Sports supplements

By Dr. Ixchel Corcuera — Family and Emergency Medicine

Every week someone asks me in my practice whether they should be taking protein, creatine or some pre-workout. Sometimes they arrive with the tub already bought and ask if it's okay. Other times they come with genuine questions: they saw something on social media, a gym buddy told them something, or they simply want to know if it's worth the money.

The honest answer is that it depends. It depends on what you're taking, how much, what for, and who's taking it. The sports supplement market has grown spectacularly in recent years — 14% in Spain alone in 2024, with protein sales up 175% according to the Cofares Trends Observatory — and that growth has brought serious research, but also a lot of noise and a lot of empty promises.

This article isn't trying to sell anything. It's trying to explain what the science actually says about the most consumed supplements, so you can make an informed decision.

First, a clarification about what "scientific evidence" means

When I say a supplement has scientific evidence behind it, it doesn't mean it's magic or that it will transform your body. It means that in controlled studies, with comparison groups, measurable and reproducible effects have been observed. Those effects tend to be modest — a few extra reps, slightly more strength, less fatigue — but they're real and consistent.

The opposite also applies: when I say something doesn't have enough evidence, it doesn't mean it doesn't work. It means we don't yet have solid enough data to say so. The absence of evidence is not evidence of absence.

With that clear, let's get to it.

Creatine monohydrate: the most studied, and the one that least disappoints

If there's one supplement I'd recommend without hesitation to a healthy person who trains for strength, it's creatine monohydrate. Not because it's trendy — it's been studied for decades — but because the data is consistent, the effects are clear, and the myths surrounding it are well and truly debunked.

Creatine is a natural compound the body produces itself and that is also found in foods like meat and fish. Supplementation raises phosphocreatine stores in the muscle, which allows ATP (the cell's energy currency) to be regenerated more quickly during explosive, intense efforts. The practical result is that you can perform better in heavy sets, recover faster between reps, and over time gain more strength and muscle mass.

What the science says:

It improves strength, power and performance in high-intensity exercise. This is well documented across hundreds of studies.

No loading phase required. A daily dose of 3 to 5 grams is effective long-term. The aggressive loading protocols you used to see on tubs ten years ago are not necessary.

The benefits aren't just for bodybuilders. Efficacy has been shown in football, basketball, racket sports and athletics. And also — something I find especially relevant in my practice — in older adults, to slow the loss of muscle mass and strength that comes with aging.

There are indications of cognitive benefits, though this area needs more research.

On the myths that come up in practice:

Does it damage the kidneys? No, in healthy people at recommended doses. There are over twenty years of research showing no renal damage. If you have pre-existing kidney disease, check with your doctor before taking it, as with anything.

Does it cause problematic water retention? Short-term there can be a slight increase in intracellular muscle water, which is precisely what helps you perform better. It's not pathological retention.

Does it cause hair loss? No. One isolated study suggested a possible increase in DHT, but broader reviews have not found evidence that creatine causes hair loss.

Is it a steroid? No. It has nothing to do with anabolic steroids or their risks.

A clinical note that rarely gets mentioned: creatine is also being researched in neuromuscular diseases such as muscular dystrophy, Huntington's disease and amyotrophic lateral sclerosis. Preliminary results are interesting, though more evidence is needed for formal recommendations. I mention it because it illustrates well that creatine isn't just a gym supplement — it's a molecule with serious physiological implications.

Protein powder: useful when diet falls short, not as a replacement for it

Protein powder is the world's best-selling supplement and also one of the most misunderstood. It's not a magic formula for building muscle. It's a convenient, efficient way to cover daily protein requirements when the regular diet doesn't get there.

How much protein do you need if you train? The International Society of Sports Nutrition recommends between 1.4 and 2 grams per kilogram of bodyweight per day to optimise the benefits of training. Above 1.6 g/kg/day, the additional benefit for muscle mass becomes marginal according to current evidence. Exceeding 3 g/kg/day consistently in healthy people hasn't shown clear additional benefits either, though it doesn't appear dangerous in the short term.

Timing matters more than most people realise. Taking protein at night — before sleep — has been associated with increased muscle protein synthesis during rest and improvements in strength and mass after weeks of resistance training. It's not essential, but if you have the habit and the caloric room, it's a smart moment to include it.

On which type to choose:

Whey protein has the best essential amino acid profile and is the most studied. Its rapid digestion makes it particularly useful after training. It comes in concentrate (with some lactose), isolate (virtually lactose- and fat-free) and hydrolysate (pre-digested, though practical differences are minimal for most people).

Casein digests slowly and releases amino acids in a sustained way over several hours. It works well as a nighttime dose.

Plant proteins — soy, pea, rice — are completely valid alternatives. Soy has the most complete amino acid profile among plant sources. Combining plant sources covers requirements without issue.

Meat or collagen protein has a poorer amino acid profile for muscle synthesis and less scientific backing. It's not the first choice if the goal is muscle mass.

Caffeine: the supplement you already have at home

Caffeine is probably the most consumed supplement in the world, though most people who take it don't call it a supplement — they call it coffee. And it works. The ergogenic effects of caffeine on physical performance are among the best documented in all of sports supplementation.

The mechanism is well known: caffeine blocks adenosine receptors in the brain, which are responsible for the sensation of fatigue. The result is that you perceive effort as lower, you tire later, and you can maintain intensity for longer.

A meta-analysis published in 2024 in the journal Nutrients analysed 14 randomised controlled trials on the effects of caffeine on muscular strength and endurance. The specific data: taken at a dose of 6 mg/kg of bodyweight around 45 minutes before exercise, it produces a measurable increase in muscular strength and allows approximately 1 to 2 extra repetitions in resistance exercises. Effects are statistically significant but of small magnitude — an effect size of between 0.2 and 0.25 in technical terms — which in practice means a real but not transformative advantage.

At lower doses, below 3 mg/kg, it improves alertness, concentration and mood without relevant side effects.

What's worth knowing:

Tolerance varies a lot between people. Some metabolise caffeine quickly, others slowly. In the latter, an afternoon dose can significantly affect sleep quality, and sleep is where much of muscular recovery happens. Chronically poor sleep cancels out any advantage caffeine can offer.

The dehydrating effect at habitual doses is minimal and has no clinical relevance. This myth has been debunked for years.

Benefits are achieved at moderate amounts. There's no physiological reason to chase high doses unless the context is elite competition.

Beta-alanine: when the muscle starts to burn

Beta-alanine is less well known than creatine or caffeine, but it has an elegant mechanism of action and fairly solid evidence for a specific use profile.

It's an amino acid that, when taken as a supplement, raises muscular carnosine levels. Carnosine acts as a buffer against muscular acidity: during intense exercise, the muscle produces hydrogen ions that lower pH and cause that characteristic burning sensation that forces you to stop. More carnosine means more capacity to neutralise that acidity, which delays fatigue and allows intensity to be maintained for longer.

Four weeks of taking between 4 and 6 grams daily significantly increases muscular carnosine concentrations. Benefits are most pronounced in efforts lasting between 1 and 4 minutes — that range of high intensity and medium duration where muscular acidosis is the limiting factor. In very short or very long efforts, the benefit is less marked.

The only relevant side effect is paraesthesia: a tingling or prickling sensation on the skin, especially on the face, neck and hands, appearing around 15-20 minutes after taking it. It's not dangerous, but it can be uncomfortable. It's easily avoided by splitting the dose into 1.6-gram portions throughout the day or using a slow-release formula.

It's common to find beta-alanine combined with creatine in pre-workout supplements, and it makes sense: creatine improves power in the first seconds of each set, while beta-alanine delays fatigue when the effort is prolonged. Complementary mechanisms, not redundant ones.

Sodium bicarbonate: the buffer that acts from the bloodstream

Sodium bicarbonate works on a similar logic to beta-alanine — reducing muscular acidity — but from outside the muscle, in the blood, rather than inside the cell. While beta-alanine is an intracellular buffer requiring weeks of daily supplementation to work, bicarbonate is an extracellular buffer with an acute effect: you only need to take it on the day of the effort.

The evidence supports its use in high-intensity exercises lasting between 1 and 7 minutes. The standard dose is 0.2 to 0.3 grams per kilogram of bodyweight, taken 1 to 2 hours before exercise.

The main problem is digestive: nausea, abdominal discomfort and diarrhoea are relatively common side effects. Not everyone tolerates it well. Starting with lower doses and taking it with a meal can reduce these symptoms, but in some people it's simply not a viable option.

Supplements under investigation: promising but no clear verdict yet

There's a broad group of compounds generating scientific interest but for which there isn't yet enough data for firm recommendations: branched-chain amino acids or BCAAs, citrulline, HMB, phosphatidic acid, nitrates and quercetin, among others.

Being under investigation doesn't mean they don't work. It means the available evidence isn't yet solid or consistent enough to know with confidence in which contexts they're useful, at what doses, and for what type of person or training.

BCAAs are perhaps the most illustrative example: enormously popular for years, current evidence suggests their benefits are minimal when total protein intake is already adequate. If you eat enough quality protein, adding BCAAs separately probably adds nothing relevant. It's a supplement with more marketing than science behind it in most contexts.

When supplementation makes sense and when it doesn't

After years in practice I've reached a fairly simple conclusion about this.

It makes sense if your diet doesn't reach the requirements for a specific nutrient for practical reasons — schedules, preferences, intolerances — and a supplement solves that simply. It also makes sense if you train at a level where small performance improvements have real consequences and you want to leverage the margins that evidence offers. Or if you have a proven deficiency of some micronutrient.

It doesn't make sense if you're trying to compensate with a tub for what isn't working in your diet, training or sleep. No supplement repairs a deficient diet, a poorly designed programme or chronic sleep deprivation. That's mathematically impossible, and anything selling you otherwise is lying to you.

A clinical note worth adding: some supplements can interact with medications or be unsuitable in certain health conditions. Creatine warrants caution in kidney disease. Caffeine can be problematic in arrhythmias or uncontrolled hypertension. Bicarbonate should be avoided in people with sodium restrictions or heart failure. None of this is reason to demonise them, but it is reason not to take them without thinking, especially if you're on any medication.

To finish

The supplement market will keep growing. Social media will keep filling up with before-and-afters, perfectly photographed tubs, and promises that sound too good to be true. My job isn't to tell you not to take anything — it's to help you understand what's behind each product so you can decide from knowledge, not from marketing.

What has solid evidence, used correctly and in the right context, can offer something real. What doesn't may work just the same — or you may be paying for flavoured water.

The difference between the two is knowing how to read the science. Or having someone nearby who does.

Dr. Ixchel Corcuera

Family and Emergency Medicine

contact@horizontegear.com

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