A. It's not so much that fat-soluble vitamins dissolve in fat, but that they are carried across the intestinal cell barrier by lipid (fat) molecules.  So, while it is true that fats are necessary for transport and absorption of fat-soluble vitamins, it doesn't take much!

A couple of years ago, there was a study that found that eating avocado with vegetables increased the absorption of fat-soluble beta-carotene from the vegetables. However, a study that looked specifically at vitamin D found that vitamin D was absorbed just as well from both skim milk and orange juice as it was from whole milk. (Maybe the fiber in the vegetables plays a role somehow?)

The most likely causes of fat-soluble vitamin deficiency includea missing or malfunctioning gall bladder, bariatric (weight loss surgery), intestinal resection, or other serious digestive diseases that interfere with absorption of fats.