Contrary to popular belief, they don’t mean that all but 1% or 2% of the fat has been removed. Rather they refer to what percentage of the total weight is milk fat.
For example, one cup of milk weighs about 225 grams. Of that weight, 2% milk holds 5 grams of fat and whole milk contains 8 grams. So whole milk isn’t much fattier than 2%.
In fact, a gallon of 2% has more than half the fat as a gallon of whole milk.
The FDA requires whole milk to have at least 3.25$ fat by weight. But the amount of fat can range from 3.25$ to 5$ depending on the cow.
Whole milk is most similar in fat content to what comes straight from the cow. But during processing, some of that fat is either removed or extra fat is added to create the variety you see in stores.
If you’re drinking milk straight, nutritionists recommend milk with at least some fat. The fat slows digestion and can help prevent a spike in blood sugar.