Asked by: Christoffer Soderberg, by email
Because we didn’t evolve in a world full of sugar. For our ancestors in Africa, sugar from ripe fruit or a precious bee hive would have been a rare treat, and well worth prizing for its energy value. Those who liked the taste and ate the sugar might have gained an advantage and so passed on their ‘sweet tooth’ through their genes.
Today sugar is in nearly all processed foods as well as readily available sweets, jams, biscuits and fizzy drinks. Sugar is unhealthy because it causes an increase in the hormone insulin in the bloodstream. This in turn causes the body to switch over from burning fats to burning sugar and sending the fat into storage. So eating sugar makes you fat. In large quantities it disturbs the natural role of insulin, ultimately leading to diabetes. Even worse, we quickly adapt to the taste of sugar and need more to get the same pleasure. So we can become addicted in a way that was simply impossible for our ancestors.