With all the studies, surveys, diets and weight-loss claims pummeling you with advice everywhere you turn, it's no wonder that so many myths and misperceptions about weight loss persist. To help clarify the fact from fiction, TIME put a few pressing questions to the experts.
Why doesn't exercise help you lose weight?
This is a controversial issue that researchers are still debating. It's true that as people start exercising, they may not lose weight because they tend to eat more to compensate for increased hunger, or as a reward for working out. It's also true that with exercise, people lose fat but gain muscle, which is heavier than fat. But it's not necessarily true that exercise doesn't help you lose weight.
It's worth noting that weight loss does not depend on exercise alone. Weight loss happens only when you take in fewer calories than you burn. And people are notoriously good at miscalculating how many calories they sweat off at the gym. Think an hour on the treadmill can work off an entire chocolate cake's worth of calories? Not even close — 60 minutes of running barely accounts for a single slice.
Exercise clearly doesn't guarantee weight loss, but it's a pretty reliable route to good health — exercise buoys mood, keeps your brain sharp and lowers your risk of chronic disease. But just remember that to drop pounds, it takes a lot of time and sweat to burn calories, plus equal effort to reduce the amount of calories you eat.
Which is better for my health — more frequent sessions of moderate activity or fewer bouts of intense exercise?
There's no right or wrong way to exercise, say obesity experts. How much you should move depends on what your goals are — to stay healthy or to lose weight — and what level of physical fitness you're starting with.
If you are currently sedentary or get very little exercise, for example, most fitness professionals advise starting slow. Rather than focusing on the amount of activity you do, just focus on doing something. That can include walking for even a few minutes a day; studies show that sedentary women who began walking 10 minutes a day saw benefits in heart health. "There are such huge returns on the investment of just getting off the couch," says Dr. Tim Church, director of preventive medicine research at Pennington Biomedical Research Center.
The point is to avoid being sedentary. Some exercise is better than none, and most people should stay as physically active as their bodies allow, ideally exercising every day. Check out the U.S. Department of Heath & Human Services' Physical Activity Guidelines for solid activity advice by age group.
Why does it get harder to lose weight the older I get?
Age is a major contributor to weight gain, for many reasons. With each passing year, adults lose more muscle mass, the biggest consumers of calories we have. That's why resistance training — working out with weights to build muscle — is important, even for aging adults. Strong muscles help keep excess pounds off, and lower the risk of dangerous falls.
Another reason weight loss gets harder with age is that the body's metabolism slows down, as cells and organs begin showing the wear and tear of years of faithful service and get less efficient at consuming calories. Starting regular exercise in childhood — though it's never too late to start — is a pretty good way to keep the body running more efficiently later in life.
And, finally, don't forget the social factors that make weight gain easier in adulthood. In midlife, people are more likely to be able to afford more and richer foods than they could in their younger days. They're also less likely to have as much time for physical activity because of job and family pressures, and they're also more likely to give up walking or biking for more comfortable modes of transportation, like driving.
Can diet sodas actually make you gain weight?
Diet soda contains fewer, or no, calories compared with the sugared versions, but recent studies have shown that people who drink diet soda tend to gain more weight than those who drink regular soda.
The reason may be that the brain can't be fooled by the artificial sweeteners found in many diet drinks and foods. While the sweet taste of diet soda may satisfy the palate, the body feels swindled out of the calorie rush it was expecting. That may only whet the appetite, encouraging diet-soda-consumers to seek out sugar from other sources, or alter their metabolism as if they had actually consumed the sugar — both of which may lead to weight gain.
Another reason may involve the amped up sweetness of artificial sugars, which are 100 times sweeter than natural sugar. It's possible that people who eat a lot of artificially sugared foods become so accustomed to intense levels of sweet that their palates can no longer appreciate natural flavors, of fruit or other foods. Since natural foods are more nutritious than artificially processed alternatives, people may start to choose less healthy foods overall.
The evidence is still coming in, but it's an area of intense research to figure out how our bodies react to the mismatch between artificially sweetened taste and the absence of corresponding calories.
Why is it so hard to lose those last five to 10 pounds?
The bigger you are, the easier it is to lose weight. When an obese, sedentary person starts a new exercise and diet program, those first few pounds will melt off pretty quickly. That's because bigger people have a higher metabolic rate than smaller people, which means their bodies are faster to use up calories they eat. "Think of yourself as a big furnace chewing up calories," says Pennington's Church. "The bigger you are, the more cells you have in your body, and the more cells you have using energy. A very large person has a pretty high resting metabolism, or can burn a lot of calories a day just by existing."
But as people continue to lose weight and shrink the number of cells they have, their metabolism slows down to match their reduced size — if it didn't, they would be burning off way too many calories compared to what they take in. (Which wouldn't be a bad thing from a weight loss perspective, but running a constant deficit and having always-hungry cells takes an unhealthy toll on tissues and organs that work overtime to survive.)
So as the weight comes off, you have to work harder to burn the same amount of calories. You may have started off walking 30 minutes a day, for instance, but that activity is no longer enough to push your body to eat up extra calories. Now, you might need to walk for 60 minutes or start running for 30 minutes instead.