Obesity is considered the emerging epidemic of the 21st century, becoming one of the major public health problems. Excessive body weight increases morbidity and mortality risk, while decreases the quality of life and expectance. The prevalence of obesity almost has doubled in the last 20 years. According to the World Health Organization, 39% of the population is overweight and 13% of the population is obese.

Obesity is a multifactorial origin disease, where genetic plays an important role. However, lifestyle factors, such as unhealthy diets and physical inactivity are the main cause for the development of obesity and associated comorbidities such as hypertension, dyslipidemia, diabetes and even some types of cancer. The prevention and control of obesity as well as its comorbidities requires interventions at individual and population level.

Intervention studies based on hypocaloric diets show poor adherence in the long term. Moreover, high energy density diets accompanied by snacking between meals contribute to weight gain. Therefore, the inclusion of bioactive compounds with satiating capacity within healthy and personalized dietary patterns could be a strategy to improve adherence in a dietary plan, and consequently reduce morbidity and mortality rates associated to obesity.

Considering this background, the general aim of this investigation is to perform an acute postprandial study to evaluate the effect of a dietary protein intake on the feeling of hunger and satiety. To carry out this objective, different data will be analysed, such as the measurement of gut hormone circulating concentrations, lipid and glucose profile, energy compensation after the postprandial period and the total energy intake during the day.

This study is designed as a crossover, randomized, three-arm postprandial study. All participants attend the Nutrition Intervention Unit of the Centre for Nutrition Research in the University of Navarra three times separated by at least one week. The day before each study day, participants should avoid vigorous physical exercise, alcohol consumption or high-fiber food consumption. Moreover, they are asked to follow a standardized dinner before 9 pm.

On each study day, participants visit the Nutrition Intervention Unit in fasting state. After 5 minutes rest and having answered the first hunger / satiety visual analogue scale (VAS) questionnaire, blood pressure is measured. After that, participant are asked to collect a baseline urine sample.

Once the cannulation is placed, first blood collection is performed in fasting state (time 0). Then, the participant is provided with the randomly assigned standardized breakfast (250 g of custard) with the addition of 20 g of experimental protein or 20 g of casein or 20 g of water. After custard consumption, volunteer is asked to drink 50 mL of water.

When participant finishes the breakfast, the time is registered and every 15 minutes the participant have to complete a VAS questionnaire (15´, 30´, 45´, 60´, 75´ and 90´). Moreover, blood samples are drawn at different time points after breakfast intake (15´, 30´, 60´ and 90´). The cannula is removed when the last blood sample is collected. In addition, participants are asked to collect the urine sample at 90 minutes postingestion and to fill a questionnaire about gastrointestinal symptoms.

Finally, participant is offered an ad libitum lunch (ham and cheese sandwiches) to eat until feeling comfortably satiated. Once completed, participant leaves the Centre for Nutrition Research with the necessary material to register the food intake (solids and liquids) during the rest of the day. Likewise, the participant is provided with the questionnaire of gastrointestinal symptoms to be filled before the dinner of the same day.

Inclusion Criteria:

• Women and men aged 20-65 years.
• Overweight or obese (BMI: 24.9 - 34.9 kg / m2).
• Physical characteristics and vital signs normal or clinically without relevance to the experiment.
• Volunteers undergoing drug treatment will be included if the dose is stable for at least three months before the start of the study with the exception of treatments that alter gastrointestinal function, lipid lowering and antidiabetics treatments.
• Able to understand and be willing to sign the informed consent form and to follow all the study procedures and requirements.

Exclusion Criteria:

• Subjects with relevant functional or structural abnormalities of the digestive system, such as malformations, angiodysplasia, active peptic ulcers, chronic inflammatory diseases or malabsorption.
• Consuming more than 14 units of alcohol intake per week in women, or more than 21 units per week in men.
• Pregnancy or lactation.
• Subjects who have undergone surgical interventions with permanent sequelae (for example, gastroduodenostomy).
• Subjects with some liver disease.
• Subjects with some type of cancer or in treatment of it, or less than 5 years after its eradication.
• Subjects with allergy to any component of the products under study or some other food that interferes and makes difficult to follow the study.
• Subjects that present some kind of cognitive and / or psychical impairment.
• Subjects with poor collaboration, or with difficulty to follow the study procedures.
• Subjects who exhibit restrictive or specific behaviors in the diet (Eating Attitude Test-26 equal or more than 20 points).