A small but compelling new study out of Yale University is suggesting low-calorie sweeteners can disrupt metabolic processes, but only when consumed with carbohydrates. The research presents a conclusion that aims to reconcile previously conflicting studies investigating links between low-calorie sweeteners and the development of metabolic disorders such as diabetes.
Despite having a consistent presence in human diets for decades, low-calorie sweeteners are still the source of great debate in scientific literature. A significant volume of epidemiological research has suggested low-calorie sweetener consumption leads to higher rates of obesity and metabolic disease, however, there are also rigorous studies concluding they can lead to weight loss and lower BMI.
Resolving this ongoing debate requires understanding how low-calorie sweeteners could mechanistically be leading to obesity or metabolic impairments. One of the more compelling explanations offered has been dubbed the ‘uncoupling hypothesis,’ and it's perhaps best encapsulated in a 2013 journal article by Purdue University behavioural neuroscientist Susan Swithers.
This hypothesis suggests when sweet taste is uncoupled from the subsequent energy the body expects from these foods, general metabolic processes are disrupted. This can hypothetically include consequences such as interference with normal hunger signals, or disruptions to glucose metabolism that are triggered by sweet taste receptors. Essentially, the hypothesis assumes a kind of metabolic confusion occurs when a sweet taste is not followed up with the expected caloric energy load.
The new Yale University research set out to test the uncoupling hypothesis in humans, recruiting 45 adult subjects and randomly administering three different beverages: a sugar sweetened drink, an artificially sweetened drink containing sucralose, and an artificially sweetened drink that also contained a carbohydrate called maltodextrin. As well as conducting blood tests measuring glucose tolerance, the subjects’ brain responses to the drinks were imaged using fMRI.
“The subjects had seven low-calorie drinks, each containing the equivalent of two packages of Splenda, over two weeks,” explains senior author on the study, Dana Small. “When the drink was consumed with just the low-calorie sweetener, no changes were observed; however, when this same amount of low-calorie sweetener was consumed with a carbohydrate added to the drink, sugar metabolism and brain response to sugar became impaired.”
If the uncoupling hypothesis were true the researchers should have observed metabolic dysfunction developing in just the group drinking the low-calorie sweetener drink, as that was the only group of the three who were consuming a beverage with a discordance between a sweet taste and subsequent caloric load. However, this was not what the study discovered. Instead, the low-calorie drink group showed no acute changes to glucose metabolism, despite being decoupled from calories.
The implication of the study is low-calorie sweeteners only cause metabolic disruptions in the presence of carbohydrates. Small suggests this may somewhat explain the inconsistencies in epidemiological studies on the effects of low-calorie sweeteners, and recommends diet drinks should be not consumed with meals.
“This is an important information, particularly for people with diabetes who shouldn’t consume sugars,” says Small. “The bottom line is that, at least in small quantities, individuals can safely drink a diet soda, but they shouldn’t add French fries.”
The study does have a significant number of caveats leading to a degree of caution in how these results can be interpreted. Alongside the very small cohort, the study only focused on one artificial sweetener, sucralose. While sucralose is certainly one of the most frequently used artificial sweeteners, it is unclear how applicable these results are to other sweeteners. The study does hypothesize the results may be transferable to other artificial sweeteners, but Sarah Berry, from King’s College London, is not so sure.
“… these results cannot be generalised to all sweeteners because the main types of different sweeteners commonly incorporated into our foods and drinks (including sucralose, aspartame, saccharin and Ace-K) are metabolised differently and therefore will have different health effects,” says Berry, who did not work on this new study.
Berry does point out the results are interesting, and the study design is robust, so this is undeniably compelling and relevant research. Further work is certainly necessary to validate these findings but Berry suggests the study does serve as a useful reminder that the safest alternative to sugar and sugary drinks is not artificial sweeteners but simply removing sugar and its alternatives from a diet altogether.
“As with all foods and drinks, occasional consumption of diet drinks or foods containing sweeteners is not going to be harmful to health,” says Berry. “However, this research supports previous findings to suggest that we should not see diet drinks as a healthy alternative to sugar sweetened drinks.”
The new study was published in the journal Cell Metabolism.
Source: Yale University