The Lese are subsistence farmers living in the Ituri Forest of north-east Zaire. They exhibit significant birth seasonality, with lowest frequencies of conception when food production is least, nutritional status is low and ovarian function, as measured by salivary steroid hormone levels, is reduced. Efe pygmy foragers, who live in the same geographical area but are less dependent on cultivated foods and have a more flexible life style, do not exhibit frequent fluctuations in nutritional status nor significant birth seasonality. These findings support a model of birth seasonality relating climatic variables to variation in fertility through a causal chain linking rainfall to food production to energy balance to ovarian function to fertility. The model, which emphasises an ecological approach to the study of human reproduction, should have broad applicability since seasonality of food production and energy balance is widespread geographically and across a wide variety of economies and cultures.
as a cause of human cancer: the Richard and Hilda Rosenthal Foundation Award Lecture. Cancer Res 1988; 48: 246-53. 3 Ellison PT. Measurements of salivary progesterone. Ann N Y Acad Sci (in press). 4 Ellison PT. Salivary steroids and human reproductive ecology. Ann NY Acad Sci (in press).
Objective: To assess dietary composition in relation to energetic status and ovarian function. Design: An eight-month prospective study undertaken in 1989. Setting: Ituri Forest, northeast Democratic Republic of Congo. Subjects: Sixty-four female volunteers of reproductive age (16±45), with a subsample of 30 for nutritional focal follows, 39 for analysis of salivary progesterone levels, and 18 for analysis of salivary oestradiol. Interventions: Regular anthropometric measurements of heights, weights, and mid-triceps skinfolds, 204 h of nutritional focal follows when all foods prepared and consumed were recorded and weighed, analysis of dietary composition using African food tables, collection of saliva samples every-other day for radioimmunoassay of salivary oestradiol and progesterone. Results: The primary staple in the Lese diet is manioc, consumed at nearly every meal, but the diet is subject to seasonal¯uctuations. Important seasonal crops are groundnuts and rice. Carbohydrates comprise 64% of the diet, protein 14% and fat 22%, but seasonal¯uctuations in food items create signi®cant differences in protein content (P 0.007). Energy intake falls by 25% in the hunger season. Lese energy balance re¯ects this lack with women losing a mean 7% of total body weight. The mean BMI for Lese women at the beginning of the study was 22.8 but, during the hunger season, the BMI for 20% of women fell to`18.5, indicative of chronic energy shortage. Mean levels of Lese salivary oestradiol and progesterone are chronically and signi®cantly lower than healthy, Western controls (P 0.0001 for progesterone; P 0.03 for follicular values of oestradiol, P 0.0001 for midcycle values, and P 0.0002 for luteal values). Mean salivary progesterone levels were signi®cantly lower for those Lese women losing weight (P 0.03), and signi®cantly lower for weight-loss women when comparing levels at the beginning and end of the hunger season (P 0.03). Discussion: The relatively low-fat, high-®bre diet of the Lese appears healthy, but there are occasional seasonal de®ciencies in protein-energy and micronutrient content, especially for pregnant and lactating women. Dietary composition may affect Lese levels of reproductive steroids, partly explaining the chronically low salivary oestradiol pro®le of this population.
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