Embarking on a weight loss journey is often characterised by initial success, shedding the first ten kilograms with ease. Then, as the weeks progress, the once steady decline in weight may hit a frustrating plateau. The question arises: Is my metabolism broken? The answer lies in the concept of Adaptive Thermogenesis, an intricate mechanism caused by the body in response to prolonged calorie restriction.

Our bodies are always striving to maintain homeostasis—a state of relative stability. Adaptive Thermogenesis comes into play as a defence mechanism during caloric scarcity. As you persist in your weight loss pursuit, your body adapts to the reduced energy intake by slowing down energy expenditure. This phenomenon is not a malfunction, but a natural response to safeguard against excessive fat loss.

Hormonal Effect of Weight Loss

While swift weight loss is often the goal, it triggers a cascade of hormonal adaptations that make sustained weight loss more challenging. Key hormones involved include the thyroid hormone which regulates metabolism and decreases with prolonged weight loss. Leptin, the satiety hormone, decreases, while ghrelin, the hunger hormone, increases. Insulin also decreases, collectively creating a hormonal effect that fosters increased hunger and reduced metabolic efficiency.

What actually happens?

Weight loss causes a reduction in Total Daily Energy Expenditure as your body size decreases. The loss of muscle tissue also decreases your Basal Metabolic Rate, which is the amount of calories your body expends to survive. The preservation of muscle mass during weight loss is linked to mitigating these metabolic adaptation, but complete complete prevention remains elusive.

The Severity of Calorie Restriction Plays a Role

Research underscores the correlation between the degree of energy imbalance and the magnitude of metabolic adaptation. Severe calorie restriction exaggerates this adaptation, affecting the hormone leptin, which plays a vital role in regulating energy expenditure. The thyroid hormone T3 is also implicated, which plays a role in regulating your metabolism and reduces decreases overall metabolic rate.

Methods of Preventing and Delaying Metabolic Adaptation

In a bid to counter Adaptive Thermogenesis and facilitate sustained weight loss, strategic interventions become important. Increasing energy expenditure through purposeful activities, such as higher step counts or cardio, proves beneficial. Refeeds, temporary increases in calorie intake, temporarily elevate leptin levels and stimulate metabolic rate. The importance of diet breaks emerges as a practical tool in long-term weight loss strategies. A study by the University of Tasmania reveals that intermittent dieting, with breaks in between, may yield more sustainable results compared to continuous dieting. This approach avoids the pitfalls of rapid weight regain commonly associated with restrictive diets.

Preserving Muscle is Key 

Recent studies emphasise the importance of understanding the magnitude of this adaptation and its correlation with weight loss success. It’s evident that crash dieting is counterproductive. Preserving muscle mass and incorporating maintenance periods into long-term plans become strategic tools against the tide of metabolic adaptation.  Recognising that a history of chronic dieting may amplify Adaptive Thermogenesis responses, a gradual reverse diet may be warranted after a transformation.

Conclusion

In the pursuit of rapid weight loss, clients and trainers must be wary of these metabolic intricacies. Utilising maintenance periods, diet breaks, and consistent monitoring of hormonal responses can enhance the sustainability of weight loss and promote lasting transformations.

References:

• Johannsen, D.L., Knuth, N.D., Huizenga, R., Rood, J.C., Ravussin, E. and Hall, K.D. (2012). Metabolic slowing with massive weight loss despite preservation of fat-free mass. The Journal of Clinical Endocrinology & Metabolism, 97(7), 2489-2496.
• Knuth, N.D., Johannsen, D.L., Tamboli, R.A., Marks‐Shulman, P.A., Huizenga, R., Chen, K.Y., Abumrad, N.N., Ravussin, E. and Hall, K.D. (2014). Metabolic adaptation following massive weight loss is related to the degree of energy imbalance and changes in circulating leptin. Obesity, 22(12), 2563-2569.
• Mäestu, J., Jürimäe, J., Valter, I. and Jürimäe, T. (2008). Increases in ghrelin and decreases in leptin without altering adiponectin during extreme weight loss in male competitive bodybuilders. Metabolism, 57(2), 221-225.