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.
Myth No. 10: Eating Late at Night Makes You Fat
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."
Myth No. 9: Muscle Turns to Fat When You Don't Exercise
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."
Myth No. 8: Diet and Exercise Are All You Need to Lose Weight
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.
Myth No. 7: Natural Ingredients Make Shampoos Better
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."
"All of those cute little plant extracts they throw in, the teeny amounts of apples or chamomile or whatever sexy-sounding herb or plant that grows, that's not what's cleaning your hair," Begoun told "20/20."
"The unsung heroes of the hair care industry are synthetic ingredients," she added. "But it's hard to sell synthetic ingredients as having any sex appeal."
Ingredients like the laureth sulfates are what's actually cleaning your hair, but nobody's touting chemicals on shampoo bottles.
Myth No. 6: Waxing Is Better Than Shaving
Shaving's been around for thousands of years, and waxing dates back to the ancient Egyptians. Which is the best method for hair removal?
"When you wax the hair, you're pulling it from under the surface of the skin. So it can take several weeks, three to four weeks, before you actually see the hairs resurface," said dermatologist Pat Wexler.
If you shave, Wexler said, you'll see new hair in a couple of days and the hair will grow back coarser. "Because when you shave the hair you're cutting the edge of the hair blunt, so when it grows in you always feel the sharpness," said Wexler.
With waxing, Wexler said the hair will grow back finer. "You create scarring in that hair follicle from the constant pulling," said Wexler. "And the scarring will diminish the number of hairs that grow back."
Myth No. 5: Moisturizers Prevent Wrinkles
Skin care fads will come and go, but many of us still hold on to what seems to be the best and most basic way to ward off wrinkles -- moisturizer. Facial creams account for a $250 million a year business, but can moisturizers actually prevent wrinkles?
"They can treat fine lines and wrinkles and improve the appearance of skin, but they are not going to prevent wrinkles," said dermatologist Andrea Cambio. And yet some cosmetics companies promote their products as a method for wrinkle prevention.
"It's very misleading, yes … if there was anything else that could prevent wrinkles that was so easily accessible, we would all look 20," said Cambio. She suggests some things you can do to help. For starters, don't smoke. It's terrible for your skin. And do not leave the house without sunscreen, or a moisturizer with an SPF of at least 15.
Finally don't assume that high price equals high quality. Inexpensive creams are often just as good.
Myth No. 4: Reading in Low Light Hurts Your Eyes
When the lights are out, what if your kids are under the covers reading with a flashlight? Will reading in dim light hurt their eyes?
Dr. Robert Cykiert, associate professor of ophthalmology at New York University, said he's often asked about the myth and it's not true.
"Can it hurt your ears if you listen to a whisper? Of course not," said Cykiert. "And certainly you can't damage your eyes if you read in the dark."
Can staring up close at a television set or computer screen strain the muscles and harm your vision? "Again, totally false," said Cykiert. "You will get some fatigue, you will feel tired … but in fact, that does no damage to your eyes whatsoever."
And if you think eyeglasses or contact lenses create dependency, that's another myth.
"Your eye is either nearsighted or farsighted or has astigmatism because of the anatomical shape of the eye. Then you need glasses or contact lenses or now laser vision corrections to correct that problem," said Cykiert.
By the way, here's some advice your mother got right -- eat your carrots. Recent studies confirm that beta carotene, an anti-oxidant found in the orange, yellow and red fruits and vegetables, is very healthy for eyes.
Myth No. 3: Male Fertility Is Reduced by Tight Underwear, Laptops and Hot Tubs
What do male underwear, laptop computers and hot tubs all have in common? According to contemporary urban legend, they all lower fertility and can have cause serious problems for couples trying to have a child.
"The testicles are outside the body because they need to be cooler. Anything that increases the temperature of the scrotum can adversely affect sperm production," said Dr. Harry Fisch, who treats male fertility and has written a book, "The Male Biological Clock."
He said with briefs, there's no definitive research, so most likely it's a myth.
The hot tub can be more damaging to fertility. Fisch said if the water increases the body temperature to 104 degrees there can be a dramatic effect on sperm count. "As a matter of fact, sperm counts decline for the next two months. And it may take four to six months for the sperm counts to recover," said Fish.
Latops can kick out a heat of 104 degrees after an hour of use. Dr. Yefim Sheynkin of the State University of New York recently published a study on laptops that found they could cause permanent fertility problems when used directly for extended periods of time on the lap.
Myth No. 2: Chocolate Is Bad for You
Chocolate is typically described as both a sinful pleasure and a fattening food. But recent studies show there are ways in which the sweet treat can be good for you.
Cocoa beans are rich in compounds called flavonols that produce specific health benefits.
"Chocolate can have very beneficial effects for your heart," said Katherine Tallmadge, a spokeswoman for the American Dietetic Association who has also written the book "Diet Simple."
She described the health benefits of chocolate as "relaxing blood vessels. Maybe reducing blood pressure and reducing blood clotting, which is an aspirin-like effect, as well as reducing inflammation, which is an emerging risk factor in heart disease," said Tallmadge.
Flavonols, also found in red wine, green tea, apples and onions, are very concentrated in the cocoa bean. But they're generally processed out of the chocolate because of their bitter taste.
Until it becomes common for manufacturers to measure and list their flavonol content, there are some basic tips if you're looking for the healthiest kind of chocolate. Drinking unsweetened cocoa is one way to start.
"You want the product that has as little processing as possible," said Tallmadge. "Look for the darkest chocolate you can find and try to find a product that has a high level of cocoa and a low level of calories," said Tallmadge.
The bad news: Because it is high in sugar and fat, chocolate is not a health food. If you're really into its benefits, Tallmadge said a one-ounce serving of dark chocolate is enough.
Myth No. 1: Revenge Is Sweet
For the No. 1 myth, John Stossel took a look at revenge:
In the movies, revenge is applauded, and I love those moments of revenge -- the satisfaction of watching the bad guy get his just punishment. But if revenge is sweet, Stanford psychologist Fred Luskin say, forgiveness is much sweeter.
There's a lot of research pointing to the negative effects of hostility.
"Makes you much more likely to have heart disease … It increases your risk of stress-related disorder. It raises your blood pressure," said Luskin. "Wanting to hurt somebody is like pouring Drano into your own insides."
It's natural to want revenge. Marietta Lane was on a camping trip with her family in Montana when her 7-year old daughter, Susie, was kidnapped. Lane wanted to kill the kidnapper.
"I was just so furious that I could have done it with my bare hands and a smile on my face," said Lane.
But, within a year, Lane decided to forgive whomever it was who took her child. "As a Catholic Christian, that's what I'm called to do. And just psychologically I knew that hatred was not healthy … it would have obsessed and consumed me," said Lane.
One year after Susie was taken, the kidnapper called Lane, and her forgiveness so surprised him that he stayed on the phone with her for an hour. That gave police enough clues to find him. Susie had already been killed. In jail, the kidnapper killed himself. Then Lane befriended the man's mother and they eventually went together to visit his grave.
"People say forgive and forget. Well, you'll never forget. I will never forget what happened to my little girl," said Lane. "But it's precisely because I can't forget that I have to find a way to move on with my life."
And that approach is good for the health, said Luskin. He says forgiveness makes you less depressed, less angry and less stressed. "Revenge may feel good for a moment," said Luskin. "Forgiveness helps you heal your whole life."