More Americans than ever are losing the battle of the bulge; according to the US Centers for Disease Control and Prevention, more than 30 percent of all Americans are now obese, a dramatic increase during the past 20 years. And Americans are also spending more than ever in an attempt to lose weight: according to Business Week, we shell out $40 billion a year on weight-loss products and programs. One recent trend claims that "negative-calorie foods" promote rapid weight loss, but the jury is still out on negative-calorie claims.
What Are "Negative-Calorie Foods"?
All foods have three elements: nutrients (proteins, carbohydrates, and fats); vitamins and minerals; and calories. A calorie is a unit of energy: one calorie contains enough energy to raise the temperature of one gram of water by one degree Celsius.
When you eat any food, you take its calories into your body. Your body then spends a certain number of calories processing that food--calories used in chewing, digesting, and metabolizing the food and eliminating the waste. If you take in more calories than you burn in your daily activities, the extra calories are stored as fat.
So-called "negative-calories foods" are foods reputed to burn more calories in digestion than are contained in the food.
It's All Due to Cellulose
The so-called "negative-calorie foods" are fruits and vegetables that contain high percentages of water and a substance called "cellulose," a fiber that can't be broken down by the body. There's only one truly negative-calorie "food": cardboard, which is 100 percent cellulose. Because you don't have the enzyme required to digest cardboard, simply moving it through your body would require more energy (calories) than you'd get from the cardboard.
The Facts
So what's the truth about "negative-calorie foods"? Some foods are truly low in calories--but the digestion process doesn't use as many calories as you might think. For example, one of the most commonly touted "negative-calorie" foods is celery. A medium celery stick contains 6 calories. The amount of energy your body uses to digest that medium stick of celery is .5 calories.
If they don't burn more calories to digest than they contain, then, what are the facts about these foods? The so-called "negative-calorie foods" play a role in weight loss in several possible ways. One is obviously the low calorie count of these foods. Another is the fact that their high water volume and high fiber content make you feel full faster and cause your stomach to empty more slowly, causing you to eat less. Still another is the fact that most of these foods are high in vitamins; as a result, the body produces extra digestive enzymes--enough to not only break down the calories in that food, but in other foods you eat as well.
The "Negative-Calorie Foods"
With those caveats in mind, then, here are the foods considered to be "negative-calorie foods":
Apple
Asparagus
Beet
Beet Root
Blueberries
Broccoli
Cabbage
Cantaloupe
Carrot
Cauliflower
Celery
Celery root
Chicory
Cranberries
Cucumber
Dandelion
Endive
Garlic
Grapefruit
Green Beans
Honeydew
Hot chili peppers
Lemon
Lettuce
Lime
Mango
Onion
Orange
Papaya
Peach
Pineapple
Radishes
Raspberries
Spinach
Strawberries
Tangerine
Tomato
Turnip
Watercress
Watermelon
Zucchini
The Jury Is Out
Referring to "negative-calorie foods," Dr. Nancy Snyderman told Time magazine, "The problem is that it's not true. The calories your body burns in fueling the digestive cycle are minuscule compared with the calories in the food itself. Although chewing celery might seem like a strenuous activity, it burns about the same amount of calories as watching grass grow."
Even though they don't agree with the notion of "negative-calorie foods," many agree that the foods on the list should be part of a well-balanced, nutritional diet. The US National Institute of Health recommends five servings a day of fruit and vegetables for women, and nine servings a day for men. But foods from the list should not be the only thing you eat; they don't provide all the nutrients necessary for optimum health.
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