This article is a collaboration between MedPage Today® and:
Overweight and obese people who followed a low glycemic index diet in the context of an overall DASH-type diet had no greater improvements in insulin sensitivity, lipid levels or systolic blood
This article is a collaboration between MedPage Today® and:
Overweight and obese people who followed a low glycemic index diet in the context of an overall DASH-type diet had no greater improvements in insulin sensitivity, lipid levels or systolic blood pressure compared with study subjects who ate high glycemic index foods, in a randomized, controlled feeding study.
The OmniCarb Randomized Clinical trial was a cross-over study conducted to better understand the effect of glycemic index (GI) and total dietary carbohydrate on risk factors for cardiovascular disease and diabetes.
Following a low-glycemic index, low-carbohydrate diet, compared with a high-glycemic index, high-carbohydrate diet did not affect insulin sensitivity, systolic blood pressure, LDL cholesterol or HDL cholesterol, but it did lower triglycerides during the from 111 to 86 mg/dL (-23%, P≤0.001), researcher Frank M. Sacks, MD, of Harvard School of Public Health, and colleagues wrote in the Dec. 17 issue of JAMA.
"Paradoxically, the low-glycemic index, high-carbohydrate diet decreased insulin sensitivity and increased LDL cholesterol and LDL apolipoprotein B levels while other dietary factors that affect LDL levels such as saturated fat, cholesterol and fiber were held constant," the researchers wrote. "These findings are contrary to our hypotheses on glycemic index."
Glycemic Index: What's in a Carb?
The health effects of certain carbohydrates have been the subject of much speculation and debate among the general public, health professionals and policymakers, with the increased recognition that different types of carbohydrate-rich foods have different effects on blood glucose levels, the researchers wrote.
This property, called the glycemic index, is represented by a number reflecting the total rise in a person's blood glucose following consumption of a specific food. The glycemic index is quantified according to the amount 50 grams of its carbohydrate compared with 50 grams of glucose increased blood glucose over the course of 2 hours, the researchers noted.
"For example, a banana increases blood glucose more than an apple that has the same amount of carbohydrate. Boiled sweet potato increases blood glucose more than boiled carrot. Meals or complete diets may be designed using these tables to have a desired overall glycemic index," the researchers wrote.
They further noted that even though some have advocated eating low-glycemic foods as a strategy for improving health, "the independent benefits of glycemic index are uncertain, especially when persons are already consuming a healthful diet rich in whole grains, vegetables and fruits."
Feeding Study Included 163 Overweight Adults
The OmniCarb trial included 163 overweight adults with baseline systolic blood pressure readings of between 120-159 mmHg who were randomized to four different diets, including all meals, snacks, and calorie-containing beverages, for 5 weeks, with each participant crossing over to a different diet for a second feeding period.
For any pair of the four diets, there were 135 to 150 participants contributing at least one primary outcome measure.
Eligible participants began an 8-day run-in phase, in which each study diet was given for 2 days. After the run-in, they were randomized to a sequence of the 4 study diets.
"For a crossover study with four diets to be administered, there are 24 possible sequences, of which we used eight," the researchers wrote. "We wanted to ensure that the high– and low–glycemic index diet components were each used in the first two periods for all participants."
Each diet was given for 5 weeks separated by a break of at least 2 weeks during which study participants ate foods of their choosing. Calorie intake was adjusted to maintain initial body weight. Participants completed a daily food diary for each day on the controlled diets, recording any foods that they did not eat and any additional items eaten.
On-site, weekday meal attendance was recorded and m