[Carlyn Waffa is a senior at The University of North Carolina at Chapel Hill. She is majoring in Exercise and Sport Science, and a National Academy of Sports Medicine Certified Personal Trainer. She is currently an Athletic Development Intern at Athletic Lab.]
An athlete’s metabolism, or their physiological capacity to transform chemical energy in food (kcal) to other types of usable energy in the body, is an adaptable mechanism that adjusts based on substrate availability and imposed physical demands. In athletes, weight cycling is a common phenomenon. Just like a yo-yo oscillates up and down, an athlete’s weight may go up and down in the same fashion, as an athlete’s weight frequently fluctuates between “in-season” and “off-season” training schedules. Weight loss phases are achieved from a caloric deficit, which may be the result of increased exercise or caloric restriction – or a combination of the two.
Nonetheless, quick-fix, short-term methods of weight-loss are not employed without consequence. Recent research suggests a causal link between the number of times an athlete cyclically loses and regains weight and a higher percentage of body fat later in life (Saarni, 2006).
Oscillating weight loss and gain wreaks havoc on an athlete’s metabolism, and the success rate of long-term weight loss from yo-yo dieting is painfully low. In fact, while dieting may work for an athlete to “make weight” in the short term, cyclical weight loss and regain is detrimental to weight control in the long term – and may even predispose an athlete to obesity later in life (Saarni, 2006). Dieting can create a caloric deficit, or a negative energy balance, within the body. This is a less-than ideal situation from a biological perspective, as the human body naturally strives to maintain equilibrium between energy input and output, or even to have an excess of stored energy.
In response to weight loss, the body experiences a decrease in anabolic, anorexigenic, and thermogenic hormones such as testosterone, insulin, leptin, and thyroid hormone (T3). Conversely, there is an increase in orexigenic and catabolic hormones such as cortisol and ghrelin. This hormonal shift, causes the dieter to experience increased hunger and decreased satiety. Moreover, their metabolism adjusts to preserve energy, and thus energy expenditure decreases. A hypocaloric regimen threatens the preservation of lean body mass, the athlete’s compliance to a hypocaloric regimen, and exponentially increases their susceptibility to weight regain (Trexler, 2014). Perhaps most notably, these effects persist despite the cessation of a diet (Rosenbaum, 2008). The enduring repercussions of yo-yo dieting are a result of the compounding consequences of post-starvation hyperphagia and body fat overshooting.
Post-starvation hyperphagia, an excessive caloric phase, is marked by compulsive overeating in the wake of extreme caloric restriction. This compelled increase in calories leads to the creation of energy stores within adipose tissue – or fat. Body fat overshooting typically results as the athlete’s weight not only returns toward their pre-diet weight, but actually exceeds it. Furthermore, during this period of weight regain, the athlete more easily regains fat. Body fat overshooting continues until lean body mass is restored (Dulloo, 2012).
During a post-diet period, a rapid increase in calories, driven by post-starvation hyperphagia, actually suppresses energy expenditure, and increases energy stores within the body. Thus, as previously discussed, weight regain ensues, which is marked by less lean body mass, more fat mass, and a lower metabolic rate due to body fat overshooting and adipocyte hyperplasia – an increase in the number of fat cells (Trexler, 2014; Jackman, 2008).
Nonetheless, instead of breaking a diet with a rapid increase in calories, an athlete may slowly increase their caloric intake in small increments, which is a technique known as reverse dieting. Reverse dieting provides the athlete with an excess of calories, but one that is just the right amount to restore endocrines, and the athlete’s metabolic rate, to normal values. Moreover, in cases of muscle catabolism, reverse dieting allows lean body mass to recover, while avoiding adipocyte hyperplasia (Trexler, 2014).
Dieting is a complex practice, often driven by fads or short-term goals. Nevertheless, the long-term effects of an extreme caloric deficit, specifically body fat overshooting and a predisposition for obesity, are important factors for an athlete to consider before committing to unrealistic crash diets that are unsustainable and sure to fail in the long-term.
Author’s note: During my time at The University of North Carolina at Chapel Hill, I was afforded the opportunity to study Sports Nutrition under the direction of Dr. Abbie Smith-Ryan, PhD, CSCS, CISSN. Her teaching reflected her research, which was influential in my writing of this blog.
Dulloo, A.G., Jacquet, J. and Montani, J.-P. (2012) ‘How dieting makes some fatter: from a perspective of human body composition autoregulation’, Proceedings of the Nutrition Society, 71(3), pp. 379–389. doi: 10.1017/S0029665112000225.
Jackman MR, Steig A, Higgins JA, Johnson GC, Fleming-Elder BK, Bessesen DH, MacLean PS. Weight regain after sustained weight reduction is accompanied by suppressed oxidation of dietary fat and adipocyte hyperplasia. Am J Physiol Regul Integr Comp Physiol. 2008;294:R1117–29.
Rosenbaum M, Hirsch J, Gallagher DA, Leibel RL: Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight. Am J Clin Nutr. 2008, 88: 906-912.
Saarni, S., Rissanen, A., Sarna, S., Koskenvuo, M., Kaprio, J., 2006. Weight cycling of
athletes and subsequent weight gain in middle age. International Journal of Obesity, 1639-1644.
Trexler, Smith-Ryan. et al. Metabolic adaptation to weight loss: implications for the athlete. JISSN 2014