Understanding Metabolic Adaptation and the Negative Effects During Weight Loss

Obesity has become a worldwide epidemic, with almost 650 million adults globally being classified as obese and 1.9 billion being classified as overweight. Obesity is a chronic disease contributing to a slew of related health complications, including diabetes, heart disease, and stroke. With such dangerous implications, individuals may take drastic measures to begin losing weight and bettering their health.

Calories restriction is one of the most popular methods overweight individuals use to start shedding the pounds. In vigorous attempts to lose weight, some individuals may overly restrict their calorie intake, almost starving themselves. While often efficacious initially, prolonged and drastic restriction can have detrimental effects on your weight loss journey. One of these consequences is metabolic adaptation. This article will define metabolic adaptation and explain how it can negatively impact your weight loss journey¹.

What is metabolic adaptation?

Metabolic adaptation occurs when your body changes its processes to decrease components of your energy expenditure, better metabolic efficiency, and raise cues for energy intake. Your body’s adaptations include changes to your hormones, efficiency of your mitochondria, and thermogenesis with the goal of lowering your energy expenditure, lowering satiety, and increasing hunger.

Intense caloric restriction can cause metabolic adaptations. The consequences of strict dieting can make it difficult to continue to lose weight and pose the threat of weight regain².

What causes metabolic adaptation?

We established that metabolic adaptations are caused by changes to our energy balance in the body. Several factors influence this energy balance in the body, including behavioral, nutritional, behavioral, psychological, and physiological influences. These factors contribute to how your body uses energy, which involves a balance between total daily energy intake (TDEI) and total daily energy expenditure (TDEE).

Your diet and activity levels can cause metabolic adaptations in the following ways:

Starvation. A common misconception among overweight individuals is that excessively cutting calories will generate fast and dramatic results. While this may be true in the beginning, starving yourself can actually induce metabolic changes that work against you.
Poor nutrition. Several factors contribute to your TDEI, including the food you eat. Therefore, having a poor diet affects your TDEI, affecting the energy balance in your body.
Lack of exercise. Exercise and physical activity contribute to your body’s TDEE. Living a sedentary lifestyle, therefore, will influence your body’s energy balance³.

What are the mechanisms underlying metabolic adaptation?

As previously mentioned, there are several potential mechanisms underlying metabolic adaptation. These include changes to your body’s metabolic rate, your body’s endocrine response, and changes to mitochondrial efficiency.

Changes to metabolic rate

To understand the concept of metabolic adaptation, it is important to first define resting metabolic rate (RMR). RMR, also referred to as resting energy expenditure, is the amount of energy the body needs to operate in a resting state. More specifically, it refers to energy expended when you are awake having not exercised for at least 12 hours³. RMR makes up the majority of our body’s energy requirements, accounting for up to 60 to 70 percent of your total daily energy expenditure (TDEE)¹.

With drastic weight loss, the RMR can decrease more than what is typically expected. For example, one study found that after three weeks of calorie restriction and weight loss, energy-expending tissue accounted for one third of RMR decline. The additional two-thirds of the RMR decline were unaccounted for but likely have to do with a decrease in metabolic activity in other tissues. Therefore, experts postulate there are two main contributors to RMR decreases: a reduction in metabolically active tissue and a decline in metabolic activity in other tissues⁴.

In summary, a decrease in metabolically active tissue results in adaptive thermogenesis, referred to as a decrease in TDEE. Some researchers postulate that the body does this to try to restore one’s original body weight. This may explain why individuals often hit a plateau in weight despite continuing to restrict their calorie intake and weight regain².

Changes to your hormones

Hormones are a key contributor to regulation of energy and body composition. Likewise, they are likely implicated in the process of metabolic adaptations. Such hormones include:

Thyroid hormones. Triiodothyronine (T3) is a thyroid hormone that controls your body’s metabolic rate. Likewise, having increased thyroid hormones (hyperthyroidism) can increase your metabolic rate, while having lower levels of thyroid hormones (hypothyroidism) can decrease your metabolic rate.
Leptin. Your body releases leptin from its body fat tissues to help maintain weight. It is also an indicator of energy availability, energy expenditure, and satiety.
Insulin. Though insulin’s main function is to manage your blood sugar levels, it also signals energy availability and satiety.
Though testosterone is mainly implicated in regulating muscle protein and muscle mass, it may also regulate fat mass.

Research evaluating the body’s endocrine response to caloric restriction demonstrate hormone changes that lower metabolic rate and increase hunger. For example, trials have demonstrated that energy restriction decreases in thyroid hormones, insulin, leptin, and testosterone².

Changes to mitochondrial efficiency

The mitochondria exert several actions implicated in the energy production process. Processes such as proton leak are closely related to energy expenditure and metabolic efficiency.

The mitochondria generate adenosine triphosphate (ATP), an important energy molecule, by moving protons across the mitochondrial membrane. Protons can leak across the membrane via UCPs in a process known as “proton leak”. Proton leak contributes to energy expenditure. When decreasing your calorie intake, proton leak decreases in parallel. This mitochondrial adaptation, along with several others, causes energy restriction, making weight loss difficult and promoting weight gain².

What are the consequences of metabolic adaptation?

Via the aforementioned mechanisms, metabolic adaptations can negatively affect weight loss. A common misconception among patients is that they should implement intense calorie restriction in order to shed pounds fast. However, this ends up working counterintuitively in most cases. Starvation leads to lower muscle mass, a decreased RMR, and hormone changes that prevent you from effectively losing weight. Additionally, these metabolic adaptations can also contribute to weight regain even after achieving your weight loss goals. Therefore, to effectively manage and maintain weight, it is important to implement healthy and balanced methods for the best results.

How do I lose weight in a healthy and effective way?

Studies have indicated that moderate and severe caloric restriction, though effective in the initial months, were associated with weight regain over time⁵. This is likely due to metabolic adaptations and the mechanisms underlying them.

Starvation may be a “quick fix” to rapidly shed the pounds, but it is ineffective after extended periods of time. The consequence of metabolic adaptations maybe discouraging for those looking to lose weight, however, there are safer and more effective ways to lose weight, some of which include:

Eating an abundance of vegetables: Vegetables are low-calorie food options low in fat and packed with fiber, making them excellent components of a well-balanced diet aimed at weight loss. Additionally, they are a great source of vitamins and minerals, supporting your overall health as wellness.
Make protein intake a priority: The average human should never consume less than 60 grams of protein per day divided into 20-24 grams per meal to maximize protein syntheses. Requirements increases as activity increases or for individuals with large amount of muscle mass.
Choosing healthy, whole foods: Just because something is low in calories does not make it healthy. Reading food labels can help you to know what you are putting into your body and ensure that those ingredients are supporting your nutritional needs and weight loss journey.
Avoid processed foods and sugar: In line with eating whole foods that are close to the source, also avoid eating overly processed foods. Additionally, eliminate refined and excess sugar from your diet.
Increase your intake of fiber: Fiber can help you feel full, preventing you from eating more calories. You can find fiber in foods sources such as vegetables, beans, lentils, brown rice, and whole grain bread.
Exercising regularly: Engaging in physical activity is essential to losing weight, as it can help you burn calories in addition to lowering your caloric intake through diet. Exercising can also help you maintain your weight once it is lost, preventing regain. There are also several other health advantages to physical activity, lowering your risk for certain diseases and conditions.
Other preventive strategies include GI health, managing stress, quality sleep, and nutraceutical supplementation.

Conclusion

Excessively restricting calories can be detrimental to your health and weight loss journey by inducing metabolic adaptations. Metabolic adaptations can take on many forms, including changes to your energy balance, hormones, and bodily processes. Ultimately, metabolic adaptations can work against you, preventing you from losing weight or promoting weight gain. Thus, it is important to instead implement healthy weight loss strategies, such as exercising regularly and intaking a nutritious and well-balanced diet.

References

Martin, A., Fox, D., Murphy, C. A., Hofmann, H., & Koehler, K. (2022). Tissue losses and metabolic adaptations both contribute to the reduction in resting metabolic rate following weight loss. International Journal of Obesity, 46(6), 1168–1175. https://doi.org/10.1038/s41366-022-01090-7
Trexler, E. T., Smith-Ryan, A. E., & Norton, L. E. (2014). Metabolic adaptation to weight loss: Implications for the athlete. Journal of the International Society of Sports Nutrition, 11(1), 7. https://doi.org/10.1186/1550-2783-11-7
Casanova, N., Beaulieu, K., Finlayson, G., & Hopkins, M. (2019). Metabolic adaptations during negative energy balance and their potential impact on appetite and food intake. Proceedings of the Nutrition Society, 78(3), 279–289. https://doi.org/10.1017/S0029665118002811
McMurray, R. G., Soares, J., Caspersen, C. J., & McCurdy, T. (2014). Examining variations of resting metabolic rate of adults: A public health perspective. Medicine and Science in Sports and Exercise, 46(7), 1352–1358. https://doi.org/10.1249/MSS.0000000000000232
Wadden, T. A. (1993). Treatment of obesity by moderate and severe caloric restriction: Results of clinical research trials. Annals of Internal Medicine, 119(7_Part_2), 688. https://doi.org/10.7326/0003-4819-119-7_Part_2-199310011-00012

Author

David J. Bauder, PA-C David Bauder, PA-C, is a certified physician assistant and the assistant medical director at Weight Loss and Vitality in Manassas and Alexandria, Virginia, Washington, DC; and Gaithersburg, MD. He enjoys helping patients optimize their physical and mental health to improve their overall well-being. He earned his physician assistant degree from the University of Texas Health Science Center at San Antonio. Afterward, he gained admission into the reputable graduate program for physician assistant studies at the University of Nebraska Health Science Center in Omaha. David has over 26 years of experience working as a physician assistant. He’s practiced in podiatry, family medicine, emergency medicine, general surgery, urgent care, and functional medicine.