Abstract: Increased energy consumption, especially increased consumption of sweet energy-dense food, is thought to be one of the main contributors to the escalating rates in overweight individuals and obesity globally. The individual’s ability to detect or sense sweetness in the oral cavity is thought to be one of many factors influencing food acceptance, and therefore, taste may play an essential role in modulating food acceptance and/or energy intake. Emerging evidence now suggests that the sweet taste signaling mechanisms identified in the oral cavity also operate in the gastrointestinal system and may influence the development of satiety. Understanding the individual differences in detecting sweetness in both the oral and gastrointestinal system towards both caloric sugar and high intensity sweetener and the functional role of the sweet taste system may be important in understanding the reasons for excess energy intake. This review will summarize evidence of possible associations between the sweet taste mechanisms within the oral cavity, gastrointestinal tract and the brain systems towards both caloric sugar and high intensity sweetener and sweet taste function, which may influence satiation, satiety and, perhaps, predisposition to being overweight and obesity.
Alex’s Notes: The sweet taste response argument against sugar and artificial sweeteners is an interesting one. Although it is clear that artificial sweeteners do assist in weight loss, many still argue that sweetness without the associated energy may actually increase appetite and encourage consumption of other foods. The review at hand aims to discuss the possible associations between sweet taste and satiation and satiety.
So what is taste? Quite simply, it is the activation of taste receptor cells (TRC) within the taste buds on the surface of the tongue. It is one of our five traditional senses, the others being sight, hearing, smell, and touch, and has strong evolutionary implications, as the authors write,
“The human taste system is now widely accepted to include five taste qualities: sweet, salty, bitter, sour, and umami . From an evolutionary perspective, it is postulated that the human taste system functions as a gatekeeper of the digestive system to ensure that we consume essential nutrients for survival and functioning, while rejecting potentially harmful or toxic foods . For example, a salty taste quality signals the presence of either sodium or minerals; umami indicates the presence of proteins; excessive sour taste signals spoiled food; bitter taste quality often indicates the presence of poisons; and sweet taste indicates the presence of carbohydrates or energy in the food [20,21].”
Thus, taste may play an essential role in modulating food acceptance and energy intake. Interestingly, the sweet TRCs are termed the “Venus fly trap domain” which senses a large variety of sweet substances ranging from sugars to sweet amino acids like glycine to artificial sweeteners. Once these suckers are activated, they transmit the sweet sensation to both the brain and the gut. But the fun doesn’t stop in the mouth, as it has become increasingly clear that sweet TRCs also exist in the small intestine and pancreas (but we can only consciously perceive sweetness from oral stimulation).
So we can see how this may lead to trouble with artificial sweeteners and how the idea of them messing with our food regulation system came to be. Some studies do show evidence that artificial sweeteners may bind to the intestinal receptors and produce similar downstream actions as sugar, but most in vivo studies fail to confirm that the satiety response is similar. For instance, Ace-K, stevia, sucralose, and D-tryptophan did not evoke a release of GLP-1 or GIP in rats despite being given at concentrations 1000-fold greater than that found in diet sodas. This has also been demonstrated in humans with sucralose.
Regardless of the hormonal response, we must also look to the brain. The authors as the simple question,
“Does one feel the same level of satisfaction and pleasure upon ingesting artificially sweetened food as compared to sugar or does appetite increase or satiety decrease upon ingestion of foods containing HIS [high-intensity sweeteners].”
This question is critical, as the body’s food reward system may place a center-stage role in the regulation of eating behavior. Indeed, a couple studies using MRI to analyze the brain during sugar and artificial sweetener ingestion found interesting results. One such study found that both caloric sugars and zero-calorie sweeteners were able to activate the primary taste pathway in the brain, but only the caloric sugars were able to stimulate the brain’s reward pathway. This was confirmed a few years later, suggesting that our brains may prefer caloric sweeteners over zero-calorie sweeteners, but raising the question of whether differences exist between habitual and non-habitual consumers. A recent study found that diet soda drinkers demonstrated greater overall activation to sweet taste in several reward processing brain regions to both caloric and artificial sugar compared to a non-diet soda drinker group. Within the diet soda drinkers, there was no difference in the brain’s response to both caloric sugar and artificial sweeteners.
So then what about the sweet taste itself? We all know people who can take their coffee black, while others will add truckloads of sugar to it, and these variations in sweet taste sensitivity are likely a product of both genetic and environmental factors. In fact, taste detection thresholds for sugar were found to be significantly lower in obese females after 12 weeks of dieting. Amusingly, this improvement in sweet detection went hand-in-hand with drops in leptin. Nonetheless, other studies have found no significant associations between sweet taste intensity and dietary intake of sweeteners.
That lack of an association should not come as a surprise.
“A study by Rolls et al.  investigated the effects of sucrose and aspartame-sweetened (HIS) gelatines on appetite ratings and subsequent food intake using a cross-over design. Participants were instructed to consume either a high-calorie gelatine (sweetened with sucrose) or a lower-calorie version (sweetened with aspartame) . Interestingly, there were no significant differences found between rated sensory-specific satiety, hunger, fullness and desire to eat following consumption of both versions of the gelatines . Similarly, another study by Rolls et al.  further investigated if there were differences in terms of short-term appetite and food intake following consumption of drinks sweetened with either sucrose or aspartame (HIS) in men. The results suggest that there were no differences between consuming a sugar-sweetened beverage or an aspartame-sweetened (HIS) beverage in short-term hunger ratings and subsequent food intake .”
“Two other studies examining the effects of sweet taste on short-term hunger were conducted among habitual high and low consumers of beverages sweetened with HIS [112,113]. It was found that the effects of the sweet and non-sweet lunches on short-term hunger differed significantly in terms of individuals’ habitual consumption of sweet low-calorie drinks (i.e., an increase in short-term appetite ratings in response to sweet taste was demonstrated among low consumers of beverages sweetened with HIS, whereas high consumers did not show this increase) [112,113].”
What the above should make perfectly clear is that habitually consuming sweeteners – be them artificial or real – will increase your ability to feel satisfied from their consumption. In this light, although counter-intuitive, it actually makes sense to consume stevia and co. in order to bolster your defenses against excess hunger from sweet foods.
Too long, didn’t read
People are always looking for a scape-goat to demonize, commonly ignoring that current health problems like obesity are the result of multiple factors. One area receiving the spot-light is increased energy intake from sweet & energy-dense foods. The popular solution is to substitute the sugars with artificial sweeteners, in order to maintain the sweet joy while reducing calories. However, the role of sweet taste in energy intake and appetite regulation is controversial.
The reward pathways of non-habitual consumers of artificial sweeteners are generally not activated when consuming these products as opposed to sugar, suggesting that the artificial sweetness may impair and adapt the brain’s capability to detect or sense nutrients. However, it is uncertain why the brain will adapt to sense these zero-calorie products as nutrients. Overall, the idea of sweet taste in energy intake is largely hypothetical, but is nonetheless an interesting model and potential factor to understand being overweight and obesity.