Nutrition

The sports supplement industry generates over $50 billion annually, much of it from endurance athletes. The marketing is compelling. The evidence is frequently not. Understanding which supplements have genuine, replicated performance evidence — and which are expensive placebos — is one of the most practically useful things an athlete can know.

How to Evaluate Supplement Evidence

Not all research is equal. The hierarchy of evidence for supplement claims:

1. Meta-analyses and systematic reviews — pooling multiple studies. Highest confidence.
2. Randomised controlled trials (RCTs) — gold standard for single studies. Look for placebo-controlled, double-blind design.
3. Observational studies — correlation, not causation. Hypothesis-generating only.
4. Case studies and testimonials — anecdotal. No scientific weight.

Many supplements have category 3 or 4 evidence presented as if it were category 1. The Australian Institute of Sport (AIS) Supplement Classification framework is the most rigorous public resource for evaluating endurance supplements — it categorises products into Groups A through D based on evidence quality and safety.

Tier 1: Strong Evidence, Safe, Legal

Caffeine — The Most Effective Legal Performance Supplement

Caffeine is the most extensively researched ergogenic aid in sport. Effects:

• Reduces perceived effort at a given intensity (RPE reduction of 1–2 points on a 10-point scale)
• Delays fatigue onset, particularly in events over 60 minutes
• Improves power output and endurance performance by 2–4% in meta-analyses
• Enhances fat oxidation at moderate intensities (modest effect)

Effective dose: 3–6mg per kg body weight, taken 45–60 minutes before exercise. For a 70kg athlete: 210–420mg. A standard coffee contains 80–120mg caffeine; energy gels typically 50–100mg per serving.

Important consideration: Caffeine is a stimulant with well-documented side effects at high doses (anxiety, GI distress, impaired sleep). Individual tolerance varies significantly. Test in training before race day. Avoid within 6 hours of intended sleep.

Dietary Nitrates (Beetroot / Nitrate Supplements)

Dietary nitrates (found in beetroot juice, spinach, and rocket) are converted to nitric oxide in the body, which reduces the oxygen cost of exercise — effectively improving running economy. Effects:

• Reduces oxygen cost by 2–3% at submaximal intensities
• More pronounced in less-trained athletes and at moderate altitudes
• Performance improvements of 1–3% in events of 5–30 minutes

Protocol: 300–600mg dietary nitrate (equivalent to 500ml concentrated beetroot juice) daily for 3–6 days before an event, with a final dose 2–3 hours before race start. Single-dose acute loading is less effective than chronic loading.

Creatine Monohydrate

Creatine is primarily associated with strength and power sports but has genuine relevance for endurance athletes:

• Improves high-intensity interval training quality (relevant for VO2max sessions)
• Attenuates muscle damage during sustained exercise, improving recovery
• In masters athletes, partially counteracts sarcopenia alongside strength training
• Does not improve aerobic endurance performance directly — but improves the quality of training that does

Dose: 3–5g/day continuously. No loading phase required. Evidence for daily maintenance is stronger than intermittent use.

Beta-Alanine

Beta-alanine increases muscle carnosine concentrations, which buffers hydrogen ions during high-intensity exercise — delaying acidosis-induced fatigue. Most relevant for efforts of 1–4 minutes at maximum intensity (800m–1500m running, hard cycling climbs).

• Performance improvements of 2–3% in events of 1–4 minutes in meta-analyses
• Less relevant for marathon and ultra-distance events dominated by aerobic fatigue rather than acidosis

Dose: 3.2–6.4g/day in split doses over 4–6 weeks to saturate muscle carnosine stores. Side effect: paraesthesia (tingling sensation) — harmless but distracting. Slow-release formulations reduce this.

Tier 2: Moderate Evidence or Specific Conditions

• Sodium bicarbonate: Buffers blood acidity during high-intensity efforts. 0.3g/kg body weight 60–90 minutes before exercise. GI distress is a common limiting side effect. Evidence strongest for 2–10 minute maximal efforts.
• Iron supplementation: Directly improves performance in iron-deficient athletes. No benefit in iron-replete athletes. Essential to test serum ferritin before supplementing.
• Vitamin D: Deficiency impairs muscle function and immune response. Supplementation at 1,500–2,000 IU/day is appropriate for athletes with documented deficiency or limited sun exposure.
• Omega-3 fatty acids (EPA+DHA): Reduces post-exercise inflammation and may improve recovery speed. 2–3g/day from fish oil or algal sources. More relevant during heavy training blocks than rest periods.

What Not to Waste Money On

Many popular endurance supplements have minimal independent evidence:

• BCAAs (during training): Not superior to adequate total protein intake for muscle protein synthesis
• Glutamine: No meaningful performance or recovery evidence in well-nourished athletes
• HMB (β-hydroxy β-methylbutyrate): Limited and inconsistent evidence in trained athletes
• Most proprietary "endurance" blends: Under-dosed ingredients, non-peer-reviewed formulations, no independent testing

Third-Party Testing

Anti-doping contamination is a real risk even in reputable supplements — studies of randomly selected supplements have found prohibited substances in 10–15% of products tested. For competitive athletes, use only supplements certified by NSF Certified for Sport, Informed Sport, or equivalent independent testing programme.

For deeper dives into specific supplements covered here: see our guide to caffeine for endurance performance, the full breakdown on creatine timing and dosage, and the guide to iron deficiency in runners — one of the most common and most overlooked performance issues in endurance sport.