Supplements: what the evidence supports, and what it doesn't

Supplements sit at the very top of the priority pyramid, which means they matter least. No supplement is associated with long-term weight loss, and the people who spend the most on them usually get the least from their nutrition, because the money buys a quick-fix mindset. That said, a handful have real, modest, well-replicated effects on training, recovery and sleep. This is the list, with the amounts used in the studies, so you can read a label with a straight face.

How marketing twists a study. A supplement group drops from 20% to 17% body fat; the placebo group from 19% to 17%. The difference is not significant. The advert says "slashes body fat by 50%" (3% vs 2%). Ask for the absolute numbers, every time.

01 · Strong evidence

Supplement	What it does	Amount used in studies	Notes
Creatine monohydrate	The best-evidenced legal, non-hormonal aid for strength, power, lean mass and fatigue resistance.	3 to 5 g a day, saturating in about 4 weeks; or 20 to 25 g a day for 5 days then 3 to 5 g (saturates in a week, more stomach upset).	About 30% of people respond little (already saturated). Early weight gain is water inside the muscle, not fat. Ethyl ester, buffered and HCl forms have no advantage over monohydrate.
Caffeine	Less perceived fatigue, more strength, power and endurance in people who train. No effect on fat loss or hunger on its own.	3 to 6 mg per kg of bodyweight about an hour before training; individual response ranges from 75 to 500 mg.	99% absorbed within 45 minutes, half-life 4 to 6 hours, so keep it away from bedtime. Tolerance builds: a week off now and then, timed with a deload or a maintenance break, resets it.
Whey protein	A convenient, high-quality protein; nothing magical after training beyond reaching your daily total.	20 to 30 g raises muscle protein synthesis in most people; the ceiling is around 40 g per serving.	About 11% leucine against 8% in most other sources. Concentrate is ~80% protein, isolate ~90% (less lactose). Hydrolysed, grass-fed and goat whey show no extra benefit. See the cleanest protein powders.
Vitamin D	Many people who get under 20 minutes of direct sun a day are low; restoring it supports testosterone, energy and, in deficient people, small weight-loss and health benefits.	1,000 to 3,000 IU a day; about 3,000 IU restored testosterone in deficient men over a year.	Fat-soluble: do not go much higher without a blood test. If you are replete, more does nothing. Estimate your sun exposure with the vitamin D calculator.

02 · Moderate evidence, specific uses

Supplement	What it does	Amount used in studies	Notes
Fish oil (EPA/DHA)	EPA slows muscle protein breakdown; less soreness, better recovery, useful while in a deficit.	About 1,860 mg EPA + 1,500 mg DHA a day in the key study (4 g of a concentrated oil).	Standard capsules carry only 180/120 mg per gram, which would mean 10 to 11 capsules: buy a concentrated product and take it with meals.
Melatonin	Shortens time to fall asleep; dieting disrupts sleep, and poor sleep hurts fat loss and recovery.	3 to 5 mg, 30 to 60 minutes before bed (1 to 10 mg studied).	Plasma peaks about an hour after taking it. Small positive effects on body composition in some trials.
Betaine (trimethylglycine)	Modest gains in power output and lean mass.	2.5 g a day.	Needs a few weeks to build up. Avoid the hydrochloride form with acid reflux.
L-carnitine (LCLT / ALCAR)	Less fatigue and muscle damage, better recovery; ALCAR crosses into the brain for cognition. A small, significant weight effect in a meta-analysis.	About 2,000 mg a day (LCLT 1 to 4 g; ALCAR 630 to 2,500 mg).	Not a meaningful "fat burner" through fat transport; the weight effect is small.
Rhodiola rosea	Less perceived fatigue, better mood and endurance performance.	50 mg a day long-term, or 300 to 600 mg before an effort (3% rosavins, 1% salidroside).	Bell-shaped dose response: more than 600 mg can cancel the benefit.

03 · Conditional or weak

Supplement	Verdict
BCAAs and EAAs	Recovery aids more than muscle builders: 10 to 20 g before training reduces soreness; they helped keep lean mass in one calorie-restricted trial. If you eat enough protein they add little; EAAs (about 15 g) are the better choice for fasted training, which we do not recommend anyway.
HMB	Anti-catabolic rather than anabolic: small lean-mass and strength effects in beginners and in muscle-wasting conditions, little or nothing in experienced trainees. 3 g a day in the studies.
Multivitamin	Equivocal for most; useful when a restricted diet drops iron (no red meat) or other micronutrients. Prefer products with the full daily amount of iron and vitamin D rather than mega-doses of B vitamins; D3 over D2, natural vitamin E over synthetic. Once a day at breakfast is enough.
"Fat burners"	The stimulant and herbal weight-loss agents sold in this category have at best small effects, side effects on heart rate, blood pressure and sleep, and are not something we recommend or sell. Prescription medicines belong to your doctor.

Order of operations. Sustainable habits, a moderate deficit, exercise, self-monitoring, protein and fibre, then carbs and fat. Then, if the budget allows, creatine, caffeine around training, a protein powder to hit your target, vitamin D if you are low. Everything else is optional.

Studies

Amounts are those used in the cited studies, for information; they are not directions for any WITH ME product and not medical advice. Talk to your doctor before taking supplements with medication, in pregnancy, or with a health condition.

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Supplements: what the evidence supports, and what it doesn't

01 · Strong evidence

02 · Moderate evidence, specific uses

03 · Conditional or weak

Studies

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