The Obesity Code: Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight)

by Jason Fung

This effect was demonstrated in 2011, in an elegant study of hormonal adaptation to weight loss.14 Subjects were given a diet of 500 calories per day, which produced an average weight loss of 29.7 pounds (13.5 kilograms). Next, they were prescribed a low-glycemic-index, low-fat diet for weight maintenance and were encouraged to exercise thirty minutes per day. Despite their best intentions, almost half of the weight was regained. Various hormonal levels, including ghrelin—a hormone that, essentially, makes us hungry—were analyzed. Weight loss significantly increased ghrelin levels in the study’s subjects, even after more than one year, compared to the subjects’ usual baseline. What does that mean? It means that the subjects felt hungrier and continued to feel so, right up to end of the study. The study also measured several satiety hormones, including peptide YY, amylin and cholecystokinin, all of which are released in response to proteins and fats in our diet and serve to make us feel full. This response, in turn, produces the desired effect of keeping us from overeating. More than a year after initial weight loss, the levels of all three satiety hormones were significantly lower than before.