People tend to regulate intake by the weight of food rather than its energy content, making energy dense foods, especially those combining salty, fatty, and umami tastes, more likely to promote passive overconsumption. Lowering energy density can reduce daily energy intake, but often decreases palatability, whereas umami can enhance palatability, and sometimes decrease food intake. This suggests that adding umami to a regular energy dense diet could reduce food intake over time, and that adding umami to a reduced energy dense diet could sustain palatability and limit compensatory energy intake. Therefore, the aim of this study is to assess the effect of a 2-week dietary intervention of adding umami and/or lowering energy density on food intake. Secondary objectives are whether adding umami and/or lowering energy density affect dietary satisfaction, appetite, perceived umami intensity, food preferences, bodyweight and composition, and wellbeing ratings.

This will assessed in a double-blind crossover, randomized controlled trial of three times two weeks, each separated by two weeks washout in 33 healthy Dutch adults between 18-65 years of age, with a BMI between 20-30. Umami taste will be added through MSG supplementation of the three main meals. Supplementation will depend on both intervention group, and individual participants' body weight. Energy density will be lowered by swapping regular products for low-fat, low-sugar or higher water products.

The three intervention diets will vary in umami taste intensity, and/or energy density: 1) regular energy density without added umami (control), 2) regular energy density with added umami, 3) reduced energy density with added umami. Umami will be supplemented by supplementing food items with 55-60 mg MSG per kg bodyweight daily, divided over three eating occasions. Foods will be offered ad libitum, and participants will add a seasoning sachet containing MSG to their selected portion.

The primary objective will be to compare average daily food intake (kcal) over two weeks between the three dietary interventions differing in umami taste intensity and energy density. Secondary outcomes are dietary satisfaction, appetite, perceived umami intensity, food preferences, bodyweight and composition, and wellbeing ratings.

Inclusion Criteria:

• Healthy: as judged by the participant;
• Age 16-65 years at the time of inclusion, assessed by date of birth;
• Proper understanding of the Dutch language, as questionnaires will be in Dutch;
• Able to visit Wageningen University, as required for dietary intervention and testing;
• Body mass index 20-30 kg/m2;
• Having normal taste ability, assessed using Mueller taste strip test, ≥12 out of 20 assessed correctly.

Exclusion Criteria:

• Suffering from endocrine- or gastro-intestinal diseases or other diseases that might influence study outcomes (such as diabetes, Crohn's disease, cardiovascular disease, hypertension, etc.);
• Diagnosed with eating disorders (currently or in the past);
• Diagnosed with taste or smell disorders in the past six months;
• Pregnant or lactating during the study intervention;
• Following a strict dietary regime;
• Extreme physical activity (>10 hours per week moderate/high intensity exercise);
• Gain or loss of more than 5 kgs in the last six months prior to study entry;
• Suffering from lack of appetite for any reason;
• Use of medication that may influence the appetite (medication will be judged by the medical investigator);
• Having a food allergy and/or intolerance for foods used in the dietary intervention (e.g. lactose intolerance, gluten intolerance, MSG sensitivity). This will be assessed with an open question;
• Consumes more than 14 (women) or 21 (men) glasses of alcohol per week;
• Consumes MSG-rich sauces (soy sauce, ketjap and/or curry paste) more than once per day, or consumes more than 3 savoury food items (paprika chips, instant noodles, sundried tomatoes and/or pre-packaged seasonings) per day. This will be assessed with a frequency of consumption table;
• Irregular eating pattern. This will be measured with a frequency of meal/food consumption table, and is defined as: frequency of breakfast consumption less than once per week;
• Unwilling to maintain regular exercise pattern during the study period. This will be assessed with a yes/no question;
• Unwilling to quit use of soft or hard drugs during the intervention;
• Student or personnel of the division of Human Nutrition and Health, Wageningen University;
• Participating in any other intervention study/studies or planning to participate in another intervention study during the study period.

Individual participant data that underline the results reported in an article after de-identification will be shared.

Following the publication. No end date.

Anyone who whishes to access the data for secondary analysis must contact corresponding authors of specific publications for their approval. Next to this, they must reference the source of the data to provide appropriate credit to those who generated the data and allow searching for the studies it has supported.