For those of us with a sweet tooth, an extra helping of dessert can seem irresistible.
Nutritionists and doctors though, do not dismiss this as an arbitrary craving. In fact, many have hypothesized that a key cause behind these cravings is a diminished ability to taste sweet compounds. A new study by Prof. Robin Dando, food science, hopes to shed light on this mechanism and could have serious implications on how obesity is managed.
“Several research projects in the past have found that taste is weakened in the obese. But we don’t know if this even matters. The motivation behind the project was to ask ‘if taste is weaker, does this affect what people actually choose to consume?’” Dando said. “We had people come to our sensory evaluation facility on four separate days and run a series of taste tests with a blocker of taste function applied at different levels.”
During the experiment, participants consumed tea containing different levels of the herb Gymnema sylvestre. Native to the tropical forests of southern India, the herb is known to temporarily suppress sweet receptors. Exposure to the herb for 60 seconds left the participants with dulled sweet receptors for nearly 45 minutes.
Each participant was then given an unsweetened drink and two solutions, labelled ‘more sweet,’ containing plenty of sucrose and ‘less sweet,’ containing no sucrose. As participants sipped their drink, they adjusted it to their desired sweetness by slowly adding the two additional solutions.
“We found that people who taste less effectively select stronger tasting and higher calorie foods,” Dando said.
In fact, Dando observed that those with dulled receptors added between 8 to 12 percent sucrose in their drink, comparable to ratios found in soft drinks. Consequently, Dando hypothesized that for those with a 20 percent reduction in their sweet-tasting abilities, an extra teaspoon of sugar would be required to compensate.
Referring to whether such an effect was observable for other tastes, “It is possible, however we didn’t see it in our testing,” Dando said.
According to Dando, the study suggests that diminished sweet tasting abilities and its corresponding effects on eating habits could be a key factor in causing obesity. Scientists have long believed in such a connection, and though Dando partly validates this hypothesis, the authors of the study emphasize that empirical testing of this connection still needs to be carried out.
“This project wasn’t really about the food industry, but could mean that taste dysfunction is contributing to obesity. Really this just tells us that we have to be mindful of what we’re eating, and if we’re drifting towards bad eating habits,” Dando said.
Caffeine Affects Sweet Tastes Too
In a separate study, Dando noticed that caffeine also affects our perception of sweetness. Participants were separated into two groups and given decaffeinated coffee; one group had caffeine re-added to their drinks. Both groups were then made to taste various bitter, sour, salty, umami and sweet compounds. The group with added caffeine reported that their coffee and subsequent sucrose solutions were less sweet, while there was no difference in the perception of other tastes.
According to the study, this is due to caffeine’s ability to block adenosine receptors. Adenosine plays a crucial role in energy transfer during biochemical processes.
“[In a previous study involving mice], we blocked adenosine receptors and saw smaller [sweet-evoked] calcium signals in their taste buds,” Dando said.
By not allowing adenosine to bind to its receptors, caffeine prevents neural activity from slowing down and promotes wakefulness. But a diminished ability to taste sweet compounds may be an important side effect of this process.