I tried to explain to a friend when food companies take the fat out of something, they replace it with sugar. I gave the example of skim milk and 2% milk since they had both in their fridge. Upon looking at the nutrition label, I realized I picked a bad example.
The skim and 2% do have proportionally more sugar. If you compare 100 calories of whole to 100 calories of skim, the skim will have more sugar (and more protein). Many SAD eaters prefer skim or 2% because it has less calories by volume and/or because of a fear of saturated fat. If you're looking to restrict calories over the long run, to me the question is which is more satiating per calorie. Probably no clear answer there. Is fat more satiating? Is there an effect on insulin from the carbs/protein that may play a role? Is more calorically dense less satiating? I don't know the answer, but my gut tells me to go with the most natural form (not skimmed). Though, that's just my paleo bias. Also, I believe many of the nutrients are in the fat.
Actually, the more I think about it, maybe it's hard to even argue that skim is more or less natural than whole. To get skim, you just let the milk naturally separate and then skim the fat off the top. If eating the skim (or skimmed milk) isn't natural, then eating the fat (or cream) from the top isn't either, and plenty of people here use cream. Therefore, I think it does come more down to macronutrient ratio (if you care), lactose, casein, nutrients in the fat, satiety, etc. Goes without saying that unpasteurized, unhomogonized milk (from a safe source) is ideal as far as milk goes. And of course, if you're trying to reduce caloric intake, liquid calories probably aren't helpful anyway (whether it's skim or whole).
It's not that they add sugar to low fat or skim milk, but they take out the fat so the sugar is more concentrated. It's not a huge difference. 12 gms carbs in skim milk, 11 gms in whole milk. A cup of heavy cream, OTOH (you probably would not drink a whole cup!) has 7 gms of carbohydrate.
Where you really see the difference is in low fat processed foods where they do replace the fat with sugar.
Can ice cream aid in digestion? 9 Answers
Day 3, grain-free flu? 2 Answers