Does Dieting Make You Fat? Evidence and Debate

Introduction: The Dieting Paradox

"Dieting makes you fat." On the surface, this assertion seems counterintuitive. After all, dieting for weight loss usually involves calorie or carbohydrate reduction, restricted eating, eating by certain rules, and/or exercise — all of which typically result in weight loss to varying degrees. Yet most dieters regain the majority of the weight they lose. The lack of success of most popular diets has caused many people to assert that dieting actually makes the dieter fat, based on metabolic damage combined with the psychological deprivation that dieting causes.

This paper argues that, given the weight of the evidence, although the physiological case that dieting leads to weight gain through metabolic damage remains inconclusive, there is substantial evidence that dieting can foster a negative relationship with food that causes weight gain in the long run.

Metabolic Effects of Yo-Yo Dieting

"A decreased rate at which the body burns calories; more fat and less muscle tissue; a greater preference for fatty foods; more difficulty losing weight the next time around; an increased risk for heart disease and diabetes; even premature death. Those are just some of the hazards researchers have theorized may result from yo-yo dieting, the losing and regaining of the same pounds many times over the years" ("Theories on yo-yo dieting unwind," Diet & Nutrition Letter, 1994). Studying metabolic rates between dieters and non-dieters can be challenging because it would not be ethically acceptable to force someone to gain and lose weight repeatedly over many years. However, descriptive research studies do indicate a correlation between lower metabolic rates and extreme dieting.

One study of 163 non-Hispanic white women measured dietary restraint and disinhibition and found that women "who reported dieting at study entry were heavier at study entry and gained more weight over time than did nondieters. Finally, a significant interaction between restraint, disinhibition, and dieting showed that restraint moderated the effect of disinhibition on weight differently in nondieters than in dieters" (Savage, Hoffman & Birch, 2009). For individuals not actively dieting, restraint was associated with lower body weights, but for dieters, higher body weights were associated with attempts at restraint — indicating that dieting encouraged a feast-and-fast binge cycle (Savage, Hoffman & Birch, 2009).

A meta-analysis of 43 separate studies on the topic proved inconclusive overall. Most studies evaluating the influence of weight cycling on metabolism "showed no adverse effects on body composition, resting metabolic rate, body fat distribution, future successful weight loss, or risk factors for cardiovascular disease," but there was an association between extreme weight variation and increased mortality and morbidity ("Yo-yo dieting may not be a problem," HealthFacts, 1995).

Critics of the thesis that dieting causes weight gain point out that another problem with research on chronic dieters is that with every successive diet, the dieter becomes older — and with age, muscle mass decreases in proportion to fat, and metabolism slows even among normal-weight individuals. There is evidence that studies claiming "repeated dieting causes a rise in the proportion of body fat to lean muscle tissue failed to account for the fact that over the years people tend to put on more fat and lose more muscle" ("Theories on yo-yo dieting unwind," Diet & Nutrition Letter, 1994). Apparent difficulties with losing weight may simply reflect the reality that dieters are getting older with each successive attempt, which would explain why weight loss seems progressively harder with age.

Age, Muscle Loss, and Confounding Factors

Research on body composition and metabolism from the National Institutes of Health underscores how complex the interaction between dieting, aging, and metabolic function truly is, making clean causal claims difficult to establish from observational data alone.

Even more significant in support of the idea that dieting makes people fat are comparative studies of adolescents and young adults, who are not yet subject to age-induced muscle loss and slowed metabolism. These studies indicate that dieters still gain weight over time. One study of wrestlers found that those who frequently engaged in weight restriction and severe yo-yo dieting not only weighed more but had lower metabolic rates, pound for pound, than wrestlers who did not actively control their intake. It is true that "the study did not determine whether the yo-yo dieting reduced the wrestlers' calorie-burning ability or whether they burned fewer calories than the non-cyclers to begin with — and therefore needed to diet more often to 'weigh into' their desired weight category" ("Theories on yo-yo dieting unwind," Diet & Nutrition Letter, 1994). In other words, wrestlers who struggled to make weight may have had slower metabolisms to begin with, rather than having developed them through dieting.

Evidence from Adolescents and Young Adults

A similar finding emerged from a study of adolescents in general. In one longitudinal study of 1,902 young adults tracked from middle school through late adolescence, frequent dieting was associated with greater BMI increases compared to non-dieters as they matured. "For example, females using unhealthy weight control behaviors at both Time 1 and Time 2 increased their BMI by 4.63 units as compared with 2.29 units in females not using these behaviors" (Amber & Standish, 2012). Notably, for girls, both healthy dieting and unhealthy weight control behaviors were associated with long-term weight gain, while for boys "the picture was less clear-cut," with only unhealthy strategies such as fasting found to be associated with weight gain (Amber & Standish, 2012).

It is possible that teens already at risk for higher BMIs are more prone to dieting than their peers, although the finding that only boys who used extreme crash dieting — not moderate dietary controls — experienced weight gain suggests there may be something particularly damaging about radical weight reduction strategies. Girls, even those who did not use unhealthy weight control behaviors, may also be more prone to chronic dieting in order to meet unrealistic cultural expectations, given the well-documented greater cultural pressure on females to be thin.

In general, the fact that adolescents who begin dieting show significantly higher weights over time than those who did not diet, combined with existing research on adults, tends to support the notion that dietary restriction over time decreases metabolism and increases weight gain. At the very least, a strong correlation has been established between dieting and weight gain, indicating that traditional diets are ineffectual as a means of long-term weight control.

Dieters themselves often report extreme hunger when restricting calories, even though their metabolisms are said to have slowed. The reasons for this are not entirely clear. Weight regulation is a still-evolving area of research, and there is some evidence that dietary restriction can interfere with the feedback loop between fat depletion and appetite signaling. Studies indicate that "human subjects recovering from starvation continue to overeat well after body fat has been restored to pre-starvation values, thereby contributing to 'fat overshooting'… feedback signals from both fat and lean tissues contribute to recovering body weight through effects on energy intake and thermogenesis, and that a faster rate of fat recovery relative to lean tissue recovery is a central outcome of body composition autoregulation that drives fat overshooting" (Dulloo, Jacquet, & Montani, 2012).