As the problem of overweight and obesity has grown in the United States, so has the number of diets, fads, supplements, and drinks claiming to help people lose weight. Many are controversial; some are actually dangerous. Yet the “secret formula” for losing weight could hardly be simpler: consume less fuel (in the form of food) than your body burns (by your activities).

Human beings—and all other living things, for that matter—burn fuel to stay alive. The more active you are, the more fuel your body needs. We measure that fuel in units called calories. Calories (scientists call them “kilocalories”) come from the food you eat.

Much evidence suggests that your body doesn’t really care where the calories come from; proteins, carbohydrates, and fats all can be turned into fuel. A recent study compared a low-fat versus a low-carbohydrate weight-loss diet, and after one year there was little difference in the results.

Nevertheless, there is a need for more study because there is no consensus about how a person should best split his or her consumption of carbohydrates, fats, and proteins. Some experts are saying that the low-carbohydrate diets cannot be dismissed.

People need to find what works best for them—and the strong recommendation from the American Heart Association is that you should restrict your consumption of saturated fats. You gain weight when you consume more calories of food than your body uses, or “metabolizes.” You lose weight when the balance is tipped, even only slightly, the other way.

Not all foods pack the same caloric punch. Fats, for example, contain far more calories per gram of weight than other foods. You can lose weight by eating less, even if you change nothing else about your life.

But it’s also true that you can lose weight by continuing to eat what you always have and simply increasing your physical activity level. Either way, you’ll be burning more fuel than you consume, and fat (which essentially is a kind of reservoir of stored energy in your body) will get used up.

At any one time, about one-quarter of adult men and almost half of adult women are trying to lose weight. Of course, each of us has certain inherited predispositions for weight gain or loss, and the balance between energy intake and energy use varies from individual to individual.

But doctors have found that the most successful approach to weight loss and weight maintenance is a combination of diet, exercise, and motivational strategies. Only after trying this first-line approach for at least six months should you and your doctor consider other approaches to weight loss.

Fewer Calories

Contrary to popular belief, losing weight doesn’t simply mean eating less fat. It means eating fewer calories—of every kind. Your goal should be to lower, in a balanced manner, the total number of calories you consume in a given day from all sources.

That’s one reason why it’s important to read nutrition labels on the food you buy: so you know not just how many calories they include, but also where those calories come from. How much should you cut your calorie intake?

The American Heart Association recommends that to lose weight, women should eat at least 1,200 and up to 1,500 calories per day and men should eat at least 1,500 and up to 1,800 calories per day. Most people are typically consuming well over 2,000, and often over 3,000 calories, each day. Therefore, it is a good idea to cut back gradually.

The key is to remember how many calories your body actually needs so that you can aim to consume a total number of calories that is lower than or up to your daily need. How many calories you need depends upon your current weight, your current level of physical activity, and—importantly—your own specific health needs.

That’s why you should work out your weight-loss program with your doctor. To start, you can get a general idea of how many calories you need each day by multiplying your weight (in pounds) by 15. This represents the average number of calories used in one day if you’re moderately active.

If you get very little exercise, multiply your weight by 13 instead of 15. (Less-active people burn fewer calories.) You can use the table on the previous page for reference. These numbers may actually overestimate daily calorie needs, but they can provide a useful reference point for most people.

According to the American Heart Association, here’s what your diet should contain:

• No more than 5 to 8 teaspoons of fats and oils per day, including the fats used in cooking and baking and in salad dressings and spreads.
• 6 ounces or less of lean meat, fish, or skinless poultry daily.
• No more than 3 or 4 egg yolks per week.
• 2 to 4 servings of nonfat or low-fat dairy products daily.
• At least 5 servings of fruits and vegetables per day.

But the American Heart Association and the National Institutes of Health have also looked hard at the amounts and types of fats in our diet (and of sodium as well) and concluded the following:

• Total fat intake should be less than 30% of total calorie intake.
• Saturated fatty acid intake should be less than 10% of total calorie intake.
• Polyunsaturated fatty acid intake should be no more than 10% of total calorie intake.
• Monounsaturated fatty acid intake should make up the rest of total fat intake, about 10–15% of total calorie intake.
• Cholesterol intake should be 300 mg per day at most.
• Sodium intake should be 3 g per day at most.

More Exercise

While exercise alone can reduce total body fat, it is actually not as effective as diet at reducing weight overall. On the other hand, when you combine diet and exercise you lose more weight, and do so more quickly, than if all you do is diet. What’s more, exercising regularly helps keep you from regaining the weight you’ve lost—and that “rebound” weight gain is probably the most disheartening thing that happens to people who only diet.

And, of course, exercise increases your cardiovascular fitness and is good for your heart in all the ways mentioned in Strategy #3. For weight management, the National Institutes of Health guidelines recommend that you start off by walking for 30 minutes per day, 3 days per week, and then gradually build up to 45 minutes of intense walking for at least 5 days per week, and preferably every day.

This regimen will help you burn an estimated 100 to 200 calories per day or more, improve your overall health, and strengthen your heart. By the way, a recent study showed that you don’t have to enroll in a formal exercise program; you can get the same benefits simply by increasing the level of physical activity in your daily routine (for example, taking the stairs instead of the elevator, or walking instead of driving).

A Support System

The key to success in losing excess weight is staying motivated. But that’s easier said than done. Progress will be slow. How do you stay motivated? By monitoring your progress, managing stress, avoiding other triggers that make you want to eat, and getting friends and family to help.

You may want to talk to your doctor or a nutritionist about the motivational strategies that can help you get the most out of your weight-management plan. Research has demonstrated that this approach works.

People who combine a low-calorie diet and exercise with behavioral therapy can expect to lose 5 to 10 percent of their starting weight over the course of four to six months. This level of weight loss is usually enough to improve many obesity-related conditions. Sometimes, however, it isn’t enough.