Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity

Abstract

IMPORTANCE Foods that have similar carbohydrate content can differ in the amount they raise blood glucose. The effects of this property, called the glycemic index, on risk factors for cardiovascular disease and diabetes are not well understood. OBJECTIVE To determine the effect of glycemic index and amount of total dietary carbohydrate on risk factors for cardiovascular disease and diabetes. DESIGN, SETTING, AND PARTICIPANTS Randomized crossover-controlled feeding trial conducted in research units in academic medical centers, in which 163 overweight adults (systolic blood pressure, 120–159 mm Hg) were given 4 complete diets that contained all of their meals, snacks, and calorie-containing beverages, each for 5 weeks, and completed at least 2 study diets. The first participant was enrolled April 1, 2008; the last participant finished December 22, 2010. For any pair of the 4 diets, there were 135 to 150 participants contributing at least 1 primary outcome measure. INTERVENTIONS (1) A high–glycemic index (65% on the glucose scale), high-carbohydrate diet (58% energy); (2) a low–glycemic index (40%), high-carbohydrate diet; (3) a high–glycemic index, low-carbohydrate diet (40% energy); and (4) a low–glycemic index, low-carbohydrate diet. Each diet was based on a healthful DASH-type diet. MAIN OUTCOMES AND MEASURES The 5 primary outcomes were insulin sensitivity, determined from the areas under the curves of glucose and insulin levels during an oral glucose tolerance test; levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides; and systolic blood pressure. RESULTS At high dietary carbohydrate content, the low– compared with high–glycemic index level decreased insulin sensitivity from 8.9 to 7.1 units (−20%, P = .002); increased LDL cholesterol from 139 to 147 mg/dL (6%, P ≤ .001); and did not affect levels of HDL cholesterol, triglycerides, or blood pressure. At low carbohydrate content, the low– compared with high–glycemic index level did not affect the outcomes except for decreasing triglycerides from 91 to 86 mg/dL (−5%, P = .02). In the primary diet contrast, the low–glycemic index, low-carbohydrate diet, compared with the high–glycemic index, high-carbohydrate diet, did not affect insulin sensitivity, systolic blood pressure, LDL cholesterol, or HDL cholesterol but did lower triglycerides from 111 to 86 mg/dL (−23%, P ≤ .001). CONCLUSIONS AND RELEVANCE In this 5-week controlled feeding study, diets with low glycemic index of dietary carbohydrate, compared with high glycemic index of dietary carbohydrate, did not result in improvements in insulin sensitivity, lipid levels, or systolic blood pressure. In the context of an overall DASH-type diet, using glycemic index to select specific foods may not improve cardiovascular risk factors or insulin resistance. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00608049

A systematic review on the relations between pasta consumption and cardio-metabolic risk factors

“…In another crossover study, a low-GI diet decreased insulin sensitivity and increased LDL cholesterol compared to high-GI diet in the context of high carbohydrate content, and decreased triglycerides in the context of low carbohydrate content. [39] Other than these results, none of the outcomes differed significantly between the pasta-containing low-GI diet group and the high-GI diet group. [41][42][43][44] Overall, RCTs comparing pasta to other high-GI starchy foods are lacking.…”

“…[37] Seven independent studies were included in this category with outcomes including insulin sensitivity, [38,39] HbA1c, [40][41][42] fasting plasma glucose, [38,[40][41][42][43] total plasma cholesterol, [40][41][42][43][44] low-density-lipoprotein (LDL) cholesterol, [39-41, 43, 44] high-density-lipoprotein (HDL) cholesterol, [39][40][41][42][43][44] LDL/HDL cholesterol ratio, [40,41] plasma triglycerides, [39][40][41][42][43][44] body weight, [38,[40][41][42]45] waist circumference, [40,45] and blood pressure. [39,40] We were not able to locate trials with T2D or CVD as outcome, but one study calculated the 10-year Framingham coronary heart disease (CHD) risk score. [40] • Third, 14 studies were identified where different types of pasta were compared, including 3 studies that compared whole grain to refined grain pasta, [46-48] 6 studies that compared fiber-fortified to non-fiber-fortified pasta, [49]…”

4. Prevention or Delay of Type 2 Diabetes

“…For example, recent work supports the Mediterranean diet, which is relatively rich in monounsaturated fats, as a means to help to prevent type 2 diabetes (15). Studies evaluating glycemic index to guide carbohydrate recommendations have been inconsistent (16,17); however, data suggest that consumption of a diet enriched in whole grains is helpful in preventing type 2 diabetes (18). Finally, increased consumption of nuts (19) and berries (20) in the context of a diet high in vegetables and whole fruits has been correlated with reduced diabetes risk.…”

Estimating the reliability of glycemic index values and potential sources of methodological and biological variability

“…Although there are some clinical data to support a modest benefit of low GI and GL diets in the management of diabetes (5,6), in the nondiabetic population the evidence is mixed (7). Meta-analysis of prospective studies supports a positive association between high GI diets and increased chronic disease risk (8), but data from randomized clinical trials indicate an inconsistent relation between dietary GI and GL values and insulin sensitivity (9), cardiovascular disease (8,10), weight loss (11,12), and cancer (13,14). Some of this discrepancy in the literature has been attributed to methodologic issues with its measurement (15)(16)(17)(18).…”