I practiced in the nutrition field for 20 years before I finally understood the drivers of obesity, Type 2 diabetes, polycystic ovarian syndrome and metabolic illness. I wish I could go back in time and slap my own face for the recommendations I gave people early in my career, but I only knew what I was taught.
Insulin is a hormone that is a key player in weight gain. Hormones are chemical messengers that tell the body to do something. They are all powerful! There are many regulatory hormones that intermittent fasting can have an effect on. The hormones insulin, leptin and ghrelin impact how the body stores fat, as well as your energy levels. Insulin is a storage hormone, it signals your body to store fat and glucose (sugar). First, we fill up all our glycogen (carbohydrate) storage capacity in our liver and skeletal muscle. We can only store so much glycogen, a typical adult stores about 1800-2000 calories worth, 400 in the liver and 1600 in the muscles. When glycogen stores are full, your body has to do something with the extra calories not burned, and it converts everything extra to fat.
It is very important you understand the relationship between the hormones insulin and glucagon. The hormone glucagon tells your body to break down stored energy when food is not present or available. This hormone is high in periods of fasting. As we have learned, insulin signals your body to store energy as soon as you eat. Insulin (store energy) and glucagon (release energy) basically tell your body to do opposite things, when one is high the other is low.
They cannot both be high at the same time.
In people with obesity and diseases of insulin resistance, insulin has been the dominant hormone for months, years or decades. If insulin has been dominant, which is the case for most Americans, it can be healthfully balanced out with eating less carbohydrates, periods of intermittent fasting and extended fasts.
Between meals, as long as we don’t snack, our insulin levels will go down and glucagon rises, signaling our liver and fat cells to release their stored energy. The liver and muscle cells will release glycogen (glucose) and the fat cells will release fatty acids. We lose weight if we let our insulin levels stay quiet. The entire idea of intermittent fasting is to allow the insulin levels to go down far enough and for long enough that we burn off our excess sugar, and eventually, fat. Yay!
Understanding the relationship between insulin and glucagon is vitally important to weight control. In today’s culture, we live in a toxic world of chemical foods which all, without exception, increase insulin resistance. Insulin resistance leads to higher and higher insulin to glucagon ratios, and eventually obesity. Having insulin dominant for longer periods than glucagon essentially keeps your body in energy storage mode rather than energy burning mode, regardless of the number of calories you are ingesting.
We need to treat weight gain as the hormonal imbalance that it is. It is not only a calories in vs. calories out problem, as we have been taught for the past 40-50 years.