Originally developed as research tools, the glycemic index and glycemic load can also be used to help predict how different types of carbohydrate foods will affect blood glucose levels. The term "glycemic" means "sugar in the blood". The GI and GL rank carbohydrates on a scale from 0 to 100, based on their immediate effect on the "sugar in the blood" after eating. This is called the glycemic response.

Foods with a high GI/GL are those which are rapidly digested and absorbed, resulting in marked fluctuations in blood sugar levels. Low GI or GL foods produce gradual rises in blood sugar and insulin levels, and have proven benefits for health. However, keep in mind that for diabetes and weight control, portion size is also vital, regardless of a food’s GI/GL rating.

To have stable blood glucose levels, the bulk of your carbohydrates should be of low GI/GL. Mostly this means eating less sugars and refined grains and more vegetables and unrefined grains, but there are a few surprises - some of the complex carbohydrates behave more like simple sugars, with a quick release of glucose. For example, white potatoes, French fries and many breakfast cereals such as cornflakes all have a high GI/GL.

Although GI/GL can be helpful for understanding how carbohydrates work in the body, research has not yet proven that a low GI/GL diet will prevent diabetes. The GI/GL should by no means be used in isolation, but as a tool.

"Contains 0 net carbs!" is a claim often used in food advertising. Such a claim may sound pretty good at the outset, but unfortunately it has insufficient scientific basis.

Net impact carbs is more of a marketing strategy than anything else. It is “calculated” by subtracting certain carbohydrates, such as fiber and sugar alcohols, from the carbohydrate count. Often a low net-carb value is achieved by substituting certain carbs for others, such as wheat flour for soy flour.

Net-carb labeling can be misleading; some products that claim to have low net carbs are actually high in real carbohydrates and in calories. For example, Atkins Cookies ‘n’ Crème Advantage Bar contains "only 2g net carbs", but 22 grams of actual carbohydrate. The bar also has 259 calories, but because of the “net carb” value, calories are calculated on the package as only 220.

The Center for Science in the Public Interest (CSPI) is currently urging the FDA to prohibit the “net carb” claim altogether, arguing that it is invalid and deceptive.