Effects of high vs low glycemic index of dietary carbohydrate on cardiovascular disease risk factors and insulin sensitivity: the OmniCarb randomized clinical trial.
Level 2 - randomized trial
Individual randomized crossover-controlled feeding trial
PubMed 25514303 · doi:10.1001/jama.2014.16658
What was done
In a randomized crossover controlled-feeding trial (OmniCarb), 163 overweight adults with systolic blood pressure of 120 to 159 mm Hg received complete meals, snacks, and caloric beverages for 5-week periods across four DASH-pattern diets. The diets crossed glycemic index (high: 65% vs low: 40% on the glucose scale) with carbohydrate content (high: 58% vs low: 40% of total energy). Primary outcomes were oral glucose tolerance test–derived insulin sensitivity, LDL cholesterol, HDL cholesterol, triglycerides, and systolic blood pressure, evaluated across pairs of diets in 135 to 150 participants per contrast.
What was found
At high carbohydrate intake, consuming a low- compared to high-glycemic index diet reduced insulin sensitivity from 8.9 to 7.1 units (-20%, P = .002) and increased LDL cholesterol from 139 to 147 mg/dL (+6%, P ≤ .001), with no significant effect on HDL cholesterol, triglycerides, or blood pressure. At low carbohydrate intake, lowering glycemic index did not change insulin sensitivity, blood pressure, LDL, or HDL, but decreased triglycerides from 91 to 86 mg/dL (-5%, P = .02). Comparing the low-glycemic/low-carbohydrate diet to the high-glycemic/high-carbohydrate diet showed no effect on insulin sensitivity, blood pressure, LDL, or HDL, but reduced triglycerides from 111 to 86 mg/dL (-23%, P ≤ .001).
Why it matters
These findings challenge the premise that selecting foods primarily based on a lower glycemic index improves insulin sensitivity or cardiovascular risk factors when consumed as part of an already healthful dietary pattern.
Limits
Each dietary phase lasted only 5 weeks, precluding assessment of long-term adherence or hard cardiovascular events. The study was conducted in overweight adults with elevated blood pressure within an overall healthy DASH-type background diet, so results may not generalize to other populations or lower-quality baseline diets.
Cited by
- supports A study conducted by Harvard researchers failed to demonstrate a significant relationship between dietary glycemic index and LDL or other lipid levels.