> that's not true. calories in vs. calories out is the only factor that matters in the end for weight gain / weight loss. For that to be true, the following also has to be true: 1. The human body is a closed system. 2. There is only one metabolic pathway for all nutrients. Since both of those are false, calories are not the only factor. In fact, they're not even a terribly important one. The epidemic of obese lard dumpsters is the result of this calorie cult. Yes, you *can* lose weight by calorie restriction alone. Almost nobody can lose weight and keep it off by calorie restriction, though. It's always very temporary because in the end biology will win over willpower. What's interesting is the part about how you get fat. You get fat when your body deposits extra energy in your fat tissue. There's only one way to do that: insulin. Without elevated insulin you *can't* deposit fat. That is why ketogenic diets work so much better than any other, and why people don't put on weight eating lard, fatty steak, butter, and bacon - because their body has no way to do it.