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The Truth About Calories

We count them, cut them, burn them, obsess over them. Yet for most people, calories -- what they are, how they affect us -- remain a mystery. For instance, a 2009 poll of 1,000 people revealed that 70 percent were concerned about their weight, but only 11 percent knew how many calories they could eat each day without gaining. A study from famed "mindless-eating" researcher Brian Wansink, Ph.D., of Cornell University shows that the bigger the meal, the more people underestimate the calories in it. It shouldn't come as a surprise, then, that new research suggests eating too much -- not exercising too little -- accounts for the rise in obesity in our country. But there's more to calories than the pounds they cause people to pack on. To help you better understand these tiny puzzlers -- from how your body uses them to the impact they make on your health -- we take a closer look.

What are energy-dense and nutrient-dense foods? Energy density may sound like a good thing -- after all, we all want more energy. But in the food world, energy just means calories, so an energydense food is high in calories. Nutrient- dense foods, on the other hand, usually offer exactly what their name declares -- lots of vitamins, minerals, and other good-for-you nutrients. Ideally, you want the majority of your foods to rank low in energy density but high in nutrient density. Say, for instance, you're given a choice of a third of a Milky Way bar or a cup of blueberries. Both contain 84 calories, but you'll get 19 percent of your daily vitamin C requirements from the blueberries, plus 14 percent of your fiber and important antioxidants. A candy bar can't compete.

What is a calorie?
Back in science class, most of us learned the answer to this simple question: A calorie, like an inch, is a unit of measurement. It quantifies the amount of energy that our bodies get from food. To determine calorie counts, scientists burn food in a water-enclosed chamber called a bomb calorimeter; the number of degrees by which the burning food raises the water's temperature equals the number of calories in the food.

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How do you use them?
To create the energy it needs, your body burns calories in a process called metabolism. It then expends this energy in several ways. The amount used for basic continuous functions (breathing, circulating blood) is known as the basal metabolic rate (BMR). Even if you did absolutely nothing, your cells would still draw on energy to function; this accounts for 65 to 75 percent of your total calorie needs. Interestingly, some of your organs demand more energy than others: To keep your brain humming, for instance, takes around 20 percent of your BMR. Separate from BMR, digesting, absorbing, and storing food accounts for about 10 percent of your total calorie needs. Any physical activity, from walking around your house to running a marathon, consumes the remaining 15 to 25 percent.

Does it matter where calories come from? 
The answer depends on why you're asking. From a nutrition standpoint, the answer is a resounding yes. Food provides more than just calories; nutrients such as vitamins, minerals, and omega-3s are essential for good health. But let's focus on two other factors: the energy a food provides and the pounds you gain or, more important, would like to lose.

Energy can come from any of the three macronutrients: carbohydrates, protein, and fat. For quick energy, it's hard to beat carbohydrates. Your body breaks them down and converts them to glucose, its favorite energy source, more easily than it breaks down fats and proteins (which is why marathon runners often indulge in a big pasta meal before a race). While some cells in your body can use either fatty acids or glucose for energy, your brain and nervous system run solely on glucose. Case in point: When dieters in a recent study severely restricted their carbohydrates, they performed poorly on memory-based tasks. Fat contributes energy for sustained activity, but some of the fat you eat goes into storage to be used later when -- and if -- it's needed. So what about protein? It, too, can provide energy, but it takes the most effort to convert. Your body prefers to use it to build and repair tissue (such as muscle).

Weight loss is a trickier subject. We've all heard about -- or perhaps tried -- diets that emphasize one type of food, whether it's protein, fat, or carbohydrates, over another. But does it really matter where your calories come from? Research shows that protein generally produces the greatest satiety, so a meal high in protein should help you feel full longer. You also burn more calories metabolizing protein (because it's so tough to convert to energy). High-fiber carbohydrates make you feel full longer, too. Fats may possess a luxurious texture and make foods taste rich, but they aren't particularly satiating.

Given this information, researchers have tried for some time to determine if emphasizing one macronutrient over another helps people lose weight. So far, results vary, although one common thread has emerged: People often abandon diets that radically alter their eating habits. While scientists may disagree about which type of diet promotes the best weight loss, they typically agree that in the long run, the diet you'll lose weight on is the one you'll actually stick to.

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How many calories do you need?
In a given day, your body requires enough calories to fuel its basic functions plus all your activities. To calculate your specific needs, look for an online calculator that accounts for your height, weight, sex, age, and activity level (such as mayoclinic.com/health/calorie-calculator/NU00598). The results will tell you approximately how many calories you can eat each day to maintain your current weight. For example, a 40-year-old, 130-pound, 5-foot-4-inch woman who is moderately active (exercises two to three times a week) can eat 1,750 calories; a sedentary 56-year-old, 145-pound, 5-foot-9-inch woman needs 1,600 calories. Both of these women are at healthy weights (i.e., they don't need to drop pounds), but the more active woman can eat more, even though she's five inches shorter. Keep in mind that these tools are generalized and don't account for all variables, such as body fat percentage. However, for most people the estimate is good enough, say experts.

How do you burn them? 
Programmed to hold onto energy, your body doesn't like to waste calories, so it stores any unused energy as fat. To lose fat, you need to expend more calories than you take in -- 3,500 for each pound. If you operate at a deficit of 500 calories each day for seven days, you'll lose one pound of fat. You can create that deficit by eating less, exercising more, or, ideally, both. For example, skip the roll (100 calories) with butter (100 calories) and that serving of chocolate ice cream (250 calories for a half cup), and you're well on your way. Add a half-hour walk at a moderate pace (burns 100 calories), and you've surpassed your 500-calorie-reduction goal for the day. Kerry Neville, R.D., spokesperson for the American Dietetic Association, recommends a 500-calorie daily deficit as a sensible, sustainable amount for people trying to lose weight. Going too low -- trying to subsist on 1,000 calories a day, for instance -- is not only difficult to maintain but can sabotage your efforts by causing your metabolism to slow down to conserve energy, she says.

How does metabolism figure in? 
You probably know people who seemingly eat whatever they want and never gain weight, and others who eat very little yet can't keep the pounds off. Are individual differences in metabolism to blame? To some degree, yes. But let's start with what is most likely not the problem. Metabolic disorders that prevent you from losing weight are rare. For example, the thyroid gland, which manages metabolism, often gets blamed for an inability to lose weight. Your thyroid can begin to work less efficiently as you age, says Kristine Clark, R.D., director of sports nutrition for Pennsylvania State University, so if you suspect a problem, get it checked. But only two to three percent of Americans have pronounced hypothyroidism, and Clark points out that even less-than-optimal thyroid function doesn't prevent you from losing weight altogether.

Now let's look at what does affect metabolism. Genetics play a part, as does body composition. Lean muscle mass burns more calories than fat, so an athlete will possess a higher metabolism than a couch potato. (Men, being more muscular, tend to have higher metabolisms than women.)

Age affects metabolism, too. As the years go by, your organs, muscles, and bones become less efficient. Since the majority of your energy demands come from basic bodily functions, this slowdown lowers your need for fuel. After about age 25, your metabolism decreases by two percent for every decade that you live. We also all tend to lose muscle mass as we grow older, a process called sarcopenia. Because muscle mass burns more calories than fat, you need fewer calories to maintain your weight as your ratio shifts in favor of fat. Women approaching menopause must contend with yet another factor: Because fat, as well as ovaries, produce estrogen, a premenopausal woman's body starts to produce more fat cells to compensate for declining estrogen production from her ovaries.

All of that said, weight gain isn't inevitable, says Clark, especially if you're armed with awareness. Most often, if you don't understand why you can't drop the pounds, you're overestimating the calories you need -- and underestimating the amount you eat. As you get older, be especially diligent about watching your intake and staying physically active, including weight-bearing exercise, she advises. If you work out consistently, you'll burn calories while also adding lean muscle and bone mass, which can have lasting effects not only on your weight but also on your health.

How can I keep track? 
If you want to stop overeating, don't trust your gut to tell you when you've reached your quota. "By the time we're adults," says Barbara Rolls, Ph.D., a nutrition professor at Penn State and author of The Volumetrics Eating Plan, "we've eaten thousands of meals and are used to filling our plates with a certain amount of food, regardless of how many calories it contains." Studies reveal that when we're served a large portion, we eat more. They also show we're not good at guessing the number of calories in a given food. When you consider that downing an extra 50 calories a day can translate into five pounds a year, the significance of these misjudgments becomes apparent.

There's a simple solution, though. The surest way to know how many calories you eat is to count them. Online calorie calculators can do a good deal of the work for you, and many are free. (One such site is fitday.com.) Until you get more familiar with serving sizes, take the time to measure and weigh what you eat as well. Don't forget the calories you drink -- milk, juice, alcohol, and even certain water drinks add to the tally.

Granted, recording every single thing you eat probably seems like a drag. But the process gets easier as you go along. If you're a creature of habit who eats the same foods every day, that can work in your favor. Many online calorie counters let you review previous days and choose foods from a list of what you've already eaten. So if you liked Monday's 12-ingredient salad enough to have one again on Thursday, you just go back and check off the ingredients.

If you can't stand the thought of calculating every bite you take, simply write down what and when you eat -- noting portion size instead of calories -- in a notebook, says Neville. Recording everything in this way has been shown to help weight loss.

Analyzing the diets of more than 7,500 people, Rolls and her colleagues found that those who favored a low-energy-density diet tended to eat more fruits and vegetables, fewer fatty foods, and drink water rather than soda. They also got higher amounts of important nutrients -- including iron, calcium, potassium, and vitamins A, C, B6, and folate -- than people whose diets consisted mainly of high-energydensity foods. And even though the low-energy-density participants consumed a greater volume of food, their calorie intake was lower -- a winwin situation overall.

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Some foods like nuts are both energy and nutrient dense. One ounce of almonds, for example, has about 160 calories, but it also provides healthy amounts of fiber, vitamins, and minerals. You don't want to eliminate these foods. Instead, eat reasonable portions, and you'll gain the nutritional benefits but not the pounds.

Does it matter when I eat? 
"There's no metabolic reason that calories consumed at night are different from calories consumed at other times of day," says Neville. The difference, she says, is that you don't have as much time to burn extra calories in the evening. Clark agrees. "Your body does not break down and use calories differently depending on the time of day they're consumed." Indeed, most people get all the calories they need for the day by the time dinner ends, she notes. But if you eat an unusually large dinner or snack late at night, you now possess excess calories. "If you wind down for the evening by sitting and watching television, you're not going to burn them," notes Clark. Bottom line: Regardless of when you eat, too many calories results in weight gain.

How I Counted Calories and Lost 13 Pounds 
In the 25 years since I left college, my weight has slowly but steadily gone up. Because I'm tall and never strayed from the "healthy" range (and because I love to eat), I managed to ignore this trend until it became impossible to wear my jeans and breathe at the same time. I was seriously considering forking over almost $200 for a pair of jeans guaranteed to make me look thinner when I had a reality check: Why not lose some weight?

Not a fan of diet plans, I decided to count calories. I registered at a free online calorie counting Web site, set a modest weight-loss goal (12 pounds in 12 weeks), determined my daily calorie intake (1,800), and got started. Since I work on a computer, tracking my meals online turned out to be convenient. I rarely dine out, so I knew exactly what I had eaten and how much. Counting was sometimes tedious, but I treated the process like a challenge, not a chore. (Check out a typical day of my diet, below.)

Was I tempted to cheat? Sure. But I didn't. What would be the point? I might have fooled the program, but I couldn't trick the scale. Setting realistic goals helped. Knowing I was supposed to lose only a pound a week -- and hitting my goal -- kept me motivated. And it worked. At the end of 12 weeks, I lost not 12 but 13 pounds. More important, the clothes that had been relegated to the back of my closet once again fit comfortably.

I've since stopped counting calories and have maintained my weight. A couple of lessons in particular have helped. I no longer mindlessly snack; there are calories in those foods, I now realize. The world won't end if I'm a little hungry (in fact, hunger pangs often pass). I can still enjoy sweets -- if I use some common sense. Instead of downing a half-dozen chocolate chip cookies (and "treating" myself to 800 calories), I eat just one cookie for dessert -- very slowly, so I can enjoy every bite.

Text by Cheryl Redmond

Total calories in a day: 1,782

Breakfast 312 calories
Oatmeal with milk and maple syrup: 210 calories
Cranberry juice: 102 calories
Green tea: 0 calories
Water: 0 calories

Lunch 739 calories
French lentil salad with lemon vinaigrette, goat cheese, and toasted walnuts: 649 calories
Dark chocolate: 90 calories
Plain selzer: 0 calories

Dinner 731 calories
Tilapia with bread crumbs: 298 calories
Mashed sweet potato: 135 calories
Broccoli with butter: 105 calories
Gingerbread: 152 calories
Plain seltzer: 0 calories
Cappuccino: 41 calories

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