Lactase is high in the newborn intestine, allowing him to digest the high amounts of lactose present in breastmilk. From weaning, lactase is genetically programmed to decrease, reaching residual levels in the adult. This situation occurs in 75% of the world population and is known as "adult primary hypolactasia" while the remaining 25% is "lactase persistent" i.e. maintains in adulthood lactase values similar to these of newborns. In subjects with hypolactasia, the intake of milk products can produce digestive symptoms, making that the affected individuals spontaneously reduce the consumption of these products and, therefore, their intake of calcium and proteins.

In addition to lactose-free milk and exogenous lactase, a strategy for the intolerant subjects to continue consuming dairy products is, for example, to consume yogurt, due to the fact that the lactase of the yogurt bacteria continues to function in the intestine of the consumer, hydrolyzing lactose and decreasing the development of digestive symptoms. Similarly, many probiotic strains, such as L. acidophilus NCFM, L. casei CRL431, B. longum 401 and B. bifidum Orla Jensen 1424, express β-galactosidases that hydrolyze lactose, preventing its fermentation and the production of gases. The acute administration of these strains improves lactose tolerance. In addition, a recent study reported that dietary supplementation of intolerant subjects for 4 weeks with L. casei Shirota and B. breve Yakult reduced digestive symptoms and breath hydrogen excretion not only at the end of the period of administration of the probiotics but also 3 months after having discontinued the use of probiotics.

Based on this background, the aim of this study is to determine whether the regular consumption of an ice cream with the strain B. bifidum 900791 improves lactose intolerance in hypolactasic subjects, even after the suspension of the consumption of the product. To determine if this effect is due to the adaptation of the microbiota, the investigators will also evaluate changes in the composition of the microbiota and the generation of volatile fatty acids.

Inclusion Criteria:

• Diagnosis of hypolactasia and lactose intolerance

Exclusion Criteria:

• Diarrhea
• Previous gastrointestinal pathologies
• Current or recent intake of antibiotics, anti-inflammatory drugs, laxatives or drugs interfering with intestinal transit
• Alterations of intestinal anatomy or function
• Pregnancy
• Chronic diseases of different etiologies (auto-immune, inflammatory, tumor, etc.).