Dr. Dwayne Jackson

The Vital Science Blog

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HMB: An old dog with new tricks!

Intermittent fasting (IF) is one of the fastest growing diet trends for fat loss. However, it generally means going for 12 to 24 hours without ingesting calories of any kind. Millions of people have benefitted from the rapid weight loss associated with IF, but restricting nourishment, especially without protein or amino acids for hours runs risk of elevating cortisol (a catabolic hormone) and putting the body in a state of catabolism—potentially sacrificing your hard-earned gains. A recent study published in The British Journal of Nutrition suggests that β-Hydroxy β-methylbutyrate, commonly known as HMB- Free Acid (HMB-FA), may be an ideal supplement for those who partake in the practice of IF. 


For those of you who don’t know, HMB is an active anabolic metabolite of the essential branched chain amino acid leucine, which resides in all human muscle cells. HMB is found in foods like avocado, alfalfa, catfish, and citrus fruits. In a recent study, researchers from Texas Tech University assessed the effects of HMB-FA supplementation on catabolism (muscle breakdown), cortisol release, testosterone (an anabolic hormone), and resting energy expenditure (REE), during a period of acute fasting.  Eleven healthy males and females participated in this randomized, double-blind, and placebo-controlled cross-over trial, where they received an HMB-FA supplement or a placebo (1g, 3x/day) during a 3-day meat-free diet, followed by a 24-hour fast. 


Urinary HMB concentrations confirmed compliance with supplementation. Interestingly, markers of catabolism were unaffected by acute fasting, so there was no observed impact of HMB on muscle breakdown. However, with HMB supplementation, the fasting cortisol response was blunted by 32%, with no effect in the placebo group! In males, the testosterone to cortisol ratio (T:C) increased 162% from 0 to 24 h of fasting with HMB-FA, but not placebo, this was mainly due to reductions in cortisol. 

ACTION POINT: So, if you are using IF as a dieting strategy or if you just want to keep cortisol managed, it seems that HMB-FA might provide some supplemental support. According to HMB research, the best to dose HMB is at 38 mg/kg body mass (approximately 17 mg/lb) of body weight daily, split into 3 equal doses. Take 1 dose 30-60 before training, another immediately after training, and another with a meal. On rest days, take your 3 doses with breakfast, lunch, and dinner. You will notice the greatest effects of HMB after 2 weeks of supplementation and chronic consumption is deemed safe.



Tinsley G, Givan AH, Graybeal AJ, Villarreal MI, Cross AG. β-Hydroxy β-methylbutyrate free acid alters cortisol responses, but not myofibrillar proteolysis, during a 24-h fast. Br J Nutr. 2018 Mar;119(5):517-526.

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