44 pages • 1 hour read
Jason FungThe Obesity Code: Unlocking the Secrets of Weight Loss
Nonfiction | Book | Adult | Published in 2016A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Themes
The Limits of "Eat Less, Move More"
Conventional wisdom holds that eating too many calories and exercising too little cause obesity, a belief that gave rise to the “Eat Less, Move More” approach to weight loss. Drawing on decades of research, Fung debunks these pervasive myths. Eating too much may be the proximal cause of weight gain, but it is not the ultimate cause. Further, exercising does not prevent obesity. “Eat Less, Move More” implies that obesity is a choice or a personal failing because it frames an individual’s daily choices as the cause of weight loss or gain, ignoring underlying factors. Fung contests these views, arguing that obesity results from a hormonal imbalance of hyperinsulinemia.
Homeostasis, or the body’s tendency toward equilibrium, explains why caloric reduction doesn’t yield weight loss. Studies reveal that the body adapts to reduced calories metabolically: The heart rate slows, blood pressure and body temperature fall, and the heart volume decreases to conserve energy. The body also responds hormonally to caloric reduction by increasing hunger hormones and decreasing satiety hormones. Dieters initially lose weight when they reduce their food intake. However, the body soon adapts, causing them to plateau and regain the lost weight, and then some. In other words, caloric reduction results in temporary, rather than long-term weight loss. It also produces undesirable psychological effects, such as listlessness, inability to concentrate, and obsessive behavior around food. As Fung notes, caloric reduction causes the body to shut down, preserving itself by implementing: “across-the-board reductions in energy output” (38).
Studies reveal that, like caloric reduction, exercise minimally impacts weight loss. The body expends most of its energy on metabolic tasks, and relatively little on exercise. Health authorities started promoting exercise as a weight loss strategy in the 1950s in response to concerns about heart disease. However, the research consistently shows that countries with low exercise rates have lower obesity rates than those with high exercise rates, and that people who exercise, even intensely over a period of many years, do not lose weight. The phenomenon of compensation may account for these results, as people tend to eat more after rigorous exercise. Although exercise has many health benefits, such as increasing cardiovascular health and lowering blood pressure, weight loss is not among them. Despite decades of studies, however, “Eat Less, Move More” continues to be hailed as the gold standard for weight loss, and because it focuses on an individual’s behavior and choices, dieters blame themselves for failing to keep the weight off. However, the problem lies not with dieters, but with the method.
The Hormonal Theory of Obesity
Fung argues that obesity is a hormonal disease, not a caloric disorder. After years of treating patients with advanced kidney disease, Fung turned his attention to the root causes of obesity and obesity related diseases, notably, type 2 diabetes. Both conditions result from persistently high levels of insulin, which Fung describes as a storage hormone. In addition to regulating the metabolism of carbohydrates, proteins, and fats by promoting the absorption of blood glucose into the liver and other tissues, insulin prompts the body to store sugar and fat. Insulin levels rise after meals, stimulating the fat-storage process, and persistently high insulin levels lead to insulin resistance.
Overweight people secrete high insulin levels compared to lean people, and their insulin levels also remain high for longer periods. Research shows that diabetics treated with insulin gain weight, and that the more insulin they take, the more obese they become. Insulin also causes non-diabetics to gain weight. Medications that magnify the impact of insulin have comparable effects while alpha glucosidase inhibitors, which block enzymes that aid carbohydrate digestion, hinder glucose absorption and decrease insulin levels, lead to significant weight loss. SGLT-2 inhibitors, which block the kidney’s reabsorption of glucose and lower blood sugar (thereby reducing insulin production) also lead to weight loss. Indeed, studies consistently show that medications that raise insulin levels cause weight gain, while those that lower insulin levels cause weight loss, leading Fung to conclude that obesity results from a hormonal imbalance of insulin.
Hormones also work against people trying to lose weight. The body has a set weight, which it strives to maintain hormonally. Weight loss significantly raises ghrelin levels, the hormone that signals hunger. Curbing dietary fat lowers satiety hormones, such as peptide YY, cholecystokinin, and amylin, making dieters feel less full and leading to over-eating. Incretins, a group of metabolic hormones, also play a role in Fung’s hormonal theory of obesity. Incretins slow digestion, making people feel fuller longer. Thus, low incretin levels, which result from low-protein, low-fat diets, encourage frequent eating. Research also shows that obese people are leptin resistant, which prevents their bodies from regulating fat storage. Finally, while all foods provide caloric energy, they differ in their metabolic processing, resulting in different hormonal stimuli. Refined carbohydrates are especially problematic for those trying to lose weight because they are easily and quickly absorbed by the body, which fuels insulin spikes and insulin resistance.
Caloric maintenance is still an important aspect of Fung’s dietary formula. A study published in Cell Metabolism shows that intermittent fasting improves insulin sensitivity even when weight loss is not present. The investigators fed prediabetic men enough calories to maintain their weight during a five-week period of intermittent fasting. Though the subjects did not lose weight, a number of health factors, including insulin sensitivity, improved. These results show that 1) improved insulin sensitivity does not necessarily lead to weight loss and 2) caloric reduction is still necessary for people using Fung’s approach of intermittent fasting with attention to reducing insulin resistance to lose wight (“Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes” 5 June 2018).
When to Eat: The Positive Effects of Intermittent Fasting
Fung argues that when to eat is as important as what to eat for long-term weight loss. Breaking the cycle of insulin resistance requires recurrent periods of low insulin levels, or intermittent fasts lasting between 24 and 36 hours. Fung draws a distinction between starvation and fasting: The former entails abstaining from food involuntarily while the latter is “the voluntary abstinence from food for spiritual, health or other reasons” (238). Fung demystifies fasting by pointing out that the term “breakfast” refers to “the meal that breaks the fast—which we do daily” (132).
Fasting triggers important bodily responses. First, it activates ketosis, prompting the body to switch from burning glucose to burning fat. Although blood glucose remains stable during fasts, insulin levels drop. Regular fasting also reduces insulin resistance and improves the kidney function, notably, its ability to rid the body of excess water and salt. The research shows that fasting results in rapid and long-term weight loss, stimulates the growth hormone that maintains bone and muscle mass, and raises adrenaline levels, which increase the metabolism. Studies also reveal that the body’s energy expenditure increases during fasting. Feelings of hunger, while acute at the start, eventually decrease.
Fung draws attention to the benefits of fasting compared to conventional diets. Unlike dieting, which requires consistency, fasting is intermittent and therefore lowers insulin levels and insulin resistance. Reducing insulin sensitivity is so critical to combating obesity that Fung refers to fasting as “the missing piece in the weight-loss puzzle” (240). Indeed, diets that reduce food intake reduce insulin levels but fail to address insulin resistance. By contrast, fasting efficiently reduces insulin resistance because the condition requires both high and persistent insulin levels.
Fung emphasizes that anyone can practice fasting. In fact, fasting is already widely practiced worldwide by Christians, Muslims, and Buddhists: “Almost one-third of the population of the entire world is supposed to routinely fast throughout their entire lives” (240). However, Fung does not mention the segments of the population for whom intermittent fasting could be dangerous. An article from Harvard Health Publishing states: “[P]eople with advanced diabetes or who are on medications for diabetes, people with a history of eating disorders like anorexia and bulimia, and pregnant or breastfeeding women should not attempt intermittent fasting unless under the close supervision of a physician who can monitor them.” (“Intermittent fasting: The positive news continues” 28 Feb 2021). The same article notes that most studies on intermittent fasting have been conducted on rats and that “Studies in humans, almost across the board, have shown that IF is safe and effective, but really no more effective than any other diet.
Fung stresses the ease of intermittent fasting: It is compatible with all diets, including the Atkins and Mediterranean diets, and it is a time saver because it cuts down on shopping, cooking, eating, and cleaning up. However, many people find it difficult to fast. As with any diet, compliance is the key to effectiveness, and if an individual cannot maintain a long period of fasting during the day and night, the body’s insulin levels will remain elevated, and the positive effects of fasting will be lost.
According to Fung, intermittent fasting is as important as making healthy food choices, reducing stress, and getting enough sleep. In this sense, aside from the restricted time periods that intermittent fasting requires, his advice for healthy eating is not all that different from traditional dieting advice. His focus on the body’s insulin response to dietary changes makes Fung’s work revolutionary, but intermittent fasting only works if an individual follows a sensible diet of whole foods and cuts out sugar and other refined carbohydrates.
