What if I told you there are certain foods that can make you lose weight through the sheer act of eating them? That’s right—sit in front of the TV, eat these foods, get thinner. There are things we can eat that make us consume fewer calories than not eating at all does? Sign me up.
Being the extreme Web searcher that I am, I decided to do some research on the term “negative-calorie food” while looking for recipes online. Some websites (mostly disreputable blogs and weight-loss sites) claim that certain foods, because they’re tricky for our bodies to digest, actually burn more calories than they’re worth and therefore help us lose weight. This diet folklore surrounds low-cal foods like citrus, melon, and celery.
“It’s a huge rumor in the eating disorder community,” says Elaine Fung, a former anorexic who recently completed her master’s thesis on pro–eating disorder websites. “The thought is, if you eat these foods, they’ll help you lose even more weight than if you don’t eat at all.”
When I first came across this idea, I brushed it off as a silly diet myth. But I soon found that in a backward sort of way, there is some truth to this view of certain foods. But is it enough to make foods “negative calorie”? Not exactly.
Legend Has It …
According to diet legend, there are specific foods that cause our bodies to burn more calories than the amount we take in by eating them. Here’s how it works, according to NegativeCalorieFoods.com (come on, of course it exists): No food actually has a negative amount of calories, because all foods have some caloric value. But the overall effect of these particular foods balances out as negative because the energy we use to digest them is greater than the energy (or calories) than we consume in eating them. Skeptical? This diet “logic” gets even crazier.
This negative-calorie effect, according to diet lore, is true of only a special handful of foods that not only are low-calorie, but take a lot of work for our bodies to digest. “I figured if I ate one hundred calories of a food that only takes fifty calories to burn, I’m left with fifty extra calories. But if I ate one hundred calories of a food that takes 150 calories to burn—now, there’s something to shoot for,” remembers Fung.
When I quickly peruse a few of these diet websites, it’s easy to see why she would think so. “Typically, a twenty-five-calorie piece of broccoli (100 grams) requires eighty calories to digest,” claims NegativeCalorieFoods.com, “resulting in a net loss of fifty-five calories.”
Eighty calories?! That’s like biking for ten minutes. This is either the diet holy grail or a darn good piece of urban food legend. Foods on the negative-calorie list include apples, asparagus, beets, berries, broccoli, cabbage, cauliflower, celery, cucumber, garlic, grapefruit, lemon, lettuce, onion, spinach, watermelon, and zucchini.
Even though it all sounded great to my non-nutritionist ears, I still found myself with more questions than answers. Does it really take different amounts of calories to digest different foods? What does nutrition science have to say about all this? And if these foods truly burn more than they’re worth, shouldn’t eating them be considered exercise, meaning I could literally eat my way to a smaller size?
Science or Wishful Thinking?
According to a heart disease study performed by Dr. Dean Ornish of the University of California, San Francisco, in which research subjects stuck to a diet consisting mostly of fruits and vegetables (the stars of the negative-calorie food lists), each of the subjects lost an average of twenty pounds—without exercising or adhering to any other diet plan. But was this really because of negative-calorie foods, or just because the participants avoided eating ten slices of bacon every day?
In hopes of getting to the bottom of this, I decided to start with the basics: calories. The calorie is the tiniest unit of energy we count; the more calories a food has, the more energy it gives us. A regular stalk of celery has about six calories. Apples have about seventy. And chocolate cake? We’re talking up to one thousand. Does eating celery burn more than eight calories, or an apple more than seventy?
All foods are made up of calories and nutrients (carbs, fats, and protein), plus vitamins and minerals. When we swallow certain combinations of these in various foods, they tell our bodies to produce certain amounts of enzymes, which show up just to digest whatever we eat. Negative-calorie believers assert that these special foods leave our bodies producing more enzymes than we need—meaning we use more calories in creating them than the food is worth.
Fuzzy science? “Yes! There’s no evidence that any of these foods make us burn more calories than we would without eating them,” says Olivia Ramos, a Los Angeles-based nutritionist.
There’s Fiction, and Then There’s Fact
Clearly, I’m no nutritionist. So I enlisted Ramos, who helped me make sense of all the seemingly conflicting information.
The Fiction: Negative-calorie foods not only are very low in calories but also have a unique, powerful makeup that puts our bodies in superburn mode—powering through foods so quickly that we lose weight simply by eating.
The Fact: Eating and digesting food do create a slight spike in our metabolism, but it doesn’t add up to much—actually, less than 30 percent of the calories our bodies burn at any given time, says Ramos. Though celery, the poster child of negative-calorie foods, does contain a mere six calories, we expend only about half a calorie to digest it, according to Global Metabolism Myths, by Mitt Hickey. Guess that negative-calorie math doesn’t exactly measure up when we get specific. Bummer.
The Fiction: There are so few calories in negative-calorie foods that just chewing and swallowing them burns up more than the calories they contain (plus that cookie you ate a few minutes ago).
The Fact: Chewing, according to the popular diet website HungryGirl.com, burns about eleven calories an hour. Sticking with the celery example, it probably takes about five minutes to chew a piece of celery (and that’s for a slow, slow eater). I was no math major, but even I can do the simple division that shows you’d have to chomp for longer than that to actually chew away the calories.
Although chewing up celery sticks may seem strenuous, it’s probably not going to leave us burning enough calories to make any real difference. Even to lose just one pound, we’ve got to burn off 3,500 calories. The idea that a certain food will act as a magic pill that helps us burn off other foods is just not true—celery or no celery. “Classifying foods as negative calorie is misleading,” says Ramos. “All food has energy, and therefore calories. And we need calories.”
The verdict? What we can take away from those negative-calorie food lists is the power of fruits and veggies. Studies find consistently that people who eat diets high in them lose weight—probably not because these foods act like diet pills in our systems, but because they help us stay satisfied with fiber and nutrients so we don’t crave the junk food that leaves us craving more junk. Negative calorie or not, regularly including these foods in our diet will keep us not only at a healthy weight, but just plain healthy.
Updated December 1, 2010