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Is the glycemic index actually useful for making food choices?

Effects of high vs. low glycemic index of dietary carbohydrates on cardiovascular disease risk factors and insulin sensitivity.

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

Introduction

Foods that contain similar amounts of carbohydrates may differ in the amount and speed at which they raise blood glucose levels. This quality is referred to as the “glycemic index” (GI), and is based upon the blood glucose response (total area under the glucose curve) over two hours to 50 grams of its carbohydrate content, as compared with 50 grams of glucose.

The higher a GI value is, the more the food raises blood sugar in a way similar to pure glucose. Lower GI carbs are those that digest more slowly and don’t raise raise blood glucose to the same degree. However, GI can also be a function of insulin response, and not just a function of carbohydrate digestion or meal composition.

It has become common practice among healthcare professionals to suggest an individual consume “low glycemic index” carbohydrates. However the effects of GI on diabetes and cardiovascular disease (CVD) risk factors have been equivocal in trials[1], as well as meta-analysis[2] of observational studies.

Further complicating matters is the fact that carbohydrates are not eaten in isolation, but generally as part of mixed meals containing fat, fiber, potassium, polyphenols, and other nutrients that can affect health measures. It is still uncertain what (if any) practical significance there is for manipulating GI in the context of an otherwise healthy diet.

The DASH diet, or Dietary Approaches to Stop Hypertension, is an eating plan recommended for people with hypertension or prehypertension. The DASH diet has been shown to reduce blood pressure[3], lower risk of coronary heart disease[4], and improve bone mineral status[5]. The diet puts a big emphasis on increasing fruit and vegetable consumption, controlling sodium intake, and reducing processed food.

The objective of this randomized controlled crossover feeding study was to determine the effects of GI and amount of total dietary carbohydrate in the context of a DASH-type diet, on various risk factors for diabetes and CVD.

Sidebar: A sample guide to the DASH diet

A sample guide to the DASH diet

Who and what was studied?

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The big picture

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Other Articles in Issue #04 (February 2015)