Males and Female competitors experienced decreases in thyroid and leptin with increases in ghrelin while dieting. The study concluded that extreme dieting practices of bodybuilders for both males and females result in equal reductions in metabolism and losses in muscle size. Both male and female competitors experience a decrease in metabolic rate that could not be explained by losses in muscle mass. The study emphasizes the extreme metabolic cost of dieting for a bodybuilding show.
SUMMARY OF ADAPTIVE THERMOGENESIS RESPONSES IN MALE AND FEMALE COMPETITORS
Males and Female competitors experienced adaptive thermogenesis while dieting with decreases in thyroid and leptin with increases in ghrelin.
The study concluded that extreme dieting practices of bodybuilders for both males and females result in equal reductions in metabolism and losses in muscle size.
Both male and female competitors experience a decrease in metabolic rate that could not be explained by losses in muscle mass.
The study emphasizes the extreme metabolic cost of dieting for a bodybuilding show.
Competing in a bodybuilding show requires rigorous calorie restriction (i.e., strict bodybuilding meal prep) combined with a well-planned training program. Previous studies have documented that males competing in bodybuilding contests can reduce their body fat to less than 5% of total body mass. (Mäestu et al., 2010; Rossow et al., 2013)
As opposed to the offseason, when the goal is building muscle. During the competition phase, bodybuilders want to maintain muscle while losing as much fat as possible. However, strenuous dieting and training take a toll on metabolism and other hormones making bodybuilders susceptible to losing lean body mass and metabolic rate slowing down (i.e., reduced number of calories burned daily).
WHAT IS ADAPTIVE THERMOGENESIS?
Metabolic adaption or adaptive thermogenesis (AT) is the process of our body slowing down resting energy expenditure (i.e., how many calories you burn at rest) in response to low calories for prolonged periods of time.
Resting energy expenditure consists of calories burned for essential body functions, such as the muscles and organs, including the brain and liver. Use the resting energy expenditure calculator to know your calories or use the harris and benedict metabolic equation to track total energy expenditure.
Most people assume that the reduction in metabolism is just because of reduced muscle mass. However, AT accounts for greater reductions in metabolism than what can be predicted from the reduction in body weight and fat or lean mass alone.
ADAPTIVE THERMOGENESIS DECREASES IN THYROID AND LEPTIN WHILE INCREASING LEVELS OF GHRELIN
Other factors related to dieting can contribute to a slower metabolism, such as decreases in thyroid hormones, decreases in leptin, increases in cortisol, and losses in lean muscle mass. (Mäestu et al., 2008; Wasserfurth et al., 2020) Loss of excessive levels of body fat has also been associated with reduced testosterone levels.(De Maddalena et al., 2012)
Any bodybuilder or classic physique competitor who has dieted for a show will tell you that fat loss slows as the diet continues despite high protein and resistance exercise. The prolonged use of low calories and increasing total daily energy expenditure can slow metabolic rate. Our genetics has not changed in several thousand years; there were no bodybuilding shows when we were cavemen. Our bodies were not designed to be shredded for bodybuilding shows.
When an extreme fat loss phase occurs during a bodybuilding prep, the body thinks there is a food shortage (i.e., a famine), so it signals the brain and other tissues to slow all metabolic processes down to preserve energy. This results in a slower rate of calories burned while dieting.
Studies on Adaptive Thermogenesis
The body does not want to burn more calories than it needs. Studies have found that AT can reduce calories burned by anywhere from 50 to 75 calories per day while dieting. (Leibel et al., 1995) In a review of the literature of over 33 studies, AT reduced resting calories burned in 23 of 29 studies; it not only reduced calories burned, but they also found subjects who were on a calorie deficit for a long period burned fewer calories burned during sleep. (Nunes et al., 2022)
The research has had only a few case studies and short-term AT in bodybuilders, but a new long-term study in bodybuilders has just been published. A new study examined the effects of several hormones related to metabolism and resting energy metabolism 5 months before and 5 months after a bodybuilding show.
METABOLIC RESPONSES TO DIETING FOR A SHOW AND AFTER THE SHOW A BODYBUILDING SHOW
The study tracked 10 females and 13 males as they went thru a bodybuilding prep and followed them after the competition. As a control group, they used non-competing males and females (i.e., off-season bodybuilders) who maintained their normal training routines and were not dieting.
The researchers tracked muscle mass, body fat, and other hormones such as thyroid, insulin, leptin, and ghrelin. They used indirect calorimetry to measure resting energy expenditure. All the bodybuilders in the competition turned in their food logs throughout the study to analyze their macros. The average time frame spent dieting was 20 weeks for the competition.
The males and female competitors significantly dropped their calories while dieting for the show. Males averaged a 1249 calorie deficit, and females averaged an 889 calorie reduction, mostly through fat and carbohydrate reduction. Resistance training volume was maintained in both groups during the 23-week prep, but aerobic activity increased.