happens to me many a time, and what I have "most" commonly found is that people just dont eat ENOUGH. They eat healthy, which sure is great, but they eat 3 meals a day each consisting of 600-700 calories. They don't believe me when I tell them that I eat 6-8 meals a day, depending on what part of precontest I am, as well as my macronutrients in the ranges of 3500-5500 calories, 200-400g protein, 50-300 grams fat, and ~0-800grams carbohydrates. Obviously when I am at the upper range of that carb interval, a large part of them are simple carbs from things like Optimum Nutrition's Serious Mass.