ARTICLE: Decreasing the Consumption of Foods with Sugar Increases Their reinforcing Value: A Potential Barrier for Dietary Behavior Change
AUTHORS: Flack KD, Ufholz K, Casperson S, Jahns L, Johnson L, Roemmich J
SOURCE: Journal of the Academy of Nutrition and Dietetics.2019;119(7):1099-1107
SUMMARY BY: Robyn Flipse, MS, MA, RDN
The preference for sweet-tasting foods is considered an evolutionarily conserved trait. This can be explained, in part, by the fact the hedonic value of sweet taste is mediated by the opioid system and that sugar can increase extracellular dopamine in the area of the brain involved with motivation, similar to reinforcers like alcohol. It is also known that the reinforcing value of foods is a prime driver of eating choices and energy intake, all of which may make it harder to reduce the consumption of foods high in added sugars than previously understood.
The Dietary Guidelines for Americans have recommended reducing added sugars in the diet since their first publication in 1980, yet consumption by Americans continues to exceed recommended levels. Flack, et.al., propose that the difficulty in reducing the intake of added sugars may be due to the increase in their reinforcing value when their consumption falls below a baseline level, which based on a theory called the “Disequilibrium Approach.” More specifically, in the “response deficit” form of disequilibrium, when access falls below the baseline amount it results in an increase in reinforcement. If these researchers are correct, the reinforcing value of foods high in added sugars would be a mechanistic barrier to the behavior changes needed to reduce their consumption.
This study investigated the effect of adhering to a diet low in added sugar on the reinforcing value of foods high in added sugars relative to foods lower in added sugars (termed “relative reinforcing value of sugars” or RRVsugars ), while keeping total energy intake consistent. It was hypothesized that the RRVsugars would increase after a one week period of restriction of foods high in added sugars, with obese people showing a greater increase in RRVsugars than normal weight subjects.
After screening 100 potential participants, the final sample included 42 people (37 females) who all reported habitually consuming more than 10% of their daily calories from added sugars. They were between 18 and 39 years of age, with 23 classified as normal weight (BMI <25) and 19 as obese (BMI >30). A pre-post study design was used, including food frequency questionnaires and resting metabolic rate, and pretreatment RRVsugars was measured before the 7-day dietary intervention which reduced intake of sugar below 10% and on the final day of the dietary intervention. All participants were blinded to the purpose of the study and were strictly instructed not to consume any foods or beverages (other than water and black tea or coffee) outside of what was given to them during the controlled feeding intervention period.
Each participant’s diet was designed to keep them in energy balance and meet the average macronutrient distribution from the National Health and Nutrition Examination Survey “What We Eat in America 2011-2012” survey for adults (approximately 16% protein, 51% carbohydrate, 33%fat). The diets included 2.5% to 4% of total energy from added sugars. Foods high in natural sugars (approximately 4% of total energy) and nonnutritive sweeteners were deliberately limited due to their sweet taste similar to foods high in added sugars.
Before the intervention, participants completed taste tests of foods both high and low in added sugars and rated each one on overall liking using an 11-point scale. Their highest-liked food in each category was used to assess their RRVsugars by evaluating the amount of operant responding (mouse button presses) they performed to gain access to their favorite food high in added sugars relative to their favorite food low in sugar.
The baseline RRVsugars did not differ across BMI, but there was a significant increase of 32.7% in RRVsugars after the dietary intervention in both normal weight and obese participants. This finding differs from previous work showing obese subjects having a greater RRV of food and energy intake than non-obese. Satiety scores assessed prior to each RRV task did not affect the results, suggesting the participants were responding for food during the RRV task out of a motivational drive to eat, not hunger.
The study found the reinforcing value of a behavior (e.g., eating sweet-tasting foods such as those high in added sugars) is increased when the rate of that behavior is decreased below the baseline rate, which has strong theoretical underpinnings in Disequilibrium Approach Theory. The authors state, “Great and abrupt energy restriction produces obsessive preoccupations with sweet foods, increased hedonic ratings of food, and an increased rewarding value of food.” Consequently, restricting foods high in added sugars could have the unintended consequence of increasing the RRV of foods these foods making it more difficult to adhere to dietary guidance to lower their intake.
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.