Secret Ingredients: Calcium, complex carbohydrates, and fiber
How they work: Complex carbohydrates and fiber pump up metabolism by keeping insulin levels low after you eat. That's good, because spikes in the production of insulin send a signal to the body that it's time to start storing fat. And in order to stockpile fat, your body has to slow down your metabolism, causing you to burn fewer calories, says Margaret McNurlan, Ph.D., a professor of nutrition and medicine at the State University of New York at Stony Brook. Since oatmeal breaks down slowly in the stomach, it causes less of a spike in insulin levels than foods like bagels, she says.
Besides helping to keep insulin production down, eating breakfast can also help stoke your daily calorie burn. When the U.S. Navy studied the metabolisms and eating habits of a group of its personnel, it found that eating breakfast helped raise the men's metabolisms by as much as 10 percent. "By skipping meals, you slow down your metabolism and prime your body to store fat," says McNurlan.
The calcium in milk is a metabolic trigger as well. A University of Tennessee study found that dieters who consumed between 1,200 and 1,300 milligrams (mg) of calcium a day lost nearly twice as much weight as dieters getting less calcium.
Jalapenos, Habaneros, Cayennes
Secret Ingredient: Capsaicin—the chemical in peppers that gives them their bite
How it works: By speeding up your heart rate.
A study from the late '80s found that eating a single spicy meal can boost your metabolism by up to 25 percent, with the spike in calorie burning lasting for up to 3 hours after you finish eating. More recently, a study from Laval University in Quebec found that men who consumed coffee plus red pepper-packed snacks and meals were able to burn nearly 1,000 more calories a day than a control group.
Small snacks can also help keep your body from running out of fuel-preventing those 3 p.m. office blahs. "When you restrict the number of calories your body has for fuel, your metabolic rate can drop temporarily," says Susan Roberts, Ph.D., chief of the energy-metabolism laboratory at Tufts University in Boston. That makes it easier to pack on the pounds and harder to burn them off again.
Green Tea, Coffee
Secret Ingredients: Caffeine and a chemical in the tea called EGCG
How they work: Caffeine helps speed up your heart rate. The faster your heart beats, the more calories you burn. EGCG works in a similar way, but instead of revving up your heart, it causes your brain and nervous system to run more quickly-again helping you burn more calories.
In studies, researchers found that a combination of caffeine and a 90-mg dose of EGCG taken three times a day can help you burn an extra 80 calories a day. And that's just when your body's at rest. A study conducted by the Canadian government found that soldiers who consumed caffeine in the 12 hours prior to a physical-fitness test not only were able to work out longer before becoming exhausted, but also consumed more oxygen while working out. The body's oxygen requirements are directly related to the speed of-guess what-your metabolism, so the more oxygen you use, the more calories you burn during your workout.
Lean Beef, Pork, Chicken, Turkey
Secret Ingredient: Protein
How it works: It takes more energy for your body to digest the protein in meat than it does for it to digest carbohydrates or fat, according to Doug Kalman, R.D., director of nutrition at Miami Research Associates, a nationally recognized pharmaceutical-research facility. "That means that the more protein you eat, the harder your body has to work to digest it, and the more calories you'll burn in the process," he says.
When researchers at Arizona State University compared the benefits of a high-protein diet with those of a high-carbohydrate diet, they found that people who ate a high-protein diet burned more than twice as many calories in the hours following their meal as those eating carbs. Even better, researchers in Denmark found that men who substituted protein for 20 percent of the carbs in their diets were able to boost their metabolisms, increasing the number of calories they burned each day by up to 5 percent.
Salmon, Tuna, Sardines
Secret Ingredient: Omega-3 fatty acids
How they work: By altering levels of a hormone called leptin in your body. Several recent studies suggest that leptin directly influences your metabolism, determining whether you burn calories or store them as fat.
Researchers at the University of Wisconsin found that mice with low leptin levels have faster metabolisms and are able to burn fat more quickly than animals with higher leptin levels. The best way to lower your leptin? Eat fish.
Mayo Clinic researchers studying the diets of two African tribes-one of which frequently ate fish and one of which didn't-found that fish eaters had leptin levels nearly five times lower than the levels found in tribes that primarily ate vegetables.
The good news, if you don't like fish: Fish-oil supplements may work just as well as the stuff with scales. French researchers found that men who replaced 6 grams of fat in their diets with 6 grams of fish oil were able to boost their metabolisms and lose an average of 2 pounds in just 12 weeks.