Sweet Tooth: Nature or Nurture? Role of Long-term Dietary Sweetness Exposure on Sweetness Preferences

In recent years, social pressure has been exerted towards lowering sugar and sweetness levels in foods, with the aim of decreasing the sweetness preference of the general population. However, the resilience/flexibility of sweetness preferences and the impact on energy intake is a fundamental knowledge gap. Recent, relatively long-term studies limited to no more than 3 months did not find a relationship between sweetness exposure and sweetness preferences. Therefore, a longer-term systematic investigation is necessary to objectively evaluate whether sweetness preferences can be altered via varying the sweetness exposure and whether it can affect other outcomes, such as perceived taste intensity, food intake, body weight, body composition, glucose homeostasis and sweet liker type. The study sample will consist of 180 subjects. Enrolled participants will be distributed into three intervention groups; regular dietary sweetness exposure (n=60); low dietary sweetness exposure (n=60); and high dietary sweetness exposure (n =60). The intervention is semi-controlled for a period of six months. Preference and perceived taste intensity of a series of familiar and unfamiliar foods will be assessed at baseline (Day 0), during the intervention (Month 1, Month 3, Month 6) and in the follow-up period (Month 7, Month 10). Furthermore, outcomes such as observed food choice and intake during a test meal, reported food preferences, reported food cravings, sweet-liker type, glucose homeostasis, body weight, body composition and biomarkers related to diabetes and cardiovascular disease will be assessed as well.

Evidence supporting sweetness preference alterations via variations in dietary sweetness exposure is limited. Most studies investigating this focused only on specific sweet elements in the diet, (e.g. beverages; mono- and disaccharides; high-energy dense snacks) instead of sweetness in the diet as a whole. Furthermore, there is no clear evidence about the relation between dietary sweetness exposure and weight gain. Therefore, longer term, sufficiently-powered studies with a 'whole diet' approach are needed to address the question whether sweet preferences can be altered (suppressed or stimulated) by variations in sweetness exposure. It is important to answer this question so that dietary recommendations can be scientifically tailored accordingly. The present study will provide breakthrough evidence about the flexibility/adaptability of sweetness preferences, in terms of effect sizes and direction, duration of effects, and impact on dietary intake, glucose homeostasis and body weight. This information is particularly relevant for product development by food industries in the context of reformulation strategies, and for governments to base their dietary guidelines upon.

The primary study objective is to assess the effect of a 6-month low, regular and high dietary sweetness exposure on sweetness preference in a series of familiar and unfamiliar foods. Preference will be assessed in both familiar and unfamiliar foods since, preferences in familiar, commonly eaten foods might by harder to change compared to those for unfamiliar foods, because there is no consumer-expected sweetness level associated with unfamiliar foods. The secondary objective is to assess the effect of a 6-month low, regular and high dietary sweetness exposure on sweetness perception, food choice and intake during a test meal, dietary taste patterns, taste preferences, food cravings, sweet-liker type, glucose homeostasis, biomarkers related to cardiovascular disease (CVD) and diabetes, body weight and body composition. Participants will be matched on age, gender, BMI and sweet liker status and randomly allocated to one of the three intervention arms: (1) regular dietary sweetness exposure (25-30 percent daily energy from sweet foods) (control) (n=60); (2) low dietary sweetness exposure (10-15 percent daily energy from sweet foods) (n=60); and (3) high dietary sweetness exposure (40-45 percent daily energy from sweet foods) (n=60). The intervention is semi-controlled, meaning that 50 percent of the foods will be provided to participants. Foods are offered ad libitum, on a weekly basis and macronutrient composition of the offered foods is similar in energy and macronutrient composition, that is fat, protein, carbohydrates and fibres, but different in sweetness. New methodology of our group enables us to assess sweetness exposure within a diet, by profiling foods based on six taste clusters (neutral; salt, umami \& fat; sweet and fat; sweet and sour; fat; bitter).

Preference and perceived taste intensity will be assessed during hedonic and sensory evaluation of eight foods; three sweet familiar, three sweet unfamiliar and two salty familiar ones. Foods are solid, semi-solid and liquid. Furthermore, observed food choice and intake during test meals, reported food preferences, reported food cravings, sweet-liker type, glucose homeostasis, body weight, body composition and biomarkers related to diabetes and cardiovascular disease will be assessed. Outcomes will be assessed several times; at baseline (Month 0), during the intervention Month 1, Month 3, Month 6 and in the follow up period (Month 7, Month 10). Compliance will be assessed with 24-hour urine sample and dietary assessment methods (24-hour recalls).

Eligibility Criteria:
Inclusion Criteria:

* Good general health;
* Age 18 - 65 years;
* Body mass index 18.5 - 30 kg/m2;
* Having normal taste ability (assessed with taste strips test);
* Having normal glucose levels in blood (assessed with a finger prick);
* Able to provide informed consent;
* Able to attend Wageningen University, as required for testing.

Exclusion Criteria:

* Diagnosed with diabetes currently or in the past;
* Has been notified to have insulin resistance currently or in the past;
* Diagnosed with endocrine diseases or other metabolic diseases that influence metabolism;
* Diagnosed with eating disorders;
* Diagnosed with taste or smell disorder;
* Pregnant or lactating during the study intervention;
* Gain or loss of more than 3 kg in the last three months prior to study entry;
* Suffering from lack of appetite (self-report);
* Use of medication that may influence study results; such as medication that may affect blood sugar;
* Having a food allergy or/and food intolerance for foods used in the preference testing (e.g. lactose intolerance, celiac disease, egg allergy);
* Consumes more than 14 glasses of alcohol per week;
* Use of soft or hard drugs (e.g. cannabis);
* Student or personnel of Nutrition and Health at Wageningen University;
* Participating in another study/studies or planning to participate in another study.

Specific criteria for withdrawal:

* Pregnancy;
* Weight change of 4 kg or more. In a case of systematic weight change - a subject has gained or lost 4 kg or more at the 3-month period, he/she will be excluded from the study (stop criterion).