|A participant of the Minnesota Starvation Experiment (Source)|
There are diets (restricting food intake) and there are diets (eating a particular type or mix of food). This article focuses on the former. The Washington Post discusses the topic with Tracy Mann, a researcher at the University of Minnesota. Mann explains:
What people tend to think is that if only Joe had self-control then he could succeed on his diet forever. And that's not accurate, as it turns out. That's not true.Although not mentioned in the article, the University of Minnesota undertook a study on near starvation in 1944, known as the as the Minnesota Starvation Experiment. This article at the American Psychological Association gives a brief description of the experiment:
After you diet, so many biological changes happen in your body that it becomes practically impossible to keep the weight off. It's not about someone's self-control or strength of will.
What kind of biological changes?
There are three biological changes that take place that seem most important to me.
The first is neurological. When you are dieting, you actually become more likely to notice food. Basically your brain becomes overly responsive to food, and especially to tasty looking food. But you don't just notice it — it actually begins to look more appetizing and tempting. It has increased reward value. So the thing you're trying to resist becomes harder to resist. So already, if you think about it, it's not fair.
Then there are hormonal changes, and it's the same kind of thing. As you lose body fat, the amount of different hormones in your body changes. And the hormones that help you feel full, or the level of those rather, decreases. The hormones that make you feel hungry, meanwhile, increases. So you become more likely to feel hungry, and less likely to feel full given the same amount of food. Again, completely unfair.
And the third biological change, which I think people do sort of know about, is that there are metabolic changes. Your metabolism slows down. Your body uses calories in the most efficient way possible. Which sounds like a good thing, and would be good thing if you're starving to death. But it isn't a good thing if you're trying to lose weight, because when your body finds a way to run itself on fewer calories there tends to be more leftover, and those get stored as fat, which is exactly what you don't want to happen.
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Dieting is actually a lot like starving, physically. It's living like you're starving. A lot of people do it, but what they're actually doing is living as if they're starving. They're putting their body into that exact same state that it would be in if they were literally starving to death.
The research protocol called for the men to lose 25 percent of their normal body weight. They spent the first three months of the study eating a normal diet of 3,200 calories a day, followed by six months of semi-starvation at 1,570 calories a day (divided between breakfast and lunch), then a restricted rehabilitation period of three months eating 2,000 to 3,200 calories a day, and finally an eight-week unrestricted rehabilitation period during which there were no limits on caloric intake. Their diet consisted of foods widely available in Europe during the war, mostly potatoes, root vegetables, bread and macaroni. The men were required to work 15 hours per week in the lab, walk 22 miles per week and participate in a variety of educational activities for 25 hours a week. Throughout the experiment, the researchers measured the physiological and psychological changes brought on by near starvation.
During the semi-starvation phase the changes were dramatic. Beyond the gaunt appearance of the men, there were significant decreases in their strength and stamina, body temperature, heart rate and sex drive. The psychological effects were significant as well. Hunger made the men obsessed with food. They would dream and fantasize about food, read and talk about food and savor the two meals a day they were given. They reported fatigue, irritability, depression and apathy. Interestingly, the men also reported decreases in mental ability, although mental testing of the men did not support this belief.
For some men, the study proved too difficult. Data from three subjects were excluded as a result of their breaking the diet and a fourth was excluded for not meeting expected weight loss goals.
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The Minnesota Starvation Experiment ended in October 1945. Its results painted a vivid picture of the physical and psychological decline caused by starvation and offered guidelines on rehabilitation. In the restricted rehabilitation, calories were increased in increments. The experiment also looked at unrestricted rehabilitation and — even though participants were warned against it — some engaged in extreme overeating. Of the various diets and supplements that were studied during the rehabilitation phase of the experiment, the most reliable weight-gain strategy was high caloric intake. Simply put, starving people needed calories. Food and lots of it was the key to rehabilitation. It was as true for those released from the laboratory in Minnesota as it was for those freed from the privations of war in Europe.(See also "Starvation: What Does it Do to the Brain?" discussing the psychological/emotional issues that the participants suffered). An article at io9 discussing the study further relates:
During the three-month rehabilitation period, different groups of men were supposed to receive different amounts of food. Researchers quickly scrapped that idea after the lower-calorie-diet men didn't show signs of recovery. Some even lost weight after their calorie intake was increased. The lack of calories had caused some of the men's legs to swell with water, and a calorie infusion allowed them to shed the excess liquid. Despite the sincere efforts of the researchers, almost no men felt recovered after just three months. On the day they were allowed to eat again, quite a few overate and got sick. One had his stomach pumped. Even getting back to their earlier weight didn't help. They packed on the pounds well beyond that. Some said they couldn't stop obsessively eating for a year. There was never "enough" food for them.