## “Calories in, calories out” completely debunked by not being an idiot about chemistry

ΛE = Λq + ΛW

That is the equation to calculate the amount of energy (positive or negative) in a chemical reaction. E is total energy, q is the temperature of the system and W is the work done on or by the system.

To find q, you would need to know the substances you’re dealing with, their specific heat capacities, and what reactions they’re going through. If you’re applying more than one reaction, you need to take the equations for both reactions and add them together.

Furthermore, specific heat capacity only applies under given conditions. Most specific heat capacities will be tailored to standard laboratory conditions (ambient pressure ≈101.4 kPa, temperature ≈24°C), but heat capacity varies based on temperature (the heat capacity of water is 4.1855 [J/(g·K)] at 15°C and 2.259 [J/(g·K)] at 25°C), and the human body has an internal temperature of 36.6°C.

“But Setar, isn’t there a lot of energy in food? You know those labels say calories when they mean kcal, right?”

Oh, I know. There’s two problems with that:

1) The body expends energy to break the food down in the first place. Your digestive system is not run by a wizard (though that would be cool, and explain irregular bowels quite well), it needs energy just as much as the rest of your body does.

2) Obviously, not all of the food we eat is taken up by the body in the first place, otherwise I wouldn’t be talking about bowels at all.

3…wait, crap, let me start over again. Among the problems with saying that there’s a ton of energy in the food and therefore the first law of thermodynamics holds…

3) Not all of the energy is taken up in the same way, and the body manages how that is done quite well.

4) Remember how I said that the equation only applies to a single given reaction under set conditions? Well, nutrients go under a hell of a lot more reactions after they’re taken up. The most famous cycle is the citric acid or Krebs cycle, and to get the energy output, you’d need to add up the energy equations for ALL of the reactions in that cycle.

And then you’d need to add in the reactions from all the other cycles in the cell that help to convert the nutrients into usable energy, and you’d have the total energy output over that cycle of reactions. You’d then somehow need to tie the energy inputs to concentrations of nutrients, and trace those nutrients back to the food they came from, and figure out how much of the energy present in that food actually makes it to the cell.

Getting complicated yet? Because it gets worse.

If you do all that, you will get the food intake to energy output ratio…for one cell. In one part of your body, under one set of conditions. And the intake-output ratios will be vastly different over differing types of cells in your body, and different parts of your body. To get the intake and translate it into something meaningful like weight loss — such as fat deposits — you’d need to intensely monitor what you ate, figure out what it would get taken up as in the digestive system, and then monitor your body and see how it worked out and where all this food actually ended up. You’d also need to account for other confounding factors such as your genetic structure and general life. Then you’d need to figure out how much energy your body puts out over a given period of time — and that is a lot more than just exercising; you would probably want to use a given 24-hour period to cross a range of activities including sleep. And then you’d need to monitor how changing that affected your fat/muscle/energy distribution.

And then you’d figure out exactly how much fat you’ll put on by having that extra brownie or bigger slice of cake. My guess, however, is not much, and if you’re not willing to have that bigger slice of cake then I guess it just means more for me ^_^

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### 4 Responses to “Calories in, calories out” completely debunked by not being an idiot about chemistry

1. John Morales says:

To get the intake and translate it into something meaningful like weight loss — such as fat deposits — you’d need to intensely monitor what you ate, figure out what it would get taken up as in the digestive system, and then monitor your body and see how it worked out and where all this food actually ended up. You’d also need to account for other confounding factors such as your genetic structure and general life. Then you’d need to figure out how much energy your body puts out over a given period of time — and that is a lot more than just exercising; you would probably want to use a given 24-hour period to cross a range of activities including sleep. And then you’d need to monitor how changing that affected your fat/muscle/energy distribution.

Written like a theoretician.

An experimentalist would just keep lowering the calorie intake (while monitoring body mass and body fat) until weight loss occurred.

The simplest solution for weight loss was pithily noted by Dr. Rudy: “eat less”. 😉

2. jt512 says:

One can debunk your article by not being an idiot about nutrition.

1) The body expends energy to break the food down in the first place. Your digestive system is not run by a wizard (though that would be cool, and explain irregular bowels quite well), it needs energy just as much as the rest of your body does.

The energy expended to metabolize food is known as thermic effect. It’s a component of total energy expenditures—you know, “calories out.” The energy required to fuel the digestive system at a basal rate is part of—durr—basal metabolic rate, another component of total energy expenditures.

2) Obviously, not all of the food we eat is taken up by the body in the first place, otherwise I wouldn’t be talking about bowels at all.

That is taken into account in calculating the energy content of the food. The energy content on nutrition labels and in nutrition tables is physiologic energy—the calorimetric energy content of the food minus adjustments for incomplete absorption and incomplete oxidation.

3…wait, crap, let me start over again. Among the problems with saying that there’s a ton of energy in the food and therefore the first law of thermodynamics holds…

Of course the first law of thermodynamics holds. The physiologic energy of the food cannot just disappear. It has to be accounted for by storage and expenditure.

3) Not all of the energy is taken up in the same way, and the body manages how that is done quite well.

That sentence is incoherent.

4) Remember how I said that the equation only applies to a single given reaction under set conditions? Well, nutrients go under a hell of a lot more reactions after they’re taken up. The most famous cycle is the citric acid or Krebs cycle, and to get the energy output, you’d need to add up the energy equations for ALL of the reactions in that cycle.

The heat generated in all those reactions is part of the thermic effect of the food. See #1.

I suggest you do a little research on energy balance in humans, and in general try writing about subjects you actually understand. You get a total FAIL for this article.

• herp says:

Actually you both have something right, however you’re looking at it from two directions. First, the chemistry point of view is correct for the most part. The physiological point of view also has some correct aspects to it. If you take into consideration that the Atwater system is still based on a total calorie ITC measured reaction and only subtracts things such as fiber, which we know is not absorbed the rest is still a total calorie calculation and only marginally guesses at the “physiological” calories.

To put this in perspective, we know that the food we consume is not always completely digested. This is where the original comment was going with saying that not everything is absorbed. Just think of eating corn on the cob. If your body was not able to get every kernel digested because there was a partial protection from the fibrous exterior, you don’t get the calories (or vitamins and minerals for that matter).

As for the thermic effect of the Kreb cycle and other ATP/NADH/lipid storage cycles, the real thermic effect of food is only something on the orger of 10% of the calories consumed. So I think what you COULD say is that for all the calories you eat, you’re only getting to USE 90% of them for running, writing, reading, etc. the rest was used for storing the energy for later. This does not say that “calories in, calories out” is incorrect when it comes to conservation of energy, but including the thermic effect as ‘lost’ calories due to processing and the inefficiencies we have in our digestive system, not every calorie that passes out lips ends up on our hips.