Glycemic index has quickly become a popular way to judge the sugar content of foods. The index looks at how fast foods increase the amount of sugar in your blood. Simple sugars like table sugar are absorbed quickly and cause your blood sugar to spike rapidly after you eat. More complex sugars, like those found in a carrot or apple, are absorbed more slowly so blood sugar takes longer to increase. Other components of a sugar-containing food, like fiber, can also slow the absorption of sugar.
These spikes in blood sugar are thought to contribute to diabetes. The refined sugar found in many of today’s foods moves more rapidly into the blood than our body is prepared to handle. That can stress our ability to control blood sugar and lead to diabetes. The theory behind glycemic index was that eating foods with a low glycemic index decrease these spikes and stress the body less, thereby slowing progress to diabetes.
While this makes sense when comparing apples to Twinkies, it was unclear whether this was a good way to test healthy foods against each other. But fruits and vegetables often contain many other vitamins, minerals, and nutrients in unique combinations that our body needs to stay healthy. A group of researchers set out to see how glycemic index and the amount of carbohydrates in a person’s diet would influence markers of their overall health.
They gathered 160 men and women who were overweight or obese and looked at their blood pressure, blood sugar, LDL (bad) cholesterol, and blood triglycerides (circulating fat). They then split them into two groups: one followed a higher carb diet called the DASH diet promoted by many American medical organizations and the other followed a low carb diet based on the Mediterranean diet. Within these groups, participants either ate higher glycemic index foods or lower glycemic index foods.
The study was a cross-over study, which meant that after five weeks on one diet each participant was “crossed over” to another diet. After five weeks on the second diet, they switched to the third and then to the fourth after another five weeks. Participants did the diets in different orders, but eventually did all four kinds of diets. They were given all their food during the diets to make sure they stuck to the food they were supposed to eat.
At the end of all four diets, the researchers found that low carbohydrate Mediterranean diet lowered blood pressure and blood triglycerides compared to the high carb DASH diet. Compared to where the participants started, both diets lowered blood cholesterol and blood pressure.
Glycemic index had no effect on cholesterol or blood pressure. When it came to blood sugar and sensitivity to insulin, the hormone the body uses to control blood sugar, low glycemic index foods actually increased circulating blood sugar and decreased how sensitive the body was to insulin, the complete opposite of what you might expect. The researchers did not know why this was the case.
This research indicates that the healthiness of the food you eat, determined by the wholeness of the food and the vitamins, minerals, and other nutrients found in a food, is much more important than how much it increases your blood sugar. In fact, glycemic index has been studied by many other research groups and hasn’t been found to improve the many markers of health doctors look for like cholesterol, blood sugar or blood pressure. What matters is that your diet is lower on total carbs and full of healthy fruits and vegetables, regardless of their sugar content.