I am usualy not recommending fat free products. A am also not a big fan of low fat as well.
In fact, there is no scientifically proven evidence that consumption of fat free or reduced fat food has any significant advantage of normal food. However, there is a research that proves the opposite.
There are different studies compare caloric intake between groups of kids consumed low fat food or low fat milk and kids consumed normal fat food/milk. There were no difference in total caloric intake between groups. Kids who consumed low fat food were supplementing themselves with calorie from other food sources, mainly junks. In fact, low fat group had significantly higher consumption of sugar which may cause obesity and related diseases, e.g diabetes, heart disease, etc. Furthermore, kids in low fat group were more hungry by the evening and had more snacking episodes in afternoon and evening.
Fat free and low fat food mainly excludes animal (saturated) fat from the food. It changes the balance between different types of fat in our food and increases dramatically the part of omega-6 fat in the diet. Omega-6 converted in our body to omega-6-eicosanoids that in turn increase inflammation, have negative effects on cardiovascular disease, increase triglycerides, blood pressure, and arthritis. Research show that increased ratio of omega-6 fatty acids to omega-3 fatty acids is one of the significant factors that promotes cardiovascular disease, cancer, and inflammatory and autoimmune diseases. The ratio of omega 6 to omega-3 fatty acids in diet of person who consumes low fat products is ~20:1 of omega-6 : omega-3. Research shows that decrease of this ratio to 4:1 was associated with a 70% decrease in total mortality from cardiovascular disease.
There are 4 fat soluble vitamins: A, E, D, K. Vitamin A is responsible for vision cycle, reproduction and immune system. Vitamin E is an antioxidant and also responsible for neurologic function. Without vitamin K we may have problem with blood clotting. Low blood levels of vitamin D are associated with increased mortality, multiple sclerosis and bone disease. All those vitamins may be absorbed only if fat presents in gastro-intestinal tract. No fat - no absorption of fat soluble vitamins. Presence of vitamin D, for example, in skim milk doesn’t assure your body will receive it. It will enter the guts but will not be able to be absorbed to the body without fat and so will just leave your body as is with feces. A lot of moms when giving to child morning cereal with fat free milk for breakfast actually prevent from the kid to receive fat soluble vitamins not only from milk but also from cereal.
4. Hunger-satiety mechanism between meals.
The fat plays significant role in our hunger regulation. It’s responsible for prolonged satiety between meals. When we eat low fat or fat free food we decrease the satiety time and increase hunger periods, and so make ourself to look after an additional snack more frequently.
5. In addition, fat plays role in taste mechanism and as the result our satisfaction from food is less after low fat/skim food and that may increase the meal size.
6. Some fat free food have more sugar or starch added to cover decreased weight of product with less fat content. For my diabetes patients I usually recommend to compare regular cottage cheese or yogurt with fat free one to learn the difference in sugar content.
So, why it's promoted so aggressively? Let’s do some simple math.
8 oz whole milk provide 8 g fat.
8 oz 2% milk provide 5 g fat.
8 oz of 2% milk = 5 oz whole milk (that provides 5 g fat) + 3 oz of water (to fill up the volume).
And the customer pays the same price for whole milk or milk diluted with water.