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.
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.
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:
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.
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.
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:
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.
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.
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.
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:
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.
