So you’ve tried a Paleo diet, Whole 30 and a raw vegan plan and you’re still looking for the perfect weight-loss strategy. Before you buy that swampland in Florida, let’s talk about negative-calorie foods.

You may have heard the term before. A negative-calorie food seemingly burns more calories to eat than it contains. For example, could it take more energy to munch iceberg lettuce than the minuscule calories iceberg contains? And if so, why not go on a negative-calorie food diet filled with nothing but negative-calorie foods, right?

The voice of nutrition reason

Sadly, that rationale is all wrong. "Although it is nice to believe we can actually eat 'free foods' or foods that do not equal any calories once inside our body, it is too good to be true," says Beth Warren, MS, RD, CDN, founder and CEO of Beth Warren Nutrition in Brooklyn and author of "Living Real Life with Real Food."

"There is no scientific evidence that foods like celery, carrots, tomatoes, apples and lettuce are what are referred to as 'negative-calorie foods,' and burn more calories through digestion than what the food itself contains."

These supposedly "catabolic foods" — or foods that require more energy to chew, digest and absorb than the calories which they contain — aren’t really "negative-calorie" foods.

Sure, you can eat all the celery, grapefruit and iceberg you want and you may even ditch a dress size doing it, but while metabolism is increased after eating, the calorie expenditure of eating food is too small. What’s more, no study has ever demonstrated its effect.

"Biologically the notion just doesn’t add up," says pediatrician and registered dietitian Natalie Digate Muth, M.D., MPH, RD, senior advisor for Healthcare Solutions for the American Council on Exercise. "Why would we evolve to eat food that provides us with negative energy?"

Unfortunately, evolutionarily, we aren’t made to eat food that inherently makes us lose weight. If that were the case, obesity wouldn’t be epidemic.

That’s not to say you can’t lose weight eating these foods. In fact, lists of low-calorie, catabolic foods are being touted as negative-calorie foods all over the Web with outstanding results purported by dieters claiming eating loads of celery, asparagus and lettuce leaves is the answer to your weight-loss woes.

Calories in, calories out

celery stalk Sure celery is very low in calories, but you won't actually lose calories by munching on some stalks. (Photo: ArtCookStudio/Shutterstock)

But let’s look closer. Take celery. It’s mostly water and fiber, right? So you might think the act of munching and digesting a stalk would burn more calories than the stalk contains. This thermic effect of food accounts for about 10 percent of burned energy since our body is constantly busy digesting and absorbing nutrients from our food daily. However, if a serving of celery contain 10 calories and 1 calorie (10 percent) is burned through digestion that still leaves a 9-calorie surplus. Of course, that’s practically micro-calories in the scheme of food and eating, but it’s not negative calorie.

"The truth is that there is no scientific research in support of a catabolic diet or any 'negative-calorie' foods," says Muth.

"If someone is successful in weight loss by following a diet using negative foods, it's typically because they are whole foods that are not calorically dense," says Warren.

That said, these low-calorie foods are great additions to a healthy diet. Of course, you can’t subsist on just celery, carrots and lettuce leaves, nor would you want to, but you can and should include low-calorie foods in a healthy eating plan to help keep your weight-loss efforts on track, says Muth.

Try these low-calorie foods as part of a healthy diet:

Artichokes (60 calories, 6 grams fiber)

Blueberries (50 berries contain only 40 calories)

Bok choy (1/2 cup has only 10 calories)

Carrot (1 large has 30 calories, 2 grams fiber)

Cucumber (1/2 cucumber has 20 calories)

Egg whites (1 large has 20 calories, 4 grams of protein)

Grapefruit (40 calories in a medium fruit)

Spinach (2 cups has only 14 calories)

Tomato (1 medium is 25 calories)

Watermelon (1 cup has fewer than 40 calories)

Do negative-calorie foods really exist?
We ask the experts if it's true that some perfect foods really burn more calories than they contain.