Gary Taubes explains that in any basic biology textbook, insulin is known as the fat storage hormone. Its job is to direct your fat cells to store energy as fat. If you produce more insulin than your neighbor from ingesting the same amount of food, you will also store more of that food energy as fat.
Carbohydrate provokes the release of insulin, in some individuals more insulin than in others for the same amount of carbohydrate. That is why two people can eat the same food and exercise the same amount and one can gain weight while the other doesn’t.
It gets worse. Call the weight gainer Jim and the weight maintainer Steve. Jim will be hungry sooner than Steve. Why? Most or all of the energy in the food Jim just ate will have been tidily stored away in fat cells, instead of being available for Jim to use. Jim will feel hungry again in response to the lack of energy.
Jim will also feel tired, because the food energy has been sequestered in fat cells rather than remaining available for use.
Protein and fat do not provoke insulin production to nearly the same extent as carbohydrate. The energy that is eaten is not stored as fat; it remains available for use. Controlling insulin production is the key to better energy and a healthy weight. And the key to controlling insulin production is controlling carbohydrate intake.
Taubes concludes that the logical eating plan for weight control (and a host of other health benefits I haven’t described here) is one that limits carbohydrates to much lower levels than the USDA-approved Standard American Diet.