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.

Herbs and supplements

Get up with green tea

Although green tea may have less metabolism-fueling caffeine than a regular cup of joe, it may pack more metabolism-boosting nutrients. Recent research shows that green tea's catechin-polyphenol called epigallocatechin gallate (EGCG) works with caffeine to supercharge your metabolism—a magical effect that lasts longer than if you have caffeine alone.

Brewed green teas have varying levels of caffeine and polyphenols, so if you're serious about weight loss, Lieberman recommends taking a standardized extract that contains 50 mg of caffeine and 90 mg of EGCG per dose three times a day before meals.

Trim the fat with conjugated linoleic acid (CLA)

One small study on humans found that dieters taking CLA, a naturally occurring compound found in meat and dairy products, lost more body fat than those taking a placebo, though both groups shed the same number of pounds. It's not pounds per se that CLA targets—but fat (which actually weighs less than muscle).

By interfering with lipoprotein lipase, a substance that encourages your body to store fat, CLA can even help burn flab—get this—while you sleep. “CLA reduces overall body fat, but in particular it works well for the belly and legs,” Lieberman says. Few, if any, other supplements target those soft spots. Take 3 to 3.4 grams of CLA daily in divided doses with meals, says Lieberman.

Fight fat with fish oil

Studies show that fatty fish and fish oil may help melt away pounds in overweight individuals, especially when combined with exercise. The omega-3 fatty acids in fish power up insulin sensitivity, which prevents the loss of muscle mass. “

Fish oil has the opposite effect of trans fats,” says Hyman. “It turns on metabolism and decreases inflammation.” Hyman recommends taking 1 to 2 grams of fish oil a day.

Blunt blood sugar with Glucosol

A proprietary herbal extract of the plant Lagerstroemia speciosa, Glucosol works by blocking the sugar rise associated with eating high-GI foods and thus prevents body-fat storage.

“If you're out traveling and between a rock and a hard place when it comes to menu choices, you can use carb blockers,” says Lieberman. “That way, you won't gain while you're on holiday.” Glucosol often comes combined with other blood-sugar-curbing nutrients, such as chromium.

Lifestyle factors

Weight train

Yo-yo dieters often lose muscle and gain back fat. Although you burn more calories and stored body fat while doing aerobic exercise, weight training to build muscle is key to maintaining your figure.

Aerobic exercise does boost metabolism, an effect that lasts hours afterward, but muscle burns more calories than fat, even when you're lazing on the couch. A well-rounded fitness routine should include aerobic exercise—at least 30 minutes three times a week, according to Lieberman—plus plenty of strength training.

Snooze to lose

Scientists have discovered that sleep deprivation increases ghrelin, the hunger hormone, and decreases leptin, the hormone that makes you feel full. The end result: You can't stop your cravings for high-calorie, high-carbohydrate foods.

Plus, sleep helps lower levels of cortisol—the stress hormone that leads to “beer gut” syndrome. Get at least eight hours of z's each night to keep your body humming along.