The Dangerous Health Implications of Low-Calorie Diets

When you think about dieting, what comes to mind?

Hunger? Rapid fat loss? Rebound weight gain? Metabolic adaptation?

These are all relatively well known effects of dieting.

We’ve all suffered through the hunger pangs of skipping meals. Most of us have gone through the roller coaster of emotions that accompany fat loss and the discouraging experience of an expanding waistline as we regain lost weight.

It is well publicized that more than 90 percent of dieters will regain all the fat (and then some) that they lose while dieting. What’s less known but just as chilling is the severe and harmful effects prolonged dieting can have on mental function.

Based on the landmark Minnesota Semi-Starvation Experiment and subsequent research into how eating disorders change brain architecture, this article will describe the dangerous effects that long-term dieting can have on the body and mind.

The Minnesota Semi-starvation Experiment:

It sounds like something out of Frankenstein or the Twilight Zone: In 1945, 36 conscientious World War II objectors were enrolled in an experiment at the University of Minnesota to determine the physical and psychological effects of prolonged low-calorie intake with the goal of identifying the best rehabilitation strategies for assisting famine victims at the end of World War II. The subjects were all healthy, psychologically normal men who volunteered for the study as an alternative to military service.

During the first three months of the study, subjects ate normally while their behavior, personality, and eating patterns were studied in detail. Calorie intake was approximately 3,200 a day for maintenance.

During the next 6 months, the men were restricted to approximately half of their former food intake and lost on average 25 percent of their weight. They ate 1,570 calories daily (which is precisely the level of caloric deficit used to define “conservative” treatment for obesity). The men were also fairly physically active, having daily work assignments and walking regularly, totaling 22 miles a week. After the 6-month low-calorie period, they had a 3-month period of rehabilitation during which they were gradually re-fed.

Overall, the men experienced dramatic physical, social, and psychological changes that persisted during the re-nourishment and rehabilitation phases:

First, subjects had a dramatic increase in food preoccupation. Food became a principal topic of conversation, reading, and day dreams. Subjects reported getting a vivid, vicarious pleasure from watching others eat or from just smelling food. Concentration on non-food related activities grew increasingly difficult because subjects became plagued with incessant thoughts of food and eating.

Cookbooks, menus, and information bulletins on food became intensely interesting to subjects who previously had little or no interest in dietetics or agriculture. Despite little interest in culinary matters, about 40 percent of the men mentioned cooking as part of their post-experiment plans. For some, the fascination was so great that they actually changed occupations after the experiment with three becoming professional chefs.

Food-related behavior began to change as well: Unsurprisingly, gum chewing, and coffee and tea consumption increased dramatically and had to be limited to 9 cups of coffee or tea a day. Mealtimes became ritualistic with subjects lengthening meals, often spending as much as 2 hours eating where they would have previously eaten in minutes. Many subjects started smuggling food out of the dining room to consume it in their bunks.

Stockpiling wasn’t just limited to food. Subjects began collecting food utensils, coffeepots, and hot plates, along with non-food related items such as old books, second-hand clothes, and other junk. Often after making such purchases, which could be afforded only with sacrifice, the men would be puzzled as to why they had bought them.

A second effect was an inability to control their eating. Although some subjects tolerated the restriction fairly well, others experienced a complete breakdown in control and episodes of binge eating followed by self reproach. During re-feeding many subjects lost control of their appetites and ate more or less continuously.

One man ate immense meals (as much as 6,000 calories daily), yet would start snacking an hour after his last meal. Weekend meals were even more of a problem with many subjects unable to stop eating, having daily intake commonly ranging between 8,000 and 10,000 calories.

The lack of meal satisfaction and the feelings of constant hunger persisted even after 12 weeks of re-feeding. By 5 months after the return to their normal diet, most subjects regained their normal eating patterns, but there still were a few who felt that they could never get full and were eating abnormal amounts.

These findings are supported by a large body of research indicating that habitual dieters display marked overcompensation in eating behaviors that is similar to binge eating. Based on more recent studies on the effects of calorie restriction, it’s likely subjects experienced leptin resistance. Leptin is a hormone secreted from fat tissue that blunts hunger in response to a meal. The brain’s sensitivity to leptin can be altered in response to a long-term calorie imbalance.

A third area of impact was in terms of psychological and social behavior. Many subjects experienced significant emotional deterioration that was typified by depression, mood swings, anxiety, and irritability. Outbursts of anger were common, as was apathy, as subjects who were once neat and fastidious started to neglect aspects of personal hygiene.

Additionally, subjects became progressively more withdrawn and isolated over the study. Humor and a sense of comradeship decreased amidst feelings of social inadequacy. Relationships with women declined and those who continued to see women socially found that their relationships became strained.

Finally, subjects had changes in neurological function. They demonstrated decreased need for sleep and a hypersensitivity to light and noise. They also reported impaired concentration and memory, however, interestingly, there was no evidence of diminished intellectual abilities based on testing.

Subjects also had slowing of physiologic processes including a drop in body temperature, and a decrease in heart rate and respiration. Metabolic rate dropped by 40 percent below normal levels. Basically, all physiological processes slowed down, reflecting the body’s extraordinary ability to adapt to a low-calorie intake by reducing its need for energy.

Significance of The Semi-Starvation Study

Evolutionarily, starvation was one of the greatest threats early humans faced. This study highlights the changes humans experience in response to long-term caloric restriction: They became more oriented toward food, undergoing physical adaptations that allow the body to preserve energy as well as brain changes that shifted most aspects of behavior to be geared at finding food.

Changes To Brain Chemistry

Based on studies done on subjects with anorexia, we know that people experience changes in brain chemistry that are not easily recovered from when engaging in long-term, low-calorie dieting. For example, in anorexia patients who are underweight, brain volume and grey matter are significantly reduced. This decrease in brain chemistry negatively impacts cognitive function, mood, anxiety, and behavior towards food.

Scientists theorize that anorexics are unable to develop healthy food-related behaviors due to the lasting changes in brain chemistry and structure that occur in response to a sustained low-energy intake.

This highlights the catch-22 of recovery from anorexia. Individuals with anorexia are typically cognitively impaired and require sustained time at a healthy weight for cognition to fully improve. Yet, it is partly the cognitive symptoms that make sufferers believe there is “nothing wrong” and reject treatment.

The Question Of Willpower

In public health, there is a popular notion that body weight is easily altered if one simply exercises “willpower,” eating less and moving more. Based on the behavioral and physical adaptations dieters undergo, “willpower” is not enough to override the drive for food and survival that kicks in.

This study also questions the theory (or hope) that the human body will simply get reprogrammed at a lower set point once weight loss is achieved. In the Minnesota study, the volunteers’ experimental diet was unsuccessful in overriding their bodies’ strong propensity to defend a particular weight level—on average they gained back their original weight plus about 10 percent.

This is common in yo-yo dieters who typically end up at a higher body weight once they start gaining back the weight. Contradictory to most reports of weight cycling dieters, the Minnesota subjects typically had weight gradually decline so that by the end of the follow up period they were approaching their pre-experiment weight levels.

What About Longevity-Focused Calorie Restriction?

You may have heard about the practice of calorie restriction—a practice in which subjects restrict calories below normal in an effort to achieve longevity and health benefits. Animal studies show that calorie restriction can extend lifespan and lower disease risk.

A large-scale study called CALERIE from Tufts University found that normal-weight subjects who lowered energy intake by 25 percent for 2 years reduced body weight and experienced a range of positive health and mental effects: Compared with a control group, the calorie restrictors had improved mood, lower tension, better sleep, and improved general health.

The primary difference between CALERIE and the Minnesota study is the degree of calorie restriction. The CALERIE study dropped energy intake by a quarter, and calorie intake was personalized with each person having their metabolic rate and average activity levels tested in order to determine calorie needs.

For example, a male doctor in the study normally burned 3,300 calories and was reduced to 2,500 for the CALERIE study. A female molecular biologist who normally burned 2,226 had her energy intake reduced to 1,670—a value that is still higher than that given to the men in the Minnesota experience who were probably much more physically active based on their work detail and walking requirements.

It is also noteworthy that some subjects in the CALERIE trial were asked to leave because they were developing anemia or bone mineral loss, showing that even moderate calorie restriction is not appropriate for everyone.

What Can We Take Away From These Studies?

At first glance it might seem that the Minnesota study isn’t relevant to today’s overweight population. But consider the following facts:

• Despite evidence that they don’t work for long-term weight loss, low-calorie and fad diets continue to be popular
• It’s common for young women to slash calories below 1,200 calories a day in an effort to lose body fat.
• A staggering 2/3 of collegiate female athletes are actively dieting in an effort to lose weight
• Eating disorder rates are increasing despite greater awareness of the dangers.
• The strongest public health message for combating obesity is to “eat less, move more.”

There’s no easy solution to obesity or to the obsession our culture has with body weight. The healthiest thing we can do is take an approach in which we strive to eat mindfully and intuitively, opt for the most nutritious, whole foods available, and train in a way that enhances physical function and body composition.