Do Artificial Sweeteners Promote Weight Gain?
The biggest reason to avoid artificial sweeteners is not related to their potential toxicity, but is rather related to their purpose. The only reason to use a zero-calorie sweetener is to avoid the excess calories one would ingest through the use of a real sugar, in an effort to reduce total daily caloric intake. While this goal is achieved in the very short-term, all evidence suggests the use of artificial sweeteners perpetually leads to increased daily caloric intake.
Research shows that when we consume an artificial sweetener, it triggers the first food reward pathway (sensory) but not the second (postingestive). Because we only partially trigger the food reward pathway, we are left feeling unsatisfied with the neurological result of increased hunger, particularly for the sweet food our body thought it was going to receive. Glucose, on the other hand, triggers both food-reward pathways and suppresses hunger signals in our hypothalamus.
The danger associated with partially triggering our food reward pathways goes even further. When the brain is habitually tricked, it changes its expectations to match the new information, which says that sometimes food is not as satisfying as our mouth thought it would be. This leads to a diminished sense of reward from eating, which means it takes more food or drink to reach the same level of neurological satiety, or fullness. Furthermore, because the artificial sweeteners are so sweet, they influence our taste for food and we begin to crave sugar more than normal.
Different than the neurological response to artificial sweeteners is the psychological one. When we consume foods and drinks with artificial sweeteners, we are less likely to make healthy choices with the rest of our meal because we feel we can ‘splurge’ a little. More often than not, the result of this splurging is more calories than would have been ingested had we consumed sugar but made otherwise healthy choices.
When combined with the neurological effects, consumption of artificial sweeteners consistently leads to increased caloric intake, not reduced. It is not a statistical fallacy that the body mass index (BMI) of habitual drinkers of artificially sweetened beverages raises more over time, and is consistently higher, than those who do not.
There is also evidence that certain artificial sweeteners, such as saccharin, induce cephalic phase insulin response, meaning that they cause the insulin level in our blood rises. The theory goes that when insulin rises but glucose does not, the result is actually a falling level of blood glucose which would then stimulate hunger.
This is not very likely to produce increased appetite, however, as other hormones are primarily responsible for our hunger signals and the effect insulin does have on hunger is depressive, not stimulative. More likely the increased hunger is due to the neurological and psychological reasons mentioned above. That being said, it is never a good idea to mess with hormones, and there very well may be other deleterious effects to raising insulin, such as increased risk of diabetes or metabolic syndrome.