The glycemic index (GI) is a value of foods (on a scale of 1-100) based on how quickly the blood glucose level changes after you eat. Foods with a low GI have a longer digestion period with slower blood glucose release, while foods with a high GI are quickly digested, followed by larger increases in blood sugar levels.

Low GI food can promote weight loss and better blood glucose control, while high GI food helps those in the recovery phase after intense exercise or hypoglycemic episodes. If you have diabetes, it would be better to eat low GI food to promote sugar control.

The test is a two-day study and performed under a standardized protocol. A healthy individual was given 50 grams of carbohydrate (test), followed by blood glucose measurement after two hours. On the second day, the same individual was given 50 grams of pure glucose (reference), followed by glucose level measurement.

Then, the GI of the test food is calculated by dividing the glucose AUC for the test food by the glucose AUC for each person’s reference food, and the final GI value will be an average of the total participants. [1] University of Sydney, Australia, maintains the GI database.

The level of GI can be divided into 3 groups: low GI (0-50), medium GI (51-69), and high GI (70+).

Glycemic index is failed to specify the amount of particular you would need to eat to reach a certain level. E.g., watermelon has a GI of 80, which puts this food into a high GI category. However, watermelon has few digestible carbohydrates in a regular serving, and you would need to consume a lot of watermelons to raise your blood glucose level.

To modify this limitation, researchers developed a new measurement system called glycemic load (GL). GL calculates both the quality and quantity of the food being eaten.

Glycemic Load = GI x Carbohydrate (g) content per portion ÷ 100

GL can be classified as following (Per Sydney University):

• Low: 10 or less
• Medium: 11 – 19
• High: 20 or more

Knowing the glycemic index of various foods would help you choose a diet that wouldn’t cause a sudden increase in blood sugar levels.

Carbohydrate consumption is critical for those who are aiming for bodyweight control or weight loss. The researcher attempted to compare effects of various diet compositions (a low-protein and low-glycemic-index diet, a low-protein and high-glycemic-index diet, a high-protein and low-glycemic-index diet, a high-protein and high-glycemic-index diet, or a control diet) on weight loss maintenance. In this study, the best result for weight loss and maintenance was achieved in high protein and low GI food. [2]

A meta-analysis of six randomized controlled trials was performed to compare the effect of a low glycemic index or load diet with a higher diet or other diets in overweight or obese people. It reported that lowering the diet’s glycemic load seems to be an effective method for weight loss and improving lipid profiles. [3]

Consumption of low glycemic index food appears to have cardiovascular risk factor modification by having better blood pressure and cholesterol control. The concept was tested by comparing the effects of low- and high-GI foods on 24-hour ambulatory blood pressure. The research study included 30 women who were given two different GI foods followed by 24-hour blood pressure measurement and revealed a significant reduction of BP (systolic –10.6 mmHg and diastolic –7.5 mmHg) with low GI foods. [4] Moreover, a meta-analysis of low GI diet effect on blood cholesterol level showed a reduction of total and LDL-cholesterol but no effect on HDL-cholesterol or triglycerides. [5]

On the contrary, another meta-analysis, including fourteen studies with 229,213 participants, reported that high GL and GI diets were associated with a significantly increased risk of cardiovascular disease, specifically for women. [6] Recently, Dr. Jenkins and his colleagues performed an analysis on a large, geographically diverse population living on five continents, with a median follow-up of 9.5 years. The result demonstrated again that a diet with a high glycemic index was associated with an increased risk of cardiovascular disease and death regardless of underlying comorbidities.[7]

The impact of various glycemic effects is thought to be one of the contributing factors to the development of diabetes. Meta-analysis showed that high GI diets could increase the risk of developing Type 2 diabetes by up to 87%. [8] Low GI diets were associated with better glycemic and body weight control in those with prediabetes or diabetes.[9] Although there is a concern for hypoglycemia with low GI diets, another study showed that low GI diets improve glucose control in diabetes individuals without increasing hypoglycemic events than conventional healthy diets.[10]

Pregnancy can cause various medical problems such as elevated blood pressure and gestational diabetes mellitus. As dietary control is the mainstay treatment of diabetes patients, clinicians wonder about the utility and safety of low GI diets in pregnancy. A meta-analysis of 9 randomized controlled trials of low GI diet in pregnancy-related DM showed a beneficial effect of less frequent insulin use and lower birth weight than control diets. [11]

Glycemic Index of various foods based on level

The lower the glycemic index, the lesser effect on blood glucose and insulin levels while the higher GI score can result in higher blood sugars level quickly.