When we eat sugar, it triggers our brains and stomachs. In our brains, it alerts the dopamine pathway, emitting a pleasurable response. It also releases hunger hormones, such as leptin, which signal that food is reaching our stomachs and we won’t start to feel as hungry. When sugar reaches our stomachs, insulin is released from the pancreas, taking glucose into the blood to be used as a fuel source, or stored as fat in the event of excess sugar.
The problem with artificial sweeteners, however, is that they don’t contain any calories. How can this be? Artificial sweeteners contain a strong sweetness, up to 300x sweeter than sugar! However, they do not contain any calories because they’re not metabolized through the same biochemical pathways as sugar to yield energy in the form of ATP. Therefore, when artificial sweeteners hit our taste receptors on our tongue, they signal to our brain that a load of sugar is about to hit our bodies. But, when the AS gets to our stomach, there is nothing to metabolize for energy and this may leave us hungrier and in desire of more calories than if we just ate the sugary food itself.
In one study done in Brazil, rats were fed plain yogurt either sweetened with aspartame, saccharin, or sugar, as well as their normal rat chow, for 12 weeks. After 12 weeks, addition of either saccharin or aspartame to the yogurt resulted in increased weight gain compared to the addition of sucrose (sugar), EVEN THOUGH total caloric intake was not significantly different among groups. Total caloric intake did not vary because the AS group consumed more chow, due to the possibility that AS may adversely affect appetite control mechanisms, as I discussed before.
In the San Antonio Heart Study, examining 3,682 adults over a 7-8 year period, those who drank AS beverages had higher BMIs at the follow-up, with dose-dependence on the amount of consumption. This means that those who consumed more AS beverages had higher BMIs. In the Nurses’ Health Study, saccharin use was also associated with eight-year weight gain. Saccharin is also a controversial AS: it was originally placed on the US national toxicology report because a study found that it caused bladder cancer in rats. However, it was delisted in 2000 because the mechanism in the rats was not relevant to humans and there wasn't any other clear evidence.
Aspartame, another artificial sweetener, contains phenylalanine and large doses of this amino acid can lower levels of serotonin, a neurotransmitter that influences satiety. Decreased serotonin levels reduce feelings of satiety and this can lead to overeating, weight gain, and subsequent consequences such as obesity.
Overall, what’s the verdict on artificial sweeteners? I would proceed with caution. I don't think they’re a good alternative to all of the sugar bombarding our daily lives. I think the more important issue at hand to target is the fact that Americans are addicted to sweetness and we need to find ways to remedy this with wholesome natural foods such as fruit, and a diet full of healthful fat for satiety. I think the Yale Journal of Biology and Medicine sums up the predicament perfectly:
“Increasing evidence suggests that artificial sweeteners do not activate the food reward pathways in the same fashion as natural sweeteners... Lastly, artificial sweeteners, precisely because they are sweet, encourage sugar craving and sugar dependence... Unsweetening the world's diet [not through artificial sweeteners, but through whole foods such as fruit] may be the key to reversing the obesity epidemic.”