Complex sentence: This allowed people to swap foods of similar nutritional value (e.g. carbohydrate) for another, so, for example, if wishing to have more than normal carbohydrates for dessert, one could cut back on potatoes in one's first course.
Split into simpler sentences: This allowed people to swap foods of similar nutrition value (e.g., carbohydrate) for another. For example, if wishing to have more than normal carbohydrates for dessert, one could cut back on potatoes in one's first course.