Physiological processes are constantly occurring within our bodies in an effort to maintain homeostasis. The fact that we have such a complex nervous system which allows us to make incredibly smart decisions and self-regulate is one that sets mammals apart from most other creatures on earth. (2) When our bodies interpret a situation as stressful or threatening, mechanisms are utilized and adaptations occur in an attempt to reverse the threatening situation and get back to a state the feels “safe”, aka restore homeostasis. One of these adaptations which gets examined frequently in the health space, particularly in the context of weight loss or getting to extreme body compositions such as in the sport of bodybuilding, is the decrease of the hormone leptin throughout a period of caloric restriction.
What exactly is leptin?
Leptin is a protein that is primarily synthesized by white adipose tissue. Leptin has strong ties to energy stores, is crucial in determining satiety, and appropriate levels are required for proper meal termination. Without a sufficient level of leptin, an individual will have trouble feeling full or “satisfied” after a meal or in between meals. (3,4) Leptin travels through the bloodstream and acts in the satiety center of the brain, (a subregion of the hypothalamus called the ventromedial hypothalamic nucleus) the VMN, to keep appetite and adiposity in check. Typically, the more fat tissue a person carries, the higher his/her level of the hormone, and the less fat tissue a person carries, the lower his/her level of the hormone.
Research on leptin such as the study done by Trexler et. al, (2014) state that short-term energy restriction and lower body fat levels are associated with decreases in leptin. In the context of bodybuilding, a case study carried out by Rossow et. al, (2015), found that leptin levels were nearly cut in half from the beginning of the competition diet (2.58ng/mL) to 6 months later at the time of the competition (1.36ng/mL). Clearly, leptin aids in the regulation of energy homeostasis, so it is no wonder that this hormone is disrupted when homeostasis is diminished through a period of caloric restriction. (1)
How exactly does leptin act?
Leptin operates in a similar way to the thermostat in your home. There is a feedback system between the VMN and leptin that will elicit increases or decreases in the hormone depending on the current state of your body composition in relation to what your body “wants” your composition to be (think your set point). As your body fat levels start to decrease, so will your leptin levels. As this is happening, you may notice your appetite beginning to ramp up making it harder for you to maintain the deficit – which is just what your body wants to happen. (2) You may also start to experience extreme food focus or food anxiety because your body is begging to be fed. The ideal situation from a homeostasis perspective is that you will begin to satisfy the feeling of hunger by eating food until you have returned back to a range around your set point. Essentially, low leptin levels elicit a profound starvation response. (2) Research has also shown other inevitable adverse adaptations that occur during a period of caloric restriction such as decreased metabolic rate (you will have to eat less and exercise more to lose weight further), decreased non-exercise activity thermogenesis (you will not fidget as much, etc. in an effort to conserve energy), activation of brain reward center (you will become hyper-focused on calorie-dense foods), and increased levels of ghrelin (the hunger hormone.. stay tuned for more on that).
How can we combat these adverse effects of dieting, particularly the decrease of the hormone leptin? While these adaptations cannot be avoided while dieting, there are protocols that can be put into place over the course of a diet to help attenuate them.
Do not diet too harsh for too long. The longer you are in a deficit (regardless of severity), the more set up you are becoming to regain body fat. Research has shown that even a short-term caloric restriction will begin to reduce levels of leptin, so don’t overstay your welcome in this phase.
Incorporate diet breaks. Give yourself long enough to diet that you can take the occasional diet break (1-2 weeks of eating higher calories) to give your body a bit of a break and take it out of the stressed-out state.
Eat higher protein for the satiety effects
Do not diet too extreme right out of the gate. You should always start at the minimal effective dose: what is the most you can eat, and the least amount of expenditure needed to move the needle.
Resistance training may help keep the lipostat satisfied. The hypothalamus is the body’s lipostat which is the brain region that regulates appetite and body fatness. As you lose fat, the lipostat will engage the above-listed mechanisms to try to promote regaining the lost fat. (2)
While we may not be able to inhibit the mechanisms put in place by our bodies to maintain homeostasis (which we should be grateful for), being aware of the adaptations and making the most educated moves possible to respect our bodies while working towards a goal is imperative and can make the process much smoother.
Bouret, S. G., Draper, S. J., & Simerly, R. B. (2004). Trophic Action of Leptin on Hypothalamic Neurons That Regulate Feeding. Science, 304, 108-110.
Guyenet, S. J., & Aoki, S. N. (2017). The hungry brain: Outsmarting the Instincts that make us overeat. New York: Flatiron Books.
Keim, N. L., Stern, J. S., & Havel, P. J. (1998). Relation between circulating leptin levels and appetite during a prolonged energy deficit in women. American Society for Clinical Nutrition, 68, 794-801.
Morton, G. J., Blevins, J. E., Williams, D. L., Niswender, K. D., Gelling, R. W., Rhodes, C.J., Schwartz, M. W. (2005). Leptin action in the forebrain regulates the hindbrain response to satiety signals. The Journal of Clinical Investigation, 115(3), 703-710.
Rossow, L. M., Fukuda, D. H., Fahe, C. A., Loenneke, J. P., & Stout, J. R. (2013). Natural Bodybuilding Competition Preparation and Recovery: A 12-Month Case Study. Sports Physiology and Performance, 582-592.
Trexler, E., Smith-Ryan, A., & Norton, L. (2014, February 27). Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition, 11, 1-7. DOI:10.1186/1550-2783-11-7