For a while now, I have been hearing about the benefits that calorie-restricted diets and fasting can have on health—particularly in regard to extending life span and reducing the risk of cancer, diabetes, and heart disease. So, when I was asked to review The FastDiet by Michael Mosley, M.D., and Mimi Spencer, I was instantly intrigued.
The overall concept of the FastDiet is the 5:2 plan; while you are trying to lose weight, you eat regularly for five days of the week and fast for two days per week. On the fasting days, your calories are limited (500 calories for women and 600 for men). Once you have reached your target weight, you move onto the maintenance phase, which involves fasting only one day per week. Dr. Mosley uses health markers such as weight, waist circumference, blood glucose, cholesterol, and triglycerides to show the effectiveness of his diet. Additionally, he uses IGF-1, which Mosley explains as the “measure of cell turnover and therefore of cancer risk” and what “may also be a marker for biological aging.” The FastDiet, as a result, focuses on intermittent fasting to reduce levels of IGF-1. While it is widely accepted by the scientific community that fasting/calorie restriction will temporarily lower IGF-1 levels in the body, the degree to which one has to fast in order to accomplish this has not been scientifically established. What we do know is that a ten percent weight loss through healthy, moderate lifestyle changes can lead to improvements in the same measured health markers—without severely restricting calories for two days per week.
I have many concerns with the concepts proposed in Dr. Mosley’s book. First, fasting for two days per week will most likely lead to a preoccupation with food, especially for those already struggling with disordered eating. Any time food is restricted, thoughts around food increase. When food is made available again, most people have the tendency to overeat and some will end up binging. Second, I find it hard to agree with Dr. Mosley when he says that one of the “bonuses that can come into play” is that FastDiet practioners start choosing healthier foods, explaining that as “instinctively retreat[ing] from bread” and “consum[ing] more vegetables.” I firmly believe that bread can be part of a healthy diet, and that the best way to consume (and like) more vegetables is by finding the ones you prefer and choosing simple and healthy ways to prepare them.
Fasting will not help those who are interested in getting in sync with their hunger and fullness cues, since signals sent by the body are ignored and sheer will power is required to get through the fasting days. Additionally, readers of Austin Fit Magazine are probably interested in maintaining a healthy diet to fuel workouts. If you fast on two days—whether they are consecutive or not—you are lowering your blood sugar, and reduced glycogen levels may lead to decreased athletic performance.
Perhaps the worst advice in Dr. Mosley’s book is found in conflicting statements regarding the appropriate length of fasts. When asked if, since two days of fasting is good, would three days be better, he replies with conflicting statements. He says, “there’s no reason not to” but shortly after states that “experience tells us that two days is enough”; he then, again, refutes himself with another comment: “if, however, you have a date and a small size of party pants on standby, an occasional, single sneaky extra day shouldn’t hurt.” I think it is common knowledge that quick weight loss inevitably leads to quick weight re-gain and an even more distorted body image.
At this point, you may be wondering if there is anything I agree with in Dr. Mosley’s book. Well, there is. I do agree with Dr. Mosley that our patterns of eating are vastly different than they were 30 years ago. Food is readily available around every corner, and snack manufacturers are brilliant in the way they market food and encourage the desire to eat constantly. These practices often lead to mindless eating, eating without regard for satiety or need. However, I firmly believe we can get back in tune with our hunger and fullness cues by eating intuitively and choosing food that nourishes our bodies.
Overall, I think the FastDiet is just what the name implies: another diet, one that may lead to quick weight loss but will leave its followers preoccupied with food…and wishing for the day the diet will end.