Funded by Abbott Nutrition, USA, researchers from the firm and the University of Nottingham, UK, conducted the study to explore whether adding 3 g of HMB to a 40 g dose of whey protein would enhance muscle anabolic responses—particularly muscle protein synthesis (MPS)—in older men and women, compared with whey protein alone.
“These data provide mechanistic evidence for the clinical potential of HMB in conjunction with high protein to improve muscle anabolism in populations at greater risk of muscle loss and falls, especially older adults,” wrote the researchers.
Abbott Nutrition sells a range of muscle health shakes which combine whey protein with TSI’s clinically validated myHMB, specifically formulated to slow muscle breakdown and muscle maintenance, strength, and recovery from surgery, illness, or aging.
Can HMB boost muscle growth in older adults?
Aging leads to a decline in muscle mass, strength and function, making muscle preservation an important target for improving healthspan. Dietary protein supports muscle maintenance by stimulating MPS, which helps replace amino acids lost between meals and maintain muscle mass in younger adults.
However, older adults experience anabolic resistance, meaning their muscles respond less effectively to protein intake. As a result, they require larger protein doses to achieve the same increase in MPS as younger individuals.
Researchers have linked anabolic resistance to factors such as impaired protein digestion and absorption, increased amino acid uptake by internal organs, reduced muscle blood flow and defects in muscle cell signalling. Studies also suggest sex differences, with older men showing greater post-meal MPS responses than older women.
Some research has explored strategies such as increasing protein quantity and quality, changing meal timing and using nutritional supplements. Previous research shows that HMB, a metabolite of the amino acid leucine, may help preserve muscle mass and strength in older adults, potentially promoting muscle growth by activating the mTOR signalling pathway and reducing muscle protein breakdown.
Protein plus HMB improves muscle metabolism
The researchers recruited 24 healthy adults aged 65–75 years to receive either 40 g whey protein alone or 40 g whey protein plus 3 g HMB. Each participant completed two testing sessions separated by 21–28 days in a randomized, double-blind crossover design.
After an overnight fast, participants underwent body composition assessment, blood sampling, muscle biopsies, and stable isotope tracer infusion to measure MPS. Researchers collected baseline measurements before participants consumed the test drink and then monitored post-meal responses over three hours. They also measured muscle blood flow, amino acid concentrations, HMB levels, muscle protein breakdown and albumin synthesis.
Results showed that both whey protein alone and whey protein plus HMB increased MPS in older adults. However, adding HMB produced a greater increase in MPS in older women, while no additional effect was observed in older men.
“The exact mechanisms tied to the augmented increase in the MPS in older women are unknown,” the researchers noted. “Although hypothetical, it is possible that in women, HMB was able to activate protein synthesis via an mTOR-independent pathway via concurrent activation of phospholipase D2, in addition to its well-known anabolic effect via the mTOR-dependent pathway.”
HMB also prolonged the suppression of muscle protein breakdown (MPB) in both sexes, compared with protein alone.
Plasma and muscle HMB concentrations increased substantially after supplementation, which the researchers noted confirmed successful uptake. They also noted that protein feeding increased essential amino acid concentrations and albumin protein synthesis regardless of treatment, while HMB had no additional effect on albumin synthesis. Blood flow to the leg increased after feeding, but HMB did not significantly affect microvascular blood flow.
“We conclude that high-dose whey protein bolus feeding increased MPS in older men and women,” the researchers concluded.
“Surprisingly, whereas 40 g of whey protein was not able to overcome the anabolic resistance in older women, the addition of adjuvant HMB was able to further enhance the MPS feeding response to high protein. HMB also suppressed the MPB response to protein feeding over a longer period of time.”
The researchers noted that although the study was not designed to fully investigate sex differences, the findings underscore the need for larger, sex-stratified trials to better understand potential differences in nutritional responses among aging populations.
Journal: Nutrients; doi: 10.3390/nu18091449; “The Effect of β-Hydroxy-β-Methyl Butyrate (HMB) upon Acute Fed-State Muscle Protein Turnover in Older Men and Women: A Randomized Double-Blind Controlled Crossover Clinical Trial.” Authors: Smith, K. et al.
