Lactose Digestion Capacity and Adaptation in New Zealand Tokelau

Abstract

This biocultural study examines the relationship between nutritional stress, lactose digestion capacity, symptomatic expression, and dietary manipulation in Tokelauans residing in New Zealand. Breath hydrogen analysis and dietary surveys were conducted in a sample of 58 Tokelauans (aged 15-71 years) from Porirua and the Hutt Valley. Dietary surveys were also carried out for 137 Tokelauans (aged 18-49 years) from Porirua, and 64 European New Zealand Auckland University students (aged 18-28 years). Results indicate that lactase restriction occurs in 63.8 percent and lactase persistence in 22.4 percent of the Tokelau population. The majority of persistence observed is explained by gene flow and founder effect. Tokelauans residing in New Zealand have increased dairy product consumption to levels equivalent to those reported by European New Zealanders. Using a single stress, single response, unidirectional model of adaptability it is predicted that dairy product consumption acts as an environmental stress causing gastrointestinal symptoms in lactase restricted individuals. This induces a behavioural adaptive response of reduced dairy product consumption. Results indicate that the majority of Tokelauans do not experience symptoms after consuming normal dietary amounts of lactose. Furthermore, there is no correlation between lactose digestion capacity, gastrointestinal symptoms, and dairy product consumption patterns. It is argued that the simple, unidirectional model can not adequately account for these results because: (l) lactase restricted individuals have physiologically adapted other means for the digestion of lactose, thereby preventing symptoms; (2) symptomatic individuals do not interpret symptoms as different from normal, and therefore are not motivated to alter dietary behaviour; (3) lactase restricted individuals do not perceptually associate symptoms with dairy product consumption and thus do not change dietary behaviour; (4) lactase persistent individuals alter dietary behaviour after associating unrelated symptoms to dairy product consumption. An alternative model of biocultural interaction is proposed to explain the observed relationship between dietary stress, gastrointestinal symptoms and adaptive response. Key Words: Nutritional Anthropology, Biocultural, Adaptation, Medical Anthropology, Polynesian, Dietary Surveys