For endurance athletes the keto diet sounds
ideal. By keeping carbohydrate consumption low, fat becomes the primary
fuel for muscles during exercise. Increased fat burning translates into
increased lean body mass. Like many propositions, it sounds too good to be true
and it is.
Although your muscles primarily use carbohydrate and fat for fuel they are
not necessarily interchangeable. Whether your muscles use fat or carbohydrate
(glycogen) for fuel depends on both the duration and intensity of your
exercise. At low intensity exercise your muscles can efficiently use a
preponderance of fat as fuel however as exercise intensity increases glycogen
becomes the mandatory fuel. And if you don't supplement
carbohydrate during exercise you will quickly deplete your muscle's
limited supply of glycogen. When muscles
fatigue, endurance performance plummets.
There is also another excellent reason to consume carbohydrate during
endurance exercise. Low carbohydrate availability has a detrimental effect
of protein balance. Studies have shown that when carbohydrate is limited there
is an increase in muscle protein breakdown. High carbohydrate consumption
during exercise decreases protein breakdown and maintains net protein
balance whereas low carbohydrate decreases protein synthesis and
reduces net protein balance. Greater muscle protein loss translates into
greater post-exercise muscle damage, soreness and a tougher recovery.
