I think "training low" has benefits but testing fat oxidation during exercise can be dominated by recent fat:cho intake ratios... so a short term high cho intake can mask underlying high fat ox capabilities (and vice versa).
Also, utilizing cho oxidatively, by increasing slow twitch lactate usage, could be damaged on low carb.
thanks Dan, I agree that it's hard to ger reliable numbers when periodizing carbs, especially with this type of testing (which given the need for indirect calorimetry, can only be sporadic).
I am thinking to test on a relatively low carb day (which is my normal day now - even though very far from a keto diet), and then after cho ingestion (limited, e.g. one gel, then test after ~20 minutes), mostly to try to see some of these acute changes.
A large cho-based breakfast would however likely have yet another impact.
Eventually we can only try to get some indications of how things are changing based on training and diet, without relying too much on the actual numbers (or extrapolating from them).
This article is almost as if I wrote it myself. I am mid 40s, until about 3 years ago my weight was somewhere between 90 and 95Kg and had been for years, but I began a weight loss journey in January 2022 (didn't follow any programme, I simply ate less) and came down to about 74Kg by late 2022 over the past 2 years, I've been sat somewhere between 70 and 73Kg, very occasionally outside of those parameters. I'm 72Kg now, but my body fat is higher than it was a couple of years ago. I'm not concerned about my weight, but I want to reduce my body fat levels and as counterintuitive as it sounds, I'm adopting a low carb diet rather than my typical 'all the carbs' diet, and really giving focus to protein intake. I like Alan Couzen's guide - 50g of CHO per day baseline, plus 100g of CHO per hour of exercise at what he calls zone 1. (50g of CHO is hard work!!!). I'm also doing my easy runs before breakfast to try and encourage my body to burn fat rather than the sugars floating around. (The rule I set was 1 hour easy run, no breakfast - but today I got to the end of the hour, pace was good, HR was good, fatigue was non-existent and so kept going - 90 minutes/15km in the end, including four sets of hard intensity hill repeats at the end). This, I feel, is a good sign. For my long easy run (planning 2h45 on Wednesday), I will have breakfast and wait 2 hours before my run, and take CHO on during my run, but less than usual - I tend to get extremely fatigued even when running very easy HR at these times. As I have a marathon planned for late April, my hope is to gradually increase my easy long run duration closer to 4 hours before huge leg fatigue kicks in - after all, if I can't run for 4 hours at easy intensity, then what chance of running 4 hours at marathon pace.
I expect that despite huge amounts of low speed training as a proportion of my weekly running, my fat oxidation levels are virtually non-existent.
I've also noticed in the days since reducing calorie intake, restricting carbs, increasing protein that my overnight HRV has increased substantially and my overnight resting heart rate has also dropped (41 last night, apparently).
This is a very interesting blog you have and I love seeing your regular updates on Strava.
thank you Ian, this is great to read, and indeed even without counting but using a bit of common sense, I think we end up doing similar things (also in terms of CHO/day + CHO/training). Alan wrote some really nice blogs already many years ago about this (I found also Dan Plews' work very relevant). All fascinating stuff. Let's see how it goes for the both of us, all the best for your training!
Hey Marco - am I reading your substrate graph correctly. At 60% of VO2Max, you are burning 2.5 cals/min out of a total of 15 cals/min? Meaning you are burning roughly 16% fat and 84% carbs? That seems absurdly low. I have never seen such low levels in the athletes that I coach. I must be reading this graph incorrectly...
many years of training have been useful to improve economy to 'normal' levels, but I am now trying to see if fat oxidation can be better improved with dietary changes as well. I did book a lab test for the end of February, so we'll find out soon
Wow. Well I’m glad you’ve been able to chip away at that. No one can claim you don’t love running after sticking with it with 6 years without improvement! I’ll be curious to see your results on February!
Great article, Marco, look forward to reading of your progress. I think a podcast between yourself and Zac Bitter would be enlightening based on his history of performance utilising the same approach you are.
hi Eric! The old data comes from a Cosmed K4b2 (indirect calorimeter I was using during my PhD studies). The more recent data comes from another metabolic cart from a lab I used in Amsterdam (not sure about the brand).
not familiar with Lumen (but I have strong doubts now that I looked it up ..), while Calibre can only be used at rest (I had a call with them and the sensors cannot work in conditions like running). Even the more expensive (but still cheap for this type of technology) ones, like VO2master, have not shown to be particularly good (and this one in particular doesn't even have a sensor for CO2, so it would not be useful for substrate utilization). I'd love to get more frequent measurements while doing this experiment, but the barrier is quite high for valid technology when it comes to measuring VO2/VCO2, unfortunately (the Cosmed is 30K or more!). Best case scenario I will go to a lab in spring for some testing..
Hi Marco, wow this is exactly what I am doing. Whilst I have raced well I know there is more. I have been eating low carb now in this base phase for 6 weeks and it’s 100% working. I feel less hungry and on my longer bike workouts I have to force myself to eat now.
Question, what are you eating on your long runs? I have decided to eat a trail mix (nuts, dried banana, sultanas etc) I am trying to stay away from the sugary carb drinks.
thanks Dan, great to hear about your experience. For now during easy runs I have been eating dried fruit (like figs or apricots), or regular fruit (a banana), while for workouts I am using gels like before. I'm still trying to understand what I need, I do feel a lot less hungry but likely require a bit of trial and error to make sure I can keep training well week after week
It’s funny because in my race prep I’ve said to myself I will still go high carb. But the more i think about it I wonder if that’s really needed. I will do some Ironman simulation workouts and see what’s possible.
Good luck and thanks for posting this.. it’s always good to hear these things from respected people such as yourself.
Hi Marco. Are you going to include fasting into low carb period? I have been training approximately for 2 ½ years for almost 90-95 percent of my weekly hours (about 12 hours total training) at z1-z2 with a low carb high fat dietary, and for a long time i used to fast for 14-16 hours, where i included and my low intensity training. I saw big gains improving fat oxidation, such as a big drop in my heart rate at a given pace (In the beggining i ran about 6m/klm at 130 bpm and now i run 6m/klm at 112bpm). I like the trail ultra races and i have improve a lot in energy consumption and aerobic efficiency which in turn my race times drop significantly. Low carb high fat diet with fasting and a LOT of low intensity training did the job for me.
thanks Nikos. Really interesting to read your experience. At the moment I do not plan to include fasting, mostly because I've already made a large change and I need to take it step by step (I don't exclude that it will be easier to do so in the future).
If you do not mind, I'd be curious about the following: how do you fuel your long training runs? and similarly, how do you fuel your races? thank you for your time!
It depends mainly on the effort and intensity that I will introduce into the long run training. In any case, in a completely easy effort and low-intensity training I will consume, usually starting after 2 hours, a low-carb mixture of 500 milliliters. If the training lasts from 3.5-4 hours and more, then I will also consume bars that will also contain a little protein, perhaps and a few dates. If now, I add to the long training some time in Z3 or even a few minutes in Z4, then I will also consume a couple of gels. In the races, I consume about every half hour sips of the carbohydrate mixture that I carry in my vest and in both flasks, and about every 2 hours a bar or waffle. I also eat and drink, selectively, from the race's supply stations. In general, this is my diet, but I've been looking into it a lot lately to improve it since I haven't done a laboratory analysis.
I really enjoy your writing, and your approach to your training is very what drives innovative and applicable methods for people to live & move better. You’re a bright light Marco! Thank you!
Hey Marco, thank you very much for your interesting article!
Two questions:
- Do you have examples of lower-carb plates/recipes that suit well before training as usually fats take a higher time to digest than carbs?
- I often question myself on the type of foods we eat (like wholegrain, organic, less-processed...) in comparison to just looking in terms of macros. It's often overlooked but I am fairly convinced that it can also play a role into how our physiology and metabolic flexibilty work. It's a point that Kilian discusses in his interview on the training science podcast...
Looking forward to see your results and happy training!
1) at the moment for breakfast I am rotating between an omelet (e.g. with tomatoes, avocado and some cheese) and greek yogurt with berries and nuts, or fresh cheese. I haven't experienced problems in training but I typically wait an hour or two before going out.
2) agreed. I find that when focusing on my diet more (regardless of low carb or not), it comes natural to eat better foods, so I have not touched on it here, but I do agree that it's not only about macronutrients.
That’s great to hear you’re transitioning to a low-carb diet! Are you planning to take a baseline blood test to track your progress? Testing markers like fasting insulin, blood glucose, and HbA1c can provide valuable insights into how your body responds to the changes.
I think "training low" has benefits but testing fat oxidation during exercise can be dominated by recent fat:cho intake ratios... so a short term high cho intake can mask underlying high fat ox capabilities (and vice versa).
Also, utilizing cho oxidatively, by increasing slow twitch lactate usage, could be damaged on low carb.
thanks Dan, I agree that it's hard to ger reliable numbers when periodizing carbs, especially with this type of testing (which given the need for indirect calorimetry, can only be sporadic).
I am thinking to test on a relatively low carb day (which is my normal day now - even though very far from a keto diet), and then after cho ingestion (limited, e.g. one gel, then test after ~20 minutes), mostly to try to see some of these acute changes.
A large cho-based breakfast would however likely have yet another impact.
Eventually we can only try to get some indications of how things are changing based on training and diet, without relying too much on the actual numbers (or extrapolating from them).
This article is almost as if I wrote it myself. I am mid 40s, until about 3 years ago my weight was somewhere between 90 and 95Kg and had been for years, but I began a weight loss journey in January 2022 (didn't follow any programme, I simply ate less) and came down to about 74Kg by late 2022 over the past 2 years, I've been sat somewhere between 70 and 73Kg, very occasionally outside of those parameters. I'm 72Kg now, but my body fat is higher than it was a couple of years ago. I'm not concerned about my weight, but I want to reduce my body fat levels and as counterintuitive as it sounds, I'm adopting a low carb diet rather than my typical 'all the carbs' diet, and really giving focus to protein intake. I like Alan Couzen's guide - 50g of CHO per day baseline, plus 100g of CHO per hour of exercise at what he calls zone 1. (50g of CHO is hard work!!!). I'm also doing my easy runs before breakfast to try and encourage my body to burn fat rather than the sugars floating around. (The rule I set was 1 hour easy run, no breakfast - but today I got to the end of the hour, pace was good, HR was good, fatigue was non-existent and so kept going - 90 minutes/15km in the end, including four sets of hard intensity hill repeats at the end). This, I feel, is a good sign. For my long easy run (planning 2h45 on Wednesday), I will have breakfast and wait 2 hours before my run, and take CHO on during my run, but less than usual - I tend to get extremely fatigued even when running very easy HR at these times. As I have a marathon planned for late April, my hope is to gradually increase my easy long run duration closer to 4 hours before huge leg fatigue kicks in - after all, if I can't run for 4 hours at easy intensity, then what chance of running 4 hours at marathon pace.
I expect that despite huge amounts of low speed training as a proportion of my weekly running, my fat oxidation levels are virtually non-existent.
I've also noticed in the days since reducing calorie intake, restricting carbs, increasing protein that my overnight HRV has increased substantially and my overnight resting heart rate has also dropped (41 last night, apparently).
This is a very interesting blog you have and I love seeing your regular updates on Strava.
I've
thank you Ian, this is great to read, and indeed even without counting but using a bit of common sense, I think we end up doing similar things (also in terms of CHO/day + CHO/training). Alan wrote some really nice blogs already many years ago about this (I found also Dan Plews' work very relevant). All fascinating stuff. Let's see how it goes for the both of us, all the best for your training!
Hey Marco - am I reading your substrate graph correctly. At 60% of VO2Max, you are burning 2.5 cals/min out of a total of 15 cals/min? Meaning you are burning roughly 16% fat and 84% carbs? That seems absurdly low. I have never seen such low levels in the athletes that I coach. I must be reading this graph incorrectly...
haha that's right, and thank you for confirming :)
my metabolism is meant to do anything but long-distance running, it seems (see also the energy expenditure grap here, first figure of this blog: https://marcoaltini.substack.com/p/how-to-turn-the-worst-running-economy)
many years of training have been useful to improve economy to 'normal' levels, but I am now trying to see if fat oxidation can be better improved with dietary changes as well. I did book a lab test for the end of February, so we'll find out soon
Wow. Well I’m glad you’ve been able to chip away at that. No one can claim you don’t love running after sticking with it with 6 years without improvement! I’ll be curious to see your results on February!
Great article, Marco, look forward to reading of your progress. I think a podcast between yourself and Zac Bitter would be enlightening based on his history of performance utilising the same approach you are.
What device are you using to measure fat oxidation?
hi Eric! The old data comes from a Cosmed K4b2 (indirect calorimeter I was using during my PhD studies). The more recent data comes from another metabolic cart from a lab I used in Amsterdam (not sure about the brand).
Thanks. I wonder if consumer devices like the Lumen or Calibre are accurate enough...
not familiar with Lumen (but I have strong doubts now that I looked it up ..), while Calibre can only be used at rest (I had a call with them and the sensors cannot work in conditions like running). Even the more expensive (but still cheap for this type of technology) ones, like VO2master, have not shown to be particularly good (and this one in particular doesn't even have a sensor for CO2, so it would not be useful for substrate utilization). I'd love to get more frequent measurements while doing this experiment, but the barrier is quite high for valid technology when it comes to measuring VO2/VCO2, unfortunately (the Cosmed is 30K or more!). Best case scenario I will go to a lab in spring for some testing..
Hi Marco, wow this is exactly what I am doing. Whilst I have raced well I know there is more. I have been eating low carb now in this base phase for 6 weeks and it’s 100% working. I feel less hungry and on my longer bike workouts I have to force myself to eat now.
Question, what are you eating on your long runs? I have decided to eat a trail mix (nuts, dried banana, sultanas etc) I am trying to stay away from the sugary carb drinks.
Thanks Dan
thanks Dan, great to hear about your experience. For now during easy runs I have been eating dried fruit (like figs or apricots), or regular fruit (a banana), while for workouts I am using gels like before. I'm still trying to understand what I need, I do feel a lot less hungry but likely require a bit of trial and error to make sure I can keep training well week after week
Yes agreed. Prunes are also great 😊
It’s funny because in my race prep I’ve said to myself I will still go high carb. But the more i think about it I wonder if that’s really needed. I will do some Ironman simulation workouts and see what’s possible.
Good luck and thanks for posting this.. it’s always good to hear these things from respected people such as yourself.
Hi Marco. Are you going to include fasting into low carb period? I have been training approximately for 2 ½ years for almost 90-95 percent of my weekly hours (about 12 hours total training) at z1-z2 with a low carb high fat dietary, and for a long time i used to fast for 14-16 hours, where i included and my low intensity training. I saw big gains improving fat oxidation, such as a big drop in my heart rate at a given pace (In the beggining i ran about 6m/klm at 130 bpm and now i run 6m/klm at 112bpm). I like the trail ultra races and i have improve a lot in energy consumption and aerobic efficiency which in turn my race times drop significantly. Low carb high fat diet with fasting and a LOT of low intensity training did the job for me.
thanks Nikos. Really interesting to read your experience. At the moment I do not plan to include fasting, mostly because I've already made a large change and I need to take it step by step (I don't exclude that it will be easier to do so in the future).
If you do not mind, I'd be curious about the following: how do you fuel your long training runs? and similarly, how do you fuel your races? thank you for your time!
It depends mainly on the effort and intensity that I will introduce into the long run training. In any case, in a completely easy effort and low-intensity training I will consume, usually starting after 2 hours, a low-carb mixture of 500 milliliters. If the training lasts from 3.5-4 hours and more, then I will also consume bars that will also contain a little protein, perhaps and a few dates. If now, I add to the long training some time in Z3 or even a few minutes in Z4, then I will also consume a couple of gels. In the races, I consume about every half hour sips of the carbohydrate mixture that I carry in my vest and in both flasks, and about every 2 hours a bar or waffle. I also eat and drink, selectively, from the race's supply stations. In general, this is my diet, but I've been looking into it a lot lately to improve it since I haven't done a laboratory analysis.
I really enjoy your writing, and your approach to your training is very what drives innovative and applicable methods for people to live & move better. You’re a bright light Marco! Thank you!
thank you Riley, I really appreciate your kind words.
They are True as much as they are kind!
Hey Marco, thank you very much for your interesting article!
Two questions:
- Do you have examples of lower-carb plates/recipes that suit well before training as usually fats take a higher time to digest than carbs?
- I often question myself on the type of foods we eat (like wholegrain, organic, less-processed...) in comparison to just looking in terms of macros. It's often overlooked but I am fairly convinced that it can also play a role into how our physiology and metabolic flexibilty work. It's a point that Kilian discusses in his interview on the training science podcast...
Looking forward to see your results and happy training!
thanks Constant!
1) at the moment for breakfast I am rotating between an omelet (e.g. with tomatoes, avocado and some cheese) and greek yogurt with berries and nuts, or fresh cheese. I haven't experienced problems in training but I typically wait an hour or two before going out.
2) agreed. I find that when focusing on my diet more (regardless of low carb or not), it comes natural to eat better foods, so I have not touched on it here, but I do agree that it's not only about macronutrients.
happy training to you as well
That’s great to hear you’re transitioning to a low-carb diet! Are you planning to take a baseline blood test to track your progress? Testing markers like fasting insulin, blood glucose, and HbA1c can provide valuable insights into how your body responds to the changes.
thanks Ben! Coincidentally, I did. So I have most of the data in terms of cardiovascular health markers and so. I will test again in a few months