In humans, the musculature is divided into two muscle fibre types on a first differentiation level. The so-called slow switch fibres (slow and red) and fast switch fibres (fast and white). Put simply, the slow switch fibres correspond to the muscles of the marathon runner and the fast switch fibres to those of the sprinter. It has been known for a long time that the red muscle fibers (due to the higher myoglobin and mitochondrial content, among other things) are much better supplied with oxygen than the white ones.
Why is this interesting for nutrition?
The oxygen is in the centre of the energy supply. More oxygen is needed for fat burning than for carbohydrates. We find the reason for this in biochemistry. The organic compounds of carbohydrates (e.g. glucose = C6H12O6) provide more oxygen than those of fats (e.g. alpha-linolenic acid = C18H30O2).
If we now look at the muscle fibre type of a person isolated, then someone with increasingly slow muscle fibres should rather orientate himself towards a low carb diet (high fat). Whereas a person with more fast muscle fibers tends to benefit from a High Carb (e.g. vegan) diet.
Unfortunately, however, it is not so easy. In addition to muscular genetics, oxygen transport is also influenced by many other factors, such as training, everyday stress, cardiovascular system, etc.
For example, in a marathon runner, the oxygen transport deteriorates if he or she has had a lot of stress in everyday life or bad sleep. This means that on such days, even a long-distance runner (with good fat metabolism) should increase his carbohydrate intake during the day and during training.
PS: Since all athletes (except Scott Jurek) in the movie “The Game Changers” are fast power athletes with more fast-switch fibers, this might be one of the reasons why athletes have profited so much from a plant-based diet.