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A study found that eating low-glycaemic foods did not result in substantial health benefits for people without diabetes who already had a healthy diet. Published in the Journal of the American Medical Association, the study investigated the effects of following four different diets, for five weeks each, on risk factors for cardiovascular disease and diabetes. The study enrolled 163 overweight and obese individuals with prehypertension or stage 1 hypertension. Each diet was designed to be healthy—with plenty of vegetables, fruits, lean meats, fish, beans, and grains. The diets differed in the amount of carbohydrates they contained and the glycaemic index of those carbs; the glycaemic index measures how quickly a particular food causes a rise in blood sugar. High-glycaemic foods (like white bread) cause a sharper blood sugar spike than low-glycaemic foods (like whole grains). The researchers were primarily interested in comparing the effects of switching between low-glycaemic and high-glycaemic foods when the amount of carbs stayed roughly the same. Here’s what they discovered:

• With a diet high in carbs, switching to low-glycaemic foods did not benefit HDL cholesterol, triglycerides, or blood pressure. In fact, the low-glycaemic, high-carbohydrate diet increased LDL (“bad”) cholesterol, and decreased insulin sensitivity.
• With a diet low in carbs, switching to low-glycaemic foods also did not benefit HDL cholesterol, blood pressure, or insulin sensitivity. It did result in a small decrease in triglyceride levels.
• However, switching to a diet that was lower in carbohydrates, irrespective of the glycaemic index of those carbs, substantially lowered triglyceride and LDL cholesterol levels, and slightly lowered diastolic blood pressure.

While the study suggests that reducing overall carbohydrate intake may be more important than eating low-glycaemic foods, the findings are limited to people without diabetes. However, there is evidence that suggests eating low-glycaemic foods does help with blood sugar control in individuals with type 2 diabetes. Furthermore, it's possible that eating low-glycaemic foods is a healthy choice for everyone, but that the results would only show up over a period of time longer than five weeks.

Source: Journal of the American Medical Association