if you have proteins. How do you feel about this? Note: most of my pre-training session breakfast consists of 1/2 banana, and that’s it
grazie Alessio! Great to hear you have experienced consistent changes.
I think it's difficult to assess the impact of smaller factors like the exact macros of a post exercise snack, without frequent testing (and we can't really do frequent testing unless we own a lab with indirect calorimetry). On my end I tried to push fat ox as much as possible, but I do think now that we might get away with a smaller stimulus, maybe 2-3 low days per week, 1-2 high days per week, and the rest more moderate (as opposed to staying low 4-5 days per week, which is what I'm still doing). There's something to say also about high-quality food (e.g. carbs that are glycemic index, etc.), such as the ones you bring up, those are likely beneficial for recovery and performance even if they might not push fat ox as high. At the moment when hungry I go also with greek yogurt, or protein powder + peanut butter or nuts or the usual eggs/avocado. All of these things do have some carbs :) I found it relatively easy during base training to stick to the diet but I might need to add more carbs here and there for heavier training blocks, this is something that requires some trial and error and fine tuning, adjustments based on personal preference, etc - my main point here is that we do need to provide the stimulus via the diet, but there is probably no reason to overdo it (just like with high intensity, or anything else really, a little stimulus with high consistency goes a long way!)
Thanks for sharing your case study Marco! It's amazing to see how flexible the body can be in terms of metabolism depending on choices in diet. Personally I like the example that is shown here that it is not high carb always, but nutrition should be considered as part of a periodisation and be used as a tool to drive specific adaptations as well. Both are qualities to have as an athlete.
And above all a glimmer of hope for the "low fat burners": the body will adapt even if the starting point is relatively low.
exactly! thank you Bart
I wanted to ask about gut health difficulties you have experienced. Are you talking about problems during training or competition, i.e. not being able to fuel sufficiently during exertion, or are you talking about gut health in general everyday life?
hello Jens, in terms of training I never really had issues apart from when racing 100 km (I had problems both times that I ran that long, but it's really hard there to understand the reason behind the issues, given that I do it only once per year and many factors play a role). No issues normally during training or other races, apart from maybe nausea during marathons, but that's also a bit of a different story when pushing our limits (it would not happen if not racing for a personal best, and it would not happen for the many 3-6 hours runs I did in training over the years)
my concern was more with general everyday life, as I had various problems last summer and then again last autumn, and I wasn't able to link it to anything in particular. I had stomach pain, needed to go way too often to the bathroom, etc. - for weeks at a time - but again, no specific food allergies or else. I was functioning well both in life and training even back then (meaning that I didn't feel tired or fatigued or anything, I didn't feel sick so to speak, but obviously, "not a nice experience", especially when it lasts weeks). The issues are gone now since I changed diet, and everything seems to work the way it should with my gut health. I have to say that the few days that I loaded on lower quality carbs, I still experienced some of those symptoms, hence maybe something there (?). This is also why I am trying now to load with higher quality carbs and see if I can find the right mix of foods for both low carb and high carb days, that would make me not only perform well, but also have none of those issues outside of training.
I see! So, it sounds like the change in diet was motivated by factors beyond just pure performance, meaning it might not apply universally to all athletes.
I’m asking because I want to evaluate whether the benefits are significant enough for me to make a more conscious effort in managing my diet throughout the week. The idea of a "fuel for what you need" approach makes sense, but I still need to research more to determine its overall value for me.
In my case, I see two potential benefits:
- It could help me lose some weight during a training phase.
- It might improve my race performance (5–10 hour ultras) by reducing reliance on exogenous carbs.
thanks Jens, that makes sense to me. There could be also something in terms of reducing inflammation (a likely result of low quality and high carb diets typical of endurance athletes), for recovery and performance long term. All the best!
Thank you for sharing this Marco. It’s extremely interesting to read your case study and the insightful background you have provided. I’ve been following with interest your posts about this for the last few weeks. Your results are very encouraging and I am definitely going to try a more periodised approach. I’ve experimented with low carb in the past and had less GI issues, but not performed as well, feeling more tired than with a higher carb diet. My events are in June and September so hopefully I’ve time to experiment.
thank you Steve, I really appreciate the support. Indeed my gut health and energy levels in general seem much better now, but I do see that loading on (higher quality) carbs is quite essential to execute workouts well (at least for me!). All the best for your training and events
Many thanks Marco. I noted your points about loading with higher quality carbs and I’ve started to do this. Good luck in your training too and for the Passatore
Hey Marco, enormously interesting. I've adopted a "fuel for the work required, otherwise be responsive to hunger" approach to my diet over the past few years, but haven't played around with varying the type of fuel. I certainly will be now.
A couple of questions from me:
- How would you approach fueling a gym session, in which you were doing compound lifts and plyometrics? My instinct would be to eat carbs beforehand
- How would you approach fueling during a "return to training" phase following an injury?
thanks Luke! It sounds like you had a very sensible approach.
Regarding gym sessions, I would be inclined to agree, as you are doing activities that require quick energy, even though maybe it depends also on how much work you are doing (for a few short high intensity efforts we use the phosphocreatine system to generate ATP and therefore do not really need more carbs - this is similar to when I do hill sprints, I go all out for 8-10" and always do these sessions on low-carb days, but it's only 8-10 sprints with a very slow jog of 5 minutes in between, to get the system up and running again). If your volume is higher then probably more carbs would help (just some considerations, this is not my area of expertise after all).
Return to training: the focus should be really on listening to our body and rebuilding load slowly, using nutrition as support (e.g. adequate protein for muscle repair), but we are also unlikely to require many carbs as volume and intensity will be low. I would however in this case be cautious and definitely not go in caloric deficit, hence better to have a little more than a little less than what we need in this case, otherwise we risk to mess it up big time (in my opinion!).
I hope this makes sense to you
That all makes sense, thanks for sharing your thoughts!
Congrats on your results, Marco! The data is incredibly helpful to drive home the impact. I don’t have a race until August and will be in the base building phase for a few months, so definitely going to give this a go and see how the bike/run power/effort changes
thank you Kevin! All the best for your training