Obesity has become a global epidemic, with nearly 650 million adults worldwide classified as obese and 1.9 billion classified as overweight. Obesity is a chronic disease that causes a slew of health complications such as diabetes, heart disease, and stroke. With such dire consequences, people may resort to drastic measures to begin losing weight and improving their health.
Calorie restriction is one of the most popular methods for overweight people to begin losing weight. Some people who are trying hard to lose weight may restrict their calorie intake to the point of starvation. While initially effective, prolonged and drastic restriction can be detrimental to your weight loss journey. Metabolic adaptation is one of these effects. 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 reduce energy expenditure components, improve metabolic efficiency, and increase cues for energy intake. Your body’s adaptations include changes to hormones, mitochondrial efficiency, and thermogenesis, all with the goal of decreasing energy expenditure, increasing satiety, and decreasing hunger.
Excessive caloric restriction can result in metabolic adaptations. Strict dieting can make it difficult to maintain weight loss and increase the risk of weight regain².

What causes metabolic adaptation?

We discovered that metabolic adaptations are caused by changes in our body’s energy balance. This energy balance in the body is influenced by a variety of factors, including behavioral, nutritional, behavioral, psychological, and physiological influences. These factors influence how your body uses energy, which is determined by a balance of total daily energy intake (TDEI) and total daily energy expenditure (TDEE) (TDEE).
Metabolic adaptations can be caused by your diet and activity levels in the following ways:

• Starvation. A common misconception among overweight people is that drastically reducing calories will produce immediate and dramatic results. While this may be true at first, starving yourself can cause metabolic changes that work against you.
• Nutritional deficiencies. TDEI is affected by a variety of factors, including the food you eat. As a result, a poor diet affects your TDEI, affecting your body’s energy balance.
• Lack of physical activity. Physical activity and exercise both contribute to your body’s TDEE. Sedentism, as a result, has an impact on your body’s energy balance³.

What are the mechanisms underlying metabolic adaptation?

As previously stated, several potential mechanisms underlying metabolic adaptation exist. Changes in your body’s metabolic rate, endocrine response, and mitochondrial efficiency are examples of these.

Changes to metabolic rate

To grasp the concept of metabolic adaptation, one must first define resting metabolic rate (RMR). RMR, also known as resting energy expenditure, is the amount of energy required by the body to operate in a resting state. It specifically refers to energy expended while awake after not exercising for at least 12 hours3. RMR accounts for the majority of our body’s energy needs, accounting for up to 60 to 70% of total daily energy expenditure (TDEE)¹.
The RMR can decrease more than expected when losing a significant amount of weight. One study, for example, discovered that after three weeks of calorie restriction and weight loss, energy-expending tissue accounted for one-third of RMR decline. The remaining two-thirds of the RMR decline were unaccounted for, but were most likely caused by a decrease in metabolic activity in other tissues. As a result, experts believe there are two main causes of RMR decreases: a decrease in metabolically active tissue and a decrease in metabolic activity in other tissues⁴.
In summary, a reduction in metabolically active tissue leads to adaptive thermogenesis, also known as a reduction in TDEE. According to some researchers, the body does this to try to restore one’s original body weight. This could explain why people frequently experience weight plateaus 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. T3 is a thyroid hormone that regulates the metabolic rate of your body. Similarly, increased thyroid hormone levels (hyperthyroidism) can increase metabolic rate, while decreased thyroid hormone levels (hypothyroidism) can decrease metabolic rate.
• Leptin. To help maintain weight, your body releases leptin from its fat tissues. It also serves as a measure of energy availability, energy expenditure, and satiety.
• Insulin. Though the primary function of insulin is to regulate blood sugar levels, it also signals energy availability and satiety.
• Though testosterone is primarily involved in the regulation of muscle protein and muscle mass, it may also be involved in the regulation of fat mass.

Hormone changes that lower metabolic rate and increase hunger have been observed in studies examining the body’s endocrine response to caloric restriction. Energy restriction, for example, has been shown in studies to reduce thyroid hormones, insulin, leptin, and testosterone².

Changes to mitochondrial efficiency

The mitochondria perform several functions that are involved in the energy production process. Proton leak is closely related to energy expenditure and metabolic efficiency.
By moving protons across the mitochondrial membrane, the mitochondria produce adenosine triphosphate (ATP), an important energy molecule. In a process known as “proton leak,” protons can leak across the membrane via UCPs. Proton leakage contributes to energy consumption. When you reduce your calorie intake, your proton leak decreases as well. This mitochondrial adaptation, along with others, results in energy restriction, making weight loss difficult and encouraging weight gain².

What are the consequences of metabolic adaptation?

Metabolic adaptations can have a negative impact on weight loss via the aforementioned mechanisms. Patients frequently believe that they must follow a strict calorie restriction plan in order to lose weight quickly. However, in most cases, this has the opposite effect. Starvation reduces muscle mass, lowers RMR, and causes hormonal changes that prevent you from losing weight effectively. Furthermore, these metabolic adaptations can contribute to weight regain even after you have met your weight loss goals. As a result, in order to effectively manage and maintain weight, it is critical to use healthy and balanced methods.

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

According to studies, moderate and severe caloric restriction, while effective in the first few months, is associated with weight regain over time⁵. This is most likely because of metabolic adaptations and the mechanisms that underpin them.
Starvation may be a “quick fix” for quickly losing weight, but it is ineffective over long periods of time. The consequences of metabolic adaptations may be discouraging for those attempting to lose weight; however, there are safer and more effective methods available, some of which include:

• Eating plenty of vegetables: Vegetables are low-calorie, low-fat, and high in fiber, making them ideal components of a well-balanced weight-loss diet. They are also high in vitamins and minerals, which benefit your overall health and wellness.
• Make protein a top priority: To maximize protein synthesis, the average person should consume at least 60 grams of protein per day, divided into 20-24 grams per meal. Requirements rise as activity levels rise or individuals with a lot of muscle mass.
• Choosing healthy, whole foods: Just because something has a low calorie count does not mean it is healthy. Reading food labels can help you understand what you’re putting into your body and ensure that the ingredients you’re consuming are beneficial to your nutritional needs and weight loss journey.
• Avoid sugar and processed foods: In addition to eating whole foods that are close to the source, avoid overly processed foods. Remove refined and excess sugar from your diet as well.
• Increase your fiber intake: Fiber can make you feel full, preventing you from overeating. Fiber can be found in foods like vegetables, beans, lentils, brown rice, and whole grain bread.
• Exercising on a regular basis: Physical activity is essential for losing weight because it can help you burn calories while also lowering your caloric intake through diet. Exercising can also help you maintain your weight loss and avoid regaining it. Physical activity also has several other health benefits, such as lowering your risk of certain diseases and conditions.
• Other preventive measures include GI health, stress management, adequate sleep, and nutraceutical supplementation.

Conclusion

Excessive calorie restriction can be harmful to your health and weight loss journey by causing metabolic adaptations. Changes in your energy balance, hormones, and bodily processes are all examples of metabolic adaptations. Finally, metabolic adaptations can work against you, preventing weight loss or promoting weight gain. As a result, it is critical to implement healthy weight loss strategies such as regular exercise and eating a nutritious and well-balanced diet.

References

1. 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
2. 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
3. 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
4. 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
5. 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