Browse evidence-based analysis of health-related claims and assertions
When people lose weight, their hunger increases more than their metabolism slows down, which makes it harder to keep losing weight and easier to gain it back.
When you lose muscle or other non-fat body mass while dieting, it might make you hungrier and want to eat more — but scientists aren't sure exactly how this works yet.
People with more muscle tend to eat more, likely because muscle burns more calories and signals the brain to maintain energy balance.
When people lose weight, their bodies sometimes slow down more than expected, burning fewer calories at rest — and this might be why some folks struggle more than others to keep the weight off.
When adults cut calories for a long time, their bodies may respond by increasing hunger and slowing metabolism, making it harder to keep losing weight.
If women who aren't very overweight add aerobic exercise to a calorie-reduced diet, they get noticeably better at exercising — like being able to bike or walk harder — but just dieting alone doesn't help much with fitness.
For women who aren't very overweight, adding aerobic exercise to a calorie-restricted diet doesn't help them lose more fat than just eating less — as long as both groups burn the same total calories over 8 weeks.
For women who aren't severely obese, losing fat depends only on eating fewer calories — it doesn’t matter if you cut those calories through diet alone or by combining diet with cardio, as long as the total calorie drop is the same.
If people with extra weight eat only during a shorter part of the day, they tend to eat about 200 fewer calories each day, which helps them lose weight and feel better metabolically.
Eating earlier in the day might give you better metabolism results than eating later — but only if you're not carefully matching calorie amounts. It seems like timing helps, but doesn’t do all the work on its own.
If you eat all your food in a shorter window each day, you'll lose more weight and feel better — but that's mostly because you end up eating fewer calories, not because of the timing itself.
Eating within a certain time window each day can lower blood pressure and improve blood sugar levels in people who are overweight or obese.
If you're an adult with extra weight, eating only during certain hours each day—like an 8-hour window—can help you lose about 2% of your body weight and improve your overall body shape, including smaller waist and less body fat.
Doing strength training three times a week for three months can help improve muscle size, strength, belly fat, cholesterol, blood sugar, and overall metabolic health in women around 69 years old who are otherwise healthy.
Older women around 69 years old who drink a whey protein shake every day and lift weights three times a week for three months may gain more muscle, lose belly fat, and improve their overall metabolic health more than those who just do the workouts without the protein.
When young guys burn more calories than they eat and work out hard, their stress hormone (cortisol) changes—and that’s linked to shifts in muscle and fat. But it doesn’t explain much about why people’s bodies change differently.
If young guys eat more protein while working out hard and cutting calories for a month, they’ll gain more muscle and lose more fat compared to eating less protein.
If young guys lift weights hard and do intense workouts while eating less for a month, chugging 2.4 grams of protein per pound of muscle each day helps them gain more muscle and lose more fat than eating half that much protein.
If you're already lean and trying to lose weight, you can keep your muscle if you lift weights, eat a lot of protein, lose weight slowly, and occasionally eat more carbs.
If you're lean and work out with weights, taking two days a week to eat more carbs doesn't seem to slow down fat loss compared to cutting calories all the time — both ways lose about the same amount of fat in 7 weeks.
If you're fit and lift weights, cutting calories most of the week but eating more carbs for 2 days might help your body burn calories at rest better than cutting calories every day — like keeping your metabolism from slowing down too much.
If fit people who lift weights cut calories for 7 weeks, taking two days each week to eat more carbs might help them keep almost all their muscle, losing only 0.2 kg of muscle instead of nearly 2 kg.
If you're already lean and lift weights, taking two days a week to eat normal calories—especially from carbs—while cutting calories the rest of the week might help you keep more muscle compared to cutting calories every day.
If someone with extra weight loses a lot quickly while dieting and lifting weights, they might not build as much muscle as they could if they lost weight more slowly.