Sports nutrition has more confident advice per square metre than any other area of food. Most of it comes from gym conversation rather than from the position stands and meta-analyses that actually exist. Here are nine claims you have certainly heard, checked against what the evidence says — including the places where the debunking has itself gone too far.
The short version
- The anabolic window is hours, not minutes — but it is not infinitely wide either.
- Total daily protein matters far more than timing. It was the strongest predictor of muscle growth in the meta-analysis that tested both.
- The 20 g per-meal ceiling is not real, though the practical dose in the position stands is still 20–40 g.
- Creatine’s weight gain is real — 1 to 2 kg in a month — and the kidney fear is not supported in healthy people.
- BCAAs do not do what the label says. The claim that they stimulate muscle protein synthesis is described as unwarranted.
- Fasted cardio burns more fat during the session and does not produce more fat loss. Both halves are true.
Myth 1: “You have 30 minutes after training or you wasted the session”
The anabolic window is real; the stopwatch version is not. The International Society of Sports Nutrition’s nutrient timing position stand puts the window at “immediately to 2-h post”, and its protein stand notes that “the anabolic effect of exercise is long-lasting (at least 24 h).”
The meta-regression that tested the question directly analysed 23 studies and 525 participants for hypertrophy. A simple pooled analysis showed a small-to-moderate timing effect — but once the model controlled for covariates, “no significant differences were found between treatment and control for strength or hypertrophy.” The covariate that explained the result was total protein intake, which “was the strongest predictor of ES magnitude.”
Do not over-correct. “Timing doesn’t matter at all” is the opposite error. The same authors still recommend not separating the pre- and post-exercise meals by more than about 3 to 4 hours, and the ISSN still recommends a protein dose every 3 to 4 hours across the day. The claim that survives is narrower and more useful: hit your daily total, and don’t leave a six-hour gap around training.
Myth 2: “Your body can only absorb 20 to 30 grams of protein at a time”
This one has quietly collapsed. A 2023 tracer study fed 100 g of protein against 25 g after resistance exercise and reported that “the anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans” — the response was larger and still elevated beyond 12 hours, with negligible effects on protein breakdown or amino acid oxidation.
Earlier work pointed the same way: after whole-body resistance training, 40 g of whey stimulated more muscle protein synthesis than 20 g, and lean body mass did not change the response.
But the practical recommendations have not moved much, and that tension is worth stating rather than resolving. The ISSN still advises “a 20–40 g protein dose (0.25–0.40 g/kg body mass/dose) of a high-quality source every three to 4 h”. One tracer study measuring synthesis is not the same as a training study measuring muscle. The honest version: there is no wall at 30 g, and there is also no reason to save it all for dinner.
Myth 3: “You need protein powder”
The NIH Office of Dietary Supplements is unglamorous about this: “If you are an athlete, you can probably eat enough foods that contain protein to meet your needs for protein.” Powder is convenience, and the ISSN agrees it is “a practical way of ensuring intake of adequate protein quality and quantity” — a logistics tool, not a requirement.
Two numbers frame the actual target. The ODS puts athlete requirements at 1.2 to 2.0 g per kg of body weight per day; the ISSN puts the range for building and maintaining muscle at 1.4 to 2.0 g/kg/day. For most people that is reachable with food.
One thing worth knowing before you buy anything: “FDA does not have the authority to approve dietary supplements before they are marketed.” Manufacturers hold the responsibility for safety themselves.
Myth 4: “Creatine is just water weight” and “creatine damages your kidneys”
Both are half-remembered versions of something real, and both are wrong in different directions.
On weight. The ODS confirms creatine “often leads to weight gain, because it increases water retention”, with studies finding a 1 to 2 kg increase in total body weight in a month. So the water is real. What “just” gets wrong is that a 2021 review attributes longer-term retention primarily to intracellular volume, and notes several studies finding no change in total body water at all — alongside genuine performance effects on “strength, power, and work from maximal effort muscle contractions.”
On kidneys. The review is direct: “creatine supplementation, when ingested at recommended dosages, does not result in kidney damage and/or renal dysfunction in healthy individuals.” The confusion comes from creatinine, a blood marker used to estimate kidney function, which creatine can nudge upward without anything being wrong.
| Claim | Status |
|---|---|
| Causes dehydration and cramping | Not validated by experimental or clinical research |
| Causes hair loss via DHT | Current evidence does not indicate it raises testosterone, free testosterone or DHT |
| Requires a loading phase | No — 3–6 g/day for 3–4 weeks reaches the same place without loading |
| Helps endurance sports | ODS: “of little value for endurance sports” |
Myth 5: “BCAAs build muscle”
The ODS consumer sheet is blunt: “There’s not much scientific evidence to support taking BCAA supplements to improve performance, build muscle, or help tired and sore muscles to recover after exercise. Eating foods containing protein automatically increases your intake of BCAAs.”
The mechanistic review goes further. Because muscle protein synthesis requires all the essential amino acids, and BCAAs supply only three of them, the rest must come from breaking down muscle — which caps any possible effect. Its conclusion: “the claim that consumption of dietary BCAAs stimulates muscle protein synthesis or produces an anabolic response in human subjects is unwarranted.”
Myth 6: “Water is always enough” — and its opposite
Both versions of this argument are wrong, and the threshold is unusually specific. The National Athletic Trainers’ Association states that “those participating in physical activity lasting less than 1 hour should require no substances other than water”, while activity beyond an hour “may benefit from adding carbohydrates or electrolytes (or both).”
| Situation | What is actually recommended |
|---|---|
| Under an hour | Water |
| Over an hour | Carbohydrate and/or electrolytes; 3–8% carbohydrate concentration absorbs best |
| Heavy, salty sweaters | Sodium supplementation mainly warranted above ~60 mEq/L sweat sodium with high sweat rates |
| Any session | Finish under 2% body-mass loss — performance falls consistently beyond it |
And there is a risk in the other direction that gets far too little attention: “excessive fluid consumption can lead to life-threatening exercise-associated hyponatremia” — blood sodium below 135 mmol/L during or within 24 hours of activity. Drinking to thirst is a safe default against overdrinking, though NATA notes competitive athletes relying on it “may compromise performance.”
Myth 7: “Fasted cardio burns more fat”
This is the rare myth where the mechanism is true and the conclusion is false, and most articles get only one half.
True: a meta-analysis of 27 studies found “a significant increase in fat oxidation during exercise performed in the fasted, compared with fed, state”. You do burn more fat while you are running.
False: a separate meta-analysis of training studies found effect sizes for body mass and body fat between groups of 0.02 to 0.05 — trivial — and concluded that “fasted compared to fed exercise does not increase the amount of weight loss and fat mass loss.”
Fuel used during one hour is not the same thing as fat lost over a month. Train fasted if you prefer it; do not expect a body-composition bonus.
Myth 8: “Carbs make you fat”
The cleanest test of this was a metabolic ward study in which 19 adults with obesity had either carbohydrate or fat selectively restricted, with calories matched and every meal supervised. Carbohydrate restriction increased fat oxidation and produced 53 g of body fat lost per day. Fat restriction did not change fat oxidation at all — and produced 89 g per day, significantly more.
Over a year, the difference disappears in either direction. In a 609-person trial comparing low-fat with low-carbohydrate diets for 12 months, weight change was −5.3 kg against −6.0 kg, a difference of 0.7 kg that was not significant — and neither genotype nor insulin secretion predicted who did better on which.
The ISSN puts it in one line: “A wide range of dietary approaches (low-fat to low-carbohydrate/ketogenic, and all points between) can be similarly effective for improving body composition.”
Myth 9: “High protein wrecks your kidneys”
A systematic review of 28 trials covering 1,358 healthy adults compared high-protein with normal-protein diets and found no significant difference in the change in glomerular filtration rate — the standard measure of kidney function. Its conclusion: “HP intakes do not adversely influence kidney function on GFR in healthy adults.”
Two boundaries on that. The evidence covers healthy adults and does not extend to people with existing kidney disease, who should follow clinical advice rather than sports nutrition articles. And the ODS reports no safety concerns at the athlete intakes it lists — up to about 2.0 g/kg — which is not the same as a blank cheque at any dose.
FAQ
How soon after training should I eat protein?
Within a couple of hours is well supported; within 30 minutes is not a requirement. Do not leave more than about three to four hours between the meal before training and the meal after it, and prioritise the daily total.
How much protein per day?
The ODS gives 1.2 to 2.0 g per kg of body weight for athletes; the ISSN gives 1.4 to 2.0 g/kg for building and maintaining muscle. In a calorie deficit while lean and training hard, the ISSN notes higher intakes may be needed to protect muscle.
Should I load creatine?
You do not have to. Loading with about 20 g a day for 5 to 7 days fills stores faster; 3 to 6 g a day for three to four weeks reaches the same place. Expect 1 to 2 kg of weight gain from water either way.
Are BCAAs worth buying?
The evidence does not support them for building muscle, and any food containing protein already supplies them. Money spent on total protein does more.
Do I need a sports drink for a one-hour gym session?
No. Water is what the position statement specifies for activity under an hour. Electrolytes and carbohydrate start to matter beyond that, especially in heat.
Where this fits
The everyday counterpart to this article — late eating, breakfast, detoxes, spot reduction, eggs, salt — is in fitness nutrition myths. If your interest is stomach trouble during long sessions, that is covered in the gut and athletic performance, and the sodium side of sweat losses in our sodium intake guide.
Every figure here is linked to its source in the text: the NIH Office of Dietary Supplements, the FDA, position stands of the International Society of Sports Nutrition and the National Athletic Trainers’ Association, and peer-reviewed meta-analyses and trials in the Journal of the International Society of Sports Nutrition, Cell Reports Medicine, the British Journal of Nutrition, Cell Metabolism, JAMA and the Journal of Nutrition. Checked against those sources on 2 September 2026. Educational information, not medical advice — see our medical disclaimer.
This content is for educational purposes only and is not medical advice. Always consult a qualified healthcare professional for personalised guidance.
