Do carbohydrates affect body weight?
Often, carbohydrates are referred to as fattening or as being major players in weight gain. However, they provide 4kcal/g, similar to protein, and lower than the 9kcal/g provided by lipids. In fact, it is the fats that are added to high-carbohydrate foods that may contribute to an excessive or heightened kcal count associated with such foods. For example, a medium sized baked potato will have about 160 kcal, but after adding 2 tbsp of sour cream to that potato, you will suddenly reach a kcal count of 225. No single macronutrient, whether it be fat, protein, or carbs, is fattening in isolation. In reality, it is the balance between calorie intake and expenditure that has an effect on body weight. That being said, it does not mean that some types of carbohydrates have not been implicated in weight gain (for example, high-fructose corn syrup has been implicated in weight gain).
Why is Vitamin A added to skim and partially skim milk?
Because Vitamin A is a fat soluble vitamin, it is lost when the cream is separated from skim or partially skim milk. Skim/partially skim milk is mostly aqueous and will lack Vitamin A in comparison to milk with a higher fat content.
What are the dangers of taking a supplement of a single amino acid?
Taking a supplement containing only one single amino acid may provide enough of that amino acid to impair the absorption of other amino acids. This is because amino acids with similar structures share the same transport system within the mucosal cells of the small intestine (amino acids with similar structures will compete for absorption). If there is an excess amount of any one of the amino acids sharing a transport system, more of it will be absorbed, thus delaying the absorption of the competing amino acids.