Background: The incidence of gastrointestinal infections is very high. In Western countries at least 30% of the population suffers from at least one food-borne infection per year. Mostly because of the problem of antibiotic resistance, more emphasis is put on prevention of infections. One of the possibilities is to strengthen human resistance to gut infections by consumption of milk ingredients.

Aim: To study whether a milk protein concentrate rich in phospholipids improves the resistance of humans to enterotoxigenic E. coli (ETEC).

Study design: The MIRAGE study is a parallel, double-blind, placebo-controlled 4-weeks intervention with a milk protein concentrate rich in phospholipids in healthy subjects of 18-55 yrs of age. Participants will be randomly assigned to the milk protein concentrate rich in phospholipids or placebo group (n=30 per group). Subjects will be instructed to maintain their usual pattern of physical activity and their habitual food intake, but to standardize their dietary calcium intake. After an adaptation period of 2 weeks, subjects will be orally infected with a live, but attenuated, ETEC vaccine (strain E1392-75-2A; collection NIZO food research; dose will be 1010 CFU). Before and after infection, an online diary will be kept to record all food and drinks consumption (2x2 days) to assess the habitual dietary intake. The diary will also be used for daily recording of bowel habits and frequency and severity of gastrointestinal complaints.

The following biological samples will be collected: 4x10 ml venous blood, a single fecal bolus (for screening) and 7x24 hrs feces. Blood is sampled for immune response analyses and the fecal samples are collected to quantify several infection- and immune system markers and to verify dietary calcium intake. Saliva is sampled three times before and after infection to quantify immune system markers.

Primary outcomes: Fecal ETEC excretion and severity of diarrhea (quantified by fecal output per day).

Secondary outcomes: Serum immune response to ETEC, self-reported stool consistency scores and gastrointestinal complaints, relative fecal wet weight.

Inclusion Criteria:

• Signed informed consent
• Age 18-55 yrs
• Availability of internet connection
• Willingness to replace habitual dairy product intake with the supplied low-calcium soy products
• Willingness to abstain from products with high amounts of prebiotic fibers and from products with probiotics starting 1 month prior to study start
• Willingness to give up blood donation from 1 month before the start of the experiment and during the entire experimental period.

Exclusion Criteria:

• Current or previous underlying disease of the GI tract, liver, bile bladder, kidney, thyroid gland (self-reported)
• Allergy to milk products or lactose intolerance (self-reported), since the capsules may contain milk traces from culture media
• Allergy to soy products (self-reported)
• Use of antibiotics, norit, laxatives (up till 6 months prior to inclusion), cholestyramine, acid burn inhibitors or immune suppressive agents (up till 3 months prior to inclusion), and pre- and probiotics (up till 1 month prior to inclusion).
• High titer serum antibodies against ETEC (10 ml blood sample collected at screening)
• ETEC detected in fecal sample (collected at screening)
• Vegetarians
• Vegans
• Heavy alcohol use (>4 consumptions/day or >20/week)
• Drug use