Key Points
- HMB levels rose in blood and muscle after the HMB drink
- Adding HMB further increased synthesis in older women
- Overall, muscle protein breakdown was lower with HMB later after feeding
Testing HMB Added to a Protein Drink
24 healthy older adults (13 men, 11 women, average age 68.5) drank two oral protein drinks on separate days, in random order:
- Control: 40 g whey protein
- HMB: 40 g whey protein plus 3 g calcium-HMB
Muscle protein synthesis was measured from thigh muscle biopsies, and breakdown was estimated from leg blood samples and blood flow, before and after each drink. HMB levels were also measured in blood and muscle.
HMB Levels Rose in Blood and Muscle
After the HMB drink, HMB levels increased in both blood plasma and leg muscle. They did not rise after protein alone.
“Plasma HMB concentrations rose rapidly following ingestion of the HMB supplement…”
This shows the HMB was absorbed and reached muscle tissue.
Adding HMB Further Increased Muscle Protein Synthesis in Older Women
Both drinks increased muscle protein synthesis (MPS) in older men and women. In women, adding HMB raised synthesis further than protein alone. No significant difference between drinks was seen in men, or across all 24 participants combined.
“...in older women, the addition of HMB further increased the MPS response…”
Muscle Protein Breakdown Was Lower With HMB Later After Feeding
Across all participants, muscle protein breakdown (MPB) was significantly lower with HMB than with protein alone, late in the 3-hour period after drinking.
“HMB further suppressed the MPB feeding response over a longer period of time.”
Conclusion
In this study, adding HMB to a 40 g whey protein drink further increased muscle protein synthesis in older women and lowered muscle protein breakdown later after feeding across all participants. The authors recommend larger studies to understand why the MPS response may differ between men and women.
“Confirmation of outcomes in bigger sex-stratified studies is recommended.”
What This Study Does Not Support
This study measured muscle protein synthesis and breakdown for 3 hours after a single drink, on two study days, in 24 healthy older adults. It does not show that HMB builds muscle, strength, or function over time. The women's result came from 11 women. The study was sized for the breakdown outcome, not sex-specific differences, and various outcomes were tested without correction for multiple comparisons, so it needs confirmation. Five participants had adverse events (two after control, three after HMB), including one serious event (acute coronary syndrome) in the control group. The authors reported that these were not directly related to product use, but a study this small cannot establish safety. This study does not show that HMB treats, prevents, or reverses sarcopenia or any other disease. No dosage recommendation can be drawn beyond the 3 g of calcium-HMB with 40 g of whey tested here. The study was funded by Abbott Nutrition. Four authors were Abbott employees at the time of the study or currently are, and two others have received Abbott grants or served as Abbott speakers.
