Glycemic Index and Glycemic Load

What are they? Why do they matter? How can this help us make healthier food choices?

The hidden sugar in our diet?

When we eat food containing carbohydrates (like bread, potatoes, rice and pasta) our digestive system breaks down the digestible carbs into sugar, which enters our blood.

When blood sugar spikes, extra insulin is released to lower it. If extra insulin is required regularly, resistance may occur. This can potentially lead to diabetes – especially in families where there is already a history of the illness. And diabetes increases other health risks, like stroke and heart attack.

We shouldn’t stop eating carbohydrates. They form part of a balanced diet. But we need to try to eat more ‘good’ carbs and less ‘bad’ carbs.

That’s why glycemic measures could be important

The glycemic response to food is the effect that food has on our blood sugar levels. Glycemic Index and Glycemic Load are two complementary ways of measuring this.

What is the Glycemic Index?

Glycemic Index (GI) identifies how fast foods release sugar into the blood stream. High GI foods (above 70) release sugar quickly, resulting in a rapid rise in blood sugar levels. In contrast, low GI foods (below 55) release sugar (glucose) gradually over a number of hours, so less insulin is consumed.

Food is likely to have a higher GI if it has been processed or refined, if it has been finely ground, if it has a low fibre content and if (in the case of fruit and vegetables) it is ripe.

And what is the Glycemic Load?

Research suggests it is the amount of carbohydrate you eat, rather than its GI rating, which has the biggest effect on blood glucose levels after meals. 

That’s why the Glycemic Load (GL) was developed. It takes into account both how much carbohydrate there is in a portion of food and how quickly this is likely to raise blood glucose levels. So GL uses the Glycemic Index but adds a further (carbohydrate) dimension. This means it is probably a more reliable indicator. 

Food with a GL of less than 10 is low GL and should have little effect on your blood sugar. 10 – 20 is moderate GL, with a moderate effect on your blood sugar. Foods with a GL of over 20 are the ones to be wary of – as they tend to cause blood sugar spikes.  

So what foods should I eat? 

The following foods have both a low GI and a low GL, so are recommended: 

  • Most vegetables grown in the UK: like broccoli, cabbage, carrots, cauliflower, celery, green beans, mushrooms, parsnips, peas, spinach and tomato.
  • Most fruit grown in the UK: like apples, pears, plums, cherries and strawberries.
  • Most pulses: like lentils, chickpeas and lima beans.
  • Most sources of protein: including meat, fish and nuts   
  • Dairy milk and soya milk 

Some foods have a high GI but a low GL, so are OK to eat – like watermelon and cous cous. Fruits from warmer countries tend to have a higher GI and medium GL but oranges and grapefruits have low levels. 

And what foods should I eat less of?  

White rice, potatoes, donuts, bagels and pizza all have a high GI and a high GL. Pasta has a low GI but a high GL. 

Brown rice has medium GI and GL, so is normally recommended in place of white rice. And wholemeal bread and pasta have a high GI but a low GL, so are also OK to eat. 

Does this fit with what we’re told about a healthy diet anyway? 

Yes. What you’ll probably have noticed is that (with the possible exception of red meat) most low GI, low GL foods are also ones that regularly appear on lists of the kind of foods to include in a healthy diet  - so the fact that they are low GI and low GL is an added bonus.   

What diseases might a low GL/GI diet help protect against? 

A low GL diet is associated with a significantly lower risk of type 2 Diabetes,according to a 2013 analysis of 24 long term studies.

A number of studies suggest it is also associated with a lower risk of stroke – including a study of 19,824 people in Greece, published in 2015 and an analysis of seven studies, involving 225,000 participants across six countries, also published in 2015, which suggested it was high GL rather than high GI which was the risk factor for stroke. 

In comparison a low GI diet was associated with a slight reduction in the risk of coronary heart disease , according to a review of the evidence in 2012. It may also help lower cholesterol, according to a review of the evidence published in 2013.

It has also been suggested that a low GI/GL diet helps you feel fuller, longer, meaning you’re less likely to overeat and become obese – although research findings here are more mixed.

A summary of the research findings, updated in 2016, concluded that a low GL diet is associated with a reduced risk of conditions such as obesity; type 2 diabetes; cardiovascular disease (such as heart attack and stroke), especially among women and people who are overweight or obese; and possibly gall bladder disease. The reduced risk for type 2 diabetes was described as modest but significant.

Conclusions 

  • A healthy diet is likely to contain a lot of food which has a low GL.
  • Typical low GI/GL foods include most vegetables and fruits that grow in the UK, pulses, fish, nuts and dairy or soya milk.
  • A low GL diet is associated with a reduced risk of type 2 diabetes, stroke and (for women) coronary heart disease.
  • A low GI diet may help reduce cholesterol.  

Reviewed and updated by Nadine Richards May 2014 and Kayhan Nouri-Aria March 2017. Next review date February 2020.  

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