At some point in their lives, children of caring parents are likely to hear, “True beauty is on the inside.” Then comes adolescence, and the mythology passed from older siblings and cousins: Eating carrots darkens your tan; Jell-O makes your fingernails grow. By adulthood, the corporate world of gyms, supplements and surgeries has got you. Your head is full of advice for making your hair shinier, skin tauter and teeth whiter.

The simple truth of it all is that outer beauty does start on the inside—with your health. Intuitively, this makes sense: The better you feel, the better you look, right? Yes, experts in everything from hair-styling to medicine agree, but there’s a lot of marketing spin to untangle from the science of beauty.

Start with your head

You don’t want to hear this, but the aspect of your inner health that most affects you on the outside is your mental health. Self-acceptance facilitates healthier and longer-term change more than any superficial measure does. For instance, learning to like yourself fat or thin can both provide the positive-reinforcement cycle that is conducive to weight loss and help you avoid potentially harmful diets and drugs.

“I can tell clients all day long that they look good and are getting stronger, but once they start to internalize it, you can instantly tell in their attitudes,” says Steffanie Canto, a personal trainer and aesthetician with Skin Tight Fitness and Aesthetics. “They’re happier, they sleep better and they don’t want to cheat on their diet.”

Setting aside quiet time to introspect is to mental health what going to the gym is to physical fitness, says licensed counselor and family therapist Amy Forton. “I use guided meditations that help shape clients’ thoughts,” she says. “This, in turn, helps change the way they think about themselves.”

You don’t necessarily need a professional like Forton to try meditation. The Internet abounds with slideshows and videos that teach basic meditation. A well-tested, step-by-step method is available in the Himalayan Institute’s free online classes at HimalayanInstitute.org.

If that’s still too much of a commitment, try simply closing your eyes and holding a positive thought in your mind for 15 to 20 seconds. “You can do this exercise almost anywhere,” Forton says. “Choose an experience that has filled you with joy, gratitude or a sense of accomplishment. Try to stay with the experience and the feelings associated with it. This is a simple but effective moodchanger.”

Decompress

Eyes twitching, jaw clenched, lips drawn in a tight frown … stress is not pretty. Besides having such temporary effects, it can exact a longer-term toll on your looks.

“Stress affects your hair, skin, nails and other parts of your outward appearance,” family physician Lubna Khan says. Eczema, fever blisters, and loss of hair and lunula (the white crescent at the base of fingernails) are a few examples of the many physical conditions for which physicians blame stress.

And the common wisdom about stress causing gray hair and wrinkles? It’s affirmed by voluminous research. Although there are many factors—both environmental and genetic—at play, it seems oxidant production, glycation (glucose binding to other substances) and cell damage, all possible results of stress, are the most likely culprits.

Dermatologist Victoria E. Guerra explains it to clients this way: The human body treats skin, hair and nails like accessories, reserving the bulk of energy for vital functions. “When we have major stresses, these accessories get put on the back burner,” she says.

Everyone’s going to encounter stress triggers, but making time for relaxing activities is a good way to keep stress hormones in check. Going for a walk, sitting in the sun reading, doing yoga—think of these as beauty treatments.

Sleep is also critical to checking stress. “Lack of sleep is a major roadblock for feeling and looking your best,” says Amy Forton, a family therapist.

Beyond just the luggage under your eyes, sleep deprivation makes people generally less attractive to others, according to a 2010 study by researchers in Stockholm. Despite many folks’ swearing to the contrary, countless such studies affirm that eight hours of sleep each night is the proper amount for optimal mental and physical health.

Eat light

Steffanie Canto is a fanatic about the importance of diet—not dieting, mind you, but changing your lifestyle to include healthier behaviors in every area, including the kitchen.

“I can give you a great facial, you can leave with great skin, but if you’re going to go home and eat crap, it’s not going to last,” says the personal trainer and aesthetician.

Eating for health and beauty is more complicated than counting calories. Broadly speaking, you should cut down on animal fat and cholesterol, eat more antioxidant-rich foods, such as fruits and vegetables, and avoid high-sodium foods, says Molly M. Michelman, a registered dietitian and nutrition-sciences instructor at UNLV. These practices will ward off the big appearance-related problems such as high blood pressure and weight gain.

As for foods that promote more specific components of beauty, there’s a sizable body of research supporting the role of healthy fats. The essential fatty acids in avocados, salmon and olive oil help curb both dry hair and wrinkles by increasing moisture in the scalp and elasticity in the skin. Besides containing high amounts of vitamin C and E, green tea is rich in catechins (antioxidants) that can reduce the risk of skin cancer. And crunchy fruits and vegetables— celery, carrots, apples—trigger saliva production, nature’s mouthwash, which keeps teeth white.

Sun poses the biggest threat to the skin, says dermatologist Victoria Guerra, and vitamins A, C and D protect the skin from ultraviolet light. Foods with the highest levels of these vitamins are liver, sweet potatoes and carrots (vitamin A); peppers, guava and dark, leafy greens (C); and seafood and fish oils (D).

Know your supplements

The best way to get nutrients is through food. But what you can’t get through food, you can get through supplements.

“Few of us eat enough of all our vitamins in a daily basis,” dermatologist Victoria Guerra says, “and since I recommend sunscreen everyday, supplementation of vitamin D is important.”

Saundra Carroll, manager and aesthetician teacher at G Skin and Beauty Institute, suggests her clients take vitamin B and C supplements—the latter particularly for people with skin issues, since it participates in the production of collagen.

Those who can’t get their healthy fats in food may consider taking fish oil pills. They help skin by regulating oil production, boosting hydration and delaying the aging process, which is great for desert living, says personal trainer and aesthetician Steffanie Canto.

Biotin is another frequently recommended supplement for beauty-related issues. Although the scientific evidence that it prevents thin, splitting or brittle hair and nails is weak, physicians still believe in it.

Certain groups of people need supplements more than others. Vegetarians and vegans may not get sufficient iron and vitamin B in their diets, and pregnant women must take prenatal pills with vitamins and minerals that help prevent birth defects.

Still, physician Lubna Khan cautions, too many vitamins can lead to problems. It’s worth noting that vitamins recommended for healthy skin, hair and nails are among those that hold the greatest threat for toxicity—A, D and B complex. A good overview of vitamin toxicity can be found at eMedicine.Medscape.com.

Stay balanced

The old saws about consistency and moderation are the varnish that seals healthy beauty practices.

Consider weight loss. While some experimentation with diets to find the best regimen is OK, nobody encourages crash dieting, which deprives the body of nutrients needed to stay healthy.

“Extreme efforts to lose weight—whether through restricting certain foods, self-induced vomiting, extreme exercise or laxative use—can hurt outward beauty,” says dietician Molly Michelman, noting specifically that bulimia can cause broken blood vessels in the eyes.

There’s an important mental component to this, as well. “If you want to eat chocolate, eat chocolate,” Caroll says, “just not a lot of it. If you want to drink alcohol, drink alcohol—just don’t drink too much. Don’t eliminate food groups; just have them in moderation.”

This idea extends to exercise and other healthy activities as well. “You can’t do something for a month, then, if you’re not happy, give up and try something else,” Canto says. Adopting behavior you can stick with will make a lasting difference.