Impact of the Eating Rate of Ultra-processed Foods on Dietary Intake Behavior and Metabolic Responses

The aim of this balanced-order block randomized controlled cross-over trial with 2 treatment arms is to determine the effect of eating rate (ER) of ultra-processed food diets (UPF fast ER vs UPF slow ER) on ad libitum energy intake across a two week period.

Rationale: Consumption of industrially processed foods has been associated with obesity and related adverse health outcomes. If this reflects a causal relationship, it is unknown what attributes or properties of industrially processed foods might drive this association. Extensive research has shown that foods consumed with a texture-derived slow eating rate (ER) are consumed in smaller amounts relative to foods consumed with a fast ER. ER has been suggested as one of the mechanisms why (ultra-)processed foods (with a fast ER) may promote excess in calorie intakes. We will therefore test the hypothesis that ER moderates energy intakes from ultra-processed foods.

Objective: The primary objective of this study is to determine the effect of ER of ultra-processed food diets (UPF slow ER vs UPF fast ER) on ad libitum energy intake (kcal/day) across a two week period. The secondary objectives are to compare body composition and metabolic changes that occur when on a 14 day diet of ultra-processed foods with either a slow or a fast ER.

Study design: We will conduct a balanced-order, block randomized controlled cross-over trial with 2 treatment arms, to determine the effect of ER of ultra-processed food diets (UPF fast ER vs UPF slow ER) on ad libitum energy intake (kcal) across a two week period. The study will have a run-in period to determine habitual dietary habits (baseline) and a washout period (14 days) between treatments to prevent carry-over effects. All participants will receive both treatments and are their own control (within subject design).

Study population: 39 healthy, non-smoking, adults between 21-50 years old and with a BMI between 21-27 kg/m2 will be included.

Intervention: The two treatments are 1) a 14-days ultra-processed, slow ER diet, and 2) a 14-days ultra-processed, fast ER diet. The ad libitum meal menus are matched for energy density (kcal/g), liking (hedonic range), and level of processing, but different in textural characteristics known to influence ER. During the treatment periods participants eat all of their main meals at the research site on weekdays. Participants receive pre-packed meals to consume at home for the weekends. Meals are served ad-libitum, presented in portions that are \> 200% of a regular portion size. Participants are asked to eat from each meal until they feel comfortably full. Food (gram) and energy (kcal) consumed will be recorded at the level of the meal, the day and week of the interventions.

Main study parameters/endpoints: The primary outcome is the between-treatment difference in average (across 14 days) daily energy intake (kcal/day). Secondary study parameters include between-treatment differences in: food intake (g/day), body weight and body composition changes, postprandial hormone responses and respiratory quotient changes to a mixed meal tolerance test, continuous measures of glucose levels, and changes in fasted state leptin and ghrelin levels and blood lipid profiles.

Eligibility Criteria:
In order to be eligible to participate in this study, a participant must meet all of the following criteria:

* Between 21-50 years old at the day of inclusion
* Being able to read and understand English
* BMI 21-27 kg/m2
* Good general and mental health and appetite (self-report)
* Commonly (5 out of 7 week days) eating three meals a day around approximately the same times (self-report).

A potential participant who meets any of the following criteria will be excluded from participation in this study:

Based on the information meeting:

* Difficulties with swallowing, chewing and/or eating in general
* Suffering from an endocrine or eating disorder, gastrointestinal illness or illness of the thyroid gland, cardio-vascular diseases, bowel diseases, respiratory disease, neurological diseases, or diabetes, anaemia, cancer, or psychiatric conditions such as clinical depression, burnout or anxiety or bipolar disorder.
* Having a history of low blood pressure
* Having taste or smell disorders (self-report)
* Braces (not including a dental wire) or oral piercing
* Followed an energy restricted diet during the last 2 months
* Currently using or in the past 3 months (calculated from the first day of the study) used prebiotics supplements, probiotic supplements and/or antibiotics
* Gained or lost 5 kg of body weight over the last half year
* High restrained eater (DEBQ restrained eater scale ≥ 2.90 for males and ≥ 3.40 for females \[23\])\*
* Use of medication, including but not limited to hormone therapy or medications that affect the immune system or any medication that influences study outcomes such as food intake, appetite in general or metabolic responses (self-report)
* Consuming on average more than 21 (men) or 14 (women) glasses of alcohol per week
* Pregnant or lactating women, or women who are planning on becoming pregnant within the study period.
* Smoking (daily)
* Not willing to stop using drugs during the study period (from inclusion till last test session)
* Not willing to stop consuming alcohol during the intervention weeks
* Exercising more than 4 hours per week (excluding biking and walking at a normal pace and distance)
* Following a vegetarian or vegan diet
* Allergies or intolerance to any ingredient of the test meals
* Not willing to eat the test food because of eating habits or believes
* Do not like \> 20% of the test foods or its ingredients based on descriptions of the meal (scoring items ≤ dislike on a nine point hedonic scale)\*
* Majority \> 50% of dietary food intake (g) is derived from ultra-processed foods (based on a food frequency questionnaire (FFQ) based on normative data collected in pre-trial.\* The 50% cut-off is based on median intake of UPFs in Dutch cohort studies \[24\] \[25\]
* Being unfamiliar with \> 25% of the test meals
* Signed up for participating in another research study
* Being an employee or thesis student of the Division of Human Nutrition and Health at Wageningen university
* Radiological investigation during past 7 days where iodine or barium containing contrast fluids have been used (DEXA contra-indication)
* Nuclear medical investigation involving isotopes during past 7 days (DEXA contra-indication)

Exclusion after screening:

* Haemoglobin value is not between 7.5-11.0 mmol/L (women), 8.5-11.0 mmol/L (men)
* Fasted glucose level is below \< 3.5 mmol/L or higher than 8 mmol/L
* Blood pressure is below 90/60 mm hg (below 90 and/or below 60 mm hg)
* Veins are not suited for blood sampling (as judged by trained research nurses)
* Persons with an extremely fast or slow eating rate trait, (\> 2 times the SD from the median, based on the carrot test \[26\] eating rate distribution based on data collected in previous studies in the same study population (unpublished).
* Persons with little difference (\< 20%) in the eating rate of a hard or soft carrot
* Do not like \> 20% of the test foods based tasting small portions (1 bite) of each of the meals (scoring items below ≤ dislike on a nine point hedonic scale)\* \* This exclusion criterion will not explicitly be communicated to the participants to prevent desirable answers