If you're middle-aged and your body doesn't respond well to insulin, cutting carbs and eating more fat might help you lose belly fat better than a low-fat diet. But if your body handles insulin normally, both diets work about the same for fat loss.

In middle-aged people who are overweight, eating fewer carbs and more fat for 15 weeks might help their body respond better to insulin, while cutting calories on a low-fat diet could actually make insulin work worse — and these changes happen even if both groups lose about the same amount of weight.

For middle-aged people with extra weight, cutting carbs a lot might burn more belly fat — especially the dangerous kind around organs — even if you lose the same total weight as someone on a low-fat diet.

For people who are obese, eating a low-carb diet doesn’t seem to make a noticeable difference in their blood sugar or how well their body uses insulin.

After eating mostly fat for three days, the pancreas of healthy young men released less insulin right after they drank sugar water, even though their blood sugar went higher.

Eating fewer calories—no matter if you eat more fat, protein, or carbs—helps lower bad cholesterol, insulin, and triglycerides, but diets with more protein lower insulin a bit more, and diets with fewer carbs raise good cholesterol a bit more.