If you've made nutrition mistakes in the past, your body may still forgive you if you change -- now!

By Jennifer Nelson
WebMD Feature

So you may not have made all the right nutrition choices in the past, but it's unlikely you caused any permanent harm, right?

WebMD wanted to be sure, so we took it to the experts to get the scoop on why some of the nutritional missteps you were guilty of in the past are taboo. And what, if any permanent effects, these prior dietary failings have in store for you. Can these past nutritional skeletons haunt your health today?

Yo-Yo Dieting

If your weight has fluctuated up and down the scale -- and your closet houses an array of pant sizes to accommodate your ever-changing waistline, you're not alone.

Yo-yo dieting is one of the most common nutrition mistakes you can get caught up in. Lose a few pounds here, gain them back there. What's the big deal, right? The National Task Force on the Prevention and Treatment of Obesity from the National Institutes of Health looked at whether yo-yoing, also known as weight cycling, had an adverse effect on body composition, energy expenditure, risk factors for cardiovascular disease, or interfered with future efforts at weight loss. Although conclusive data on the long-term health effects of weight cycling are lacking, the task force determined that maintaining a stable weight should be a priority. Anything beyond a 5-pound variation should tip you off.

However the WISE study (Women's Ischema Symptom Evaluation) funded by the National Heart, Lung, and Blood Institute did find that yo-yo dieting actually lowers levels of good cholesterol (HDL).

"One problem with past yo-yoing is that it can mess up your metabolism," says Keri Glassman, MS, RD, a New York City-based dietitian. When you yo-yo diet, you never really learn to eat normally. Weight cycling sets you up for binges. Plus, you probably aren't eating a variety of healthy foods. You're always either getting too many calories, which turn to fat, or your body is in deprivation mode from eating too little, so your metabolism is constantly thrown out of whack and never burns calories efficiently, which hampers any effort at weight loss.

To boost calorie burn and return metabolism to normal, stop the ups and downs and acquire a balanced healthy diet. Eat consistently every three to four hours and never go too long without food. Glassman tells WebMD, "Once you're eating regularly, you can get your metabolism back on track."

Skimping on Carbs

If tallying carbs and keeping them low was your M.O., you might have easily gone overboard. Carbohydrates are a source of concentrated energy so contrary to some beliefs the ideal is not to eliminate them at all costs. Carbs are a rich source of B vitamins and contribute to skin, hair, eye, and liver health. They also help regulate appetite and keep the brain and nervous system running optimally.

"Skimping on carbs can throw the body out of balance because something it needs isn't showing up for work," says Cynthia Sass, MPH, MA, RD, a Florida-based dietitian.

Too few carbs may lead to increased appetite and insatiable cravings. And severely restricting carbohydrates can cause you to eat too much fat -- think a whole jar of nuts in one sitting.

If eating a low-carb diet equals eating lots of saturated fat and cholesterol-heavy foods, these can increase your risk of high cholesterol, heart disease, and cancer, Sass tells WebMD.

It could also up your risk of diverticulitis, an infection in the pouches within the colon, because of the lack of dietary fiber typical on low-carb plans.

The quick fix is to jump on the veggie bandwagon ASAP. Strive for five to nine servings of produce per day to boost intake of disease fighting antioxidants and phytochemicals. This will also increase fiber, as a typical serving of fruit or vegetables contains 2-3 grams of fiber.

"Breakfast skippers may have wreaked havoc on their metabolisms."

Read labels to keep saturated fat, hydrogenated fat, and cholesterol to the USDA Dietary Guidelines limits, which is 300 milligrams of cholesterol per day from food, 10% of total calories from saturated fat (about 22 grams for a 2,000-calorie diet), and as little hydrogenated fat as possible. Hydrogenated fats come from liquid vegetables oils, which are converted into solid form during manufacturing. They are used mostly in processed baked goods, such as cookies and cakes, and can help increase the shelf life of many products. But these fats have a negative effect on cholesterol, increasing "bad" LDL cholesterol while lowering "good" HDL cholesterol.

Breakfast Skipper

Whether you were too busy sleeping in, just not hungry or truly thought this was a good way to keep your weight in check, former breakfast skippers may have wreaked havoc on their metabolisms, too. Research shows skipping the morning meal slows resting metabolism and keeps our bodies from burning calories until lunchtime. A study in the Journal of the American College of Nutrition shows breakfast skippers have a higher body mass index (BMI).

Other research shows people who eat breakfast daily may be less likely to succumb to obesity and diabetes.

"You need breakfast to get your brain and body functioning," says Glassman. If you don't feed your body, it will only hold onto the fuel it has stored and will never budge a pound.

People who skip breakfast are also the type of people who tend to go without eating in general, Glassman tells WebMD. They're the same ones who go until 3 p.m. without lunch or tend to forget to eat all day and then feast on a large dinner.

These behaviors can destroy of the metabolism over time. Also, when you eat fewer foods throughout the day, you eat fewer types of foods and may miss out on vital nutrients, says Glassman. Skipping breakfast may result in a lack of an adequate store of vitamins and minerals as well as missing out on certain phytochemicals and antioxidants that help ward off disease.

Avoid the metabolism roller coaster by regularly downing a healthy breakfast. If you can't eat first thing in the morning, wait an hour or two for your stomach to settle, and then try half an English muffin with peanut butter or a container of yogurt.

Fad Dieter

If you once followed the grapefruit diet, the cabbage soup diet, or a few other not-so-nutrition-savvy plans, you may have this nutritional blunder in your diet repertoire.

But if you were a fad-diet groupie, have you put your health at risk?

"Fad diets aren't science-based and their goal is only weight loss, not long-term disease prevention or even day-to-day energy," says Sass. You also can feel too tired to exercise and irritable and moody during a fad diet.

Depending on how wacky and lacking in nutrients the fad was, you may have lost lean muscle mass and bone density along with body fat.

The good news: Once you've dumped the fad diet, the short-term side effects like irritability and fatigue fade away. However, lost muscle mass and declining bone density can prove more problematic.

While building lean muscle through weight-bearing exercise is the key, building up bone health can be trickier and take longer to accomplish. Eating a diet rich in calcium and regularly lifting weights is a start.

Talk to your doctor about bone mineral density testing, especially if you have other risk factors for osteoporosis, such as a family history, or if you paid homage to many fad diets in the past.

And never relying on a fad diet to slim down again is the best break your bones will get.

SOURCES: National Institutes of Health. WISE study (Women's Ischema Symptom Evaluation), The Journal of the American College of Cardiology, November 2002. Keri Glassman, MS, RD, KKG Body Fuel, New York City, N.Y. Cynthia Sass, MPH, MA, RD, American Dietetic Association, Tampa, Fla. Journal of the American College of Nutrition, 2003; vol 22: pp 296-302.

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