Browse evidence-based analysis of health-related claims and assertions
If two people eat the same total amount of protein each day, it doesn’t matter whether one drinks a protein shake after the gym and the other drinks it at breakfast—both will gain muscle and strength about the same, but there’s not much research on this yet.
Causal
Eating protein right before or after your workout doesn't give you extra muscle gains if you're already getting enough protein throughout the day—so you don't need to rush your shake right after lifting.
If you're lifting weights and want to build muscle, eating at least 1.6 grams of protein per kilogram of body weight every day is the biggest factor that helps — more protein means better results, and when you eat it doesn't matter as much.
People thought taking BCAA supplements would help build muscle because lab tests showed they might affect muscle proteins, but real-life, long-term studies in people haven’t consistently shown that it actually works.
Mechanistic
Leucine is a type of amino acid that scientists think helps your muscles start growing right after you eat it, but we’re not sure if taking extra leucine over time actually makes you stronger or bigger muscles in the real world.
People sell BCAA supplements saying they help you build muscle and get stronger, but scientists aren’t sure if they really work because some studies say yes and others say no.
Taking leucine — a protein building block — might turn on muscle-building signals in your muscles, but if you're already training and eating enough protein, it won't actually make you stronger, bigger, or recover faster.
Taking leucine supplements won't help you get stronger when you're already trained and lifting weights for 8 to 12 weeks.
Taking extra leucine (a protein building block) won’t help healthy, trained young adults build more muscle from weight training, even if the dose is big enough to trigger a key muscle-growth signal in the body.
Taking leucine supplements won't help healthy, trained young adults recover faster after a tough workout, based on how sore they feel, how much strength they lose, and a blood marker for muscle damage.
Taking extra leucine — a supplement found in protein — won’t help healthy, fit young adults build more muscle, get stronger, or recover faster from workouts, no matter how much they take or how long they take it, for up to 12 weeks.
When people with type 2 diabetes take creatine and do strength training, their blood sugar control gets better, shown by lower HbA1c levels.
Taking creatine supplements along with weight training can help older adults build more muscle and get stronger, which might help them stay more active and independent as they age.
Taking creatine supplements might help the brain and spine heal better after serious injuries in animals, by keeping their energy-producing parts working and reducing damage.
Taking creatine supplements may help your muscles heal faster and get stronger again after a tough workout or injury, especially if you regularly lift weights.
Taking creatine monohydrate every day for up to five years, even at high doses, doesn’t seem to harm your kidneys, liver, or blood in healthy people or those with brain-related diseases like Parkinson’s or ALS.
Correlational
Taking creatine powder every day for a week, then a smaller dose after that, can help your muscles store more energy, making you stronger and better at intense workouts like weightlifting.
Men and women gain muscle at about the same rate when they lift weights the same way, so gender doesn't make a big difference in how much muscle you build.
Quantitative
When you lift weights, your body turns down a protein called myostatin that normally stops your muscles from growing too big, which helps your muscles get larger.
When your muscles get really big—more than 22% larger—they need extra help from special cells to add more nuclei so they can keep growing.
When you lift weights, your muscles grow bigger because your cells first make more protein-making machines (ribosomes) — and the more of these machines you build, the more your muscles grow.
When you lift heavy weights, your muscles grow bigger because your body turns on a special chemical signal (mTORC1) that helps make more muscle proteins and building tools, letting your muscles grow faster.
Taking creatine supplements the right way is probably safe and might help older people and kids stay healthy, without hurting their liver, kidneys, or metabolism, based on studies done so far.
Descriptive
Taking creatine supplements won’t turn you into a steroid user or boost your male hormones in any meaningful way—even though one tiny study saw a short, tiny spike that doesn’t really matter.