Figure 22-33Weight-loss diets make for popular reading.

Weight loss is both a simple and a complicated problem. It is simple because there is one complete and perfect plan that guarantees success; it requires only five words of description: “Eat less. Move around more.” Regardless of the genes it carries, any animal of any species will lose weight when it expends more calories than it consumes.

But weight loss is also much more complex than this. After all, we know that eating less and moving around more are all that is necessary, but while almost all short-term “diets” work in the short term, in the long run, with very few exceptions, they fail (FIGURE 22-33).

Current interventions designed to facilitate weight loss range from mild to extreme. They fall into three categories: drugs, surgery, and behavior modification. Each has both promising and problematic elements (FIGURE 22-34).

Figure 22-34A wide variety of strategies are employed in the quest for weight loss.

Drugs and Other Chemical Interventions Xenical. One of the more promising of recently developed weight-control drugs is Xenical, a product that interferes with fat digestion by binding to lipases (fat-digesting enzymes) and blocking them from doing their job. As a consequence, some of the fat in the digestive system passes through the body without absorption.

Olestra and NutraSweet. Some artificially created molecules, such as Olestra and NutraSweet, can cause the same perception as if a molecule of fat or sugar, respectively, were present. Olestra, for example, contains fatty acids and is designed to have a taste and texture similar to digestible fats, but in an indigestible molecule (see Section 2-13). Because it is a complex molecule containing eight fatty acids rather than the three fatty acids that are part of triglycerides in our diet, it ultimately is excreted rather than being digested and absorbed. Still, in several published research studies, subjects who unknowingly ingested fewer calories as a consequence of consuming products containing either NutraSweet or Olestra responded by increasing their caloric consumption in the following days. We’re not tricked quite so easily.

Caffeine and other stimulants. A variety of products claim to increase the expenditure of energy without an offsetting increase in appetite. This approach is theoretically sound, but there are no published data on either the safety or the efficiency of these unregulated products. While clinical trials demonstrate that stimulants such as caffeine can produce short-term weight loss in the range of 5–10 pounds, long-term studies reveal that most of the short-term losses do not last.

Surgery Liposuction. Liposuction is the most popular plastic surgery procedure in the United States, with more than 1.2 million performed each year. In this procedure, doctors directly remove fat cells from various parts of the body, using a hollow tube and a suction device. Over time, however, individuals tend to regain all the lost weight. In fact, the only follow-up study on liposuction found that within a few months, nearly half of the patients weighed more than they did before the surgery.

Bariatric surgery and stomach banding. More invasive surgical procedures are also possible. The most effective is also the most extreme. In a type of procedure known as bariatric surgery, surgeons bypass a significant portion of the small intestine and seal off, by stomach banding, most of a person’s stomach. This reduces both the amount of food people can eat before becoming full and the ability of their small intestine to digest and absorb nutrients. The surgery carries significant risks, though, and leads to major nutritional deficiencies in almost a third of all cases. Still, something can be said for bariatric surgery that cannot be said unequivocally for any drug or diet: it works. One study of more than 600 patients found that after 14 years, the average weight loss was 100 pounds!

Behavior Modification: Weight-Loss Diets Portion control and general caloric restriction. Can we change our eating habits permanently? To answer this question, researchers put a group of monkeys on a very low calorie diet. The monkeys shed pounds initially, then stabilized at much lower weights for two years. After two years they were given unlimited access to food. Did they maintain their new weights? No. After spending close to 10% of their lives at a constant, low weight, these monkeys quickly returned to their original, pre-diet weights.

This example and others suggest that there might be a “set point” for body weight—like the setting on a room thermostat. When weight is below the set point, the body induces calorie-seeking behavior, and when weight is above the set point, the mind and body are free to pursue other goals. In a human study equivalent to the hungry monkey study, researchers observed a group of successful dieters over time. The newly skinny people had lost an average of 70 pounds per person through a comprehensive program. Three years after completing the program, the participants had, on average, regained all of their lost weight.

General Problems with Weight-Loss Diets The main problems with most popular weight-loss diets are that (1) they focus on reducing weight (even weight due to water) rather than reducing body fat; (2) they reduce muscle mass, the body tissue best able to burn fat; (3) because they reduce body weight too rapidly, they trigger several defense mechanisms designed to preserve the body’s energy reserves; and (4) they don’t focus enough on the other side of the energy equation: exercise (FIGURE 22-35). This generally leads to four problems.

Figure 22-35Weight-loss diets often fail.

1. Nutritional deficiencies. When the body goes into efficiency mode to combat a shortage of calories, a variety of systems get modulated down or turned off. Hungry lab animals, for example, almost completely lose their sex drive and may be less adept at fighting infection. Nearly all popular diets are seriously deficient in vitamins, minerals, and fiber.

2. Metabolic rate reduction. Sudden caloric restriction leads to a rapid reduction in basal metabolic rate, and this lower rate remains for several weeks after resuming normal caloric intake.

3. Loss of muscle mass and body fluids rather than body fat. Low-calorie diets lead to weight loss, but as much as 45% of the weight loss comes from the loss of muscle mass. Muscle tissue is significantly more metabolically active than the relatively inert fat cells. As a consequence, the body’s fat-burning capacity is significantly reduced along with its muscle mass.

4. Increased lipoprotein lipase activity. With a reduction in caloric intake, your body increases the activity of an enzyme called lipoprotein lipase. This enzyme is responsible for converting nutrients in the bloodstream to fats for storage.

An evaluation by the National Institutes of Health of all the major diet programs concluded that there was no good evidence that any of the programs reliably led to long-term weight loss. A large study published in the New England Journal of Medicine came to a similar conclusion in 2009. Unfortunately, living in our modern, zoo-like environment of plenty, we’re going to struggle with natural systems that relentlessly seek out and efficiently store calories. Nonetheless, the National Institutes of Health notes that even modest weight loss (5% to 10% of total body weight) is likely to produce significant health benefits, and that it can be achieved through consumption of a moderate and balanced diet, in conjunction with moderate exercise.