Distance
Though everyone is different, the metabolic effect of consuming a lot of sugar is well described in a number of books now, and while everyone is different, it could generally be assumed as a general rule, that if sugar and carbohydrates form too a high a proportion of people's diets, there may well be problems like weight gain, mood swings, head aches, diabetes, lack of energy, constant colds, polycystic ovary syndrome, at worst; and in general craving yet more sugar (caffeine, alcohol, diet coke, raw coke).
If a person does not crave sugar all the time, because of eating the right balance of other sorts of food, then it is less likely to feel like a restrictive diet and be dropped. It can be a way of life.
Good French, Spanish and Italian food for example, relies on fresh fruit, vegetables, nuts and oils, a little meat and fish, and live cheese and yogurt rather than piles of special K, cornflakes, frosties, rice, chips, pizza, pasta in giant bowls as a main course, bread, toast with butter and jam, extra high sugar bars etc.
Look at the people at people from these countries at continental airports and then compare them to the English. They are physically very different but probably not feeling deprived, because their food is good.