GLYCEMIC INDEX, NUTRIENT DENSITY, AND PROMOTION OF ABERRANT CRYPT FOCI IN RAT COLON

We speculated that a diet with a high glycemic index (GI) or a diet wi th a low nutrient density (nutrient-to-calorie ratio) would enhance co lon carcinogenesis, presumably via increased insulin resistance. Forty -eight Sprague-Dawley (SD) rats received an azoxymethane injection (20 mg/kg) and were randomized into five groups given an AIN-76 diet cont aining 1) 65% starch by weight, 2) 65% glucose (GI = 100), 3) 65% fruc tose (GI = 23), 4) 82% starch, or 5) 39% oil and 39% sucrose. The nutr ient density of Diets 4 and 5 was one-half that of Diets 1-3. Promotio n was assessed by the multiplicity (number of crypts) of aberrant cryp t foci (ACF), an early marker of colon carcinogenesis. Insulin resista nce was estimated by the FIRI index (blood insulin x blood glucose), b y plasma triglycerides, and by visceral fat. To confirm the results in another rat strain, the experiment was duplicated in 48 Fischer (F344 ) rats. Results show that 1) the ACF multiplicity was not different in glucose- and fructose-fed rats (p > 0.7): diets with contrasting GI h ad the same effect on ACF growth; 2) diets of low nutrient density inc reased visceral fat (p < 0.05) but reduced the ACF size in F344 rats ( p < 0.001, no reduction in SD rats); and 3) indirect insulin resistanc e markers (FIRI index, blood triglycerides, and visceral fat) did nor correlate with ACF multiplicity. These results do not support the hypo thesis that diets with a high GI or low nutrient density or diets that increase some indirect insulin resistance markers can promote colon c arcinogenesis in F344 or SD rats.