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Maximal strength

No reliable effect: very short efforts under 30 seconds showed no benefit (ES 0.040), and an 8-week trial in trained lifters found no extra 1RM gain over placebo.

Maximal strength (1RM, peak force)

No effect: pooled data from 11 studies found no change in muscular strength (SMD −0.03), whether tested rested or fatigued.

Strength gains with resistance training

Possibly a small boost, but not established: pooled effects of SMD 0.60 (bench press) and 0.52 (lower body) came from just three trials, lost significance under a stricter analysis, and were rated low certainty.

Maximal strength

No overall effect on muscle strength in resistance-trained adults (SMD 0.13, 95% CI -0.21 to 0.46).

Maximal strength

Trivial at best: pooled strength effect SMD 0.08, no effect on isometric maximal contraction (SMD 0.03), and no significant effect when strength was tested rested.

Strength

At most a very small effect: one meta-analysis found SMD 0.12 (barely significant), a newer one found SMD -0.02 (no effect), with very low certainty.

Strength and power

Uncertain: a 2025 meta-analysis saw benefit in strength/power subgroups, but effects weakened when influential studies were removed and certainty was low to very low.

Strength and muscle gains

No added benefit: strength and muscle size rose equally with D-aspartic acid and placebo over 28 days (3 g/day) and 12 weeks (6 g/day) of training.

Strength gains with training

No significant extra strength in pooled data: leg press SMD 0.22 (95% CI -0.02 to 0.47) in male athletes; one 8-week trial in trained men found equal 1RM gains with fenugreek and placebo.

Strength in untrained beginners

Small strength gains in untrained men (about 10% more lower-body and 7% more average strength gain), but body-composition effects were trivial, and a later meta-analysis of young adults found no strength benefit.

Athletic performance (strength, endurance)

No benefit: 90 days of a high-potency multivitamin-mineral did not change VO2max, endurance, strength or muscular endurance in well-nourished active men.

Strength and muscle

No added strength or fat-free mass versus placebo over 5-8 weeks of training in elite rugby players and resistance-trained men.

Strength in people who are vitamin D deficient

Small at best: effects were larger below 30 nmol/L and in people 65+, but in deficient young men lifting weights, 8000 IU/day added no strength or lean mass over 12 weeks.

Strength and power in people who are not deficient

No meaningful effect: in athletes starting at or above 75 nmol/L the effect on power was trivial (SMD 0.15, not significant), and pooled strength across athlete trials was not significantly improved.

Strength in people who are magnesium deficient

Possibly helps: magnesium's benefits appeared more pronounced in older adults and people with alcoholism, groups likely to be low in magnesium, but the pooled strength effects were not significant.

Strength and muscle gains

No extra strength, muscular endurance, power or lean mass over 8 weeks of training in trained men; magnesium alone did not improve strength in athletes.

Muscle gain / body composition

No effect: pooled data from 20 RCTs found no change in fat-free mass (+0.05 kg, not significant), body fat or body mass, and an 8-week RCT found no added muscle thickness.

Muscle size and body composition

Unproven: no trial measured muscle directly; chest circumference rose more (SMD 0.86, very low certainty) and body fat did not change significantly (SMD -0.32).

Keeping muscle while dieting

Weak: one small, industry-funded trial (17 men) reported lean mass kept with BCAAs versus a carbohydrate drink, but its data were publicly questioned and only 1 of 22 BCAA trials found any body-composition change.

Muscle growth

BCAAs alone raise post-workout muscle protein synthesis 22% over a zero-calorie placebo in one trial, but less than complete protein, and a review of 24 athlete studies found negligible effects on body composition.

Builds muscle as well as whey

No: whey grew muscle thickness more than leucine-matched collagen (8.4% vs 5.6% in the thigh) over 10 weeks of training.

Muscle gain

No: meta-analyses found no effect on muscle mass (SMD 0.07) or fat-free mass (SMD 0.26, not significant), with or without resistance training.

Muscle and strength gains

Fat-free mass rose by about 0.27-0.3 kg (under 1%) in meta-analyses; trials in experienced lifters found no strength or body-composition benefit.

Lean mass and body fat

No significant change in pooled lean mass (SMD 0.19) or fat mass (SMD -0.19); one 8-week trial in trained men reported a 1.77% vs 0.55% body-fat drop.

Muscle gain

No added gain: in a 6-week training RCT, lean mass rose 2% with glutamine and 1.7% with placebo, not a significant difference, and a meta-analysis of 25 trials found no effect on body composition.

Preserving muscle in older adults

Small benefit: greater muscle mass in older adults taking HMB (standardised mean difference 0.352) with no change in fat mass.

Muscle gain and strength in trained lifters

No effect in trained athletes: pooled effect sizes were trivial and non-significant for bench press (0.00), leg press (0.09) and fat-free mass (0.16).

Endurance exercise lasting more than 10 minutes

Not shown: for exercise over 10 minutes the pooled effect (ES 0.174) was not statistically significant.

Endurance performance

Not shown: two meta-analyses found no significant effect on time to exhaustion (SMD 0.03) or aerobic performance (SMD 0.15, p = 0.08); a possible aerobic benefit in a 2026 analysis did not survive sensitivity checks.

Endurance performance in well-trained endurance athletes

Little to no benefit: no pooled effect in well-trained athletes (VO2max ≥65 mL/kg/min; d = 0.021) or in athletes generally (ES 0.04).

Endurance and exercise performance

Mixed: a systematic review found some benefits in high-intensity tests but none for moderate-intensity exercise, and an 8-week GPLC trial found no performance change at 1 or 3 g/day.

Repeated sprints (team-sport style)

No effect: across 17 RCTs, beta-alanine did not improve mean (SMD −0.018) or peak repeated-sprint performance, or fatigue during sprints.

Fat loss

One meta-analysis of 13 RCTs suggests caffeine might promote small reductions in weight and fat mass, but results were extremely inconsistent between trials.

Fat loss

No reliable fat loss: one meta-analysis found 0.73 kg less fat mass, but two others found no significant change in absolute fat mass, only a very small drop in body-fat percentage.

Fat loss

Tiny: about -0.44 kg fat mass across 70 trials, and high-quality trials showed no change in fat mass or body-fat percentage.

Weight and fat loss

At most about 1 kg: pooled estimates of -0.88 kg and -1.34 kg, while a 12-week JAMA RCT and a 54-trial herbal meta-analysis found no effect.

Reduces appetite

Mixed: one small single-blind crossover found 15-30% lower energy intake, but a double-blind crossover found no change in satiety or intake.

Fat loss

Small at best: a Cochrane review found -0.04 kg versus control in trials outside Japan, and with exercise the added effect was described as quite minimal.

Burns more fat during exercise

Inconsistent: 1-7 days of extract did not change fat oxidation in cycling men, and 8 weeks of decaf extract alone did not change it in exercisers.

Fat loss

Modest extra weight loss of 1.21-1.33 kg versus control in pooled trials, about 2 kg of fat mass in one analysis, with no change in body-fat percentage or waist size and benefits seen mainly in people with overweight or obesity.

Fat loss

No human trial of raspberry ketone alone exists. Two 8-week trials of stimulant blends containing it gave conflicting results, one industry-sponsored.

Raises testosterone

A small rise in men: a 2026 meta-analysis found +57.43 ng/dL versus placebo in men and no change in women, with rises staying within the normal physiological range.

Raises testosterone in untrained men

One 12-day trial in 23 untrained men reported a 42% testosterone rise; it has never been independently replicated, and a systematic review called the human evidence inconsistent and sparse.

Raises testosterone in resistance-trained men

No: 3 g/day for 2-4 weeks and 6 g/day for 2-12 weeks did not raise testosterone in trained men, and 6 g/day for 14 days lowered total and free testosterone.

Raises testosterone

At most a small rise in total testosterone (SMD 0.25-0.32) with very low certainty, and no reliable change in free testosterone, the active fraction.

Raises testosterone

No meaningful effect: 8 of 10 trials in one review found no change in androgens, and the only increases (60-70 ng/dL) were in men with low testosterone.

Testosterone in people who are zinc deficient

Plausible but thinly tested: in 9 marginally zinc-deficient older men, 3-6 months of zinc raised testosterone from 8.3 to 16.0 nmol/L, and restricting zinc in 4 young men lowered it.

Raises testosterone (zinc-replete men)

No: ZMA raised blood zinc but did not change total or free testosterone in trained or regularly exercising men eating enough zinc.

Recovery / soreness

Does not reduce muscle soreness; some pooled data show better preservation of strength in the 24-96 hours after hard lifting, but results are inconsistent.

Recovery from training

Weak evidence: one trial reported a smaller creatine-kinase rise, while the other found better perceived recovery only within the ashwagandha group, not versus placebo.

Faster recovery of strength and performance

No difference from placebo in muscle performance 24 or 48 hours after damaging exercise (SMD 0.08 to 0.21, not significant).

Less muscle soreness

One meta-analysis reported reduced soreness 24 hours after exercise but not at 72 hours; the 48-hour result was not statistically significant (p = 0.25), and a crossover trial found no recovery benefit.

Strengthens tendons and connective tissue

Unproven: 15 g/day did not improve tendon size or stiffness over 15 weeks of training versus placebo; a meta-analysis effect on tendons was very low certainty.

Less muscle soreness

Inconsistent: a small effect in one meta-analysis (ES -0.44, CI near zero) but no pooled effect in a newer meta-analysis of athletes.

Recovery and soreness

One 16-person crossover trial found lower soreness ratings and faster recovery of fast-speed knee strength after eccentric exercise; no meta-analysis of recovery outcomes exists.

Recovery and muscle soreness

Pooled small trials report less muscle soreness 24-48 hours after hard exercise and lower muscle-damage blood markers at some time points; the reviews give no pooled size of the soreness benefit in their abstracts.

Memory and brain function

Not shown for typical young lifters: memory gains were concentrated in older adults (SMD 0.88) with no effect in younger people (SMD 0.03); one broader analysis found a small memory benefit (SMD 0.31).

Heart health in healthy adults

Uncertain: 1 g/day did not lower major cardiovascular events (HR 0.92, not significant) in 25,871 healthy older adults, though heart attacks fell (HR 0.72); atrial fibrillation risk rose in cardiovascular trials.

Immune support

No benefit in healthy athletes: a meta-analysis found glutamine generally had no effect on athletes' immune function, and reviews conclude it does not improve immune surveillance in healthy, well-fed people.

Long-term health (cancer, heart disease, lifespan)

Little or no effect: no change in all-cause, vascular or cancer mortality across 21 trials, and an 8% lower total-cancer risk (HR 0.92) in one 11-year trial of older male doctors.

Erectile function

A meta-analysis of 8 trials in men with erectile dysfunction found modestly better erectile-function scores than placebo (IIEF-5 +3.23), with no change in testosterone; one 30-man trial found no benefit.

Fewer stress fractures during heavy training (with calcium)

Promising: female navy recruits given 2000 mg calcium plus 800 IU vitamin D had 20% fewer stress fractures (5.3% vs 6.6%) during 8 weeks of basic training.

Fewer colds and respiratory infections

Not clearly: the updated 2025 meta-analysis of 40 trials (61,589 people) found OR 0.94 (95% CI 0.88-1.00), no longer statistically significant, with no added effect in deficient people.

Bone health and fracture prevention

No effect in the general population: vitamin D did not lower total fractures (RR 1.00), hip fractures or falls, or meaningfully change bone density, at high or low doses.

Improves sleep

Limited and mixed: a 20-person trial found longer sleep and higher melatonin, but a 14-day trial of 500 mg powder found no effect.

Better sleep

Not in healthy athletes: two nights of ZMA did not improve sleep in trained men, even when sleep-deprived. Magnesium alone cut time to fall asleep by 17.36 minutes in older adults with insomnia, on low-quality evidence.