If you’ve forgotten everything you ever learned in biology, just remember this and own it: carbohydrate controls insulin; insulin controls fat storage.
It's All About Insulin (Well, at Least 80 Percent of It): Eighty percent of your ability to achieve body composition goals is determined by your diet—essentially, your ability to moderate insulin production so you can access and burn stored body fat for energy, while preserving or building muscle. Insulin is an important hormone that transports nutrients into cells for storage. When the delicate insulin balance is abused by habitually consuming too many carbs, cells become insulin resistant; more fat is stored and it becomes increasingly difficult to burn. This sets the stage for the development of serious conditions like Metabolic Syndrome, type 2 diabetes, and heart disease. Synthesis of testosterone and human growth hormone are hindered by excessive insulin production, creating an artificially accelerated aging process. There are also serious immediate drawbacks to consuming high-carb snacks or meals. The sugar high-insulin release-stress response cycle causes problems with fatigue, mental focus, mood swings, and jitters, resulting in the familiar condition of burnout. The regulation of insulin production is perhaps the most important takeaway message of the Primal Blueprint for preventing obesity and many modern health problems.
[For Weight Loss] Bottom line: It’s all about insulin to enjoy effortless lifelong weight control.It’s as simple as this: if you have excess body fat, it’s directly reflective of the amount of insulin you produce from your diet combined with your familial genetic predisposition to store fat.
No, Really—It’s All About Insulin: The insulin story is perhaps the most health-critical concept in the book, so I want you to fully understand it on both a practical and a biochemical level. Like so many things in life, a moderate amount of insulin is good and a lot can be bad —very bad.
From The Primal Blueprint by Mark Sisson2009, PDF pp. 190, 219, 30, 150, 154 respectively