What is Glycaemic Index (GI)? Should we be avoiding all foods that have a high GI and plan our meals around magic GI numbers?

The Glycaemic Index (GI) uses a scale from 1 to 100 to rank carbohydrate foods on how quickly and how much they raise blood sugar after eating.

Scientists used to think that sugary foods cause a more rapid rise in blood glucose compared to starchy foods but this is not always true. Some starchy foods like white rice and potato score even higher than honey or table sugar.

Lower GI Helps Diabetics Control Blood Glucose Levels

Eating too much high GI foods causes repeated spikes in your blood glucose. Studies show that this can lead to an increased risk for type 2 diabetes, heart disease, obesity and colorectal cancer.

For diabetics, eating lower GI foods helps to control blood glucose levels and aid weight loss efforts.

GI is Not the Only Factor to Factor When it Comes to Carbs

Does that mean that we should always choose carbs with lower GI to better control our blood glucose levels?

The GI does not represent the amount of nutrients in foods. Many nutritious foods have a higher GI than foods with little nutritional value. For example, oatmeal has a higher GI than chocolate.

Fat and/or protein combined with carbohydrates will lower the GI value of the food. For example, deep-fried potato chips have a lower GI than boiled potatoes. This doesn’t mean it is healthier to eat potato chips!

That is why a food’s GI value should not be the only thing to consider when planning your meals. Choosing foods lower in saturated fat and salt, and high in nutrients is also important for your health regardless of their GI.

GI is Not the Only Reason Sugar Spikes

Similarly, eating foods high in GI does not necessarily lead to a spike in our blood sugar levels. There are many factors affecting the GI of a food and its impact on our blood glucose.

Portion Sizes

The total amount of carbohydrate we eat is as important as the GI of the food. For example, watermelon has a high GI but for the portion size we normally eat (one slice), is low.

Side Dishes

The impact of a food on our blood glucose is different when it is eaten on its own and when it is eaten together with other foods.

For example, eating a bowl of rice on its own produces a more rapid increase in blood glucose levels than if it is eaten with meat and vegetables.

Cooking

Cooking time affects the GI of a food too. Usually, the longer the cooking time, the higher the GI.

Processing

Processed foods tend to have higher GI. For example, fruit juice has a higher GI than whole fruit.

Use My Healthy Plate

While GI values are good-to-know and they help explain spikes in our blood sugar levels, we shouldn’t be planning our meals around them.

When deciding what to eat and how much to eat for a healthy, balanced diet, we should use My Healthy Plate instead.

1. Fill ½ of your plate with fruit and veggies
2. Fill ¼ of your plate with wholegrains
3. Fill ¼ of your plate with meat and other proteins

References

1. Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLOS Medicine.
   Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17760498

2. High dietary glycemic load and glycemic index increase risk of cardiovascular disease among middle-aged women: a population-based follow-up study. Journal of the American College of Cardiology.
   Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17601539

3. Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial. Journal of the American Medical Association.
   Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17507345

4. Dietary glycemic load and risk of colorectal cancer in the Women’s Health Study. Journal of the National Cancer Institute.
   Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/14759990

5. Carbohydrate and fiber recommendations for individuals with diabetes: a quantitative assessment and meta-analysis of the evidence. Journal of the American College of Nutrition.
   Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/14963049

6. Carbohydrates and Blood Sugar. Harvard T.H. Chan School of Public Health.
   Retrieved from https://www.hsph.harvard.edu/nutritionsource/carbohydrates/carbohydrates-and-blood-sugar/