160. SUPPLEMENT QUALITY AND SAFETY FOR CYCLISTS - BY DR JEFF ROTHSCHILD
This KIW Research Note has been written by Dr Jeff Rothschild
Dr Jeff Rothschild is a Registered Dietitian (RD) with a PhD in Exercise Physiology and a Master’s degree in Nutritional Science. His work focuses on endurance performance, carbohydrate metabolism, and the practical application of sports nutrition science to real-world training. His doctoral research examined the periodization of carbohydrate availability for endurance athletes, with a particular focus on pre-training nutrition strategies.
Jeff works with a wide range of athletes, from Olympians and world champions to age-group competitors preparing for their first endurance events, helping them optimize fueling, performance, and long-term health. He is a Research Associate at the Sports Performance Research Institute New Zealand (SPRINZ) and regularly translates current research into practical guidance for athletes and coaches.
You can find Jeff at Jeff@eatsleep.fit
Enjoy the Read! :)
We’ve covered a wide range of supplements so far, from caffeine and creatine to omega-3s, iron, electrolytes, and nitrates, trying to give a picture of what the evidence shows and if/when a supplement may be useful for you. Some of these supplements have solid performance and/or health benefits under the right conditions, while others have a narrower role, or weaker evidence, than some might suggest. But there is another layer of this conversation we have not yet addressed, which is the quality and safety of the supplements themselves.
The supplement industry is enormous and largely self-regulated, and that combination creates real risks. You might not be getting what the label claims is in the bottle, and/or you might be getting things the label doesn’t mention at all, including substances that are banned by the World Anti-Doping Agency (WADA), harmful to your health, or both. Further, even well-intentioned supplement use can interact with medications in ways that are not anticipated. This article lays out some of the potential risks and steps you can take to reduce them.
1. The Regulatory Gap of the Supplement Industry
The core problem with supplement safety begins with how supplements are regulated, or more accurately, how lightly they are regulated compared with pharmaceutical drugs. In the United States, the Dietary Supplement Health and Education Act of 1994 established that dietary supplements are presumed safe and do not require Food and Drug Administration (FDA) approval or safety review before being sold. (1,2) Rather than requiring manufacturers to prove a product is safe before it reaches consumers, the burden largely falls on regulators to identify harm after the product is already on the market. This is quite different from the process used for pharmaceutical drugs, which undergo extensive premarket testing and review.
This means the supplement industry is essentially self-regulated before products reach consumers. Manufacturers are responsible for ensuring their products are safe and accurately labelled, but no independent authority routinely verifies this. As the sports nutrition market has expanded into a multi-billion-dollar sector, monitoring every product, ingredient source, and manufacturing process has become increasingly difficult for government agencies. (4)
One certification you will commonly see on supplement labels is GMP (Good Manufacturing Practice). GMP indicates that a facility meets certain manufacturing process standards: consistent procedures, cleanliness, proper documentation (e.g., batch records that log which ingredients were used and in what quantities, written standard operating procedures, and records of who performed each step). What it does not mean is that the product has been tested for WADA-prohibited substances, or screened for undeclared ingredients. GMP tells you something about how a product was made. It also tells you very little about what is actually in it. (2)
2. What’s on the Label Isn’t Always in the Bottle
One consequence of this regulatory environment is poor label accuracy. A 2023 study examined 57 sports supplements labelled as containing various botanical performance-enhancing ingredients. (5) Forty percent of products did not contain a detectable amount of the ingredient listed on their label. Of those that did contain the listed ingredient, the quantity ranged from 0.02% to 334% of the labelled amount, and only 11% of products were within 10% of the stated quantity.
In practical terms, you may be paying for a product that contains far less of an ingredient than advertised, or far more, which carries its own risks if that ingredient has dose-dependent effects or interacts with something else you’re taking.
3. What’s in the Bottle That Isn’t on the Label
The more serious concern for cyclists, particularly those who compete, is the presence of substances the label doesn’t mention at all. Multiple independent laboratory analyses have found WADA-prohibited substances in commercially available sports supplements at rates that are difficult to dismiss as manufacturing anomalies.
Researchers from the Doping Authority Netherlands purchased 66 sports nutrition supplements from Dutch web shops, selecting products based on performance claims related to hormone modulation, muscle mass, fat loss, or energy, and had them screened for doping substances. (6) Thirty-eight percent contained undeclared doping substances! What was found included stimulants such as oxilofrine, DMAA (1,3-dimethylamylamine), and beta-methylphenethylamine; the anabolic steroids boldione and 17α-AED; the beta-2 agonist higenamine; and the beta-blocker bisoprolol. For some products, the quantities detected were sufficient to pose a meaningful risk of a doping violation.
