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Item #5 

High-Glycemic-Index Foods Increase Insulin Resistance

A diet containing a preponderance of foods high on the glycemic index increase insulin resistance over time.

According to a study from England, "Postprandial concentrations of glucose, insulin, and triacylglycerols (TG) correlate to risk for CHD. Carbohydrates affect many metabolites that could have a potential effect on cardiovascular risk factors. The objective of the present study was to examine, using a randomized prospective study, the acute (day 1) and ad libitum medium-term (day 24) effects of four diets: a high-fat diet (HIGH-FAT; 50% fat, >34% monounsaturated fatty acids); a low-glycemic index (GI) diet (LOW-GI; high-carbohydrate, low-GI); a high-sucrose diet (SUCROSE; high carbohydrate increase of 90 g sucrose/d); a high-GI diet (HIGH-GI; high-carbohydrate, high-GI)."

"Daytime profiles (8 hours) (breakfast, lunch, and tea) of lipid and carbohydrate metabolism were completed during day 1 and day 24," reported A. E. Brynes and colleagues at Hammersmith Hospital and the University of Surrey. "Seventeen middle-aged men with one or more cardiac risk factors completed the study. There was no change from day 1 or between diets in fasting glucose, lipids, or homeostatic assessment model (HOMA) on day 24."

The researchers found, "The HIGH-FAT compared with the three high-carbohydrate diets was associated with lower postprandial insulin and glucose but higher postprandial TG and non-esterified fatty acids (NEFA). There was a significant increase in the 6-hour (15.00 hours) TG concentration (day 1, 2.6 (SEM 0.3) mmol/L vs day 24, 3.3 (SEM 0.3) mmol/L; p<0.01) on the SUCROSE diet. Postprandial HOMA (i.e., incremental area under the curve (IAUC) glucose (mmol/L per min) x IAUC insulin/22.5 (mU/L per min)) median changes from day 1 to day 24 were -61, -43, -20, and +31% for the HIGH-FAT, LOW-GI, SUCROSE, and HIGH-GI diets respectively.

The HIGH-GI percentage change was significantly different from the other three diets (p<0.001). Despite being advised to maintain an identical energy intake there was a significant weight change (-0.27 (SEM 0.3) kg; p<0.02) on the LOW-GI diet compared with the SUCROSE diet (+0.84 (SEM 0.3) kg)."

Brynes and coauthors concluded that "the HIGH-FAT diet had a beneficial effect on postprandial glucose and insulin over time but it was associated with higher postprandial concentrations of TG and NEFA. Conversely the HIGH-GI diet appeared to increase postprandial insulin resistance over the study period.

Brynes and associates published the results of their study in the British Journal of Nutrition (A randomized four-intervention crossover study investigating the effect of carbohydrates on daytime profiles of insulin, glucose, non-esterified fatty acids and triacylglycerols in middle-aged men. Br J Nutr, 2003;89(2):207-218).

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