Are Negative Calorie Foods for Real or Just A Bunch of Diet Hot Air? The Fitness Nerd Separates Fact from the Fiction Around Negative Calorie Diets.
Dear Fitness Nerd,
What’s your opinion on negative calorie foods? I’ve read that certain foods like celery require more energy to digest than they provide in calories. Is this true? And if it is, do you have a list of negative calorie foods? Thanks! (Aimee B — Dallas, TX)
Negative calorie foods are one of those dieting concepts that sound so good that you want to believe it’s true.
Just the term “negative calorie foods” conjures up images of eating all you want, and still losing weight. It’s a very powerful promise — and one that fad diet and weight-loss pill marketers rely on on every day to sell you their latest pill, potion or ”weight-loss-secret-revealed” eBook.
Take a look under the hood though, and you’ll find that the concept of negative calorie foods has more in common with a good urban legend than with solid nutrition advice. And like an urban legend, negative calorie foods do have a grain of truth at their center, but that’s about it.
What Is A Negative Calorie?
For those of you who are unfamiliar with the concept of negative calories and negative calorie foods, here’s the short version:
The theory is that a negative calorie food is any food that requires more energy to digest than the energy (calories) actually contained in the food. The idea here is that by eating these foods, you can burn more calories than you consume and lose weight more rapidly and efficiently.
Origins of the Negative Calorie
The concept of negative calorie foods has been around for almost a decade, and has been popularized via two main sources: Internet discussion boards and the 1999 book, Foods that Cause You to Lose Weight: the Negative Calorie Effect, by Neal D. Barnard, M.D.
Barnard is the founder of Physicians Committee for Responsible Medicine (PCRM), which is a vegetarianism advocacy group with close ties to People for the Ethical Treatment of Animals (PETA.) Critics of Barnard and his book will point out that Foods that Cause You To Lose Weight: the Negative Calorie Effectis less about negative calorie foods, as it a paean to a ultra-low fat, vegetarian/vegan diet. This in itself isn’t bad, except that Barnard cloaks his crusade for vegetarianism in a cloud of quasi-scientific mumbo-jumbo that leads people to believe that vegetables have some magic “negative calorie effect” in the body.
Barnard’s diet plan is actually fairly extreme and has you cutting out all dairy, meat, nuts, fish and even healthy fats like olive oil. While including plenty of fruits, vegetables and whole grains in your diet is clearly a fantastic goal, Barnard’s advice to avoid even healthy fats flies in the face of most current research around the broad health and fat-loss benefits of things like MUFAs and Omega-3 fatty acids present in sources like fish oil. In this regard, Bernard seems woefully behind the times.
Even more interesting is that outside of the book’s title, the term “negative calories” is rarely mentioned by Barnard. It’s hard not to conclude that its inclusion in the title was done purely for marketing sizzle, since calling the book Vegetables That Cause You To Lose Weight is a bit of a yawner. Still, Barnard gets credit for coining the term “negative calorie”, even if what he really wants you to do is just eat more vegetables.
Is Celery Really a Negative Calorie Food?
While the list of negative calorie foods has ballooned to include everything from beets to strawberries and mangoes (yes, I’m being serious here), celery is the most commonly cited negative calorie food.
From a nutritional standpoint, celery is pretty much empty. It’s basically made up of water, sodium, some trace minerals and something called cellulose — which is a form of vegetable fiber than the human body cannot digest. It contains no protein or fat and marginal carbohydrates. Any other nutrition in celery is in the form of vitamins, minerals and enzymes, which contain no calories.
In fact, aside from iceberg lettuce and cucumbers, you probably couldn’t find a less nutritious, lower-calorie vegetable to eat. These foods are already about as close as you can get to eating zero calories. Close, but not quite, as we’ll see in a moment.
A large, stalk of celery weighing in at 2.2 ounces contains only nine calories. Negative calorie diet advocates claim that the mere process of chewing and digesting celery requires an expenditure of energy that exceeds the 9 calories present in the celery. Therefore, the argument goes, celery has “negative calories.”
Again, this all sounds good in theory, but what about in practice?
Issues with the Negative Calorie Foods Theory
There are some flaws with the negative calorie food theory, however.
First, the reason that certain foods like celery are already low in calories is exactly because of their high-non-caloric nutritional content. The fact that cellulose, water and minerals like sodium contain no calories is already figured into the food’s caloric-content. That’s why it has minimal calories in the first place. Negative food advocates want to double-dip here, and have you believe that the non-caloric nutrients like cellulose lower its effective calorie levels even more, but that’s just not how it works. This is already baked-in.
Second, the whole argument that the body burns more calories chewing and digesting negative calorie foods like celery is also suspect.
Yes, the body does expend a certain amount of energy to digest food, but that expenditure — even with foods that contain a high-percentage of non-caloric nutrients like cellulose — is actually fairly minimal.
Typically, the body will expend 10 – 15 percent of the calories you consume each day to fuel digestion. Let’s just throw the negative calorie food gurus a bone and say that for foods that are rich in non-digestible nutrients like cellulose, that number is actually as high as 50 percent of calories consumed (I have no evidence for this claim — I’m just being generous to prove a point.)
In the case of celery — the poster child of all negative calorie foods – you would be burning an extra 4.5 calories per each 9 calorie, 2.2 oz serving of celery. That would put your effective net calories at 4.5 (9/50% = 4.5 calories) — hardly “negative calorie” territory.
And because the amount of energy expended on digestion of foods is always expressed as a percentage, to have a negative calorie effect, digestion would have to constitute at least 101% of the energy consumed in order to create a negative calorie environment — something which is physically impossible.
So it appears that the food that is the best candidate for qualifying as a negative calorie food — celery – can’t even hit the break-even point, let alone become “calorie-negative.”
The Negative Calorie List Grows – Damn The Science!
One of the most fascinating twists to the whole negative calorie myth is how the list of negative calorie foods has been expanded to include all kinds of fruits, vegetables and greens (regardless of their actual calorie content), including:
- Beet Root
- Hot Chili
- Garden cress
- Green Beans
It’s unclear why these particular foods consistently seem to appear on every Internet list of negative calorie foods.
Aside from their relatively high water or cellulose content, there seems to be very little rhyme or reason as to which food makes the list. It’s almost as if someone randomly picked a bunch of vegetables and fruits, published them on their website as negative calorie foods (or maybe they culled them from Dr. Barnard’s book) and the rest of the Web has just perpetuated that myth ever since.
Fruits? Negative Calories? Huh?
The inclusion of fruits in the list of negative calorie foods is particularly perplexing.
While fruit does typically contain a large amount of water and has some indigestible fiber, it’s also very high in fruit sugars (fructose.) To suggest that you will burn more calories digesting fructose than the calories present in the fructose itself is simply pseudo-scientific bunk.
Take watermelon, for example — one of the foods typically included on lists of negative calorie foods.
A 9 oz serving of watermelon has 84 calories, 1 gram of fiber, 21 grams of carbohydrates and 17.4 grams of sugar (indeed, the bulk of carbohydrates in watermelon come from sugar.) While calories are certainly low compared to a Dove Bar, any suggestion that your body will burn in excess of 84 calories simply by digesting a few slices of watermelon defies not only bio-chemistry, but also the Laws of Thermodynamics. The only way you’re going to burn that watermelon off is if you run a couple laps around the gym.
Negative Calorie Diet: The Secret is in the Enzymes?
So how does this stuff get perpetuated and how do negative calorie prophets get around the Laws of Thermodynamics?
Adherents of the negative calorie diet myth will throw around a bunch of bio-chemical hooha to justify why these foods create negative calorie environments in the body. One of the most frequently cited reasons for why these foods create a negative calorie effect is because of “enzymes.”
Which “enzymes” we’re talking about are never mentioned. This is probably because the authors themselves have no idea … they just read it once in one of the hundreds of nearly identical Internet articles on negative calorie foods.
Here’s one of my favorite explanations of how these un-named “enzymes” work, taken directly, word-for-word from a diet website that claims to understand how negative calorie foods function. The name and address of that site shall remain nameless lest the owner and author of this nonsense be labeled a quack:
All foods have a nutrient (carbohydrate, fat, protein), caloric (calories) and vitamin & mineral content. Vitamins stimulate living tissues to produce enzymes that breakdown the caloric nutrients of that food.
The foods with negative calorie contain sufficient vitamins & minerals that produce enzymes in quantities sufficient to break down not only its own calories, but additional calories present in digestion as well. This is called “negative calorie effect”.
If you’re scratching your head, you’re not alone. I have no idea what this person is talking about — and I suspect that if you asked a PhD in bio-chemistry or nutrition, they’d have an equally-perplexed look on their face. Yes, enzymes do help break down food, and yes there are enzymes in vegetables and fruits which can help with digestion, but to suggest that these enzymes create a “negative calorie effect” is pure speculation.
The great thing is that this exact excerpt — with some minor modifications here and there — basically appears verbatim within just about every article written online about negative calorie foods. Clearly the copy and paste function is popular among negative calorie fans.
The scientific citations to back up this alleged “enzyme action” in negative calorie foods are pretty thin. They typically cite two references: one from Dr. Dean Ornish that showed a vegetarian diet helped people with heart disease cut their weight by an average of 20 lbs without limiting calories and without exercise; and a reference to a 1994 article in Self Magazine by Dr. Barnard that discusses “negative calorie foods.”
The exact study by Ornish is not cited, so I was unable to confirm or review the Ornish study to see exactly what it had to say about “negative calories.” On the surface, it seems like negative calorie advocates are simply associating research about the positive weight loss effects of diets high in vegetables and low in dietary fat with the concept of “negative calories” — even though the research itself may say nothing about the ”negative calorie effect.”
In other words, beware of diet book authors bearing flimsy research.
The Lowdown on The Negative Calorie Myth: Veggies ARE Good For You
At the end of the day, the Negative Calorie Diet just seems to be a lot of wishful thinking that just keeps getting regurgitated online ad nauseum with no real scientific proof that any of these foods create negative calorie environments in the body. Like a bad joke that won’t die, the negative calorie myth just keeps getting passed around, and around, and around.
Yes, a diet high in whole food sources of fruits and vegetables will help people lose weight — and can have all kinds of health benefits that make them a smart choice and a centerpiece of a clean eating approach to diet and nutrition. But in terms of putting you into the negative calorie zone, don’t hold your breath.
Many of the fruits and vegetables that make the negative calorie food list are quite low in calories and very high in beneficial antioxidants, vitamins, minerals and phytochemicals which may prevent heart disease and cancer. They also are very filling, and because of their low calories, allow you to eat a higher volume of healthy food, which if substituted for higher-calorie junk food will help you lose weight and body fat.
So while the whole negative food myth seems to be exactly that — a myth — there certainly is no harm in loading up on these fruits and vegetables as part of a healthy diet. Just don’t expect fistfuls of celery to be the key to lasting weight loss.
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