As blood sugar levels rise, the pancreas produces insulin, a hormone that prompts edm food to absorb blood sugar for energy or storage. As cells absorb blood sugar, levels in the bloodstream begin to fall.

When this happens, the pancreas start making glucagon, a hormone that signals the liver to start releasing stored sugar. This interplay of insulin and glucagon ensure that cells throughout the body, and especially in the brain, have a steady supply of blood sugar. Carbohydrate metabolism is important in the development of type 2 diabetes, which occurs when the body can’t make enough insulin or can’t properly use the insulin it makes. Type 2 diabetes usually develops gradually over a number of years, beginning when muscle and other cells stop responding to insulin. This condition, known as insulin resistance, causes blood sugar and insulin levels to stay high long after eating. Over time, the heavy demands made on the insulin-making cells wears them out, and insulin production eventually stops. Dividing carbohydrates into simple and complex, however, does not account for the effect of carbohydrates on blood sugar and chronic diseases.

To explain how different kinds of carbohydrate-rich foods directly affect blood sugar, the glycemic index was developed and is considered a better way of categorizing carbohydrates, especially starchy foods. The glycemic index ranks carbohydrates on a scale from 0 to 100 based on how quickly and how much they raise blood sugar levels after eating. Foods with a high glycemic index, like white bread, are rapidly digested and cause substantial fluctuations in blood sugar. Foods with a low glycemic index, like whole oats, are digested more slowly, prompting a more gradual rise in blood sugar. Low-glycemic foods have a rating of 55 or less, and foods rated 70-100 are considered high-glycemic foods. Medium-level foods have a glycemic index of 56-69. Foods with a low glycemic index have been shown to help control type 2 diabetes and improve weight loss.

A 2014 review of studies researching carbohydrate quality and chronic disease risk showed that low-glycemic-index diets may offer anti-inflammatory benefits. The University of Sydney in Australia maintains a searchable database of foods and their corresponding glycemic indices. Processing: Grains that have been milled and refined—removing the bran and the germ—have a higher glycemic index than minimally processed whole grains. Physical form: Finely ground grain is more rapidly digested than coarsely ground grain. Fiber content: High-fiber foods don’t contain as much digestible carbohydrate, so it slows the rate of digestion and causes a more gradual and lower rise in blood sugar.