Evidence Trace, complete trial record
In plain terms
In plain terms: HMB (Beta-Hydroxy Beta-Methylbutyrate) shows early signals in human research but the evidence is limited -- small trials, surrogate endpoints, or not yet independently replicated. It is an emerging area, not yet a proven one.
HMB (Beta-Hydroxy Beta-Methylbutyrate)
C
Limited: small, mixed or unreplicated trials
The endpoint this grade is based on: Objectively measured functional outcome, Graded by population. Diagnosed sarcopenia: Grade C, pooled analyses disagree; one found muscle mass index and handgrip higher, another about 1 kg of grip and no change in muscle mass, and a third no handgrip gain when HMB was added to training. Adults over 50 without sarcopenia: Grade C, two pooled analyses disagree and the largest factorial trial was null on muscle mass. Resistance-trained young men: Grade D, tested without benefit. The cancer-patient review the record once rested on does not grade HMB alone.
The evidence as the record states it
Older adults: Li et al. (Front Nutr, 2025; PMID 40248035): meta-analysis of 21 randomized trials, 1,935 participants over 50; appendicular skeletal muscle mass 1.56 kg and lean mass 0.28 kg higher, handgrip 0.54 kg higher, gait speed 0.06 m/s faster, small effects. Wang et al. (Age Ageing, 2026; PMID 41934514): meta-analysis of 13 randomized trials, 561 adults aged 50 and over doing resistance training; no added effect of HMB on fat mass, muscle mass (SMD 0.05) or strength (SMD 0.04). Osuka et al. (Am J Clin Nutr, 2021; PMID 34081113): 156 women aged 65 to 79 with low muscle mass, 2 by 2 factorial, calcium HMB 1.5 g/day with or without twice-weekly resistance training for 12 weeks; no interaction and no HMB effect on muscle mass, the primary outcome, while exercise improved gait speed and strength. Sarcopenia: Gu et al. (Maturitas, 2025; PMID 39999663): meta-analysis of 5 randomized trials in diagnosed sarcopenia; skeletal muscle mass index (SMD 0.32) and handgrip (SMD 0.65) higher, gait speed unchanged. Trained adults: Tritto et al. (Int J Sport Nutr Exerc Metab, 2019; PMID 30859862): 44 resistance-trained men, HMB free acid or calcium HMB 3 g/day for 12 weeks; no effect on strength or hypertrophy against placebo. Cancer: Prado et al. (J Cachexia Sarcopenia Muscle, 2022; PMID 35301826): systematic review of 15 studies in patients with active cancer only, synthesized by vote counting on direction of effect without meta-analysis; 73 percent of studies gave HMB combined with amino acids, mostly inside oral nutritional supplements; one author is employed by, and others have consulted for or been funded by, a maker of HMB-containing oral nutritional supplements. It cannot support claims about older or trained adults and does not grade HMB alone. Context: Rathmacher et al. (J Gerontol A, 2020; PMID 32857128) tested calcium HMB with vitamin D3 in older adults with low vitamin D and is authored from the HMB manufacturer; a combination, not HMB alone. Grade C: small pooled effects in older adults set against a null pooled analysis with resistance training and a null primary in the largest factorial trial. Sarcopenia trials read individually: Yang et al. (J Nutr Health Aging, 2023; PMID 37248756), 34 older adults, double-blind, HMB with resistance training against placebo with training, handgrip 4.6 kg higher; Meza-Valderrama et al. (Arch Gerontol Geriatr, 2024; PMID 38171034), double-blind, 3 g/day after post-acute rehabilitation, physical performance battery improved and handgrip in women only; Nasimi et al. (J Am Med Dir Assoc, 2021; PMID 33067129), yogurt fortified with HMB and vitamins D and C, a combination; Wu et al. (Crit Care, 2023; PMID 38102705), HMB alone in medical intensive care patients, no change in function.
PMID 40248035 PMID 41934514 PMID 34081113 PMID 39999663 PMID 30859862 PMID 35301826 PMID 32857128 PMID 37248756 PMID 38171034 PMID 33067129 PMID 38102705
Evidence by specific use
Muscle mass and handgrip strength in adults with diagnosed sarcopenia
Grade C
Gu et al. (Maturitas, 2025; PMID 39999663): meta-analysis of five randomized trials in diagnosed sarcopenia; handgrip strength higher (SMD 0.65, 95% CI 0.05 to 1.25), skeletal muscle mass index higher (SMD 0.32, 95% CI 0.00 to 0.64), gait speed unchanged. The individual placebo-controlled trials: Yang et al. (J Nutr Health Aging, 2023; PMID 37248756), 34 adults aged 60 and over in China, HMB or placebo for 12 weeks with resistance training in both arms, double-blind; handgrip, the primary outcome, 4.6 kg higher, with faster gait and chair stands and no change in muscle mass. Meza-Valderrama et al. (Arch Gerontol Geriatr, 2024; PMID 38171034), older adults after post-acute rehabilitation in Barcelona, 3 g/day calcium HMB or placebo with resistance training, double-blind; the Short Physical Performance Battery improved, and handgrip improved in women only. Handgrip, an instrument-measured endpoint that would qualify for A, is positive across the whole sample in one trial and in a subgroup of the other, and the pooled gait speed is null, so the benefit on the qualifying endpoint is not replicated across independent groups: Two further pooled analyses read in October 2026 do not support it: Su et al. (Front Med, 2024; PMID 39071082), six trials in sarcopenia, handgrip 1.26 kg higher and no difference in muscle mass; Hernandez-Martinez et al. (Medicine, 2026; PMID 42700006), seven trials of strength training with supplements in sarcopenia, no significant handgrip gain where HMB was added to training. Pooled analyses disagree and the effect is about 1 kg of grip: mixed, C under the written definition. Trials of HMB inside fortified foods or multi-ingredient supplements (Nasimi et al., 2021; PMID 33067129) do not test HMB alone, and HMB alone did not improve function in intensive care patients (Wu et al., 2023; PMID 38102705).
PMID 39999663 PMID 37248756 PMID 38171034 PMID 33067129 PMID 38102705 PMID 39071082 PMID 42700006
Muscle mass and strength in adults over 50 without sarcopenia
Grade C
Pooled analyses disagree. Li et al. (Front Nutr, 2025; PMID 40248035): 21 trials, 1,935 participants over 50; small gains in appendicular muscle mass, lean mass, handgrip (0.54 kg) and gait speed. Wang et al. (Age Ageing, 2026; PMID 41934514): 13 trials, 561 adults aged 50 and over doing resistance training; no added effect on muscle mass (SMD 0.05) or strength (SMD 0.04). Osuka et al. (Am J Clin Nutr, 2021; PMID 34081113): 156 women aged 65 to 79 with low muscle mass, factorial trial; no HMB effect on muscle mass, the primary outcome. Positive and null poolings side by side: mixed, C.
PMID 40248035 PMID 41934514 PMID 34081113
Strength and hypertrophy in resistance-trained young men
Grade D
Tritto et al. (Int J Sport Nutr Exerc Metab, 2019; PMID 30859862): 44 resistance-trained men, HMB free acid or calcium HMB 3 g/day for 12 weeks; no effect on strength or hypertrophy against placebo. Tested in the population the product is most marketed to and no benefit: D on Route 2.
PMID 30859862
Why Grade C and not Grade B
Grade C reflects early or limited human evidence -- small trials, surrogate endpoints, or preliminary findings not yet independently replicated. The evidence points in a promising direction but does not yet meet the standard for Grade B. A single well-powered, independently replicated trial with a meaningful endpoint would move this to Grade B or higher.
What this grade covers and what it does not
Grade C on every use. The strongest is muscle mass and handgrip strength in adults with diagnosed sarcopenia, where Gu et al. (Maturitas, 2025; PMID 39999663) pooled five randomized trials, four at low risk of bias, and found skeletal muscle mass index (SMD 0.32) and handgrip strength (SMD 0.65) higher and gait speed unchanged. WHY NOT HIGHER, under the written definition: handgrip is an instrument-measured endpoint that qualifies for A, but in the individual placebo-controlled trials it improved across the whole sample in one (Yang et al., 2023; PMID 37248756) and only in women in the other (Meza-Valderrama et al., 2024; PMID 38171034), and the pooled gait speed did not move; and two further pooled analyses disagree with Gu: Su et al. (2024; PMID 39071082) found about 1 kg of grip and no change in muscle mass, and Hernandez-Martinez et al. (2026; PMID 42700006) found no handgrip gain where HMB was added to training. Pooled analyses that disagree are C (from B in October 2026). In both trials HMB was added to resistance training that both arms received. THE OTHER TWO POPULATIONS CARRY THEIR OWN LETTERS: in adults over 50 without sarcopenia the poolings disagree (Li et al., 2025; PMID 40248035, small gains; Wang et al., 2026; PMID 41934514, no added effect with resistance training) and the largest factorial trial was null on muscle mass (Osuka et al., 2021; PMID 34081113), which is C; in resistance-trained young men one trial of both forms found no effect on strength or hypertrophy (Tritto et al., 2019; PMID 30859862), which is D on Route 2. WHAT THIS GRADE DOES NOT COVER: patients with active cancer, where the review on this record (Prado et al., 2022; PMID 35301826) mixes HMB into multi-ingredient nutritional supplements and does not pool; HMB combined with vitamin D (Rathmacher et al., 2020; PMID 32857128), a combination; and any claim about healthy younger adults who do not train.
What would move this grade
A well-powered randomized trial with an objective, clinically meaningful primary endpoint and at least one independent replication would support Grade B or higher.
How to track whether this is working
Lean mass by DEXA or BIA at baseline and 8 weeks. Upper and lower body strength (grip strength, leg press) at baseline and every 6 weeks. HMB benefit is most documented in untrained older adults beginning resistance training: expect smaller effects in already-trained individuals. Free acid (HMB-FA) has faster absorption than calcium HMB (CaHMB).