The food pyramid (and most government recommendations regarding diet), as Alan mentions, has nothing to do with health. Your question illustrates this pretty well. I mean, we are all different, not only in shape and size, but in how our metabolisms work based on many variables, some being genetic, some being acquired (like yo-yo dieting affects). The problem is that the government, dieticians, some doctors, and even many weight loss authors and companies have this idea of "one size fits all." They have their own theories of what foods are healthy to eat and which will allow for healthy weight loss and maintenance of that loss, but many are simply stuck as if their chosen eating plan is THE one and everyone should have success on it. Life just doesn't work that way. This is why we all need to stop looking at one person's (or the gov't's) recommendations and try different approaches out for ourselves to see which one works best for us.