Back in 1981, Dr David Jenkins, a nutritional scientist, tested a range of foods, each containing 50 grams of carbohydrate, on people. He measured the blood sugar reactions and used them to rate the foods on a scale he called the glycaemic index (GI). He discovered that certain starchy foods, such as potatoes and cornflakes, raised blood sugar nearly as much as pure glucose. These earned high GI scores.
One thing the GI doesn’t take into account, though, is how much carbohydrate a serving of a food contains. You’d have to eat a lot of carrots to get 50 grams of carbs. A better measure, then, is the glycaemic load (GL), which includes both the GI and grams of carbs per serve and so corrects this problem.
High-GL foods cause blood glucose levels to rise sharply, prompting the pancreas to secrete insulin to bring it back down. Low-GL foods create a smaller, more sustained rise in blood glucose and require less insulin.
Why is Low-GL Better?
Studies have found that people who eat high-GL diets have higher rates of obesity, diabetes, heart disease and cancer. Several long-term studies have shown that people who ate more high-GL foods had a substantially higher chance of developing type 2 diabetes. However, multiple studies have shown that dietary changes – even minor ones – to low-GL options cut those risks. Eating low-GL can also help if you already have diabetes.
How to Choose Low-GL
First and foremost, reach for more fresh, non-starchy fruits and vegetables, nearly all of which fall very low on the GL scale. (Go easier on starchy vegetables such as potatoes, parsnips, corn and peas.) Dairy and protein foods are often very low, having few or no carbs. Choose breakfast cereals with at least 5 grams of fibre per serving and they will likely be low GL. And opt for whole grains (such as brown rice, barley, bulgur, oatmeal and coarse whole-wheat bread) over refined grains like white rice, bread and white flour products.
What Should I Avoid?
No foods are banned completely from a healthy diet, but see the chart below for foods to cut back on, eat in smaller portion sizes or swap for choices that don’t raise blood sugar as much.