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Studies of Nitrogen Balance in Male Highlanders in Papua New Guinea¹

Yoshiaki Fujita, Toyoko Okuda^*, Toru Rikimaru, Mineko Ichikawa, Shuichi Miyatani, Naemi M. Kajiwara, Chigusa Date, Takahisa Minamide^||, Hideo Koishi^*, Michael P. Alpers^¶ and Peter F. Heywood^¶

Nutrition Research Laboratory, Tokyo Metropolitan Institute of Gerontogy, 35-2 Sakaecho, Itabashi-ku, Tokyo 173, Japan ^* Faculty of the Science of Living, Osaka City University, Osaka, Japan Department of Home Economics, Yamaguchi Women's College, Yamaguchi, Japan Department of Home Economics, Kobe Women's University, Kobe, Japan School of Medicine, Osaka City University, Osaka, Japan ^|| Department of Agriculture, Osaka Prefecture University, Osaka, Japan ^¶ Papua New Guinea Institute of Medical Research, Goroka, Papua New Guinea

Nitrogen metabolism in Papua New Guinea highlanders was studied by examining their nitrogen balance when they ate their usual diet (experiment 1) or an experimental diet (experiment 2). Studies were made on 39 male highlanders between October and December in 1980 and 1982. In experiment 1, the average protein and energy intakes (mean ± SD) for three consecutive days of usual diets were 116.2 ± 31.2 mg N/kg body weight and 46.9 ± 8.9 kcal/kg body weight in 1980 and 143.5 ± 54.8 mg N/kg body weight and 47.3 ± 10.5 kcal/kg body weight in 1982, and thus the nitrogen balances were 27.7 ± 28.3 and 18.4 ± 24.2 mg N/kg body weight, respectively. Most dietary protein and energy was derived from sweet potatoes and other vegetable foods, but between 1980 and 1982 the diet changed slightly with increased consumption of imported foods such as rice and canned fish. In the second experiment, when 10 highlanders were given adequate protein diet (about 200 mg N/kg body weight and about 44 kcal total energy/kg body weight for 13 d, much of the dietary nitrogen was retained in their bodies (45.1 ± 19.3 mg N/kg body weight). When another group of men were fed a sweet-potato diet (81.1 mg N/kg body weight for 8 d followed by a low protein sweet-potato diet containing only 42 mg N/kg body weight with 50 kcal/kg body weight for 14 d, nitrogen true digestibility and net protein utilization increased and their nitrogen balance showed no significant change (-11.0 ± 5.6 mg N/kg body weight). These results show that in the highlanders, dietary energy intake plays an important role in adaptation to low protein intake.

KEY WORDS: • nitrogen balance of PNG highlanders • Papua New Guinea highlanders • protein utilization • protein nutritional status • urea supplementation

¹ Supported by grants 504158 and 56043015 from the Ministry of Education, Science and Culture of Japan.

Manuscript received 18 January 1985. Revision accepted 26 November 1985.