It's no wonder metabolism is a subject of fascination and speculation: The process that turns food into fuel powers all that we do. "Even when you're sleeping, your body requires energy for things like breathing and repairing cell damage," says Donald Hensrud, MD, medical director of the Mayo Clinic Healthy Living Program. The number of calories you need to perform such basic functions is called your resting metabolic rate (RMR)—and it can affect everything from your waistline to your energy level. Read on to learn how to keep your metabolism revved so your body is operating at just the right speed.
Dieting can lower your metabolism
"Whenever you cut calories, your metabolism slows down, often by more than you'd expect," says Kevin Hall, PhD, an obesity researcher at the National Institutes of Health. Studies have found that formerly obese people have a 3 to 5 percent lower RMR than people who've never had to lose weight. But such a drastic slowdown isn't inevitable. Other research has shown that regular exercise can counteract the effect. And a gradual weight-loss strategy can help keep your metabolism humming. A good rule of thumb: Reduce caloric intake by no more than 500 calories a day, and torch roughly the same number through exercise. A 1,000-calorie daily deficit should help you lose about 2 pounds a week.
Chronic stress slows your burn
Wigged-out and gaining weight? No, it's not in your head (unfortunately). Research suggests that when you're totally frazzled, your metabolism stalls. One reason: Chronic stress stimulates the production of betatrophin, a protein that inhibits an enzyme needed to break down fat, per a University of Florida study. Other research found that women who experienced a stressful event the day before eating a single high-fat meal burned 104 fewer calories over the seven hours following the meal than their more chillaxed counterparts. "The stressed women also had higher insulin levels, which contributes to fat storage," says study author Janice Kiecolt-Glaser, PhD, a professor at The Ohio State University. These effects could lead to a gain of 11 pounds a year, she says.
Health.com: The Best Fat-Burning Breakfasts
Intermittent fasting may help
For the most part, experts have advised against cleanses and other trendy fasts. But research now shows that alternate-day fasting—which entails eating without restriction one day, then consuming about 500 calories the next—can trigger weight loss without mucking up your metabolism. Women who followed this plan for eight weeks lost an average of 13 pounds, according to a study from the University of Illinois at Chicago. "When we compared the change in their resting metabolic rate to that of subjects who lost weight by consuming 25 percent fewer calories overall, we didn't see any differences between the two groups," says study author Krista Varady, PhD.
What's more, after the first few days, most of the women in the alternate-day fasting group didn't report feeling hungry. But Dr. Hensrud cautions that further research is needed to determine the long-term effects of this strategy. If you're tempted to try it, do so under a doctor's supervision.
Lift weights the right way
There's no question that strength training is a good way to combat the drop in metabolism that comes with age. But new research suggests that when you're lifting weights, the ideal strategy is to go slowly. Resting for two to three minutes between sets may actually promote more muscle growth than a shorter rest interval, according to a U.K. study published this year. "The most important thing is to just do it, two or three times a week," stresses Pamela Peeke, MD, author of Body-for-LIFE for Women. To reap the most benefits, add your strength training to a HIIT workout (like a boot camp class), she says.
Health.com: 31 Quick-and-Easy Fat-Burning Recipes
Protein is key
You've probably heard that the more muscle you have, the more calories you'll burn. And you know protein is essential for muscle growth; it helps prevent the breakdown of muscle tissue that happens as you get older and when you cut calories, says Caroline Cederquist, MD, an obesity specialist in Naples, Fla., and the author of The MD Factor Diet. But the trick, she adds, is to divide your intake evenly throughout the day. "You can utilize only 4 to 6 ounces of protein at a time. If you consume more than that at one sitting, it will get stored as fat."
Research backs up her advice: A 2014 study found that people who took in 30 grams of protein at each meal had 25 percent better muscle protein synthesis than those who ate 90 grams in a day in irregular portions (10 at breakfast, 15 at lunch and 65 at dinner). As for the best sources of the nutrient, study author Emily Arentson-Lantz, PhD, a scientist at University of Texas Medical Branch, suggests lean meats, seafood, legumes, eggs, dairy and nuts.
You can blast calories all day long
6 A.M.: Work out. You can melt up to 20 percent more body fat by exercising in the morning on an empty stomach, according to a 2013 U.K. study.
7:30 A.M.: Have the right smoothie. Swiss research found that folks who consumed whey protein at breakfast burned more calories throughout the morning than folks who ate a high-carb meal.
11 A.M.: Refill your water bottle. In a German study, drinking 17 ounces of H2O increased metabolic rate by about 30 percent for more than an hour.
1 P.M.: Add some sweet red peppers to your salad. They contain a metabolism-boosting chemical called dihydrocapsiate.
3 P.M.: Take a call on your headset and go for a walk. Small bursts of activity like this can torch up to 350 calories a day, found Mayo Clinic researchers.
7 P.M.: Turn off your iPad before dinner. Exposure to blue-enriched light (the kind emitted by electronic devices) during the evening meal increases insulin resistance, according to a 2016 Northwestern Medicine study.
7:15 P.M.: Enjoy some carbs. A 2014 study showed that people who saved most of their daily carbs for nighttime burned more calories after lunch than those who ate their carbs early on.
9 P.M.: Turn down the heat. Sleeping in colder temps ramps up your body's production of brown fat, a type that burns calories, per a study in the journal Diabetes.
Certain health problems can affect your metabolism
Thyroid disorders: An overactive thyroid (called hyperthyroidism) can cause your metabolism to speed into overdrive, while an underactive thyroid (hypothyroidism) can make it slow to a crawl. Fortunately, both conditions can be controlled with medication.
Prediabetes: This condition elevates insulin levels, which inhibits fat metabolism, explains Dr. Cederquist. But lifestyle measures such as exercise and a low-glycemic diet can help repair metabolism.
Osteoarthritis and rheumatoid arthritis: Neither condition affects metabolism directly, but both can make exercise painful—and not exercising enough can lead to muscle loss and a drop in metabolism, explains Dr. Cederquist.
Polycystic ovary syndrome: Women with this hormonal imbalance are at higher risk of developing insulin resistance, which can in turn impact metabolism. Possible treatments include birth control pills to regulate hormone levels and the diabetes drug metformin.