OBJECTIVE Two experimental diets were evaluated to investigate the hypothesis that dietary fat has an independent influence on metabolic control in IDDM.

RESEARCH DESIGN AND METHODS The diets had similar CHO contents (26 and 22% of energy intake) but differed markedly in fat (53 vs. 16% energy) and protein (20 vs. 62% energy). We had 10 subjects follow the low-CHO, high-fat diet, and 8 subjects follow the low-CHO, low-fat, high-protein diet. In each case, markers of glycemic and lipid control obtained after adherence to the experimental diet for 2 wk were compared with corresponding data from a preceding control period during which subjects had followed their usual diet (protein 18–19%, CHO 41–46%, fat 33–37%).

RESULTS Despite the low CHO content of the high-fat diet, insulin requirements were unchanged relative to the control diet. Moreover, the glycemic response to a standard breakfast was elevated significantly (P < 0.001), suggesting that insulin resistance had either been induced or exacerbated. The small rise in total cholesterol concentration in response to the high-fat diet was accounted for by a rise in HDL cholesterol. Glycemic control and lipid metabolism were unchanged after the low-CHO, low-fat diet, although insulin requirements fell by an average of 6 U/day (P < 0.05) relative to those recorded during the 2-wk control period.

CONCLUSIONS Diets high in fat are deleterious to glycemic control in IDDM, but general applicability is limited by the small sample size and short duration of this study.