Why follow a 1200-calorie limit?

For a long time people thought that weight issues were about an imbalance in calories: too many calories coming in (aka food), not enough being used (aka exercise). The books I've been reading lately, particularly Dr. Jason Fung's, redirect the blame to an imbalance of hormones, namely insulin. Too much insulin leads to insulin resistance, which also causes a resistance to leptin, the hormone that tells us that we're full. Too much insulin can also produce more ghrelin, the hormone that prompts us to eat. (I'll be discussing hunger specifically in a few posts!) 

The other problem is that not all calories are created equal. Some calories are devoid of nutrition. Some calories take more energy to break down. Some foods have almost no calories, yet their sugar substitutes still produce a spike in insulin production. Some calories - sugars and refined carbs - take less energy to break down and are absorbed too quickly. What Dr. Fung and the other dieticians out there aren't saying is that reducing calories is wrong: they're just saying that it's slightly misguided. We DO want to reduce calories, but the more important thing is to pay attention to what type of calories we're eating. It's not enough to give yourself a caloric maximum - in my case, 1200 calories - and then fill it any way you want. It's also not enough to eat low-calorie foods (like sugar-free jello, for instance) if they're still causing spikes in insulin and cravings for more sweet food. And obviously, if your "calories in" number still outweighs your "calories out" number, you're going to gain weight. It matters - but the specific type of calories also matters! 

Having a calorie deficit is a good and healthy thing to do if you're trying to lose weight, lose belly fat, or lower your insulin. It's just not the only thing to consider.