The Importance of Lactose in the Human Diet: Outcomes of a Mexican Consensus Meeting.

Lactose is a unique component of breast milk, many infant formulas and dairy products, and is widely used in pharmaceutical products. In spite of that, its role in human nutrition or lactose intolerance is generally not well-understood. For that reason, a 2-day-long lactose consensus meeting with health care professionals was organized in Mexico to come to a set of statements for which consensus could be gathered. Topics ranging from lactase expression to potential health benefits of lactose were introduced by experts, and that was followed by a discussion on concept statements. Interestingly, lactose does not seem to induce a neurological reward response when consumed. Although lactose digestion is optimal, it supplies galactose for liver glycogen synthesis. In infants, it cannot be ignored that lactose-derived galactose is needed for the synthesis of glycosylated macromolecules. At least beyond infancy, the low glycemic index of lactose might be metabolically beneficial. When lactase expression decreases, lactose maldigestion may lead to lactose intolerance symptoms. In infancy, the temporary replacing of lactose by other carbohydrates is only justified in case of severe intolerance symptoms. In those who show an (epi)genetic decrease or absence of lactase expression, a certain amount (for adults mostly up to 12 g per portion) of lactose can still be consumed. In these cases, lactose shows beneficial intestinal-microbiota-shaping effects. Avoiding lactose-containing products may imply a lower intake of other important nutrients, such as calcium and vitamin B12 from dairy products, as well as an increased intake of less beneficial carbohydrates.

Bases conceptuales del diagnóstico de intolerancia a lactosa, hipolactasia y mala digestión de lactosa / Conceptual basis of the diagnosis of lactose intolerance, hypolactasia and lactose maldigestion

Se revisa la fisiopatología de hipolactasia, mala digestión de lactosa e intolerancia a lactosa para aclarar confusiones conceptuales y puntualizar diagnósticos. La lactasa es la enzima que digiere la lactosa de la leche, liberando galactosa y glucosa. En adultos con fenotipo Hipolactasia Primaria Tipo Adulto (No persistencia de Lactasa), la actividad enzimática es el 10 % de la máxima, propia de la infancia; en los de fenotipo Persistencia de Lactasa se mantiene elevada. En europeos, los fenotipos están estrechamente asociados al polimorfismo C/T-13910; por consiguiente, su genotipificación constituye prueba diagnóstica; no así en caribeños colombianos por presentar moderada asociación. El diagnóstico directo de hipo-lactasia/persistencia es el enzimático; un índice lactasa/sacarasa< 0,3 indica hipolactasia. Mala digestión de lactosa, la incapacidad de digerir cierta cantidad, se evalúa con la prueba de hidrógeno en el aliento o con la de tolerancia a lactosa, las cuales permiten inferir si el sujeto es probable persistente (digestor) o probable hipolactásico (mal digestor). Intolerancia a lactosa es el síndrome clínico digestivo que, tras ingerirla, puede sobrevenir por causa de hipolactasia o de mala absorción de glucosa-galactosa; se diagnostica si al excluir la leche de la dieta durante dos semanas el cuadro desaparece y luego, al restituirla, reaparece. Mala absorción de lactosa es una irrealidad fisiológica porque la lactosa no se absorbe. No existe sinonimia entre hipolactasia, mala digestión de lactosa e intolerancia a lactosa. Son estados fisiopatológicos diferentes, no siempre asociados entre sí. La comprensión de la identidad conceptual de cada uno es fundamental para diagnosticarlos acertadamente.

The pathophysiology of hypolactasia, lactose maldigestion and lactose intolerance are reviewed to clarify conceptual confusions and convey precise diagnoses. Lactase is the enzyme that helps to digest milk lactose, releasing galactose and glucose. While in adults with primary adult-type hypolactasia phenotype, the enzyme activity reaches 10% of the maximum observed in childhood, in individuals with lactase persistence phenotype, the activity remains high. In Europeans, phenotypes are closely associated with C/T-13910polymorphism; therefore, genotyping may be used as a diagnostic test. However, this is not possible in Colombian Caribbean population due to the existence of moderate association genotype-phenotype. The direct diagnosis ofhypolactasia/persistence consists of an enzymatic method; a lactase/sacarase index<0.3 indicates hypolactasia. Lactose maldigestion, the inability to digest a certain amount of lactose, is evaluated through application of either breath hydrogen or a lactose intolerance test, which allow to infer whether the individual might be a lactase persistent (digester) or hypolactasic (maldigester). Lactose intolerance is the clinical digestive syndrome that may appear following ingestion of lactose, due to hypolactasia or to glucose-galactose malabsorption. A subject is considered to be intolerant to lactose when symptoms disappear as milk is excluded from the diet for two weeks, and reappear upon its restoration as part of his diet. "Lactose malabsorption" is a physiological misnomer because lactose is not absorbed as such. Hypolactasia, lactose maldigestion and lactose intolerance are not synonyms. They involve different pathophysiological states, which are not always associated with each other. Understanding each of these three concepts is critical for a correct diagnosis.