Sports Supplements: What Actually Works According to Science

Preliminary disclaimer

Supplements don't replace a balanced diet. They fill gaps or optimise specific aspects of performance. Without a solid nutritional foundation, they're useless.

Evidence levels: how to read this guide

We classify each supplement by its scientific evidence level:

• Level A: well-established efficacy, many concordant studies
• Level B: probable efficacy, moderate evidence
• Level C: uncertain efficacy or context-specific

Creatine monohydrate — Level A

Creatine is the most studied supplement in the history of sports nutrition. Hundreds of studies over decades converge.

What it does:

• Increases muscle phosphocreatine stores
• Improves performance on short, intense efforts (< 30 seconds)
• Accelerates recovery between sets
• Promotes lean mass gain (indirect effect via increased possible training volume)

Protocol: 3–5 g/day continuously, no loading phase needed. Timing is irrelevant.

Side effects: intracellular water retention (0.5–1 kg weight gain, harmless). No proven renal effects in healthy individuals.

Whey protein — Level A

Whey is simply a convenient dietary protein, not a drug. It's useful when daily protein targets are hard to meet through food alone.

What it does:

• Supplements protein intake
• Fast digestion — ideal post-training
• Complete amino acid profile, rich in leucine (trigger for protein synthesis)

Who it's for: clients who struggle to reach 1.6–2 g/kg/day through food.

Caffeine — Level A

Caffeine is a recognised ergogen (performance-enhancing substance).

What it does:

• Reduces perceived effort
• Improves alertness and concentration
• Increases endurance (aerobic effort)
• Slight improvement in maximal strength

Effective dosage: 3–6 mg/kg body weight, 45–60 minutes before effort. Be mindful of tolerance and sleep impact.

BCAAs — Level C

BCAAs (branched-chain amino acids) are massively over-marketed.

The reality: if your client consumes sufficient complete protein, additional BCAAs provide no demonstrated benefit. Leucine is already present in adequate quantities in whey and animal proteins.

Only possible use case: prolonged fasted training, or vegan diet with suboptimal protein intake.

Beta-alanine — Level B

What it does: increases muscle carnosine stores, buffering acidosis (burning sensation) during intense 1–4 minute efforts.

Useful for: boxing, CrossFit, swimming, short-medium cycling efforts. Little benefit for pure strength training.

Side effect: tingling (paraesthesia), benign, normal and harmless.

Vitamin D — Level B

70% of the European population is deficient in vitamin D, especially in winter. Supplementation is often justified — not as a performance booster but for general health, recovery and hormonal function.

Advice: get your clients tested. Supplement if < 50 nmol/L.

The takeaway message for your clients

1. Eat first, supplement second
2. Creatine + protein + caffeine = the only 3 supplements with solid evidence for performance
3. Be wary of "proprietary blends" and pre-workouts with unreadable ingredient lists

In itwu, you can add supplements to your clients' meals for holistic nutrition + supplementation tracking on the same platform.