Just a side note. If you are working out a lot, not having enough calories will definitely give you less energy to put into the work out. So you may work out for the same amount of time, but the net result is less calorie burn and maybe even less fat loss.

If you get enough protein and you are working out. You can eat very little and still be healthy. But that is the big kicker, if you eat too little your going to be tired and not want to work out as much.

If you aren't going to do any physical activity, then you still need the protein, but maybe not quite as much in calories. The problem is the less you eat in calories the more critical the protein, and 1 gram of protein is going to be at best about 10 calories.

So lets say you want to starve and eat protein isolate all day. You would really need to eat about 70-90 grams of protein because you don't want your body using muscle for energy. Well, that is already about 700-900 calories.

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