Having a debate with my roommate over this topic and wanted to see if y’all had any thoughts.
If someone is in a 200 calorie Deficit and they only eat protein and do not eat carbs. Would they lose the same amount of weight if they only ate carbs instead of protein? If not why? If so why?
The thermic effect of protein is significantly higher than carbs, so if they’re consuming the same amount of calories, the person eating only protein will lose slightly more weight.
The ‘calories in’ is the same, but the ‘calories out’ is marginally higher with the protein diet.
This is the reason why many diet studies (e.g. looking at carbs vs fats) need to control calories AND protein intake.
Edit: It was pointed out to me that OP specified a 200 calorie deficit. So, I suppose the thermic effect of food could already included in this deficit (meaning the carb only dieter would actually be consuming slightly more calories). In this case, I suppose fat loss would be about the same (let’s also assume the two people are clones).
I think protein takes a bit more energy to digest than other macros. Carbs (at least healthy ones) often come with fibre, though, which are filling, and some are indigestible, so you can’t use all those calories either.
Protein is more thermogenic, so you spend more calories digesting it.
Carbs also are stored as glycogen, bonded with four water molecules, meaning you hold more water when you store carbs, which wouldn’t happen with other macros.
The answer is clear
If calories are tge same weight loss will be the same although protein takes slightly more energy to digest. Protein is slower digesting than carbs so might help weight loss by keeping someone fuller dor longer but if calories are the same weight loss will also be the same.
The answer is in the question. 200 cal is 200 cal it doesn’t matter how you get there. Everyone talking about thermodynamics is missing the fact that the difference in metabolic energy is already accounted for. You would lose the same amount of weight, although getting zero protein while on a deficit would cause significantly more muscle loss.
Converting aminos is metabollicy expensive. If you only eat protein its using the straight gluconeogenesis pathway where about a third of the calories will be consumed by the conversion process. The exact amount varies by body & diet, it’s not useful to depend on.
Gluconeogenesis of aminos is not ideal, it generates lots of waste products. Fatty acid gluconeogenesis is much less of a problem. Your body will choose to convert fatty acids ahead of protein.
You should use the macros as the body evolved to use them. Carbs are current energy, fatty acids & protein are future energy and daily non-energy needs. Aminos are for protein synthesis not for energy, don’t try and use them as energy.
Carbs are not a problem. The healthiest diets are about 50% calories from carbs.