Entrée: Two ice cubes. Main Course: Oxygen.

A reader writes:

Is there such a thing as food with less than no calories?

You're supposed to be able to eat lettuce or celery or something, and the energy your body uses to digest it is more than you get out of it.

(Well, I don't really know if you're "supposed" to be able to or not, but I've certainly heard people say this.)

What about eating ice? Obviously you get no nutrition at all from that, but I've never seen a Get Thin By Eating Snow diet book, so I figure it's not practical.


There are foodstuffs that have very little "food energy". They're pretty much what you'd expect, and do include a lot of green vegetables.

But digestion is good at sucking energy out of food. Your body does better than break even, even when you're eating celery. It's not easy to gain weight eating nothing but undressed salads and vitamin supplements, but it's possible.

The eating-ice thing, in contrast, sounds like a great idea. But only if you make a particular mistake, having to do with the term "calorie".

There are 540 calories in a Big Mac. But the enthalpy of fusion of water is about 80 calories per gram. And then you need another calorie to heat one gram of water by 1°C; if your ice starts out a few degrees below zero and ends up at body temperature, that adds up. And the only place this energy can come from is your body's own reserves.

So you can more than offset the entire nutritional value of your hamburger by crunching up one lousy ice cube! Right?

Sorry, no. Because the "physics" calorie, the one being used on the melting-ice side of the equation, is one thousandth of the "dietary" calorie, on the food side of the equation.

(This is noticeable when the dietary calorie is clearly indicated, as "kcal", for instance. The modern metric alternative to the two kinds of calorie is the joule and kilojoule; fortunately, there's no colloquial tendency to call both of these units "joules".)

A hundred grams of celery is about 14 kcal. To offset only that much energy value, you'd need to eat more than a hundred grams of ice. A whole tray of ice cubes would probably do it; the ice-cube trays in my fridge hold about 160 grams.

So as few as 35 trays of ice cubes might compensate for a Big Mac!

Presuming, of course, that you actually can Freeze Yourself Thin at all.

The human body runs warm as a matter of course. If the ambient temperature is below body temperature, which it is for most humans most of the time, then the body's leaking heat all the time anyway, and eating cold stuff may change where the heat goes, more than it changes how much heat is lost.

This page at livestrong.com gives a ballpark figure of only one dietary calorie burned per ounce of ice eaten. 80 small calories of enthalpy of fusion per gram of ice, plus 40 small calories of heat to take the water from a bit below freezing to body temperature, times about 28 grams to the ounce, gives 3360 small calories or 3.36 dietary ones of raw heating power. If that only adds up to one extra dietary calorie burned, the tooth wear and ice-cream headaches don't seem like much of a trade-off. Especially since you don't actually get any ice-cream.

(If you really apply yourself to slimming via low temperatures, I would not put it past your body to decide that all this shivering indicates you're now living in a cold climate, so more incoming food should be directed towards creating a nice insulating layer of fat.)

Your natural basal metabolic rate is probably closer to 2000 kcal per day than it is to 1000. Adding a couple of dozen kilocalories to that by ice-eating may actually hurt more than doing an energy-equivalent amount of exercise.

(Exercise is not really a great way of burning calories. Run ten kilometres, burn 700 kcal. As a general rule, if you're not some sort of athlete or heavy manual labourer, exercise will make you fitter and stronger, but not thinner.)

Needless to say, Wikipedia has a page about negative-calorie food. And a funnier one about the "Negative Calorie Illusion".

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

11 Responses to “Entrée: Two ice cubes. Main Course: Oxygen.”

  1. Max Says:

    I have a problem. You say "Your body does better than break even, even when you're eating celery" - and we all know Dan is never wrong. However, the second linked article says "For example, low-calorie, high-cellulose foods such as celery, cabbage, and broccoli tend to require more energy to digest than they provide nutritionally" - and as we know, Wikipedia is definitely never, ever wrong either.
    But both cannot be true, hence space-time seems to be rather creaky around me right now, ready to divide itself by zero and collapse into a singularity at any moment. Help...?

    • Simon Says:

      > and, as we know, Wikipedia is definitely never, ever wrong either. But both cannot be true, hence space-time seems to be rather creaky around me right now...

      The reason Wikipedia is never wrong is that any statement, once observed as an error, is immediately corrected by the observer. (And before it's observed as an error, it isn't one -- proof by gratuitous abuse of quantum mechanics).

      So the paradox only arises because you saw an error without correcting it. Bad Max☺. (I've now edited the article).

  2. carnivean Says:

    I think it would be more accurate to say that exercise won't make you lighter, rather than won't make you thinner. A decent weight training regimen will shed bodyfat, and replace with muscle, which will be denser, thus your body will be thinner. Assuming that your dietary requirements are still being equally well met as before you started.

    @Max, I'd say Dan is more accurate than Wikipedia. Probably funnier too.

  3. trialex Says:

    >"As a general rule, if you're not some sort of athlete or heavy manual labourer, exercise will make you fitter and stronger, but not thinner."

    I would not consider myself an athlete, but when I train for the City2Surf (through the year 1 run per week @ 10km, race training 3 runs per week total ~35km) I lose about 2-3kg and my pants are noticeably looser.

    Anecdotal data only obviously.

  4. Mighty Says:

    I read a Scientific American article a few years ago that discussed studies done for various diets. From what I remember, it didn't matter which diet plan you chose. The only strong correlation with weight loss was calorie intake. And, that across several studies, the correlation between exercise and long term weight loss was very weak.

    There are other good health reasons to exercise regularly. But weight loss does not appear to be one of them.

    • Hydaral Says:

      Unless your exercise regimen increases your muscle mass, then your BMR will increase and you will burn extra calories just sitting around doing nothing!

    • ix Says:

      When I started exercising, I *gained* weight, but I lost a lot of body fat (depends on what you call a lot, I wasn't that fat to begin with). I agree with the basic premise, your mass only goes down if the nr of calories you expend are higher than you take in, but weight isn't the whole story.

      That doesn't mean exercise is useless for weight loss either. Muscles burn extra calories and it is sometimes easier to keep yourself from eating the 700 calories more than reducing your intake by say 500 a day. At least for me, I lost weight without even really trying, but probably because I simply had less time to sit around and eat junk food.

    • farnz Says:

      Practically (based on my experience, and that of my friends), the weight loss induced by excercise is because something about it causes you to feel hungry less often, and become satiated with less food.

      Note that not all exercise induces this effect - you need the right mix of exercise targeted at muscle building, and exercise targeted at stamina building. I've not spent enough time looking into why this is the case to know if it's well-understood by medical science, or if it's one of those things that hasn't yet been studied in enough depth.

      • ix Says:

        It might just be though that you simply learn to overeat less, and eat at set times, because you have to plan your food intake around your exercise. Indeed would be interesting to see studies on that.

        • Mighty Says:

          The SciAm article pretty specifically avoided *why* exercise didn't correlate with weight loss. Just that, over several large samples, In The Real World, that was the case. And they were making the point that it was long-term weight loss that they were looking at.

          My layman's guess is that it takes a *lot* of exercise to burn off a fairly small portion of high-calorie food. Therefore, avoiding purchasing that package of mini-donuts is much easier for most people than the several hours of exercise it would take to burn them off. That tradeoff comes up over and over. So that the not-consuming wins out across the general population of weight-loss seekers more than setting aside more workout time.

          I suspect it's a fairly small portion of the population who works out enough to make a significant impact. And an even smaller portion who keep it up enough to maintain the loss.

  5. lrwiman Says:

    Drinking icewater is a bit more promising. If you can drink the recommended 8 glasses of water a day, all ice cold (0C), that's 1,892 millileters which need to be warmed by 37C. That's a total of 70,004 calories, or 70kCal. That's like a small cookie, or most of a soda.

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