The Myth Of Starvation Mode
Chester J. Zelasko, Ph.D. | November 25, 2005

If there is one myth passed on most often by healthcare and weight loss professionals, it’s this: “You have to eat enough calories every day, or you’ll go into starvation mode and your body will shut down.” As I stated in a recent Bulletin, the problem with that statement is that there’s no scientific evidence to support it. This Newsletter will try to make some kind of sense out of the statement and review the science on which it may be based--the Minnesota Experiment (1).

Defining Starvation Mode
What people refer to as starvation mode is a very low level of caloric intake that causes the body to start burning protein stored in muscle rather than bodyfat, and weight loss will decline. This seems the opposite of what we intuitively think: the fewer calories we eat, the more weight we can lose. Starvation mode would indicate that if we eat below a certain caloric level, we won’t lose weight at the rate we think we should.

The problem is that there is no scientific evidence to support it. If there were, a target number of calories tied to initial body weight could be established. The problem is that, based on research, no one can determine the caloric level at which starvation mode begins. What is usually stated is that while a specific number can’t be given, the best guess is that it must be less than 1,000 or so calories per day. Further, no time line is given at which point starvation mode begins. We’ve all gone days without eating because of a cold or the flu. Did our bodies start to shut down because we didn’t eat? No.

The Minnesota Experiment
During World War II, Dr. Ancel Keyes of the University of Minnesota and his research group were given permission to examine the effects of starvation on human subjects. The reason was that due to the war in Europe, fewer crops would be planted and harvested; starvation was sure to occur. Thirty-two subjects were chosen from an extensive list of conscientious objectors to the war. After determining a baseline of adequate caloric intake to maintain the subjects’ normal weight, the number of calories was cut in half for 24 weeks. Extensive data were collected on metabolism, bodyfat, lean body mass, and numerous psychological parameters; this study was one of the first to identify the effects of dieting and anorexia nervosa on human beings.

As expected, the subjects all lost weight--up to 25% of their original body weight. The psychological strain was significant, and as the study continued the subjects became obsessed with food. From a metabolic perspective, metabolism decreased as caloric intake decreased, which led to the theory of starvation mode.

The important point is that the decrease in metabolism was proportional to the weight lost. Remember, the caloric intake was cut in half--the average was about 1,500 calories per day. The subjects’ metabolism didn’t shut down, it declined proportionately.

In a continuation of the study, the subjects resumed eating a normal diet to determine how long it would take to regain the weight they lost. Many subjects gained back even more weight than they had lost, and that became the basis for the “yo-yo syndrome”--but that’s a topic for another day.

Losing Fat vs. Losing Protein
What seems to have attracted attention was that subjects lost some protein mass in addition to body fat. While unexpected, it shouldn’t have attracted the attention it did. Why not? Simply because a person doesn’t need as much muscle to carry around 150 pounds as he does to carry around 200 pounds. It should be expected that a person who loses weight will lose some muscle mass as well.

In a further analysis of the original data, researchers established that the proportion of bodyfat and protein lost during the study was directly proportional to the bodyfat of the subjects at the beginning of the study (2). In short, those who had higher bodyfat lost fat first and at a higher proportion. Those who didn’t have much bodyfat lost more protein mass.

Even though the original experiment is the basis for much of what is said about starvation and weight loss today, the single most important factor that affected the results is rarely mentioned: only two subjects could be classified as overweight and none was obese. The Minnesota experiment established the effects of starvation on normal-weight people, not overweight or obese people. It has little if anything to do with the obesity crisis the United States and Canada face today. There are many other factors as to why this study has limited application to weight loss today, but the lack of obese subjects is the most significant.

So what’s the point? Am I going to endorse fasting as a method of weight loss? Absolutely not, but the nature of the questions I’ve been getting led me to believe that the misinterpretation of what starvation mode really means is affecting people’s weight loss efforts. Some readers have even asked if missing a snack would result in going into starvation mode.

Losing weight and keeping it off comes down to the same four words: eat less, exercise more. Let me add two more: eat less, exercise more, for life. How you do that is really up to you as long as you sustain your health at optimal levels.

References:
  • Keys A, Brozek J, Henschel A, Mickelsen O, Taylor HL, eds. The biology of human starvation. Vol. 1-2. Minneapolis: University of Minnesota Press, 1950.

  • Dulloo AG, et al. Autoregulation of body composition during weight recovery in humans: the Minnesota Experiment revisited. Int J Obes Relat Metab Disord. 1996 May;20(5):393-405.
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