When switching to The Paleo Diet after being on an ultra-low-carb diet, is it possible to gain temporary weight from eating the “unlimited” fruit allowed on your plan?
Let me take a roundabout way of answering this question first by explaining why almost all of the weight we gain comes from either dietary fat or dietary carbohydrate. As I pointed out in Chapter 4 of The Paleo Diet, it is physiologically impossible to gain weight when lean protein is the only food consumed because of the body’s limited ability to break down protein and excrete the by-product of protein metabolism (urea). This limit is called the physiological protein ceiling and varies between 30-40% of the normal caloric intake in most people, assuming they are consuming their usual (eucaloric) energy intake. Continued consumption of lean protein at or above the physiological protein ceiling without added fat or carbohydrate will elicit symptoms of so-called “rabbit starvation,” a malady eliciting lethargy, diarrhea, weight loss, electrolyte imbalances, and eventual death. Hence, all people will lose body weight if limited to consumption of lean protein. Lean protein has been shown r
