The answer to this question depends on what your country considers “butter.” For a product in the US, butter has to have 80% butterfat, whereas in the UK butter has to have 85% butterfat, with the rest being milk proteins and water. If the butterfat is clarified into 100% of the product sold, such as ghee, then the calories rise to 135 Calories per tablespoon, which is an example of the amount of calories in 1 pure tablespoon of butterfat from a cow.
Then the question is what percentage of butterfat is yak butter? According to the Food and Agriculture Organization of the United Nations yak butter has 12-15% water, 1% protein, and the rest fat, coming very close to the US and UK definitions of “butter.”
In the US, cow butter has about 102 Calories per tablespoon. This is the product with at least 80% butterfat. The milk from which it is made, whole milk, has 3.25% butterfat. Yak milk has about twice as much butterfat raw (7%) as cow milk raw. However, just because yak milk has about twice as much butterfat in the raw milk form does NOT mean that the butter product that is made from it would have twice as many calories in the same tablespoon.
Fat has a certain density of calories, that is 9 Calories per gram of fat, and butter, by definition, must have 80% butterfat. Since butter ranges from 80-85% fat content, it is safe to say that yak butter should have nearly the same calories as cow butter since fat has a known caloric density (9 Calories per gram) and roughly the same amount of fat grams will be in a tablespoon of any type of butter if it can be called “butter,” according to the definitions stated.
This is no where near the quoted number of 800 calories per tablespoon given in Tracy Anderson’s interview. Yak butter should have similar amounts of calories as the definition of the butter in the country where it is sold, assuming you bought a regulated source of yak butter.
This question is similar to which weighs more, 1 lb of feathers or 1 lb of gold? They weigh the same: 1 lb. Butter has a specific definition of density of butterfat, so 1 tablespoon of butter has a certain amount of calories because it has a certain amount of fat grams. This number is similar for goat butter, which has 110 calories per tablespoon, which is very similar to that of cow butter. Yak butter would be no different.
Note: Calories is capitalized next to a unit to differentiate between a calorie and a kilocalorie (1 kcal (kilocalorie) = 1 Calorie = 1000 calories). Calories doesn’t have to be capitalized when it is used generically, ie without a number preceding it. Food calories are always in kilocalories, so a 2000 Calorie diet has 2,000,000 calories.