Weight loss is challenging for many people. It sounds easy enough, just reduce your calorie intake and burn more calories through exercise to create an energy deficit. Unfortunately, it doesn’t always work this way. That’s partially due to a phenomenon called adaptive thermogenesis.
What is Adaptive Thermogenesis?
Adaptive thermogenesis is a term that describes how your body responds to calorie restriction. Your body’s goal is to maintain a stable environment where it has enough energy to do the many energy-requiring tasks it needs to do. So, it really DOES have your best interests in mind. To maintain homeostasis, it reacts to changes in energy balance by speeding up your metabolism (when you eat too much) or by slowing things down when you don’t consume enough energy. Adaptive thermogenesis refers to a slowing of metabolism that’s greater than expected based on lean body mass. When you lose weight, you also lose muscle. This reduces your energy needs and your metabolism slows slightly. Adaptive thermogenesis is a slowdown in metabolism that’s independent of muscle loss.
It’s nice to have a self-regulating system like this but such an efficient system can get in the way when you’re trying to lose weight. It also explains why weight loss plateaus are so common. Once you’ve reduced your calorie intake for a certain period of time, adaptive thermogenesis kicks in and your metabolism slows. Some people’s bodies are more efficient than others. In some cases, adaptive thermogenesis can kick in very early in the weight loss process, making it hard to lose weight at all.
There’s some evidence that very efficient metabolic adaptation partially explains why obese people have difficulty losing weight. Some obese individuals have a more extreme adaptive response to calorie restriction that makes it hard for them to shed extra pounds. Not only does adaptive thermogenesis make it hard to lose weight, but it also makes it difficult to maintain the weight once you lose it. There’s a reason up to 90% of people regain the weight they lost and often add more. After losing weight through calorie restriction, much of the weight you regain is body fat. This is referred to as post-starvation obesity.
What Causes Adaptive Thermogenesis?
Adaptive thermogenesis involves interaction between a number of hormones including hormones that control your appetite, like leptin, insulin, thyroid hormone and stress hormones like cortisol, norepinephrine, and epinephrine. Studies have looked at factors that might contribute to overly efficient adaptive thermogenesis. One such factor is body weight cycling where a person’s weight varies significantly over a period of time. Yo-yo dieters often get caught up in a cycle of losing weight and regaining it. Some studies show that even a single cycle of weight loss/regain significantly slows the resting metabolic rate due to adaptive thermogenesis.
Here’s something that may surprise you. Pollutants in your bloodstream may contribute to adaptive thermogenesis. You’re constantly exposed to chemicals from the environment and from the foods you eat. Meat, fish and dairy foods commonly contain organochlorides. When you’re exposed to these chemicals, they’re stored in fat tissue. Obese people tend to have higher levels of organochlorides stored in their fat relative to normal-weight people. When you lose body fat, these chemicals are released into your bloodstream. Research has found a link between higher levels of circulating organochlorides and a reduction in resting metabolic rate. One possible way organochlorides slow down resting metabolism is by altering thyroid hormone activity.
Other Factors That Contribute to Adaptive Thermogenesis
Changes in hormones like thyroid hormone, leptin, insulin, and stress hormones explain some of the metabolic slowdown that comes from adaptive thermogenesis. Other factors may come into play that makes maintaining weight loss more challenging. You may unconsciously become less active – move around and fidget less. As a result, you expend less energy after losing weight than you did before. Hunger can also become a factor as leptin levels drop. These are all adjustments your body makes to conserve energy.
What Can You Do About It?
Unfortunately, there’s little research looking at how to prevent adaptive thermogenesis. Plus, it’s not even clear what factors make one person more likely to have significant metabolic slowdown relative to another. One thing you can do is avoid weight cycling since this appears to be a major contributor to adaptive thermogenesis. This means you shouldn’t yo-yo up and down. If you try to lose weight by aggressively reducing calorie intake, your body is more likely to slow your metabolism to avoid starvation. Plus, you’ll likely cycle right back up if you manage to lose weight.
Keep your calorie deficit reasonable – 20 to 25% of the calories you need for maintenance. Research suggests using the smallest calorie deficit possible that still allows you to lose weight to avoid a metabolic slowdown. Slow weight loss takes a little more patience but it’s worth it. Make sure you’re consuming enough protein and eating mostly whole foods – no junk. Increase your calorie intake once a week to close to maintenance to increase your leptin level and boost your metabolic rate. Make sure you’re resistance training and incorporate some high-intensity metabolic resistance training into your workouts.
As far as weight loss maintenance after a calorie restricted diet, slowly increase your calorie intake in a stepwise fashion while monitoring your weight closely. Gradually increasing your calorie intake may help normalize your hormone levels and your metabolism without creating enough of a calorie surplus to cause significant weight gain.
The Bottom Line?
Adaptive thermogenesis certainly doesn’t make it any easier to lose weight and extreme diets and yo-yo dieting can make it worse. Slow and steady wins the race when it comes to sustained weight loss.
References:
International Journal of Obesity (2007) 31, 204-212. doi:10.1038/sj.ijo.0803523.
Rev Environ Contam Toxicol. 1997;152:1-55.
Medscape.com. “Role of Adaptive Thermogenesis in Unsuccessful Weight Loss Intervention”
Obesity. Volume 21, Issue 2, pages 218-228, February 2013.
Journal of the International Society of Sports Nutrition. 2014. 11:7.
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