Acute and chronic changes in response to dietary modifications, fat oxidation rates, impact of training vs nutrition, shifts in substrate utilization during prolonged exercise, and more.
“ If you are targeting an event shorter than 3 hours, improving fat oxidation is unlikely to make a large difference. However, if the event is longer, then we start to enter a territory in which glycogen sparing does matter”
I think the paper you link supports this idea but wanted to ask for clarity: Do you think the above quote applies only to running events or would Ironman (or any endurance event that is 6-9+ hrs) also fall into this category?
Hi Jeff! Yes for sure fat oxidation is key in all endurance sports and in an Ironman. It’s important in the marathon as well, but the longer the race, the more likely we are to run out of glycogen stores if we can’t be metabolically flexible and use plenty of fat as fuel at various intensities. Same considerations for the 50 km, I think working on my metabolism was the only reason that led to a recent breakthrough for me in that distance (3 h 43’), see this blog https://marcoaltini.substack.com/p/trainingtalk-winschoten-50-km-2025
Thank you for this great update! As an integrative GP and runner (up to marathon distance) the idea of metabolic flexibility has always made so much sense to me. You’re right - it varies for each individual but you give some good general guidelines without extreme measures. The most important point you make is the quality of the food, which for many athletes is unfortunately not good- especially around race time and after. Lots of poor quality processed carbs. All the best!
Thank you again Marco, this sharing is so inspiring! Do you finally find an answer to your question « Can we periodize nutrition less and still have 90% of the gains? When do we start to make it worse? ». Where do you find how to design your meals for that experimentation : nutritionist? UESCA course ? 🙏
thank you. Regarding the 90% story, it's simple but also complex, what I mean is that sure, you can be flexible, but you still need to periodize your diet and eat lower amounts of carbohydrates on most days if you are in a situation like mine metabolically. Letting go here and there, in modern society, is a slippery slope, as we are bombarded with all sorts of crap wrapped as food (enter any cafe or bar in Italy, and there isn't anything that is not either fried or a sugar bomb, or ultraprocesesed - not really the Mediterranean diet!). We spend little time talking about the quality of the foods more than the macronutrients, and these matter a lot, as there are large hormonal differences in response to the same calories and even the same macronutrients. For my meals I keep it simple, breakfast either with greek yogurt, nut butter, nuts, and berries or an omelette with avocado and cheese, lunch is always a salad with a bit of everything, from legumes to farro to possibly some fish or chicken, and dinner is similar but typically with cooked vegetables. I do have more fish now than I used to, and tend to snack mostly on nuts and yogurt. For higher carb days I also try to keep it very similar but just add some fruit, potatoes, oats for breakfast, and occasionally I'll have a pizza or eat out and have some pasta, but again, living here if you don't make an effort you end up eating like that every day, and that's not going to work for my fat oxidation and associated performance.
More seriously, after trying to figure out how to rise FatMax/FatOx with training only (pushing or pulling…) without success, your journey is really inspiring !
When you say 160g of oats you mean dried oats ?! I ask this because with 50g of dried oats + milk I’m full !
One key aspect of quality diet is fibers. Whether it is through microbiota change or carbs availability, I feel (no met cart sorry) that having a high fiber breakfast for example that makes me satiated till lunch without the urge to snack on something. And I hope that this phenomenon is also a sign of better fat oxidation between meals.
agree on the fiber, I think that similarly, fat and protein help (a lot of it it’s about glycemic control after all, if we snack on sugar 24/7 - which is what people do, let’s not pretend carbs to be “some extra veggies” - we get quickly out of whack hormonally, which has implications even for the same caloric content. Regarding oats, agreed, I eat a lot of them before a big day (marathon or ultra), but it’s a task. Normally it works out if I do it about 3 hours before the race.
Regarding this statement:
“ If you are targeting an event shorter than 3 hours, improving fat oxidation is unlikely to make a large difference. However, if the event is longer, then we start to enter a territory in which glycogen sparing does matter”
I think the paper you link supports this idea but wanted to ask for clarity: Do you think the above quote applies only to running events or would Ironman (or any endurance event that is 6-9+ hrs) also fall into this category?
What about a road 50k that’s around 4 hrs?
Hi Jeff! Yes for sure fat oxidation is key in all endurance sports and in an Ironman. It’s important in the marathon as well, but the longer the race, the more likely we are to run out of glycogen stores if we can’t be metabolically flexible and use plenty of fat as fuel at various intensities. Same considerations for the 50 km, I think working on my metabolism was the only reason that led to a recent breakthrough for me in that distance (3 h 43’), see this blog https://marcoaltini.substack.com/p/trainingtalk-winschoten-50-km-2025
Thank you for this great update! As an integrative GP and runner (up to marathon distance) the idea of metabolic flexibility has always made so much sense to me. You’re right - it varies for each individual but you give some good general guidelines without extreme measures. The most important point you make is the quality of the food, which for many athletes is unfortunately not good- especially around race time and after. Lots of poor quality processed carbs. All the best!
Thank you again Marco, this sharing is so inspiring! Do you finally find an answer to your question « Can we periodize nutrition less and still have 90% of the gains? When do we start to make it worse? ». Where do you find how to design your meals for that experimentation : nutritionist? UESCA course ? 🙏
thank you. Regarding the 90% story, it's simple but also complex, what I mean is that sure, you can be flexible, but you still need to periodize your diet and eat lower amounts of carbohydrates on most days if you are in a situation like mine metabolically. Letting go here and there, in modern society, is a slippery slope, as we are bombarded with all sorts of crap wrapped as food (enter any cafe or bar in Italy, and there isn't anything that is not either fried or a sugar bomb, or ultraprocesesed - not really the Mediterranean diet!). We spend little time talking about the quality of the foods more than the macronutrients, and these matter a lot, as there are large hormonal differences in response to the same calories and even the same macronutrients. For my meals I keep it simple, breakfast either with greek yogurt, nut butter, nuts, and berries or an omelette with avocado and cheese, lunch is always a salad with a bit of everything, from legumes to farro to possibly some fish or chicken, and dinner is similar but typically with cooked vegetables. I do have more fish now than I used to, and tend to snack mostly on nuts and yogurt. For higher carb days I also try to keep it very similar but just add some fruit, potatoes, oats for breakfast, and occasionally I'll have a pizza or eat out and have some pasta, but again, living here if you don't make an effort you end up eating like that every day, and that's not going to work for my fat oxidation and associated performance.
Thanks for this Marco, very interesting round up and great to see your thoughts alongside the examples of your own training and racing.
thank you Steve!
Superb. Can’t wait to read your next post about double labeled water and 100k events ;)
More seriously, after trying to figure out how to rise FatMax/FatOx with training only (pushing or pulling…) without success, your journey is really inspiring !
When you say 160g of oats you mean dried oats ?! I ask this because with 50g of dried oats + milk I’m full !
One key aspect of quality diet is fibers. Whether it is through microbiota change or carbs availability, I feel (no met cart sorry) that having a high fiber breakfast for example that makes me satiated till lunch without the urge to snack on something. And I hope that this phenomenon is also a sign of better fat oxidation between meals.
agree on the fiber, I think that similarly, fat and protein help (a lot of it it’s about glycemic control after all, if we snack on sugar 24/7 - which is what people do, let’s not pretend carbs to be “some extra veggies” - we get quickly out of whack hormonally, which has implications even for the same caloric content. Regarding oats, agreed, I eat a lot of them before a big day (marathon or ultra), but it’s a task. Normally it works out if I do it about 3 hours before the race.