Blood sugar, insulin, weight: linked !
It's the low fat, very high carbohydrate diet that we've been eating for the last 40 years, which raises levels of the hormone insulin and programs fat cells to go into calorie storage overdrive. I like to think of insulin as the ultimate fat cell fertilizer.
When someone with Type 1 diabetes first comes to attention, their blood sugar is high because they can't make enough insulin. They invariably have lost weight. They may be eating 5,000 calories a day, and they're still losing weight. You can't gain weight without insulin. The opposite is also true. If you give someone with diabetes too much insulin, they will inevitably gain weight. Insulin programs the body to store calories, and most of those calories get stored in the fat cells. If you've got too much insulin, you're going to store too many calories. This has been very well established scientifically.
Dr. David Ludwig, an obesity expert and professor of nutrition at the Harvard T.H. Chan School of Public Health