By Sarah Mahoney

Traditional wisdom holds that a sluggish metabolism is a curse of midlife, like needing reading glasses to use a smartphone or starting to worry about your retirement plan. So we fight the slowdown, eating like parakeets for a few days or launching into an intense exercise routine. When a week goes by with no miracles, we give up and resume the same bad habits—sloppy portions, half-hearted workouts, and non-petite servings of imported cheese.

Ok, put away the Brie and consider this: About 30% of your metabolism is under your control (the rest, devoted to such mundane but essential functions as digesting food and repairing cells, isn't). And as researchers get deeper into the physiology of weight regulation, they're fine-tuning their understanding of what it takes to ramp up that 30% and drop pounds. Happily, it starts with what you consume—the right foods at the right times.

1. Measure Your Meals
If simply cutting back isn't budging the scale, it's helpful to know how many calories you need each day to maintain your weight. Then, to lose pounds, you can subtract from that maintenance number. Since a woman's metabolic rate falls roughly 2% to 3% each decade, this number—alas—goes down with age. A moderately active woman in her 20s requires a daily average of 2,000 to 2,200 calories to maintain her weight. In her 30s and 40s, it drops a little to just about 2,000. After 50, it falls to 1,800.

And you? Check out the Metabolism Calculator atwebmd.com. By plugging in your gender, age, height, weight and activity level (there's a five-point range on the site, from "inactive" to "extremely active"), you'll learn what it takes to keep the status quo. For example, a 45-year-old woman who is 5'4", 158 pounds, and moderately active will maintain her weight on 2,093 calories a day. There's been some refinement of thinking on this, but in general, to lose a pound a week, she will need to consume 500 fewer calories each day (because a pound equals about 3,500 calories), or 1,593 calories.

Try to stick to your Metabolism Calculator calories for a week without changing your exercise routine. If a pound disappears, that's a calorie-needs bull's-eye. If not, adjust accordingly.

But don't be tempted to subtract too many calories. As counterintuitive as it may seem, eating too little can slow your metabolism—by as much as 20%. "If your body thinks you're trying to starve it, it fights back by burning fewer calories," says Domenica Rubino, M.D., an endocrinologist and a spokesperson for the Obesity Society.

2. Reset Your Eating Clock
For years, experts have said that working on smaller, more frequent meals is essential to a faster metabolism. But recent studies suggest that's no better—diet-wise—than eating three larger meals a day. There's no cut-and-dried approach, says Dr. Rubino. "The research is certainly clear that breakfast is beneficial," she says. "But beyond that, you need to find what works for you." Some people do best with six small meals a day, while others consume way too much on that schedule. Some do better with three square meals, but that can make others so hungry that they set themselves up to overeat.

Whichever plan you choose—and you may want to experiment if you've been frustrated in your past dieting efforts—be sure to keep an eye on calories and track your hunger throughout the day. And once you do decide on the best approach, start a diet log: Note meals, snacks, and your mood before you eat. "It's the number one way to be conscious of what you're taking in and what is (and isn't) working for you," says Dr. Rubino.

3. Pack on the Protein
You need it to build muscles—the metabolic powerhouses in your body. Indeed, every pound of muscle zaps six calories a day just doing nothing, while a pound of fat burns a measly two. A 2012 review from the Netherlands found that eating a healthy amount of protein helps you drop pounds and keep them off. What's "a healthy amount"? The study authors suggest 1.2 grams of protein for each kilogram you weigh. So our 158-pound (72-kilogram) woman might eat 86 grams of protein a day—that's one egg at breakfast (6 grams), a tuna salad sandwich at lunch (16 grams), 4 ounces of fat-free cottage cheese for a snack (12 grams), and a 6-ounce chicken breast at dinner (52 grams). If she starts by loading up at breakfast, she not only will feel more satisfied throughout the day, a new study of overweight women reports, but will also snack less at night. Remember, though, "Protein doesn't have any superpowers," says Felicia D. Stoler, D.C.N., a doctor of clinical nutrition and an exercise physiologist. "Excess calories from protein will just get stored as fat."

4. Say "Yo!" to Yogurt
This favorite snack has been associated with maintenance of a healthy weight. Now researchers believe this may be because of yogurt's bacteria. "Scientists have found that obese people have more of a certain type of bacteria that is more efficient at extracting energy from food," says Gerard Mullin, M.D., a gastroenterologist at Johns Hopkins Hospital. "It's possible that the 'good' bacteria in yogurt help counter these 'bad,' weight-gain-causing bacteria."

5. Sprinkle on Spicy Extras
Chili peppers, ginger, and turmeric have all been found to have a beneficial, albeit small, effect on metabolism. Use them often—beyond the boost, "You'll be getting phytonutrients, and they make meals more flavorful," Stoler says.

6. Be Cardio Smart
Aerobic exercise is like one of those store sales at which you buy one item at full price and get a second item for 50% off: There are the calories you burn while working out and, because your metabolic rate stays elevated, the extra calories you continue to burn while lounging on the chaise. Researchers found that about five sessions of moderate cardio per week—each lasting between 20 and 45 minutes—increased daily metabolism by an average of 109 calories in women. So even on the days the women weren't exercising, they enjoyed an afterburn.

Need more motivation? Even without dieting, cardio can lead to weight loss: In recent research from the University of Kansas, overweight women doing moderate cardio five days a week dropped 5% of their body weight in 10 months—without changing a thing about their diets.

To make sure your own workout is sufficiently strenuous, try to talk during it—having a short conversation should be possible, but not easy. Or, you can find your target heart rate here. For each age group, the rate is given as a range, so you may want to start with the lower number (especially if you're new to exercise or haven't done it in a while) and work your way up.

Try to get your workout to 30 minutes a day, and don't worry—it'll pay off: In a Danish study, previously sedentary volunteers instructed to exercise for half an hour lost just as much weight as those who worked out for an hour. (The researchers speculate that 30 minutes likely felt so doable and rewarding to those participants that they went on to do more physical activity in other ways not connected to the study.)

7. "HIIT" It 
High-intensity interval training has become the rage for a very good reason: Sprinkling just five 30-second extra-hard intervals into your normal cardio routine can torch as many as 200 additional calories in your workout. (You can do anything for 2? minutes!)

Or you can alternate intensities, going faster for one minute and then slower for the next. There's an unexpected perk to this approach, says Wayne L. Westcott, Ph.D., a professor of exercise science at Quincy College in Quincy, MA: The recovery minute feels so good to people that "time becomes their friend for that minute. It becomes more like a game and less like a workout." Research backs this up: A study from Liverpool John Moores University reports that recreational exercisers who ran using HIIT found it significantly more fun than just slogging along.

8. Get Muscular
At around age 30, we start morphing into marshmallows as we lose about 5% of our muscle mass per decade. But maintaining and building muscle revs our metabolism. Even a simple weight-training program of three 25-minute sessions a week can keep your muscles toned—and burn 100 calories per session. The happy result: You could blast a third of a pound of pure fat in a month or 4 pounds a year.

There's no need to go to the gym. Exercises that rely on body weight, such as push-ups, tricep dips, wall sits, squats, and lunges, can be just as effective as those that use weights or machines. For how-tos, check out the exercise library at theAmerican Council on Exercise.

9. Cure Sitting Sickness
If you make phone calls for one hour at your desk, you'll burn 15 calories, but if you do it while standing up and pacing, you'll blast 100 calories. It's called NEAT—Non-Exercise Activity Thermogenesis—and ongoing research at the Mayo Clinic has found that we can burn up to an additional 800 calories a day simply by getting off our keisters and moving around more. Not only does NEAT help drop pounds, but it also may have a greater impact on longevity than standard exercise. A large study from the American Cancer Society found that women who sat for more than six hours a day were 37% more likely to die during the course of the 14 years of research than those who were sedentary fewer than three hours a day. This association remained virtually unchanged even when the sitters were devoted exercisers.

Some of the ways to incorporate more activity into your day are well known—taking the stairs instead of elevators, walking to colleagues' desks rather than e-mailing them. But you can also seed mini workouts into your daily life. "Do squats or lunges while waiting for the copier to warm up," suggests Stoler. At home, get in some tricep dips while the dryer is finishing its cycle or the coffee is brewing.

10. Call "Om"
Add a bigger belly to the list of miseries chronic stress can inflict. Even if you're not eating more, changes in the way your body stores fat may cause thickening. In a just-completed study, for example, researchers found that a woman caring for a loved one with dementia had a bigger waistline than her less stressed counterpart, although both were eating the same large amounts of high-fat, high-sugar comfort foods.

It's the stress hormones and peptides at play here, which become elevated when we're under pressure. But several studies have shown that practicing yoga can tame anxiety—and also lower levels of these chemicals.

11. Melt Fat Mindfully
A study in which women practiced mindfulness techniques (meditation, yoga, and more) for four months found those who showed greatest improvement in awareness of thoughts and feelings reduced their abdominal fat the most. And such focus, experts say, may be just what you need to embark on a bigger metabolism-revving program.