'High-glycemic' carbs like these hamper blood vessel function, study shows
THURSDAY, June 11 (HealthDay News) -- Eating a diet rich in carbohydrates that boost blood sugar levels -- foods such as cornflakes or white bread -- may hamper the functioning of your blood vessels and raise your risk of developing cardiovascular disease, a new study suggests.
And another study, released Thursday at the Endocrine Society's annual meeting in Washington, D.C., found that people might actually feel fuller -- and might therefore eat less -- if they cut back a bit on carbohydrates in their diet.
In the first study, researchers from Israel's Chaim Sheba Medical Center and elsewhere evaluated 56 healthy but overweight or obese men and women, aged 35 to 60. None had diabetes or a history of hospitalizations for cardiovascular disease.
The researchers fed the men and women on four different mornings, following overnight fasts. They were served either glucose, cornflakes, high-fiber cereal or water, in descending order of glycemic index.
Low-glycemic index foods include oatmeal, most fruits and vegetables, legumes and nuts. White bread, cornflakes and instant potatoes are high-glycemic indexes. The higher the glycemic index, the more that food raises blood sugar levels.
Before and after the meals or the water, the team of researchers measured the functioning of the endothelium, the layer of cells that line the inside of blood vessels. If the endothelial function is poor, it is thought to increase the risk of cardiovascular disease.
The measurement used is called brachial artery flow-mediated dilation (FMD), which measures how well the endothelium is functioning. Researchers also measured the participants' blood sugar levels.
The blood sugar levels before and two hours after the meals were similar, but they were higher at 30 to 90 minutes after the high-glycemic meals.
The FMD was reduced two hours after eating for all groups, but the reduction was more marked after the high-glycemic meals.
The high-glycemic meals, the authors conclude, appeared to impair the endothelial function.
"Based on our study, we do urge consumers to have low-glycemic index carbohydrates instead of high-glycemic carbohydrates for better health and less potential hazards for the vascular endothelial function," said Dr. Michael Shechter, senior cardiologist at The Sackler Faculty of Medicine at Tel Aviv University in Israel.
"The main take-home message is that high-glycemic index carbs are dangerous since they reduce or inhibit endothelial function, which is the 'risk of the risk factors,' leading to atherosclerosis and potentially leading to heart disease," Shechter said.
Previous research has found that high blood sugar levels after meals is a risk factor for cardiovascular disease, not only in patients with diabetes but in the general population. Declining endothelial function is considered a key variable in the development of hardening of the arteries and heart disease.
The study is published in the June 16 issue of the Journal of the American College of Cardiology.
Another expert called the study "interesting" but added a caveat that more research is needed to confirm the findings. "The cross-over design is a real strength," said Barry Braun, director of the Energy Metabolism Laboratory at the University of Massachusetts, in Amherst. But he said some "dots" still need to be connected.
In the second study, researchers at the University of Alabama at Birmingham investigated whether a small cutback in dietary carbohydrates would actually boost that sense of satiety you get after eating.
Led by professor of nutritional sciences Barbara Gower, the team noted that Americans typically get 55 percent of their daily calories from carbs such as sugars, starches and fiber. This was the "control" diet used in the study. The team had other adult participants go on a moderate carb diet where 43 percent of calories came from carbohydrates. Protein intake (a major influence on satiety) was the same for both diets, but people on the moderate-carb diet took in a bit more fat to make up the difference.
The results: after a month, the 16 participants on the moderate carb diet had lowered blood insulin levels, more stable blood sugar, and a longer duration of a sense of fullness after a meal than did the 14 people on the control diet.
A longer time feeling full might translate into less snacking or eating and perhaps fewer added pounds, the team said. So, "over the long run a sustained modest reduction in carbohydrate intake may help to reduce energy consumption and facilitate weight loss," Gower said in a meeting news release.
To learn more about glycemic index, visit the American Diabetes Association.
SOURCES: Barry Braun, Ph.D., associate professor, kinesiology, and director, Energy Metabolism Laboratory, University of Massachusetts, Amherst; Michael Shechter, M.D., senior cardiologist and director, clinical research unit, and senior lecturer, The Sackler Faculty of Medicine, Tel Aviv University, Israel; June 16, 2009, Journal of the American College of Cardiology; June 11, 2009, news release, Endocrine Society
All rights reserved