“What do you mean?”
Exactly what I said.
“If you are hiking in a caloric deficiency your body will use stored energy, regardless of diet (macro nutrient ratios)”
Of course, but it is a question of how efficiently.
“If you eat carbs your blood sugar rises leading to your cells taking in that sugar where it gets used preferentially according to oxidative priority for energy vs ketones from stored fat.”
You need to do a little reading on how the 3 macro energy sources are metabolized in varying ratios according to the intensity of exercise, cardiovascular fitness of the individual, and altitude. It is usually determined by a VO2 max test, which will give the percentages of carbs and fat at varying levels of exercise intensity. Look up respiration exchange ratio and/or respiratory quotient for starters and go from there. The macro sources are not used sequentially, with all carbs being exhausted before fat metabolism begins. And protein comes into the equation minimally until carbs and fat have been exhausted. That is because proteins are not an efficient source of energy. They are complex molecules that require a lot of action and energy to break down and are used primarily for tissue repair.
“Assuming pure macro nutrients for a simple over-estimation: 3x 3oz serving of protein a day (~1000 cal) leaves 11oz of carbs a day (~1250 cal) for a total of about 2250 cal/day of carbs and protein. A large man hiking all day would probably need more than 2250cal/day , but since all 2250 cal/day are burned before stored body fat, they would be minimizing the use of stored energy while in caloric deficit.”
The metabolism of stored energy, both glycogen and fat proceeds concurrently with dietary sources, and protein, both dietary and stored in the form of muscle tissue, does not figure significantly in the process. Degraded muscle cell proteins in the form of the carbon skeletons of amino acids are recycled through the liver to produce glycogen, but it is not a significant source of energy under normal conditions.
“Is that what you mean by efficient use?”
There is an axiom in exercise that “fat burns in a carbohydrate flame”. It is a bit complicated to explain in a reasonably short BPL post. I will refer you to “the Krebs Cycle”. In a few words, fat is metabolized efficiently when it proceeds in the presence of a certain percentage of carbs, which varies with the level of exertion and cardiovascular fitness that delivers oxygen to support the process. Altitude also affects the process. At higher altitudes, where there is less oxygen, carbs will be increasingly preferred because they require less external oxygen to be metabolized than fats. In either case, the less oxygen available, the more carbs will be utilized, and vice versa. It is how we evolved, and with good reason. Glucose is the preferred energy source for the brain, and also for quick bursts of energy in fight or flight situations. Fat will always be preferred as the primary source of energy if there is adequate oxygen to metabolize it, simply because it provides the most calories per gram and is basically an unlimited source under normal conditions.
