Why Most Diets Fail

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It’s a common observation that most diets fail, but the reason they fail isn’t about the weight loss. In fact, most diets are successful in that regard if the dieter has any degree of discipline and motivation. The reason most diets fail is that the dieter fails to keep the weight off. You can easily observe the phenomenon in the dieting efforts of celebrities who have weight problems.

Oprah Winfrey is a notable example. Years ago Oprah went on a special liquid-protein diet that resulted in her losing 67 pounds of fat, which she proudly wheeled out in a wheelbarrow on her TV show (not her real fat, just 67 pounds of animal fat). Alas, her svelte figure turned out to be painfully ephemeral, as Oprah soon gained all the weight back and then some.

More recent examples include most participants in the popular TV show “The Biggest Loser”—although the high recidivism rate there isn’t surprising, as the program involves a crash diet with a lot of exercise. That’s a stress on the body’s reserves that cannot be sustained, and as a result, the weight soon returns.

In fact, only one out of every six dieters is able to maintain a 10 percent weight loss after a year, and studies suggest that as many as 97 percent of those who lose bodyfat from dieting alone will gain it all back, often within a year. Why is that figure so high?

When you lose weight, your body adapts to the reduced calories through a process called adaptive thermogenesis, which is a fancy way of saying that, because of the reduced mass, it burns fewer calories than it did prior to the weight loss. Unless you can continue to eat fewer calories, your weight-loss efforts are doomed.

What’s more, other studies show that your body works against you. Research done years ago suggests that there’s an “appestat” in the brain, likely in the appetite center of the hypothalamus, that must be reset to adjust to a new calorie level. The problem is that it takes years to occur—some have suggested up to five years for the brain to adjust to a chronic lower caloric intake. In the meantime you will be extremely hungry most of the time, which doesn’t bode well for long-term weight loss.

Does the type of diet you eat make a difference? Indeed, some hormonal factors are affected by diet type, which could play a major role in your weight-loss success. Leptin, a protein released from fat cells that signals to the brain that the cells are full, is one, as are insulin and thyroid hormones.

More recent research shows that the key diet factors that determine appetite control—and weight-loss success—are carbohydrate and to a lesser extent protein. Specifically, eating greater amounts of unprocessed and low-glycemic-index carbs helps control appetite and prevent fat gain by modulating the activity of insulin.

Protein is important because the body burns more calories to process it and also because it directly affects appetite. For example, several studies have clearly shown that concentrated protein supplements, such as whey, provide a satiating effect on appetite—which, of course, makes dieting a bit easier and aids your efforts.

Recently, French researchers delineated precisely how that works. After you take in a high-protein food source, small protein residues called oligo-peptides interact with certain opiate receptors in the gut, sending a message to the brain. The brain responds with a message back to the gut via the nervous system. That triggers the release of glucose in the intestine, which sends another signal to the brain that results in appetite suppression.

A major reason that the weight returns after a diet is energy expenditure. The body has two types of energy expenditure: resting, which is the energy expended to keep the body alive—heart function, brain function and so on—and total energy expenditure, which includes both resting energy and that burned in activity. You don’t have to be a scientist to realize that lowered energy expenditure after a diet is over would tend to favor a return of lost weight, especially if you also can’t maintain the calorie reduction. So what types of diets favor greater resting and total energy use?

That was the focus of a widely reported study published in the prestigious Journal of the American Medical Association.1 Twenty-one overweight men and women, aged 18 to 40, followed one of three diets, all of which contained the same number of total calories but different macronutrient contents. This was a crossover-designed study, in which the subjects followed all three diets at different times.

Before they started, however, they went on another diet and achieved a 10 to 15 percent weight loss. So the study focused on maintenance diets, designed to keep the lost weight off:

1) Lowfat diet: 60 percent carb, 20 percent fat, 20 percent protein—the diet most commonly recommended for weight loss and health.

2) Low-glycemic-index diet: 40 percent carb, 40 percent fat, 20 percent protein.

3) Very low-carb diet: 10 percent carb, 60 percent fat, 30 percent protein—similar to the popular Atkins low-carb plan. It’s also similar to the way many bodybuilders eat when trying to lose excess bodyfat, although bodybuilders would have less fat and more protein.

The subjects stayed on each diet for four weeks. Those on the low-carb diet also got a fiber supplement that supplied three grams with each meal. That’s important, as constipation is a frequent side effect of low-carb diets that eliminate dietary fiber sources, such as fruits and vegetables.

The low-glycemic diet focused on carb sources that wouldn’t produce a rapid release of glucose in the body, such as vegetables, fruits and legumes. It minimized grains, which do trigger a higher glucose release.

The results showed that the lowfat diet, the most frequently recommended diet for weight loss, produced the lowest energy expenditure of the three. The low-glycemic diet produced greater rates of both resting and total energy expenditure; however, the low-carb plan produced the highest rates of both types. Specifically, the low-carb diet burned 67 more calories a day at rest than the lowfat plan, but the difference in total energy was a whopping 300 calories a day between the two diets. That wasn’t a thyroid effect, either, since the subjects showed slightly depressed thyroid output when on the low-carb plan compared to the other two diets. Thyroid, of course, controls the resting metabolic rate. Various other studies have shown that thyroid output is lower when subjects are on a very low-carb diet, but it obviously didn’t affect the energy expenditure in this study.

The subjects showed the greatest leptin sensitivity when they were on the low-carb diet, and that may have affected the energy expenditure. The low-carb diet also produced the greatest effect on high-density lipoprotein, which is considered highly beneficial for the prevention of cardiovascular disease. Another cardiac risk factor lowered during the low-carb diet was blood triglycerides.

On the negative side, the 24-hour urinary cortisol measure was highest on the low-carb diet. That’s indicative of stress. Previous studies have also shown higher cortisol for subjects who were on a very low-carb diet but not a moderate-carb diet. While higher cortisol is associated with increased fat deposition in the trunk of the body, insulin resistance and cardiovascular disease, I suggest that the cortisol was elevated because one of its the lesser known functions is to mobilize fat for energy. I believe that the low-carb diet triggered a much greater use of fat for energy, which may explain the higher cortisol. Cortisol is also the body’s major catabolic hormone, but its activity in that regard is offset by the greater protein intake, which is a feature of low-carb diets.

The low-carb diet also produced more C-reactive protein, a nonspecific measure of inflammation. Here, too, I think the reason is that the subjects were not engaged in intense exercise, and the high fat content of the low-carb diet (60 percent) likely produced the higher C-reactive protein. Had the subjects engaged in exercise, the CRP would not be an issue, I believe, but the major explanation for the higher CRP seen with the low-carb plan was lack of fiber. While the subjects did take a supplemental three grams of fiber per meal, their total daily intake was only 11.2 grams. Compare that to the average intake of 30.3 grams on the lowfat diet and 32.8 grams on the low-glycemic diet. The suggested daily intake for fiber is 30 to 50 grams, and lack of fiber is known to boost C-reactive protein and inflammation in the body.

The authors suggest that based on their initial findings, the often suggested lowfat, high-carb diet is the most likely to result in a rapid regain of weight due to changes in energy expenditure and a negative effect on leptin activity. Although the low-carb diet produced the best effects in terms of healthful changes in the body as well as energy use, they think it may be problematic because of the adverse effects on cortisol metabolism and CRP. They suggest that the best way to go for maintaining lost weight is the low-glycemic-index diet.

For bodybuilding purposes it would need to be modified, since it contains only 20 percent protein. A better plan might be to lower the fat from 40 to 30 percent with an emphasis on “good fats,” such as omega-3 and monounsaturated sources, and an increase in protein from 20 to 30 percent to foster lean-mass maintenance and counter any cortisol effects. —Jerry Brainum



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1 Ebbeling, CB, et al. (2012). Effects of dietary composition on energy expenditure during weight-loss maintenance.