At last count, nearly two of three (64.5%) Americans were classified as overweight or obese. With this number climbing upward at an alarming rate, there has been much speculation as to the cause of America's weight problem. Some popular diet books are especially vocal about naming carbohydrates as the culprit. A few years back, the villain was dietary fat.

Somewhere along the line concern about calories took a back seat. That's too bad, because the fact is that you gain weight when you eat more calories than you burn. Period. "Obesity is a disease of excess—excess calories and excess sedentary activities," says registered dietitian Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine in New York. "The cure is to balance calories in with calories out."

Likewise, weight loss doesn't depend on whether calories come from carbohydrates, protein or fat. To lose a pound, you must create a 3,500-calorie deficit by consuming fewer calories, burning more calories through physical activity, or a combination of both.

This formula is simple in theory, but difficult for many people to put into practice. Food intakes, activity behaviors and environmental factors all play a significant role in tipping the balance toward weight gain. For instance, research shows that for a number of foods, portion sizes have increased along with the amounts Americans eat. Our enthusiasm for a labor-saving lifestyle contributes to the fact that only about one in four adults gets even the minimum recommended amount of daily physical activity.

Fortunately, the calorie equation can be balanced with increased attention to both food and physical activity habits. Experts offer this advice:

• Keep a record of food intake to raise eating awareness. "We're surrounded by tempting foods and often don't realize how much we're eating," says registered dietitian and American Council on Exercise-certified personal trainer Cathy Leman of Glen Ellyn, Illinois. "I ask my clients to keep a written log of what they eat and it's a real eye-opener. They're amazed when they see how many calories they're getting from seemingly innocent habits like nibbling food samples at the grocery store."
• Change food habits. Cutting calories does not mean a life sentence of food scales and measuring cups, as some people fear. Ayoob recommends that overweight patients gradually start trimming food portions by, for instance, filling their plates a little less or skipping second helpings. "The weight starts to come off when people change their eating habits, not by weighing and measuring everything or counting every calorie," he says.
• Find the right macronutrient mix. Although a calorie deficit is necessary for weight loss, choosing the right proportions of carbohydrates, protein and fat in the diet can have a positive impact. "Many women I counsel take the 'low fat' message to extremes," says Leman. "They're hungry all the time because they don't eat enough protein and fat for satiety. By evening, they're ravenous and eating is out of control." For each client, Leman seeks the macronutrient balance that provides enough energy and satisfaction. The 2002 National Academy of Sciences' Food and Nutrition Board report, Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Protein, and Amino Acids (Macronutrients) recommends a flexible approach in which adults obtain 45 to 65 percent of their total daily calories from carbohydrates, 20 to 35 percent from fat, and 10 to 35 percent from protein.
• Crank up calorie-burning physical activity. In addition to keeping a food log, Leman asks clients to keep a physical activity log. She finds that people usually overestimate their amount of physical activity, but few actually get enough. When someone has been inactive, Leman recommends starting with just a few minutes of daily physical activity, such as walking, and building up from there. For more seasoned exercisers, she recommends increasing their frequency or intensity by 50 percent. "People clearly benefit in terms of calorie burning when they go from two days to three days of exercise each week, or increase their workout time from 30 minutes to 45 minutes."

Calorie Myths and Facts

Have you heard the one about the fat-forming carbohydrate? Nutrition communicators continually face the challenge of dispelling common myths about calories and weight management such as the ones provided below:

Myth: Eating most of your calories in the evening promotes weight gain.

Fact: No matter when you eat them, you gain weight when you eat more calories than you burn off. However, mindless munching in front of the TV at night can push calorie intake over the top.

Myth: Fat free is calorie free.

Fact: Some people indulge in extra-large servings of fat-free foods, such as cookies, cakes and crackers, without realizing that these foods may contain the same amount or even more calories than regular versions. Get the facts on fat-free foods by checking food labels for the serving size and number of calories per serving.

Myth: Carbohydrates (or sugars) cause weight gain.

Fact: Carbohydrates do not cause weight gain unless they contribute to excess calorie intake. The same holds true for protein and fat. Findings from the National Weight Control Registry show that people who successfully maintain weight loss tend to eat diets that are higher in carbohydrates and lower in fat, in addition to watching their total calorie intake. However, some people who eat a diet that is extremely high in carbohydrates and low in protein and fat get hungry sooner, which may trigger overeating.

100 Calories to Halt Weight Gain

Researchers theorize that the upward trend in the number of overweight Americans is caused, on average, by an imbalance of only 100 extra calories per day (1). Eliminating this 100-calorie imbalance by eating a bit less and getting a bit more physical activity each day may hold the line on weight gain for many people. This can be accomplished in an almost unlimited number of ways. Below are several ideas on how people can start to trim and burn about 100 calories a day.

Five ways to trim 100 calories from food

• Swap an 8-ounce regular soft drink for a diet soft drink.
• Drink 2 cups of fat-free milk instead of 2 cups of whole milk.
• Use 1 teaspoon of mustard or ketchup or 1 tablespoon of fat-free mayonnaise in place of 1 tablespoon of regular mayonnaise.
• Split a small bag of French fries with a friend.
• Slice a typical piece of apple pie about one-third smaller.

Five ways to burn 100 calories through physical activity
(Physical activity and walking estimates based on a 150-pound person.)

• Pedal an exercise bike for 13 minutes.
• Practice some fast dance steps for 16 minutes.
• Work in the garden for 18 minutes.
• Walk briskly for 22 minutes (3.5 mph).
• Clean the house for 25 minutes.

Five food and foot power combos to cut 100 calories

• Eat five fewer potato chips and walk for 6 minutes.
• Eat one-quarter cup less of spaghetti with tomato sauce and walk for 11 minutes.
• Top toast with 2 teaspoons of apple butter instead of 2 teaspoons of butter and walk for 11 minutes.
• Spoon out 3 tablespoons less of mashed potatoes and walk for 13 minutes.
• Skip 2 half & half coffee creamers in coffee and walk for 15 minutes.

(1) Hill JO, et al. Obesity and the Environment: Where Do We Go From Here? Science 299:853-855.2003.