Do you think you know how to stay slim and look great? "20/20" is exploring 10 popularly held myths about the things you've been doing to look great and stay healthy on both the outside and the inside. You may be surprised by some of the truths.
Four out of 10 Americans work evenings, nights or on shifts, and that means a lot of us are eating later. But won't eating late-night meals pack on extra pounds because we can't burn off the calories when we sleep?
"That is a myth," said dietitian Erica Blacksburg. "Eating late at night won't make you fat unless you go over your calorie load for that day."
But beware. People can gain weight eating late at night depending on what they eat. "A lot of people save their treats for the end of the day," said Blacksburg. "They feel like they deserve something special … They'll have ice cream, they'll have chips."
For those who spend three or four days a week sweating through cardio and strength training, what happens to the muscle when you stop working out? Does it turn to fat?
Fitness guru Donna Richardson Joyner explained this can't happen. "Muscle is muscle, fat is fat. And you can't turn one into the other," she said.
It's a source of confusion for many, but there's no comparison deep inside the body. Dr. Walter Thompson, a professor of exercise science at Georgia State University, said muscle is much denser then fat and is more compact.
He said that when you stop working out the muscle becomes a bit flabby and "non-functional," but does not turn into fat.
And if you're hoping for the opposite -- sorry -- exercise does not transform fat into muscle.
"You have to get rid of fat by doing cardio, said Lara Szymanski at The Sports Club/ LA. "You have to build lean muscle. And that's what you do by strength training."
Need to lose a little weight? If you think counting calories and exercising are all it takes to melt those pounds, you could be mistaken. You might be missing out on another key weight-loss component -- sleep.
"Americans sleep the least of modern countries. And they also, as you know, are the most overweight and obese," said Dr. Eve Van Cauter, a sleep researcher at the University of Chicago. "Perhaps it is worth thinking about the possibility that we don't sleep enough and therefore our appetites are disregulated."
She and Dr. Esra Tasali, another University of Chicago sleep researcher, tested sleep-deprived individuals and found that getting as little as one hour less sleep than is needed can create a hormonal imbalance. Analysis of the sleep-deprived subjects' blood showed lower levels of the hormone leptin, which tells us we're full, and higher levels of the hormone ghrelin, which tells us we're hungry.
"I think sleep should be included in any intervention for weight loss," said Van Cauter.
Do you think botanicals and natural ingredients are better for your hair than chemicals? If you said yes, you'd be wrong, according to Paula Begoun, who has researched more than 4,000 products for her book, "Don't Go Shopping for Hair Care Products Without Me."