Part 1. Part 2. Part 3. Part 4.

In Randall Munroe’s What If?, one of the most complex questions that he declines to answer is the following:

What is the total nutritional value (calories, fat, vitamins, minerals, etc.) of the average human body?

Since he didn’t answer, I took it upon myself to try. Previously, I calculated that the average human body contains 560 3-ounce (85-gram) servings, each containing 200 calories. Now, let’s break down some of the nutritional details.

Calories from Fat

On average, the dry weight of the human body is about 44% protein, 36% fats, 4% carbs, and 16% minerals, and fats contain 8.8 calories per gram. Cooked meat is about 55% water. Do the math, and that means the human body has 120 calories from fat (60% of total calories) per serving. Wow, we are not a healthy diet, are we?

Macronutrients and Percent Daily Values: Fats

This is the middle part of the nutrition facts label (except sodium and cholesterol). This tells how much of the basic dietary components you’re eating–fats, carbs, and proteins. For example, our 85-gram serving of human contains 14 grams of fat. The labels will also give a “% Daily Value” for each nutrient, which is the fraction of the recommended daily amount of that nutrient you get per serving. Percent Daily Values are calculated based on a 2,000-calorie diet. For fats, the recommended daily amount is 65 grams or less, so you’re getting 21%.

Nutrition facts labels also list two subtypes of fat that are supposed to be especially bad for your health: saturated fat and trans fat. I couldn’t find anything about the amount of specific types of fat in the human body, but a typical saturated fat fraction for red meat is about 35%, so we’ll go with that. That gives us 5 grams of saturated fat, or 24% DV.

Trans fats are rare in nature, mostly being found in processed food, but cattle and sheep have 2%-5% of their body fat in trans fats. In humans, this varies with trans fat consumption and is as low as 1% in people who don’t eat much trans fat, but can be as high as 7% in the United States. Making some allowances for the average global diet, let’s go with 2%. This gives humans 0.3 grams of trans fat per serving, rounded down to 0 grams. There is no Percent Daily Value for trans fat because the recommendation is as low as possible.

Cholesterol

Cholesterol isn’t a nutrient per se, although you can classify it as a type of fat, but it’s grouped with the other macronutriets, so we’ll examine it here. An average 61-kilogram human body contains 31 grams of cholesterol, or 56 mg per serving. This is 19% of the Daily Value.

Carbohydrates

Unlike plants, for which carbohydrates are a structural material, animals have relatively little carbohydrates in their bodies, and they are mainly used for energy storage, while fats are the main structural material. Our hypothetical serving of human only contains about 2 grams of carbohydrates, or less than 1% of the Daily Value. We are an extreme low-carb diet.

The primary forms of carbohydrates in the human body are glucose, a sugar, and glycogen, a starch. Most other carbs are converted to one of these two forms or passed as fiber. In a healthy adult, only about 5% of this energy storage is circulating as glucose at any one time, so the sugar content per serving is basically zero. Ditto for fiber, which is just a less digestible form of carbohydrate.

Protein

Animals have lots of protein, more than any other type of nutrient. In this case, the amount is 17 grams per serving. Protein does not have a recommended daily amount, hence the relative popularity of low-carb and low-fat diets.

Next time: vitamins and minerals (and sodium, which is technically a mineral).