Diet sodas trick your saliva: Study reveals how sweetened drinks impact oral enzymes and insulin levels

By Dr. Priyom Bose, Ph.D.Sep 5 2023Reviewed by Benedette Cuffari, M.Sc.

A recent Food Research International study determines whether the intake of sweetened beverages affects the levels of salivary insulin, aspartame, alpha-amylase (AMI), and total protein (TP).

Study: Effect of sweetened beverages intake on salivary aspartame, insulin and alpha-amylase levels: A single-blind study. Image Credit: MamaMiaPL / Shutterstock.com

Background

The global consumption of foods and beverages containing sweeteners is high, as many individuals innately prefer sweet taste. In fact, many people have replaced sugar with sweeteners due to their reduced caloric density as compared to sucrose. 

The World Health Organization (WHO) advises that non-sugar sweeteners should not be used solely to control weight, as there is a lack of evidence regarding their benefits for long-term use. Some studies have indicated that sweetener use causes the development of glucose intolerance in obese individuals. Thus, more research is needed to understand whether long-term sweetener use affects metabolism or causes adverse effects.

Common sweeteners

Common sweeteners added in foods and beverages include aspartame, cyclamate, and acesulfame potassium, all of which are synthetic products. Among these synthetic sweeteners, aspartame is the most commercialized product globally. The main components of aspartame are aspartate and phenylalanine, which are metabolized in the intestinal lumen.

Sodium cyclamate is supplemented with other sweeteners due to its residual taste. Although some countries have banned the use of sodium cyclamate, others have permitted its use as a food additive at approved levels. Acesulfame potassium is a synthetic compound with high sweetening power; however, this substance is not metabolized.

In humans, the digestion of sugars starts in the oral cavity due to the presence of salivary alpha-amylase. The sweet taste is perceived through the stimulation of taste buds present in the oral cavity.

Subsequently, the sweet taste triggers many physiological processes, including increased salivary secretion and insulin secretion. Insulin secretion occurs in various phases, including the cephalic phase, which is associated with an early increase in insulin levels in blood upon oral exposure to sweetness. 

It has been hypothesized that low/no-calorie sweeteners trigger sweet-tasting receptors, which leads to insulin release, reduced blood glucose levels, and increased appetite. Salivary AMI is directly correlated with carbohydrate absorption and the glycemic index.

It is important to understand the level of secretion of salivary enzymes and hormones in response to artificial sweetener ingestion, as this will reflect digestion and carbohydrate metabolism.

About the study

The current single-blinded randomized trial investigates the levels of salivary aspartame, total protein, salivary AMI, and insulin levels after the ingestion of sweetened drinks. 

A total of 15 healthy, normoglycemic young adults were included in the study cohort, 11 of whom were women. All candidates had healthy oral conditions, and none reported any underlying chronic conditions such as diabetes, hypertension, and cancer. All participants were asked to stop the intake of sweeteners in their diets one week before the commencement of the trial and during the trial.

A total of five sessions were attended by participants, during which they were asked to drink 200 mL of test drinks at each session. The five different test drinks used in this study were diet soft drinks, regular soft drinks, mineral water with sweeteners, the same products with low sucrose content of 0.02 g/mL, and water.

At every session, participants visited the laboratory without consuming food or drinks until the end of all saliva collections. Five saliva samples were collected in each session, including before ingestion of the test drink, 15 minutes after ingestion of the test drink, after 30 minutes, after 60 minutes, and after 120 minutes, which were referred to as T0, T1, T2, T3, and T4, respectively.

Study findings

Aspartame was detected in the saliva of individuals who drank diet soft drinks and water with sweeteners. A steady rise in aspartame was observed at T4, thus indicating that aspartame remains in the digestive tract for a prolonged period.

Although both the water with sweetener test drink and diet soft drink contained the same artificial sweetener concentrations, a greater aspartame level was recorded for those who drank the diet soft drink. 

A correlation between aspartame concentration and insulin levels was observed only for diet soft drink intake and not for sweetened water test-drink. The lack of change in insulin levels after the consumption of sweetened water implies a faster metabolization as compared to diet soft drinks. Importantly, all soft drinks had a lower pH than the sweetened water test drink, which could stimulate other physiological processes than sweet taste. 

Insulin levels rose after the consumption of both regular and diet soft drinks. Although initially, both regular and diet soft drinks exhibited similar rises in insulin levels, the regular soft drink led to a greater rise between T2 and T3 and subsequent decline between T3 and T4. A similar trend was observed for glucose tolerance.

The sucrose solution did not lead to any change in insulin levels over 120 minutes and remained stable over time. No change in alpha-amylase activity was observed after ingestion of sweet beverages.

Conclusions

A greater level of salivary aspartame was observed after the ingestion of diet soft drinks than water with sweeteners. Furthermore, higher salivary insulin levels were recorded after ingesting regular and diet soft drinks compared to the control and low sucrose content drinks.