12 Physiological Effects of Food Carbohydrates Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/20/16. For personal use only.
Lactose Intolerance and Lactose Hydrolyzed Milk DAVID M. PAIGE, THEODORE M. BAYLESS, SHI-SHUNG HUANG, and RICHARD WEXLER Johns Hopkins Medical Institutions, 615 North Wolfe St., Baltimore, Md. 21205
Prevalence
Low levels of intestinal lactase activity have been found in many otherwise healthy adults and children in populations of American Negroes (1-5), Asians (6-10), Bantu tribes (11-12), South American Indians (13-14), Thais (15-17), and other population groups (18-20). Current evidence would indicate these low levels to be the norm for most populations of the world with notable exceptions being Scandinavians and those of northern European extraction. Approximately 70% of the world's adult population is lactose intolerant (21). It appears that those who have genetically acquired low lactase levels as adults are able to drink milk as infants; but gradually become increasingly lactose-intolerant after infancy. The onset of acquired lactose intolerance depends on the population studied. In developing countries, as our data from Peru indicates, 50% of the population is intolerant by 3 years of age (13). In a more technologically developed country such as the United States, 40% of the black population is lactose intolerant by the end of the first decade (Figure I). The difference between the accelerated loss of enzyme activity in children in developing areas, contrasted with the slower decline in blacks in this country, may reflect a relatively better nutritional state influencing and retarding the genetic expression of this event. Normally, i n g e s t e d l a c t o s e i s h y d r o l y z e d by t h e enzyme l a c t a s e found w i t h i n t h e b r u s h b o r d e r o f m i c r o v i l l o u s a r e a o f t h e j e j u n a l mucosa, s p l i t t i n g t h e l a c t o s e i n t o g l u c o s e and g a l a c t o s e , which a r e then absorbed. I f enzyme a c t i v i t y i s low, t h e i n g e s t e d lactose i s not hydrolyzed. F l u i d then e n t e r s t h e i n t e s t i n a l lumen t o d i l u t e t h i s h y p e r t o n i c l o a d , c a u s i n g 191
Figure I.
Normal lactose tolerance in U.S. white and black children and Peruvian mestizo children
Physiological Effects of Food Carbohydrates Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SAN DIEGO on 03/20/16. For personal use only.
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