Human bodies depend on a steady supply of glucose (blood sugar) as their principal fuel, in order for muscles to stretch and contract, nerves to fire, brains to function – and so much more. Glucose comes from carbohydrates, so the quality and quantity of carbohydrates we eat hugely impacts our energy levels and overall health.

David Jenkins (top) and Walter Willett (bottom)

Too little glucose, and we starve many bodily functions (especially the brain, which uses 11-20% of the glucose we produce). Too much, and our body scrambles to produce enough insulin to process all that blood sugar – and we may develop heart disease, eye, kidney and nerve damage. Ideally, our food delivers a steady stream of just the right amount of glucose.

But how do we distinguish foods, meals and diets that raise our blood sugar too high and too fast from those that dole out their fuel slowly and steadily to support good health? Understanding glycemic index, glycemic load and glycemic response can help.

Glycemic Index

Glycemic Index (GI), developed by David Jenkins (top, in image at right), Thomas Wolever and colleagues at the University of Toronto in 1981, ranks the quality of individual carbohydrate-rich foods on a scale of 1-100 by measuring how glucose levels rise after someone eats an amount of that food containing 50 grams of carbohydrate. Foods with a low GI score (under 55) provide steady fuel to support energy levels and overall health, while those with a high GI score (70 and up) are likely to provide an unhealthy quick rush of blood sugar followed by a sharp crash.

Glycemic Load

Walter Willett (bottom, in image at right) and colleagues at the Harvard School of Public Health created the concept of Glycemic Load. Glycemic Load (GL) combines quality and quantity, allowing us to rank how the typical serving size of a food affects blood sugar. A GL of 0-10 is considered low (slow, steady conversion to blood sugar; healthier), while a high GL is 20 and up (flash and crash – tough on health and energy levels). Research shows why GI and GL both matter: a low glycemic load can be achieved either by eating small amounts of high GI carbs, or large amounts of low-GI carbs, and some studies show that the latter approach (i.e. low-GI, low-GL) is best of all for health.

The Big Picture

While both GI and GL are useful measures of our glycemic response to certain foods or dishes, our body’s overall Glycemic Response – our management of blood sugar over time – also appears to depend on our total diet and lifestyle.

As useful as GI, GL, and GR can be, it’s important to keep in mind that understanding the effect of carbohydrates on blood sugar is just one part of choosing a healthy diet. The quality of fats and proteins matters too, as do fiber, vitamins, minerals and other factors. The bottom line? Eating a wide variety of delicious, whole, minimally-processed foods, guided by the latest science in all these areas, is the way to go.

Want to Learn More about the Science?

In 2013, Oldways partnered with the Nutrition Foundation of Italy (NFI) to bring together Dr. Jenkins, Dr. Willett and fifteen other worldwide experts on glycemic health, in Stresa, Italy. If you’re interested in learning more about the science behind glycemic health, we invite you explore presentations and proceedings from the International Consensus Summit on Glycemic Index, Glycemic Load and Glycemic Response, held June 6-7, 2013 in Stresa, Italy, north of Milan.