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Scientific evidence for the best-selling sports supplements
TABLE OF CONTENTS
The scientific evidence behind the best-selling sports supplements is the foundation on which any sports nutrition strategy seeking real results without wasting time or money should be built. In the gym or on the training field, we constantly hear about magic shakes, fat-burning pills, and performance enhancers that promise to transform our physique overnight. The sports nutrition industry generates billions of euros a year, driven by dazzling advertising campaigns. However, when we put these products through the filter of the most rigorous science, we discover that the gap between marketing and physiological reality is enormous.
To navigate this maze, leading international scientific organizations—such as the International Olympic Committee (IOC), the International Society of Sports Nutrition (ISSN), and the Australian Institute of Sport (AIS)—classify supplements according to the strength of their evidence. Analyzing this evidence does not mean dismissing supplementation, but learning to distinguish the tools that genuinely optimize our performance from those driven solely by the placebo effect or commercial speculation.
The golden rule: The hierarchy of needs in sport
Before breaking down each product, it is useful to understand how our body adapts to exercise. Imagine your physical progress as the construction of a multi-story house. The non-negotiable foundation consists of energy balance (the calories you consume compared with those you expend), a proper distribution of macronutrients through real food, adequate hydration, and restorative rest.
Ergogenic supplements occupy the pinnacle of this pyramid. This means that supplementation provides a modest margin of improvement, generally between 2% and 5%, which only becomes truly valuable when the foundations of diet and training are fully established. Investing hundreds of euros in shakes or capsules while sleeping five hours a night or training without planned progression is like trying to change the tires on a car that has no engine.
The True Performance Giants (High Efficacy)
Within the vast catalog available, there is a small group of substances with unquestionable support. They have been tested in thousands of athletes in rigorous clinical trials, and their physiological mechanisms have been perfectly demonstrated.
Protein powder (Whey, Casein, and plant-based alternatives)
Protein powders—whether classic whey (Whey) or plant-based blends of soy, pea, and rice—are probably the most widely consumed product worldwide. They are marketed as essential for immediate recovery and muscle growth.
From a metabolic perspective, when we consume protein, the digestive system breaks it down into essential amino acids. One of them, leucine, acts as a biological key that activates the mTORC1 pathway, the cellular switch that triggers muscle protein synthesis. Large-scale meta-analyses, such as the one conducted by Morton et al. in 2018 involving more than 1,800 participants, demonstrate that protein supplementation in strength-training programs produces significant increases in lean mass and maximal strength.
However, science clarifies a fundamental point: protein powder does not have magical properties superior to those of a chicken breast fillet, a serving of fish, or eggs. Its main advantage lies in its practicality, convenience, and cost per gram of high-quality protein. No additional benefits are observed from exceeding a total daily intake of approximately 1.6 to 2.2 grams of protein per kilogram of body weight. Therefore, shakes are a fantastic tool for meeting your daily requirements if you struggle to cover them with solid food, but they are not mandatory.
Creatine Monohydrate
Creatine monohydrate is, without a doubt, the most studied and cost-effective supplement in the history of sports nutrition. In skeletal muscle, the rapid energy used for heavy lifts or sprints comes from the molecule adenosine triphosphate (ATP). However, ATP stores are depleted in just a couple of seconds. This is where phosphocreatine comes into play: it rapidly donates its phosphate group to regenerate ATP and allow us to maintain power for a few more seconds.
According to leading scientific reviews such as Gualano et al. in 2019, creatine supplementation increases muscle phosphocreatine stores by between 10% and 40%, which directly translates into increased maximal strength, more repetitions per set, and better recovery between intense efforts. In addition, creatine draws water into the muscle cell (cellular hydration), a phenomenon that acts as a secondary anabolic signal for tissue synthesis.
The most effective protocol consists of taking 3 to 5 grams of creatine monohydrate daily, preferably with the Creapure quality seal, on an ongoing basis. The so-called “loading phase” (20 grams per day for one week) is optional and only serves to saturate the stores a few days earlier. It should be noted that creatine is completely safe for the kidneys in healthy people and that myths such as hair loss lack solid scientific support.
Anhydrous Caffeine
Caffeine is a central nervous system stimulant whose primary mechanism is blocking adenosine receptors in the brain. Adenosine is the substance that accumulates throughout the day to tell our body that it is tired. By blocking it, caffeine drastically reduces the perception of effort, decreases the sensation of muscle pain, and optimizes the brain’s ability to recruit muscle fibers.
Synthesis research, such as Spriet’s 2020 review, confirms that doses of 3 to 6 milligrams of caffeine per kilogram of body weight, taken 45 to 60 minutes before exercise, consistently improve both aerobic endurance and power in strength and speed sports. Taking caffeine in tablet form (anhydrous caffeine) provides faster and more precise absorption than coffee as a beverage, making it one of the cheapest and most effective ergogenic strategies on the market.
To use these products properly and avoid unrealistic expectations, analyzing the scientific evidence behind the best-selling sports supplements helps us understand that even the most effective tools require precise doses and consistency.
Supplements with moderate effectiveness or context-specific benefits (Group B)
There are substances that do work, but their effects are more modest or limited to very specific sports and situations.
• Beta-alanine: The amino acid precursor to intramuscular carnosine, a molecule that acts as a buffer or “sponge” for the acidity (hydrogen ions) generated in the muscle during very intense exercise. A meta-analysis by Hobson et al. in 2015 demonstrated that chronic supplementation with 4 to 6 grams of beta-alanine daily for at least four weeks improves performance by 2% to 3% during maximal efforts lasting between 1 and 10 minutes. It is ideal for rowers, combat athletes, CrossFit participants, or runners covering 400 to 1,500 meters. Its characteristic side effect is paresthesia (a harmless tingling sensation in the skin), which can be avoided by dividing the doses.
• Citrulline Malate: Used as a precursor to L-arginine in the blood to stimulate nitric oxide synthesis, promoting vasodilation and blood flow to the muscle. Studies analyzed by Gough et al. in 2021 indicate that doses of 6 to 8 grams of citrulline malate before training produce a modest increase in the number of repetitions completed before failure and slightly reduce muscle soreness. Its effect is subtle, but it may be useful for advanced strength athletes.
• Nitrates (beetroot juice): Naturally present in vegetables such as beetroot, they are converted into nitric oxide in the body, reducing the oxygen cost of exercise and improving respiratory efficiency and sprint power in recreational endurance athletes.
The great illusion: Overhyped products with no evidence (Groups C and D)
This is where marketing beats science. Millions of athletes consume products every day that offer no real training benefit.
Branched-Chain Amino Acids (BCAAs)
BCAAs (leucine, isoleucine, and valine) were the star product for decades for use during training. They were sold with promises of preventing catabolism and accelerating muscle rebuilding.
However, the science has been unequivocal. A meta-analysis conducted by Doma et al. in 2021 concluded that, although BCAAs may slightly reduce markers of muscle damage and delayed-onset muscle soreness, they do not improve strength or accelerate athletes’ functional recovery. The physiological reason is simple: building muscle tissue requires all 9 essential amino acids. Consuming only 3 is like giving builders only one-third of a house’s plans and bricks; the construction process stops. If you already consume enough protein in your diet, taking BCAAs is throwing money away.
Testosterone boosters (“Testo Boosters”)
Ingredients such as Tribulus terrestris, D-aspartic acid (DAA), and maca root flood the market with promises of naturally increasing testosterone. Multiple controlled clinical trials have shown that none of these herbal extracts manages to raise total or free testosterone levels in healthy men or produce changes in muscle mass compared with placebo. Their only real effect is usually a slight increase in subjective libido, but with no anabolic impact.
Thermogenic fat burners and L-Carnitine
L-Carnitine is sold to transport fat to the mitochondria and “burn” it. However, oral L-Carnitine has absorption below 15%, and muscle transporters are already naturally saturated. Thermogenic complexes, meanwhile, only increase calorie expenditure by an insignificant amount (less than 50 calories per day), basing their entire effect on high doses of caffeine that cause nervousness and tachycardia. Real fat loss is achieved only through a sustained calorie deficit.
It is vital to examine the scientific evidence behind the best-selling sports supplements to avoid being misled by miracle promises and to focus the nutrition budget solely on what science supports.
Commercial fraud and questionable ingredients
Beyond their lack of effectiveness, the market presents risks that every athlete should know about:
- Amino Spiking (Nitrogen Adulteration): Deceptive practices where some brands add cheap non-essential amino acids (such as glycine or taurine) to protein powders to artificially raise the nitrogen measurement in the laboratory and label more grams of protein than the container actually contains.
- Proprietary blends: Pre-workout formulas that conceal the exact amount of each ingredient under a registered name. This allows them to include microscopic doses of expensive compounds, such as citrulline, and fill the container with cheap caffeine.
- Cross-contamination: Between 10% and 15% of internationally analyzed commercial supplements contain traces of substances prohibited by WADA, such as undeclared steroids or illegal stimulants, due to failures in production lines. To avoid this, athletes should look for independent batch certification seals such as Informed-Sport or NSF Certified for Sport.
Understanding the scientific evidence behind the best-selling sports supplements enables us to make smart, safe nutritional decisions aligned with our true physical goals.