Welcome to Straight Talk on Health. I’m your host Dr. Chet Zelasko. Straight Talk on Health is a joint production with WGVU in Grand Rapids MI. I examine the practical application of health information. Nutrition. Exercise. Diet. Supplementation. I look at the science behind them and let you know whether it’s something to consider or not. You can check out other things that I do on my website Drchet.com and sign up for my free emails.
If there is still 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.” The problem with that statement is that there’s no scientific evidence to support it. On this podcast, I’m going to try to make sense out of the statement, review the science on which it may be based--the Minnesota Experiment, and provide a more realistic explanation of Adaptive Thermogenesis.
Let’s define starvation mode first. 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 the rate of weight loss will slow down. 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 not enough 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.
Enter the Minnesota Starvation 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 to attain a 25% weight loss in 24 weeks, cutting the baseline calories in half. 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. 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. Maybe this is where“yo-yo dieting” came from.
What seems to have attracted attention was that subjects lost some muscle 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 or she 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. In short, those who had higher bodyfat lost fat first and at a higher proportion. Those who didn’t have much bodyfat lost more muscle mass.
Even though the original experiment is most likely the basis for much of what is said about starvation and weight loss, 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.
There is also the concept of adaptive thermogenesis. After reading several papers about it, it can mean several things. The initial research suggested that weight loss was accelerated for a period of time during a weight loss program. After several weeks, the metabolism normalized to reflect the persons actual food intake and body weight. In other studies, the focus was on a longer lasting decrease in metabolism thereby requiring a further reduction in calories to maintain weight loss. Still another use of the term AT was used to explain a rapid weight gain of fat versus muscle mass after a return to a typical eating pattern. I really can’t provide clarity to you about AT because the research is relatively sparse in humans with different variables examined in studies over the decades.
Let me give you an educated theory about what may be going on with overweight or obese people who attempt to lose weight and maintain it. At the initial part of weight loss, maybe up to 6 weeks, more weight is lost than would be predicted based on the number of calories restricted every day. That could simply be attributed to inaccurate estimates of the estimated calories needed to maintain the starting weight. Calories are reduced a specific number or acertain percentage and the weight loss is greater than would be expected. I’ve experienced that myself. There are theories about leptin, brown fat, and genetics to mention a few. I would not doubt that genetics are involved but we haven’t really gotten a handle on which genes nor what they do.
Once somebody has lost the weight they want to lose, they are faced with an abundance of food in Westernized society. It’s just so easy to slowly but surely regain weight unless a person is diligent about eating and exercising. I’ve done that several times myself. It’s not mysterious. I have yet to meet a person who found a way to eat, that helped them lose weight, not maintain it as long as they continued with a healthy eating plan and sustained an exercise program.
The concern is that when weight is gained back, it’s mostly fat massinstead of muscle mass. It’s not really a mystery. It takes longer to build back muscle then it does to overeat and fill up fat cells. Yes, there is a lowering of metabolism due to the loss of muscle but if a person works to add back muscle, they can raise their metabolism to match their new distribution of fat to lean tissue in the body. It just gets harder to do the older we get. That’s my observation and interpretation of the limited science.
The solution is simple yet not easy: eat less. Eat better. Move more. For life. Simple to say, difficult to do. That’s all the time I have for this episode. If you like this podcast, please hit the share button and tell your friends and colleagues about it. Until next time, this is Dr. Chet Zelasko saying health is a choice. Choose wisely today and every day.
—-
References:
1. 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.
2. 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.
3. British Journal of Nutrition (2001), 85, 715±723
4. Metabolism. 2020 September ; 110: 154303. doi:10.1016/j.metabol.2020.154303.
5. Reviews in Endocrine and Metabolic Disorders (2025) 26:871–888
