9 common fitness myths, busted by science

Fitness advice spreads fast and gets checked slowly. Some myths have been around for decades and still show up in gyms and on social media every day. Here are nine of the most common, and what the science actually says.

Myth 1: "Sit-ups burn belly fat"

False. You can't choose where your body loses fat. In one study, people did abdominal exercises five days a week for six weeks and lost no more belly fat than people who didn't. Ab exercises make the muscles stronger; the fat on top only comes off with overall fat loss.

Myth 2: "Carbs make you fat"

False. Eating too many calories makes you gain fat, whether they come from carbs, fat or protein. In the DIETFITS trial, over 600 adults ate either a healthy low-carb or a healthy low-fat diet for a year, and both groups lost about the same amount of weight. Rice, bread and potatoes can absolutely be part of a fat-loss diet.

Myth 3: "Lifting weights makes women bulky"

False. Building big muscles takes years of hard training, a calorie surplus and, for most people, high testosterone levels. Women typically have much less testosterone than men, so lifting usually makes them look firmer and more toned, not bulky. It also strengthens bones and makes everyday life easier.

Myth 4: "Eat six small meals to speed up your metabolism"

False. The energy your body uses to digest food depends on how much you eat, not how many times. A meta-analysis found that changing how often people ate made no meaningful difference to weight loss when total calories were the same. Eat two, three or six times a day: whatever suits your life.

Myth 5: "Eating after 8 pm makes you gain weight"

Mostly false. Food doesn't turn into fat because of the time on the clock. The real problem is that night eating is often extra snacking on top of a full day. We cover this in detail in Does eating at night cause weight gain?

Myth 6: "The more you sweat, the more fat you burn"

False. Sweat is how your body cools down. It depends on the temperature, humidity, your clothes and your genes. The weight you lose from sweating is water, and it comes back as soon as you drink. Fat actually leaves your body mostly as carbon dioxide you breathe out, as researchers explained in the BMJ.

Myth 7: "Muscle turns into fat when you stop training"

False. Muscle and fat are different types of tissue; one can't turn into the other. What happens is that people stop training, lose some muscle, and keep eating the same amount while moving less, so they gain fat. It looks like a swap, but it's two separate changes.

Myth 8: "High protein is bad for your kidneys"

Not for healthy people. The International Society of Sports Nutrition says protein intakes of 1.4–2.0 g per kg of body weight a day are safe and helpful for active people. If you already have kidney disease, though, your protein should be managed with your doctor.

Myth 9: "Detox teas and cleanses flush out fat"

False. Your liver and kidneys already clean your blood around the clock. Many detox teas work as laxatives or diuretics, so the "weight loss" is water and gut contents, which return within days. They can also cause dehydration and stomach problems. Save your money.

So what does work?

• A calorie deficit you can stick to, built mostly on foods you enjoy.
• Enough protein, around 1.6 g per kg of body weight a day.
• Strength training two to four times a week.
• Plenty of daily movement, good sleep and patience.

It isn't flashy, but it's what the evidence supports. And the most useful habit of all is simply knowing what you eat. With AIMS you can text your meals, snap a photo or just say it, and it tracks the numbers for you.