Sports Supplements: What Actually Works According to Science

Clients always ask: "what should I take?". The supplement market is huge and the marketing aggressive, but only a few products rest on solid evidence. This guide summarises reference reviews (International Olympic Committee consensus, International Society of Sports Nutrition position stands) and the warnings of the French food safety agency (Anses).

It gives general guidance for coaches, not a prescription. To track your clients' meals and supplements next to their programs, see our personal trainer software page.

Your role and its limits

Coaches can share general nutrition information. Diagnosing deficiencies or prescribing therapeutic doses belongs to health professionals. Refer the client to a doctor or a dietitian whenever there is a medical condition, a treatment, a pregnancy, a minor or any doubt. And supplements never replace a balanced diet: start with the basics in our macros guide.

Evidence levels

Based on the IOC consensus on dietary supplements (Maughan et al., 2018) and ISSN position stands:

• Level A: well-established efficacy in a given context
• Level B: probable efficacy, or limited to some types of effort
• Level C: uncertain, or no benefit when the diet is adequate

Creatine monohydrate: Level A

Creatine increases muscle phosphocreatine stores, improves repeated short high-intensity efforts and, combined with training, supports gains in lean mass and strength (Kreider et al., 2017). Common protocol: 3 to 5 g per day, no loading phase required. A small weight gain from water stored in muscle is common. The ISSN considers it safe for healthy people at usual doses; kidney disease or medication calls for a doctor's opinion.

Protein powders: Level A as a convenient food

Whey, casein or plant protein powders are simply a convenient protein source. The ISSN places the needs of most people who train between 1.4 and 2.0 g of protein per kg of body weight per day, spread over the day (Jäger et al., 2017). Suggest them only after looking at what the client already eats.

Caffeine: Level A for performance, with precautions

Caffeine reduces perceived effort and improves many types of performance, typically at 3 to 6 mg per kg about 60 minutes before exercise (Guest et al., 2021). However, Anses advises against caffeine-containing food supplements before and during exercise because of reported cardiovascular and neuropsychological adverse effects (Anses). A coffee is not a concentrated pre-workout stacking several stimulants; avoid stacking sources, protect sleep, and require a doctor's opinion for heart conditions, hypertension or pregnancy.

Beta-alanine: Level B

Beta-alanine raises muscle carnosine, which helps buffer acidity during intense efforts of roughly 1 to 4 minutes. Protocols use 4 to 6 g per day in divided doses for at least 2 to 4 weeks (Trexler et al., 2015). Tingling is common and harmless. Useful for combat sports, rowing or cross-training; little benefit for classic strength training.

Vitamin D, iron, magnesium: a health matter

These micronutrients matter for health and recovery, but supplementation should follow a medical check, not a hunch. A client who is often tired should see their doctor.

BCAAs: Level C

With enough total protein, BCAAs bring no demonstrated benefit: leucine and the other essential amino acids are already in dietary protein and whey.

Fat burners and "mass" boosters: caution

Anses has received reports of sometimes serious adverse effects linked to supplements sold for muscle gain or fat loss, considers their expected benefits "extremely hypothetical", and strongly advises against them for people with risk factors, minors and pregnant or breastfeeding women. Competing athletes also risk contamination with banned substances: Anses recommends products meeting the French standard NF V 94-001 and traceable supply channels.

How to discuss supplements with clients

1. Start with the plate: regular meals, protein, carbohydrates around sessions, hydration, sleep.
2. Answer the question with evidence, without selling a product.
3. Point out limits and when medical advice is needed.
4. Write down what the client takes, to avoid stacking.

Be transparent about any commercial link (discount code, commission) when you recommend a brand. For day-to-day follow-up methods, see how to support clients as a private coach.

In I Train With You

In I Train With You, you add supplements directly to your clients' meals, next to foods from the Ciqual composition table. Clients see their plan in their app and you keep an overview. See the features.