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Diet for diabetes

Why are the Glycemic Index and Glycemic Load important for Diabetics?

The Glycemic Index and the Glycemic load, which is calculated from it, are essential tools for managing blood glucose levels. To learn how and why read on!

Richard Johnson
Reading time: 
6
minutes
Published: 
March 15, 2022

Why are the Glycemic Index and Glycemic Load important for Diabetics?

For those who have Prediabetes or Diabetes and struggle to manage their blood glucose level, glycemic index and glycemic load, which is calculated from it, which are essential tools that can help manage the condition by aiding diabetics control what foods they consume.

How Does the Glycemic Index and Glycemic Load work?

The glycemic index (GI) ranks food according to its effect on blood sugar levels (the effect on blood glucose levels once digested). Carbohydrate-containing foods are assigned a GI number (between 0 and 100). Glucose is used as the baseline (GI 100) and other foods are measured against this. The higher the number, the more it raises blood glucose levels.

The glycemic load (GL) uses the glycemic index and portion sizes to rate food according to how much it raises blood glucose levels. Because of this it is a more reliable and useful measurement than GI alone.

The glycemic load is calculated by taking a food's glycemic index, multiplying it by the carbohydrate content (measured in grams) and dividing the figure by 100. 

For example, an apple has a glycemic index of 44 and has 7 g of net carbohydrates per 100 g. So eating a small apple, which weighs 150 g, would give us 10.5 g net carbs. In this case, the glycemic load of a small apple would be (44*10.5)/100 = 4.62 (using the UK food database and the international tables of glycemic index load values 2021).

If the result is equal to or below 10 then the glycemic load is low. If it is equal to or above 20 then it’s high and if it is in between, it means that it has a medium GL. So in the case of a small apple, the calculated GL is low.

If you want to know the glycaemic load of the foods you eat, just download DiabTrend as it automatically calculates it for you when you track your food (if the tracked food also has a glycaemic index). 

Note: The glycemic index of foods only works with food that have at least 25 g / 50 g carbs per serving. Foods with really low carbohydrate content, such as herbs or non-starchy vegetables like salad, eggplant, zucchini, etc. can not be measured, nor can those with no carbohydrates whatsoever (meat, oil, fish) and are not assigned to the GI. 

GI values for some popular foods

Foods with a low GI are absorbed slower, so blood glucose levels rise slower after eating them.

Foods with a high GI are absorbed quickly in the gastrointestinal tract, so they will produce a quicker rise in blood glucose levels. 

What are complex carbohydrates and what is the benefits of eating them? 

Complex carbohydrates are carbohydrates that contain more than two simple carbs (monosaccharides). For the diabetic patients, the best complex carbohydrates are the fibre rich complex carbohydrate foods.

Choosing fibre rich foods (like fresh fruits and veggies, whole legumes, whole grains, nuts and seeds) that are slowly absorbed can help to keep your blood glucose levels stable. Additionally, fibre rich foods can help to:

  • Control your appetite by making you feel fuller for longer, helping you to eat less and lose weight if needed.
  • Avoid high blood sugar spikes after meals.
  • Lower 'bad' (LDL) cholesterol levels.
  • Contribute towards a healthy diet that could help protect against heart disease, strokes, cancer and other long-term health conditions.

What else affects GI?

The following things can affect the GI of a food:

  • The physical form of the food, e.g. high fibre foods, act as a physical barrier that slows down the absorption of starchy carbohydrates. Keeping the plant cells intact keeps the GI lower, but processing it, e.g. cutting, pureeing or mashing foods and juicing fruits and veggies, can raise the GI.
  • The type of starch, e.g. the starch in durum pasta, porridge oats and basmati rice is digested more slowly due to their higher amylose content.
  • Cooling down some starchy foods such as boiled rice or boiled potatoes increases the resistant starch content in them and also lowers their GI.
  • The type of fibre, e.g. the fibres in oats, fruit, beans and lentils slow down the rate of digestion. Water-soluble fibres are the most common in such foods.
  • Type of sugar, e.g. fructose has the lowest GI (GI=24) and glucose has the highest (GI=100), while sucrose is in between with GI=66.
  • The ripeness of fruit, e.g. riper bananas have a higher GI.
  • The cooking method, e.g. frying foods can lower the GI because of the added fat. When cooking without added fat, keep it "al dente" as cooking for too long could actually increase the GI.
  • Nutrient composition, e.g. fat and protein slow down the absorption of carbohydrates. 

Are low GI foods always the healthier choice?

No, not all low GI choices are healthier options. Fats slow down digestion and the absorption of glucose, e.g. chocolate and crisps have a medium GI, but this is because of their high-fat content and so they are not necessarily a healthier choice. 

One problem with both the GI and GL is that it does not consider the type of sugar in the food. For example, although fructose is ranked the lowest on the GI scale of all sugars at just 24 and takes the longest to raise blood sugar levels, you still shouldn’t consume it excessively. 

Even though people previously thought that added fructose could be consumed without any adverse health effects, unfortunately, that's not the case. Studies suggest that eating more than 30-50 g of free or added fructose a day could cause health issues in the long term. Free fructose appeared to increase insulin resistance in the liver, and also raise uric acid levels, which could lead to gout in the long run. 

A balanced diet using the GI, with careful consideration to sugars, is best. Avoiding excess sugar of any kind is one way to successfully manage diabetes.

Can a Low GI diet prevent Type 2 Diabetes?

The simple answer, with caveats, is yes.

In the “preview project”, funded by the EU and designed to determine if it was possible to delay or avoid type 2 diabetes, they found that it was possible to either delay or completely prevent Diabetes type 2 by altering lifestyle factors, including diet. In fact, they specifically looked at low GI diets. It was published in the November 2020 issue of the journal Diabetes, Obesity and Metabolism.

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