ARTICLE: Brain activity and connectivity changes in response to nutritive natural sugars, non-nutritive natural sugar replacements and artificial sweeteners
AUTHORS: Sze-Yen Tan and Robin M. Tucker
SOURCE: Nutrients 2019, 11(1): 94. Published 2019 Jan 5 doi:10.3390/nu11010094
SUMMARY BY: Robyn Flipse, MS, MA, RDN
There is abundant evidence that food selection and dietary intake have a major impact on nutritional status and health. It is also widely recognized that flavor has a primary influence over food choice, and that taste is an essential component of flavor. What is not well understood is which taste mechanisms and perceptions are most predictive of dietary intake. If this were known, it would allow the development of a tool to assess taste preferences and identify those who could be at increased risk of chronic disease due to their food intake behavior.
Since sugar intake has been proposed as a possible cause of the rising prevalence of global obesity, several studies have investigated whether sweet taste triggers food-seeking behaviors and increased energy intake, but a systematic review summarizing the findings has not been done. The purpose of this review was to determine if the available psychophysical tests for sweet taste were associated with dietary intake and, if possible, to determine which test is the most closely associated with dietary intake.
Taste testing can be measured using stimulus detection, intensity thresholds, and hedonic evaluation. Stimulus detection involves determining the absolute minimum concentration of a stimulus that can be detected or recognized among several that have the same stimulus in different concentrations. It is also described as the ability to detect the correct stimulus from several samples in which only one contains the stimulus of interest. Intensity measurements involve rating the intensity of a sample that contains the stimulus and answering a hedonic question about how much the stimulus is liked when comparing two or more at different concentrations. Each of these tests is independent of the others and provides separate but complementary information about how the stimulus is detected and perceived. These tests can help determine specific taste sensitivities in individuals, but do not reflect the complex sensory experiences provided by foods and beverages.
A systematic literature search was conducted of studies that collected at least one psychophysical measure of sweet taste and reported some sort of dietary intake measure. Studies were included that recruited healthy individuals with no restriction on adiposity, but excluded populations that had diabetes, alcoholism, or eating disorders; known changes in chemosensory function, such as gastric bypass patients; were pregnant; or were smokers. For this review, 3206 studies were identified and 17 included.
The selected studies were placed into three categories based on the psychophysical methods utilized: (1) sensitivity measurements consisting of detection and recognition thresholds (n=6), (2) intensity measures (n=8), and (3) hedonic evaluations with liking or preference questions (n=13).
The six studies that examined relationships between taste sensitivity and dietary intake varied in terms of the stimuli used (glucose vs sucrose vs non-nutritive sweeteners), the ranges of concentrations tested, and the dietary assessment employed. Only two observed significant associations between sweet taste thresholds and dietary intake, and neither of these studies used non-nutritive sweeteners.
The eight studies that examined the relationship between measures of sweet taste intensity and dietary intake also varied in stimuli used and concentrations tested. Only two observed significant relationships and they had contradicting results. One found negative associations between intensity ratings for glucose stimulus and sweet food intake, total energy, and carbohydrates, including starch, sugar, and fructose. The other found that intensity ratings for Rebaudioside A and sucralose, two non-nutritive sweeteners, were positively associated with mean total energy intake.
Of the 13 papers examined for relationships between hedonic evaluations and dietary intake, all but one used sucrose as a stimuli. Studies utilizing sucrose did so at different concentrations. Five of these studies also classified participants as sweet “likers” or “dislikers” since this phenotype has been associated with different hedonic responses to sweetness and could influence findings. Among those five papers, three observed relationships between sweet “liker” status and greater energy intake from sugar-sweetened beverages and refined and total sugars.
Among the remaining eight studies that did not classify sweet likers or dislikers, associations between hedonic responses and dietary intake were observed in five, although each reported different methods to measure dietary intake. Both positive and negative associations were found between preferred sweetness concentrations and total energy intake, carbohydrate intake, percent sweet calories consumed, refined and total sugars, and frequency of carbohydrate-rich food selections in these studies.
This review lends supports to the view that measuring sensitivity, intensity, and hedonic responses provides distinct but complementary information about the taste sensations experienced by an individual. It found hedonic ratings had the greatest ability to correlate with dietary intake, especially when sweet “likers” were analyzed separately, and that no one method of dietary assessment was superior in identifying taste-diet relationships.
The authors propose the discrepancies reported in these papers were likely due to the differences in the taste stimuli and concentrations that were used. They were further confounded by the fact different nutritive sugars have different potencies at the same concentration and the human sweet receptor responds to many compounds besides mono- and disaccharides, including amino acids, proteins, and non-nutritive sweeteners.
Only a small proportion of the studies reviewed reported significant associations between taste sensitivity, intensity, and hedonics with dietary intake. Of those that reported significant associations, sensitivity and intensity measurements were negatively associated with intake, while liking and preferred concentration measurements (hedonics) were positively associated with intake. Further research is needed before a standardized method of taste sensitivity and dietary intake can be considered.
POINTS TO CONSIDER
Robyn Flipse, MS, MA, RDN is a registered dietitian, cultural anthropologist and scientific advisor to the Calorie Control Council, whose 30+ year career includes maintaining a busy nutrition counseling practice, teaching food and nutrition courses at the university level, and authoring 2 popular diet books and numerous articles and blogs on health and fitness. Her ability to make sense out of confusing and sometimes controversial nutrition news has made her a frequent guest on major media outlets, including CNBC, FOX News and USA Today. Her passion is communicating practical nutrition information that empowers people to make the best food decisions they can in their everyday diets.Reach her on Twitter @EverydayRD and check out her blog The Everyday RD.