[jbd0]

You're so wrong. With only protein and fat, they would not be able to gain much weight. I've tried to gain weight on low carb/high fat, and it doesn't work. I was uncomfortably full after every meal. My tracking showed a significant calorie surplus, but my body wasn't absorbing it. Adding in more carbs made a huge difference. Hormones tell your body when to store fat.

[Attummm]

Did you know that bodybuilders in the 1950's(before anabolic steroids) used the egg and steak diet before contests as cutting diet to get lean? They would eat, as the name suggests, large quantities of steak and eggs with butter and have a carb refeeding day every 4 days. They would get really lean on a very high-calorie diet, think 4000 to 6000 calories.

The inventor of diet famously lost a contest for being too lean.