Put down the diet book that touts a carb-free, protein-rich diet and tells you all fat is your mortal enemy. Get ready to learn the mystery to permanent weight loss.

What's In That? | Quiz: How Big? | Your Needs

Eating everything is the magic bullet, experts say.

Variety is the key to not only a good-looking exterior, but a healthy body that can fight disease, according to Ann C. Grandjean, director of Omaha's Center for Human Nutrition, Inc. Grandjean suggests three golden rules for eating: balance, variety and correct servings. Mindful eating that follows these three simple concepts will create healthy bodies.

"Balance. Don't eat all meat one day and then nothing but bread the next day," Grandjean said. "(Include) variety within a given food group -- not just potatoes and green beans. Eat something green, eat something orange, eat something red. (And think of) the right amounts like those three bears -- not too much, too little, but just right."

It's the Goldilocks diet, but it isn't really meant to cause rapid weight loss. Grandjean said she's been trying to make nutrition sexy for nearly three decades and she just can't do it.

"Good nutrition is boring as hell. Just saying, 'Make sure to eat five servings of fruit' is boring. So to sell books, (people say you) have to do something mystic," she said.

That's how we've become a generation obsessed with counting carbs, cutting fat and eating 3 pounds of bacon in a day in an effort to trim our burgeoning waistlines. But limiting or overloading on any nutrient won't make you thin or healthy. You need healthy servings each of carbs, protein and even fat. Here's why:

Carbohydrates are the human body's primary source of energy. You also get energy from fat, protein and alcohol, but most of the calories we need to live come from carbs, Grandjean said. That makes them essential, so cutting them or severely restricting them is not a good thing.

But you should concentrate on getting them from whole grains. A 2003 Harvard study that followed 74,000 female nurses for 12 years found that women who ate the most whole grains weighed less than those who ate the fewest. And a Louisiana State University study of 149 women found that a low fiber intake was linked to higher body fat. Both studies were cited in a Shape.com story.

Proteins, which are made of chains of amino acids, are the foundation of the body. They help create muscles, blood, skin, hair nails and the organs.

Athletes need more protein than couch potatoes, Grandjean said, and the Center for Human Nutrition put together an easy questionnaire (PDF format) to help individuals determine exactly how much protein they need for optimum health.

Fat should be kept at 30 percent of total calories each day, unless you're physically active, Grandjean said. Active people can eat up to 35 percent of their diets in fat.

But don't avoid it altogether. Fat is in every cell of the body, and in order for those cells to function properly, they need fat from the diet. Fat sources include nearly every protein source, such as fish, meat, chicken and nuts, along with vegetable oil, avocadoes and more.

"You need all kinds of fats, and when you eat a variety of foods, you get all the kinds of fat. You can do harm by concentrating on specific foods instead of concentrating on the total diet," Grandjean said.

There's that variety suggestion again. Really -- eat everything, she said again.

The government Web site MyPyramid.gov allows you to tailor a daily menu based on your individual needs, and Grandjean said she loves it because all a user does is enter his or her age and sex and the site spits out specific foods and serving sizes.

That brings us to the third leg of Grandjean's diet stool. Instead of eating all carbs or no fat, eat the right amount of each food you consume. In a time when the local homewares store is filled with quart-sized cereal bowls and extra-large, pizza-sized dinner plates, knowing the appropriate serving can be tricky. Start with the nutrition label, then keep these tips from the International Food Information Council in mind or check out our portion size quiz. Related Item:

• Planner: Make Healthy Meals