Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily
Have you ever wondered how some people can eat whatever they want and remain thin, while others struggle to lose weight (and to keep it off)? Professor Ormsbee explains this phenomenon.
What Is Set-Point Theory?
Set-point theory—which also goes by names like your lipostat or your homeostatic control mechanism—states that you have a set weight where your body is most comfortable. By this definition, if you were to either gain or lose weight, your body would do all it could to pull you back to the original, starting weight.
For example, if you start to diet and exercise properly, it is common to lose weight rapidly at first. Then the rate of weight loss slows down—a lot. In other words, you hit a plateau.
“Too many times, I’ve seen great intentions and a great start to a new lifestyle, but in the end, despite great efforts and initial changes, body fat and weight tend to creep back up, and there is no improvement in body composition or health,” Professor Ormsbee said.
Often, if you restrict your food intake enough, it dramatically increases your hunger levels. This response is called hyperphagia or increased hunger.
Truth about Diets
Here is the truth about most diets—eventually you simply return to the ways you used to eat. Typically, this is because you change so many things all at once that you can’t keep it up.
Other times, the diets are unsustainable. In fact, roughly 78% of people who initially lose about 5% of their body weight eventually gain it back over five years.
When you eat again after a severe diet restriction, your fat mass comes back quickly compared to the slower development of lean muscle. You actually feel hungry until your muscle mass has fully recovered.
You also slow your metabolic rate—in part due to the loss of lean mass. If you combine reduced energy expenditure with increased hunger, you eventually end up with more fat mass and body weight after dieting.
Is Weight Fixed?
This brings us back to the set-point. Could it be that we are just ingrained with a body weight that our bodies work hard to defend?
“Actually, yes, this does seem to be true,” Professor Ormsbee said.
Think about your friends who can eat whatever they want without gaining any weight. You probably would say that this type of person has a fast metabolism, right? Well, you can also say they have a low set-point.
The same thing goes the other way, too. Maybe you are someone who seems to put on weight quickly. In this case, you may have a slow metabolism or a high set-point.
So, how does the set-point work? Essentially, you have a well-regulated internal control mechanism in the hypothalamus that tightly maintains your pre-set level of body fat and body weight. Your hypothalamus responds to signals from your fat cells, gastrointestinal tract, and pancreas to alter your metabolism, hunger, body fat levels, and weight.
Not only do these changes occur, but you also have some hormones like ghrelin, leptin, and serotonin that control your hunger and appetite. Just as you might expect, if you lose weight, there is a good chance you’ll end up hungry, and if you gain weight, you may end up losing your appetite.
Metabolism and Dieting
It’s important to know that with weight loss, your metabolic rate will decrease. You will require fewer calories than you used before you started losing weight. Eventually, the initial decrease in food you eat becomes the normal amount of food you require to sustain your new size.
Your body no longer sees that you are eating less, so there is no energy deficit. Now—at your lower weight—you have to adjust, reducing your calories even more to spark more weight loss.
For example, in one study, after 10 weeks on a weight loss diet, men and women did lose weight. However, some of their hormones like leptin, ghrelin, cholecystokinin, and others also changed in a way that made them hungrier and lowered their metabolic rates—and these changes persisted for months after the study ended.
The opposite is true, too—if you are trying to gain weight by eating a lot more food, you will increase your metabolic rate in an unconscious effort to bring your weight back to a set-point where it’s comfortable hanging out.
Even in overeating research studies, where people were fed a lot of extra food, the participants ended up gaining far less weight than the researchers predicted. When the participants went back to eating normally, they went right back to their initial body weights.
Time and time again,
How, then, can you change your body composition for good? Professor Ormsbee explains in tomorrow’s article.
This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.
Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his MS in Exercise Physiology from South Dakota State University and his PhD in Bioenergetics from East Carolina University.