The most recognized function of the pancreas is to normalize glucose levels by helping transport blood glucose into muscle and fat cells. When carbohydrate foods are digested and converted to glucose, blood sugar levels rise, which triggers the release of insulin to moderate blood sugar. In simple terms, carb intake is largely responsible for blood sugar fluctuations. Food need not taste sweet—think mashed potatoes or white bread—to convert rapidly to glucose. But this well known effect is just one of insulin’s roles.
The Storage Hormone
Insulin also promotes the storage of macronutrients, helping convert amino acids into protein and carbohydrates into either glycogen or fat. But even as insulin promotes the storage of nutrients, it also blocks the breakdown of protein, fat and carbohydrate in the body. When the insulin level rises, it puts the brakes on burning fat for fuel and encourages storage of incoming food, mostly as fat. That’s why as long as the diet is high in carbohydrates, the body never has a chance to burn its own fat, making weight loss difficult. However, limiting carb consumption stimulates increased fat burning and decreased fat storage.
Without the roller coaster effect of fluctuating glucose levels, cravings for a quick energy boost in the form of sugary, starchy foods abate. Lipogenesis also has an appetite-sparing side effect. Both of these factors aid compliance with the Atkins diet.
A Delicate Balance
Fat synthesis and fat burning are highly sensitive to changes in the amount of insulin released in response to eating carbohydrate foods. Small decreases in insulin almost immediately increase fat burning, and increases can activate enzymes that transform glucose into fat. Because low-carbohydrate diets significantly blunt insulin levels throughout the day, the Atkins Diet enables greater utilization of body fat for energy and decreased storage. This important adaptation also contributes to better cholesterol and other lipid profiles, decreasing risk for heart disease and improving all the features of metabolic syndrome. This is why dietary fat can be considered a dieter’s friend and consuming carbohydrate above one’s tolerance level acts as a metabolic bully.
Control Carbs to Burn Fat
Controlling carbohydrate intake and the subsequent decline in insulin levels permits most of the body’s cells to use fat almost exclusively for energy, even during exercise. During Phase 1, Induction, and Phase 2, Ongoing Weight Loss (OWL), body fat provides a large share of that energy. During Pre-Maintenance and Lifetime Maintenance, dietary fat provides most of the needed fuel. Either way, by keeping carb intake at or just below an individual’s carb threshold (known as Atkins Carbohydrate Equilibrium, or ACE), the body uses both dietary and body fat for energy. This principle is the foundation upon which the Atkins Diet is built. All that’s necessary to activate it is to change eating habits.
There’s nothing risky about relying on a primarily fat metabolism. In fact, fat is the body’s back-up energy source. The ability to carry a “fanny pack” of energy in the form of fat actually helped our distant ancestors survive in times of famine and when hunters returned home empty handed.
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S. D. Phinney, B. R. Bistrian, R. R. Wolfe, and G. L. Blackburn, “The Human Metabolic Response to Chronic Ketosis without Caloric Restriction: Physical and Biochemical Adaptation,” Metabolism 32 (1983), 757–768.