As you add birthdays, you might notice that your metabolism—the complex process by which the food you eat gets converted into energy—has put on the brakes a bit, not just because you're older but because of the choices you make.

Maybe you've slowed your pace, which means you don't burn through food as efficiently as you used to. Or yo-yo diets over the years have cost you calorie-burning muscle and not so much fat. Whatever the reason, the good news is that adopting a few natural strategies can recharge your metabolism to get you back into great shape.

Nutrition

Eat early and eat often

Breakfast is the most important meal of the day. “When you don't eat breakfast, you sabotage your metabolism, and you'll have sugar cravings later,” says Mark Hyman, MD, author of Ultrametabolism (Scribner, 2006) and The Ultrametabolism Cookbook (Scribner, 2007).

Eat a protein-rich breakfast to kick-start your system and to get essential amino acids that help you feel full longer. Although you may be tempted to skip lunch in an effort to dodge calories, don't.

“Skipping meals creates a ministarvation in between that interferes with metabolism,” says Hyman. Eat three meals a day, plus a snack or two in between. And stop eating two to three hours before bedtime. “If you go to sleep with food in your stomach, you store it and don't burn it,” Hyman explains.

Ditch fake foods, particularly trans fats

Highly processed and nutrient-devoid ingredients “pretend” to be food and can interfere with your metabolism, according to Hyman. Trans fats—often lurking in cookies, crackers, margarine, and fast food—are well known for raising total and LDL (“bad”) cholesterol and lowering HDL (“good”) cholesterol.

They also thwart dieters' best efforts by binding to cell receptors that regulate metabolism. “They slow metabolism and fat burning, and reduce insulin sensitivity, so you're more likely to gain weight,” Hyman says.

Although the government did well by requiring food manufacturers to list trans-fat amounts on labels, buyers beware: Companies can label their products “zero trans fats” if a product contains less than 0.5 gram per serving. But even trace amounts of trans fats hinder metabolism, so to steer clear, Hyman recommends scouring ingredient lists for “shortening” or any type of “partially hydrogenated” vegetable oil.

Go organic

Are you the type who always reaches a plateau where your weight won't budge anymore? Toxins could be to blame.

A recent analysis published in Obesity Reviews found that pesticides (such as organochlorines used on grains, onions, and other crops, or that persist in the water or soil from banned pesticides like DDT) and polychlorinated biphenyls from industrial pollution—both of which the body usually stores in fat tissue—get released during weight loss and then poison metabolism.

How? These toxins may reduce thyroid-hormone levels and interfere with the hormone's ability to rev up metabolism. They also inhibit fat burning and appetite control. To counter this effect, choose organic foods.

Count on beans

Calories matter, but the type of calories you consume may be more important. Focus on low-glycemic foods, says Shari Lieberman, PhD, CNS, author of Dare to Lose (Avery, 2002). A food's glycemic index (GI) is a numeric value that indicates the rate at which the food raises your blood sugar.

High-glycemic foods, such as white rice, plain bagels, and potatoes, cause blood sugar to take off, which quickens your body's release of insulin and wreaks havoc on your metabolism.

Instead, eat low-glycemic beans, whole grains, and vegetables, which not only keep blood sugar in check, but also fill you up fast, says Lieberman.

One caveat: Make sensible, nutritious food choices. “Pound cake has a low glycemic index because it has lots of butter, but, of course, that shouldn't be included,” says Lieberman.