Why calories count: 10 common myths busted

(CBS News) We know the way to lose weight is to cut pesky calories from our diet, but do we really know the skinny about the numbers we keep counting?

Nutrition experts Dr. Marion Nestle, Paulette Goddard Professor in the department of nutrition, food studies, and public health at New York University and Dr. Malden Nesheim, Professor Emeritus of nutritional sciences at Cornell University, delved into why calories matter in their new book, "Why Calories Count: From Science to Politics."

Can a person really burn a few hundred calories in mere minutes? What's really driving the obesity epidemic? With help from Nestle and Nesheim, here are calorie facts versus fiction...

1. Myth: Obesity epidemic caused by Americans being more inactive and less likely to burn calories

There's no compelling evidence that people are less active now than they were 30 years ago, according to Nestle and Nesheim. Some evidence from the Centers for Disease Control and Prevention (CDC) even suggests that people are slightly more active. The CDC studies looked at self-reported activity and inactivity levels, so either way, it's difficult to assess the reliability of that information.

Then what's fueling America's obesity problem? Plenty of evidence indicates that people are eating more than ever before. Larger portions contain more calories. Just look at muffins, for example. They used to be the size of what are now considered mini-muffins. Those were about 200 calories a piece, but typical muffins today can be three times larger and contain up to 600 calories.

2. Myth: Not skipping breakfast helps you cut calories

Some studies say yes, others say no. The studies that say yes to eating breakfast are mostly sponsored by the makers of breakfast cereals who are eager to convince Americans that breakfast equals cereal, according to Nestle. Overall, body weight depends on calorie intake no matter when they are eaten. For some people, skipping breakfast helps reduce calorie intake. For others, it makes them overcompensate later on in the day. It's always a good idea to eat when you are hungry.

Their advice? Do what works best for you. Unfortunately, there is no easy way to figure out a minimum daily calorie requirement to eat at any meal, and there are no special foods that have to be eaten at breakfast. Any foods that provide a balance of protein, fat and carbohydrates will do the trick. The variety of foods eaten throughout the world at breakfast is an indication of that diversity.

3. Myth: Spreading out calories by frequently snacking leads to weight loss

Again, overall calorie balance is what counts. If people don't reduce calories at meals to compensate for the calories eaten as snacks, weight goes up. If you don't compensate the more often you eat, the more calories you are likely to consume.

Eating small, frequent meals helps some people to maintain weight provided that the meals really are small. From the standpoint only of weight, what you eat doesn't matter. From the standpoint of satiety and health, what you eat matters a lot. It's always better to get plenty of vegetables and fruits into your diet whenever you eat.

4. Myth: You can burn 300 calories in 15 minutes

We've seen such claims on the covers of women's magazines. But if you weigh 130 pounds, jumping rope or running upstairs nonstop for 15 minutes will burn off only 150 to 200 calories. You would have to be a lot heavier and do something much more vigorous to burn 300 calories in 15 minutes.

5. Myth: Some foods have "negative calories" because it takes lots of energy to digest them

How we wish! Though some high fiber foods may be poorly digested and therefore provide less energy than well-digested foods, it only takes a few percent of calories available in foods to digest them. The calories on package labels take losses in digestion into consideration, so you might as well forget about the energy cost of digestion when you are eating.

Even though rumors say vegetables like celery give you negative calories, don't believe the hype.

6. Myth: Thinking burns off a lot of calories

Although the brain uses a lot of energy, making it work harder by solving a problem has little effect. The 20th century nutritionist H. H. Mitchell used to tell his students that they could do an hour's mental work on the calories in half a peanut.

7. Myth: People are obese because they don't take enough responsibility for what they eat

Obesity is not that simple. It involves genetics as well as interaction with the food environment. Today, we live in societies where food is everywhere, in huge portions, heavily advertised and cheap.

Everyone has to learn to manage this environment and some do it better than others.

8. Myth: If humans were to significantly restrict their caloric intake for most of their life they could increase their lifespan

When scientists severely restrict the calorie intake of rats, mice, dogs, rabbits, hamsters, fleas, fish and flies, the animals live a lot longer. But, what this has to do with human lifespan is less certain.

Human studies show that mortality rates increase in people who are unusually thin. And most humans feel miserable when starved. Studies in the U.S. show that people who live the longest have body weights in ranges considered normal - BMIs of 18 to 25 or so.

9. Myth: Calories in alcohol don't count for weight gain

Alcohol calories, alas, count just as much as those from foods.

In about 1900, the scientist W.O. Atwater enraged the temperance movement by reporting that alcohol calories could replace those in food. Pure alcohol has about 75 percent as many calories as fat. As always, larger drinks have more calories than smaller ones.

10. Myth: Foods labeled as organic or with health claims have fewer calories

Not necessarily. Studies show that a health claim - any health claim - on a food product conveys a health aura and encourages the belief that the calories in the food don't count as much. An organic label on a food, for example, makes people think the food has no calories.

Alas, organic is about production methods, not calories.