An unsupplemented 1000 kcal (4186 kJ) diet emphasizing large quantities of unrefined complex carbohydrates was evaluated for nutritional adequacy in a 20-week weight-control program for obese adults. Assessment of nutritional status, routinely obtained upon admission, was repeated at approximately 10-week intervals on 26 patients who were losing weight while adhering to the dietary guidelines. At least one repeat assessment was obtained on all 26 patients: 13 had follow-up assessment at 10 weeks, three at 20 weeks, and ten at both 10 and 20 weeks. Weight loss averaged 0.7 kg/wk over an average of 15 weeks with a mean energy intake of 1020 kcal (4270 kJ), 55 percent of baseline. At each follow-up assessment mean skinfold thickness fell significantly whereas muscle mass was maintained according to arm muscle circumference and creatinine-height index. Mean blood levels of retinol, beta-carotene, folate, vitamin B12, ascorbic acid, thiamin, riboflavin, pyridoxine, iron, transferrin saturation and calcium excretion remained within normal limits throughout treatment. Ascorbic acid levels rose significantly. The results indicate that the experimental diet, without supplementation, can fulfil nutritional requirements while restricting energy intake for weight reduction.