The Truth About Calories

We set the record straight on negative calories, low-cal diets, and the best calorie-blasting workout

Energy Expenditure, Explained

Counting calories isn’t rocket science. It’s more like basic physics, or at least the first law of thermodynamics—that energy can be changed from one form to another, but not created or destroyed. Burn the 3,500 calories that make up a pound of body fat, and you’re that much lighter.

Still, if it were that simple, we could stop here, and anyone with a pen, paper, and a calculator could slim down without a struggle. Truth is, if you’re trying to lose weight, the source of your calories matters, as does the type of exercise you combine with a low-cal diet.

“If someone is consuming many calories from fatty, sugary, low-nutrient foods, clearly they won’t be getting all the valuable nutrients they need for their bodies to function optimally,” says Elisa Zied, MS, RD, CDN, author of Nutrition at Your Fingertips. “To sustain weight loss, it’s key to keep activity level up and mix up exercises so you’re using different muscle groups or stimulating your muscles in different ways.”

You’re not alone if you’re feeling a little clueless about calories. While 77 percent of Americans say they are trying to lose or maintain weight, only 19 percent track calories, according to a survey conducted by the International Food Information Council Federation. Only 12 percent can accurately target the number of calories they should consume in a day, while 43 percent have trouble estimating how many calories they burn during everyday activities.

Knowing the facts about energy intake and expenditure can help you pinpoint why the needle on the scale gets stuck. Here, nutritionists set the record straight on five matters of calorie confusion.

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Not All Calories are Equal

It’s like the adage, “What weighs more, a pound of feathers or a pound or rocks?” Erin Palinski, RD, CPT, says the math is simple: “If you eat fewer calories than you burn, you will lose weight.”

But this isn’t your free pass to take the Hollywood Cookie Diet for a spin. “Calories from protein and fats are more filling than calories from carbohydrate sources,” Palinski says. “If you are trying to reduce your calorie intake and are eating calories mainly from carbohydrates, you may find yourself hungry, making it hard to stay within your calorie range.”

The healthiest calories come from whole grains, high-fiber carbohydrates, lean proteins, and unsaturated fats, she says. These whole foods require more energy (read: calories) to eat, digest, and absorb compared with refined or processed foods.

In a Swedish study published in the Scandinavian Journal of Clinical and Laboratory Investigations, 25 healthy weight adults snacked on either fast-acting carbs (candy) or a fat and protein combo (roasted peanuts) at a rate of 20 calories per every 2.2 pounds of body weight in addition to eating their regular diets. At the conclusion of the 2-week study, the candy group gained an average of 1.8 pounds, while those who snacked on peanuts gained only 0.7 pounds, on average. Waist circumference also increased for candy eaters, while nut eaters experienced slightly faster metabolic rates.

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"Negative Calories" Don't Exist

Nutritionists aren’t sold on the notion that so-called negative calorie foods, like celery, lettuce, apples and grapefruit, are the magic bullet for weight loss. Still, don’t clean out the produce drawer just yet.

“There really is no scientific evidence proving that certain foods cause the body to burn more calories to digest them than the calories already in the food,” Palinski says. “However, foods that have been listed as negative calorie foods are mostly low-calorie, high-fiber vegetables. Increasing the amount of these foods in your meal plan will help promote weight loss since you will find yourself feeling full from the fiber and eating fewer calories from other foods.”

Zied attributes this negative calorie theory to the thermic effect of food: “Consuming foods such as chili peppers and other foods that have capsaicin can help your body burn a small amount of calories because they raise body temperature and boost metabolism,” she says. “But don’t eat these foods expecting that doing so will help you consume fewer total calories and lose weight.”

The number of calories offset by eating, digesting, and absorbing negative energy foods is negligible. Don’t expect real results from snacking on asparagus and blueberries all day without making significant changes to your diet and exercise habits.

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The Best Diet is a Low-Cal Diet

Atkins, Ornish, Zone, South Beach—if you don’t know the difference, don’t worry. When combined with exercise, any diet that restricts calories should result in weight loss, regardless of which macronutrients are emphasized or downplayed, according to a study published in the New England Journal of Medicine.

Researchers at the Harvard School of Public Health and Pennington Biomedical Research Center in Louisiana assigned 811 overweight adults to one of four diets emphasizing various levels of fat, protein, and carbs. Each dieter was instructed to slash 750 calories a day, exercise for 90 minutes daily, keep a food diary, and meet with a diet counselor. After 6 months, study participants across all groups lost an average of 13 pounds.

While macronutrients are important, a focus on calorie counting should trump restricting fat or carbohydrates, says Zied, who recommends a diet rich in fruits, veggies, whole grains, lean protein, low- or non-fat dairy, beans, nuts, and seeds. “Limit foods with too much sugar or too much solid fat, and limit alcohol—all of these contribute lots of calories but few nutrients to the diet.”

Palinski, who agrees that tracking calories is the key to successful weight loss, suggests writing down everything you eat for a few days in order to calculate your usual calorie intake. “Subtract 500 from this amount without going below 1,200 calories,” she says. “If you stick to this calorie range each day, you will lose 1 pound per week.”

To meet nutrient needs and ward off hunger, don’t forget to balance out where your calories come from, Palinski says. “Depending on your activity level, 50 to 65 percent of your calories should come from carbs, 10 to 20 percent from protein, and 20 to 25 percent from healthy, unsaturated fats.”

“Keep portions small for foods or beverages that are sugary, fatty, and otherwise nutrient-poor,” Zied says. “That way you won’t feel deprived.”

Is your low-calorie diet as nutritious as you think?

Real Results Require Exercise

You’ve cut calories and made a meaningful effort to consume a variety of nutrient-dense foods. You’re almost there, but there’s one more piece of the weight loss puzzle: the gym.

According to a study published in the American Journal of Physiology, scientists at Oregon Health & Science University found that diet alone was not enough to promote significant weight loss in primates. The researchers fed monkeys a high-fat diet for several years, then cut caloric intake by 30 percent for sedentary monkeys and made no changes to the diets of those that were trained to exercise on a treadmill for 60 minutes each day. After a month, the exercise group weighed less, while sedentary monkeys experienced declines in energy and lost no weight.

In the beginning, you can start slow then ramp up your exercise efforts. “The heavier you are, the more calories you burn per minute,” Palinski says. “For instance, if a 120-pound woman ran for 20 minutes at 6 miles per hour and a 150-pound woman ran at the same speed for the same amount of time, the 150-pound woman would have burned a bit more calories.”

Angela Ginn, RD, a spokesperson for the American Dietetic Association, recommends 60 minutes of physical activity on most days in order to keep pounds off.

To make the most of your gym sessions, try short bursts of high intensity exercise, which burn more calories than consistent-rate cardio, like jogging on the treadmill at a set speed. In a study published in the International Journal of Obesity, Australian researchers found that three, 15-minute, high-intensity interval workouts per week lead to greater reductions in total body mass, fat mass, and leg and trunk mass, compared with steady-state exercise at the same frequency.

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Weight Loss Slows Metabolism

“If you have a very large amount of weight to lose, you may find that you hit a weight loss plateau over time,” Palinski says. “As your body gets smaller, it does not have to work as hard to move around and circulate nutrients, which can slightly reduce your overall metabolic rate.”

“When you lose weight, your metabolism slows due to a loss of lean body mass,” Zied says. “And as we get older, our bodies naturally want to gain fat and lose muscle.”

The more pounds you take off, the fewer calories you need to stay at your new weight, says Christine Gerbstadt, MD, RD. “It doesn’t sound fair, but there is one caveat: If you increase total muscle mass at your new weight, then you may be able to eat more and not gain weight.”

To hang on to muscle and keep your metabolism up as the number on the scale goes down, Zied suggests eating protein-rich foods in small amounts and, most importantly, performing weight training on all muscle groups two to three times per week. “Losing weight in a slow and steady rate—no more than two pounds per week—can also help minimize muscle loss,” she says.

If you hit a plateau, increase physical activity and decrease calories by another 100 to 200 per day without dropping below 1,200, which could further slow your metabolism, Palinski suggests. Use the daily calorie counter to determine how many calories you need at your new weight.

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