# Does the digestion of some foods burn more calories than it supplies?

Calories in food is a measurement of the amount of energy it will provide to the body. I've heard that eating some foods actually make you USE more calories than you consume. Do any foods actually contain less calories than it takes to chew and digest them?

Of course this isn't a significant amount of calories and I don't expect this to be some miracle weight loss technique. I'm simply interested if the calorie use to actually process food is small enough to let some foods "slip by" calorie wise.

• Eat ice. Zero calories, but it takes energy just to melt it. – Sklivvz Jul 9 '11 at 1:22
• My wife heard a rumour like that about jelly beans. For years we jokingly called them "diet pills". They don't work. – Graeme Perrow Jul 9 '11 at 3:15
• Sklivvz answers: "Eat ice."<br> But will eating ice burn more calories? You might pick up a jacket because you feel cold afterwards, and thus just lose less energy that way. Apart from that, it takes 1 cal to increase the temperature of 1 g of water by 1°C. So if you would drink 1 liter of ice cold water, you would use 37 * 1000 = 37kcal. To compensate for eating one Snickers [chocolate bar] (271kcal) you would have to drink 271 / 37 = 7.3 liters of ice cold water. So even if you would lose kcal by eating something, the effect will be negligible compared to eating less calorie-ri – johanvdw Jul 9 '11 at 10:59
• What about chili pepper? Does it make you hotter and burn more calory? – lamwaiman1988 Aug 26 '11 at 2:22

There seems to be some evidence to support it:

• Snopes.com claims most of the benefit comes from the energy used trying to digest what is largely cellulose; it suggests that chewing has little impact on energy use. It also states that while eating celery you are not eating something else (though I would have thought that that depends on how it is prepared and presented);

• The Straight Dope takes this second point further, showing that the time taken to eat celery involves more calorie expenditure (from being alive) than the usable calories in the celery.

So it depends on what you regard as negative-calorie food. Cold water, since the body has to heat it?

• I don't find either of these sources particularly persuasive. The Snopes article doesn't give any actual evidence. The Straight Dope article compares the number of calories in celery to the number of calories needed per hour to maintain body weight. A valid analysis would need to look at the additional number of calories required for digestion, which neither article mentions. – amcnabb Sep 10 '12 at 2:54
• @amcnabb. THe Snopes article says "It is the bodily energy devoted to the digestion of the green stalks that exhausts calories" which to me is a mention of the additional number of calories required for digestion, even if not quantified. – Henry Sep 10 '12 at 6:42

The short answer is no. For a longer answer, I'll look at the classic example of celery.

• livestrong.com: Celery contains about 14 calories per 100 grams, which makes it only slightly less energy dense than most other non-starchy vegetables which average around 20 calories per 100 grams.

• shapesense.com: "The general consensus in the scientific community is that the thermic effect of food accounts for roughly 5 to 10 % of the energy content of the food ingested."

• worldfitnessnetwork.com: Fibrous vegetables have a thermic effect of about 20%. (also claims that "many fruits and vegetables are negative calorie foods" but without giving any specific examples or substantiation).

• Assuming that most non-starchy vegetables have a thermic effect as high as 20% (from worldfitnessnetwork.com) and an energy density of 20 calories per 100 grams (from livestrong.com), we can estimate that it requires about 4 calories to digest 100 grams of non-starchy vegetables.

• Assuming that digestion of celery is comparable to that of other non-starchy vegetables, then the 14 calories per 100 grams contained in celery would far outweigh the 4 calories required for digestion per 100 grams of celery.

• For digestion of celery to burn more calories than it releases, then digestion would have to burn more than 14 calories per 100 grams of celery. This is 3.5 times the rate of other non-starchy vegetables.

Of course, one might argue that eating some food other than celery burns more calories than it releases, but this would probably push the boundaries of what can reasonably be called "food". You could burn calories by eating some sort of non-food (perhaps paper?), but we wouldn't call things "food" if they contained fewer calories than we could release by digestion.

• Please provide some reputable references to support your claims. – Sklivvz Sep 10 '12 at 6:55
• @Skliwz, I picked several of these references because they were used in the other answer, but I'll try to make some time to find some others, too. – amcnabb Sep 10 '12 at 14:05

Short answer, possible, but probably no.

The Mayo Clinic is currently of the position that

...it is theoretically possible to have a negative-calorie food, but there are no reputable scientific studies to prove that certain foods have this effect.