How much ice would I have to eat to lose 10 lbs?
I’m not a doctor, and I don’t want anyone to mistakenly think anything here can be construed as medical advice. I just write fun things about physics, and I only aim to be approximately correct. In a rare break from encouraging experimentation, I cannot recommend trying this at home.
Short answer: About 674 lbs of ice.
Long answer: If your body is consuming more energy than it uses every day, then the excess energy will be used to build body mass. If your body is consuming less energy than it uses every day, then to make up the deficit your body will use its own mass as fuel. In some sense, to lose weight, your body has to eat itself.
Despite the myriad health claims on the internet, it seems that a common number that people throw around is 3500 Calories is approximately equal to a pound of body mass. I’m sure it varies with body composition, age, and other factors, but very roughly, if a person eats an excess of 3500 Calories we can expect they’ll gain a pound, and if they have a deficit of 3500 Calories we can expect they’ll lose a pound. This claim is abundant in health magazines which say you can lose “a pound a week by trimming 500 calories each day”  .
Coincidentally, the unit of a “calorie” is defined as the energy required to heat one gram of water by one degree Celsius. A food “Calorie” is a thousand “calories,” or better called a “kilocalorie.” The idea of the question now seems pretty clear – calories spent melting ice and heating water up to your body temperature are effectively calories burned. Put another way, ice eaten amounts to negative Calories.
So how much ice do we have to consume in order to lose 10 lbs? Well, the answer from physics is pretty straight forward. We know how much energy it takes to melt ice, that’s called the heat of fusion, and it’s the energy required to break the bonds in the solid to produce a liquid. We also know how much energy it takes to heat water; that’s just the specific heat capacity.
So, to lose 1 lb of body mass, you would have to consume 67 lbs of ice. If you weighed 200 lbs and wanted to lose 3 lbs, you’d have to eat your body weight in ice. Interestingly, the density of ice is similar to the density of the human body, so if you wanted to try this at home you could hire an ice sculptor to carve a life size statue of you from an ice block, and then eat it.
Again, I can’t recommend that anyone attempt to eat this much ice in an effort to lose weight. However, if you’re a normal person, you could drink a comparable mass of cold water over the course of a year. To burn 3500 Calories, your body would need to heat 220 lbs of water from freezing up to body temperature, which amounts to a little under 275 grams a day. That’s one extra cup of ice cold water every day, for a year, just to lose one pound.
But if you’re like me, and you drink a lot of coffee, there might be an easier way to slim down next year. The Mayo Clinic tells me there’s about 2 Calories in a cup of black coffee, but adding cream and sugar can easily push that number up over 100 Calories per cup . At a cup per day those Calories add up quick, and cutting that daily shot of cream and sugar can make the difference of 36,500 Calories over a year, totaling more than 10 lbs worth of Calories.
asked by /u/changingminds
image credit: Wikimedia Commons
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