OBJECTIVE The effectiveness of a tepary bean high fat type diet, compared to a purified type high fat diet and exercise, on body composition in fatty Zucker rats was determined. METHODS Approximately 6-week-old female fa/fa Zucker rats were divided into four groups of 10 rats each: TE, fed the tepary bean type diet and exercised; TN, fed the tepary bean type diet and not exercised; CE, fed the purified type control diet and exercised; CN, fed the purified type control diet and not exercised. The exercise modality was treadmill running and the experiment lasted 13 weeks. METHODS Body weight, cumulative food intake, body composition, weights of adipose tissues and liver, heart and gastrocnemius muscle. RESULTS At the end of the 13 week experiment, TE rats weighed 511 +/- 22 g and were significantly lighter than TN, 588 +/- 15 g; CE, 606 +/- 22 g; and CN, 660 +/- 27 g. All are means +/- s.e.m. The carcass of CN rats had 58, 20 and 13% more fat than TE, TN and CE rats, respectively; P < 0.01. Lean body mass was the same for all the groups of rats and ranged from means of 216-228 g. However, TE rats had significantly more fat free dry mass (FFDM) than CN rats; 68 +/- 4 vs 58 +/- 2 (means +/- s.e.m.) and tended to have more FFDM than TN and CE rats. Inguinal fat depots weighed 20-30% less in T than in C rats (diet comparisons) and also 20-30% less in E than in N rats (exercise comparisons). Perirenal/retroperitoneal fat depots weighed 25% less in TN than in CN rats and 38% less in TE than in CE rats. Exercise did not reduce perirenal/retroperitoneal fat depot weights. Parametrial fat depot weights were not influenced by diet or exercise. CONCLUSIONS In diets which provided 37% of the energy from fat, the incorporation of tepary beans attenuated weight gain, and subcutaneous and visceral fat gain compared to a purified type diet. Exercised rats gained less weight and subcutaneous, but not visceral fat, than non-exercised rats.