The practical implication of this situation is critical to how we perceive the dietary treatment of obesity, or simply the maintenance of a healthy weight, in a world of inexpensive, easily digestible carbohydrate-rich foods. Among the more pessimistic arguments wielded against carbohydrate-restricted diets is that all diets fail eventually because the subjects inevitably fall of the diet, just as they do calorie-restricted diets. But this argument is based on the assumption that all diets work by limiting the calories consumed. It also ignores any physiological difference between a craving for carbohydrates and the hunger that results from semi-starvation. The latter is caused by the absence of sufficient calories to satisfy physiological demands. The craving for carbohydrates is more closely akin to an addiction, which is how it was described by the British clinician Robert Kemp in 1963. It is the consequence of hyperinsulinemia, which in turn is caused initially by the presence of carbohydrates in the diet, just as an addiction to nicotine or cocaine or any other addictive substance is caused by the use of these substances. There is nothing inherently natural about such addictions. The hunger that accompanies calorie restriction is an unavoidable physiological condition; the craving for carbohydrates is not.

Sugar (sucrose) is a special case. Just like cocaine, alcohol, nicotine, and other addictive drugs, sugar appears to induce an exaggerated response in that region of the brain known as the reward center—the nucleus accumbens. This suggests that the relatively intense cravings for sugar—a sweet tooth—may be explained by the intensity of the dopamine secretion in the brain when we consume sugar. When the nucleus accumbens “is excessively activated by sweet food or powerful drugs,” says Bartley Hoebel of Princeton, “it can lead to abuse and even addiction. When this system is under-active, signs of depression ensue.” Rats can be easily addicted to sugar, according to Hoebel, and will demonstrate the physical symptoms of opiate withdrawal when forced to abstain.

Whether the addiction is in the brain or the body or both, the idea that sugar and other easily digestible carbohydrates are addictive also implies that the addiction can be overcome with sufficient time, effort, and motivation, which is not the case with hunger itself (except perhaps in the chronic condition of anorexia). Avoiding carbohydrates will lower insulin levels even in the obese, and so ameliorate the hyperinsulinemia that causes the carbohydrate craving itself. “After a year to eighteen months, the appetite is normalized and the craving for sweets is lost,” said James Sidbury, Jr., about the effects on children of his carbohydrate-restricted diet. “This change can often be identified within a specific one to two week period by the individual.”