[King Grub]

One of the negative consequences of prolonged caloric restriction is a suppression of resting metabolic rate (RMR), making future fat loss more difficult. Further, some evidence suggests that the suppression of RMR is associated with the severity of the caloric deficit (the greater the caloric deficit the greater the reduction in RMR). Strategies employed to prevent the suppression of RMR during a caloric deficit include resistance exercise and a high protein diet. Currently, there is a lack of research investigating the prevalence of metabolic slowing in resistance-training individuals undergoing a short-term, intensive caloric restricted diet that is high in protein. Therefore, the purpose of this study was to examine the effects of short-term intense caloric restriction on resting metabolic rate in resistance-trained males and females eating a relatively high protein diet.

Materials and Methods

20 resistance-trained males (n=5) and females (n=15) participated in this study (age: 25.2 ± 7.8 years; height: 167.2 ± 7.9 cm; body mass: 66.6 ± 11.2 kgs). Following a period of baseline caloric tracking, subjects were prescribed 2 weeks of energy restriction resulting in an approximate 37.5% decrease in caloric intake. Subjects were instructed to ingest 2.2 g protein/kg body weight and continue their habitual resistance training routine while dieting. RMR was assessed pre and post-intervention using a Parvo Medics’ TrueOne® 2400 device (ParvoMedics, Sandy, UT). Data were analyzed using a dependent samples t-test.

Results

There was a significant decrease in RMR during the 2-week caloric deficit (p = 0.001).

Specifically, RMR decreased from 1,602 ± 211 to 1,508 ± 241 kcals (a decrease of approximately 5.9% during the study intervention).

Conclusions

In resistance-trained males and females, a two-week caloric reduction of approximately 37.5% resulted in a significant decline in resting metabolic rate. High protein intake and resistance training were not able to mitigate this decline. As such, to maintain resting metabolic rate during caloric restriction, a short-term intense caloric reduction is not recommended.

Journal of the International Society of Sports Nutrition volume 17, Article number: 59 (2020). The effect of 2-weeks of intense caloric restriction on resting metabolic rate in resistance-trained individuals.