Why is brown rice high GI?

If you’re going to use the glycemic index (GI) of food it is important to have an understanding of what ‘GI’ means – it is not referring to the AMOUNT of sugar in the food but rather the QUALITY of the carbohydrate (aka. Why are grapes high in sugar but low GI?). The GI is simply a ranking of carbohydrates on a scale from 0 to 100 according to how quickly they break down, are digested and raise our blood sugar levels after eating. Foods with a high GI have a ranking of 70 or more – so this means they break down very quickly and are rapidly digested and absorbed which results in high fluctuations in your blood sugar levels. Low GI foods on the other hand break down very slowly and take longer to absorb, causing lower fluctuations in our blood sugar levels.
The GI of a food doesn’t solely depend on the fibre content of that product. For example, brown rice has a higher GI than white basmati rice yet it has more fibre overall. The reason for this is that dietary fibre is not made up of just ONE chemical component (unlike fat and protein). Dietary fibre is made up of MANY substances, the main two being soluble and insoluble dietary fibre. Soluble fibre, which white basmati rice and grapes are mainly made up of, is quite thick and jelly-like and remains like this even after digestion in our stomach - it’s this thick, jelly-like consistency that makes it hard for our digestive enzymes to move around and break down the food hence taking longer to be absorbed and therefore produces a lower GI value. Insoluble fibre on the other hand, which brown rice is mainly made up of, is not as thick and jelly-like and tends to act more like a barricade stopping access by enzymes and therefore slowing down digestion that way – the problem is, if the insoluble fibre is finely milled which is often the case in the production/harvesting of brown bread and rice, these enzymes then have free reign allowing for rapid digestion.
When we consume watermelon – we tend to leave the fibrous component and just eat the flesh (most of us even pick out the seeds, which again makes up some of the fibre).
In terms of preventing or managing diabetes and heart disease, research is providing strong evidence that a low GI diet is beneficial in managing these conditions. Low GI diets also reduce insulin levels and insulin resistance (pre-diabetes).
Try incorporating watermelon into a fruit salad with other low GI fruits so that you can still enjoy watermelon (particularly as a seasonal fruit). There are some wild brown rices on the market that aren’t milled and therefore are low GI – this is good way to have the best of both worlds (more fibre and low GI)

Samantha Ling
Rostant Nutrition
(Find us on facebook @ www.facebook.com/rostantnutrition )

Great answer above! You may also be interested to check out the following website, http://glycemicindex.com/

At the Glycemic Index website, you can read further on what influences the GI, e.g. fibre, fats etc and also there is a panel on the left hand side where you can check the GI of foods that may have been tested. 

Conitninug to choose lower GI foods has many great health benefits. All the best to good nutritional health. 

Claudia.

The GI is a percentage value between 1-100. It is obtained by measuring the blood glucose levels in people after they have eaten an amount of food that contains 50g of digestible carbohydrate (starches or sugars). What is not so clearly understood is that different amounts of food are required to get 50 gm of carbohydrate .
For example an approximate amount of food to provide 50gm carbohydrate is.
1kg watermelon
150-160gm ( over 1 cup) cooked rice ( brown/white)
2-3 slices of bread depending on brand

Therefore to use the GI you need to think about the amount of food eaten as well.
For watermelon for example you usually do not have 1 kg at a time.  This is why watermelon looks like it has a high GI. If you only have a few slices of watermelon it will have a lower glycamic effect than some foods listed in the low GI category ( dependingon serving size) because you are eating a smaller amount.

There are different things that effect how the carbohydrate effects the blood glucose level that is why brown and white rice have different GI's and it is not just based on fibre as Samantha has said. However fibre is important for other health benefits so maybe why you might choose brown rice above white rice if you control the serving size. However when you go to the website that Claudia suggests the GI of brown and white rice varies and some values overlap and it is not one fixed percentage. And if your serving size is smaller the glycaemic effect will be lower.

Some factors that influence GI other than fibre are-

• Type of starch present in the food. Some are digested faster or slower than other types of starch
  
• The physical form of the food – e.g. particle size, ripeness (the larger the particle size the more slowly the food is absorbed and the riper the fruit the more quickly it is absorbed)
  
• The amount of cooking or processing (more cooking / processing usually speeds up absorption. For example Quick oats has a higher GI than traditional oats.
  
• The amount of soluble fibre present (slows down absorption)
  
• The type of sugar (fruit sugar is more slowly broken down than sucrose (table sugar))
  
• Fat and protein content (fat and protein usually delay absorption). Adding low fat milk or yoghurt to breakfast cereal or fruit will lower the GI even further. Having meat or legumes with potato, rice or pasta will lower the GI further also.
  
• The acidity of food – e.g. adding lemon juice or vinegar to food, delays absorption.