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The Highs and Lows of GI

Prepared by Kelly Ancuk & Kylie Norman Diabetes Dietitians

HNE Diabetes Service – TamworthUpdated November 2009

Introduction to GI Numeric measure of how different foods

containing carbohydrates impact on blood glucose levels – rate digested

Introduced in the 80’s

“Glycaemic”

– Greek for “sugar in blood”

Method of testing A 50g portion of carbohydrate is administered to an

individual – after an overnight fast.

BGLs are tested every 15 to 30 mins over a 2 – 3 hour period.

BGLs are plotted and the incremental area under the response curve above the baseline is calculated.

The area under the blood glucose response curve for the test food is expressed as a percentage of the mean response to the standard food.

The GI value is determined by repeating the procedure on up to 5 –15 individuals.

The results are averaged to obtain the GI.

Factors affecting GI Type of starch

– A higher ratio of amylose to amylopectin produces a slower rate of digestion. The highly branched nature of amylopectin makes it more susceptible to degradation and breakdown.

amylopectin

amylose

Factors affecting GI Type of sugar

– Natural sugars tend to have a lower GI (fructose, lactose)

– Fructose elicits a low GI response due to the incomplete absorption and only partial conversion to glucose.

– Sucrose has a GI of 59 – challenges the typical thinking that sugar and foods containing sugar cause an excessive rise in BGLs

Factors affecting GI Cooking and Food Processing

– Processing has been associated with increasing glycaemic responses.

• Eg rice cakes with the puffed texture (GI 82)

Viscosity of Fibre

– Soluble fibre is often viscous in solution and remains like this in the small intestine. It is harder for enzymes to move around and digest the food. Foods with more soluble fibre, have low GI values.

Factors affecting GI Particle size

– The smaller the particle size the easier for water and enzymes to penetrate.

Fat

– Fat is known to reduce gastric emptying, jejunal motility and postprandial flow rates in the intestine - reducing the GI.

Acidity

– Acid slows stomach emptying slowing the rate at which starch is digested.

Pros – Low GI Diet Low GI lead to smaller fluctuations in blood

glucose levels, compared to high GI equivalents

May improve HbA1c levels as much as diabetes medications

Lower HbA1c levels are achieved without increasing the risk of having a hypo or other side effects

Improve the body’s ability to use insulin

GI concept can be used to fine tune carbohydrate servings

Pros - Low GI Diet Improve common risk factors for heart and blood

vessel disease

May prevent people from getting Type 2 Diabetes

May help people to lose more body fat, and to conserve lean muscle when trying to lose weight

May improve ability to lose weight

Easy and sustainable – can eat everyday foods without cutting out any food groups

Cons – Low GI Diet It is unknown if people can eat lower GI diets for

long periods of time

GI does not reflect the usual amounts of food people eat as it is based on serves that contain 50g carbohydrate

Individual's blood glucose response to a food varies on a daily basis

GI of foods varies from country to country.

Labelling foods as “good“ or “bad” based on their GI.

Cons – Low GI Diet GI is not the best indicator of food choices, with

many sugary and fatty foods having low to medium GI’s

Cons – Low GI Diets Evidence supporting the use of GI in diabetes

management is mostly from relatively short term studies (3-6 months)

Other dietary measures provide greater improvements in HbA1c than GI alone

Diets high in fibre may provide similar benefits to low GI diets

Total amount of carbohydrate eaten has a strong influence on blood glucose levels and watching the grams of carbohydrate eaten or using carbohydrate exchanges is a key strategy for managing blood glucose levels.

Criteria for GI symbol Must be tested by approved laboratory using the

Australian Standard procedure.

Products must contain at least 10g of carbohydrate, or be ≥ 80% carbohydrate AND be traditionally served in multiple units of small serve sizes.

The product must meet nutrition criteria

– Energy

– Total fat and saturated fat

– Sodium

– Dietary Fibre

– Calcium

New GI symbol

Some things to keep in mind The GI only applies to carbohydrate-rich foods

You don’t need to avoid all high GI foods

– A meal that includes a high GI food such as a typical potato and a low GI food such as sweet corn will result in a lower GI overall.

The GI is not intended to be used in isolation

High GI, high nutrition

Low GI, low nutrition

Low GI, high nutrition

High GI, low nutrition

Some things to keep in mind You don’t need to add up the GI each day

– Altered by processing and cooking. Hard to calculate precise GI. Categorise as low, medium and high.

Are foods containing sugar excluded?

– Focus on overall GI and total carbohydrate content rather than sugars

References Barclay A. A debate: to GI or not to GI – that is the question.

Conquest, Autumn 2007.

Barclay A. The glycaemic index and the GI symbol program. 2009; GI Ltd & University of Sydney.

Brand-Miller J. Foster-Powell K. Colagiuri S. The new glucose revolution: the Low GI solution for optimum health. 2004; Hachette Australia.

Dietitians Association of Australia. Glycaemic index in diabetes management. Australian Journal of Nutrition and Dietetics, 1997; 54: 57-63

The Glycaemic Index website - http://www.glycemicindex.com/

The GI symbol program website- http://www.gisymbol.com.au/

Kelley DE. Sugars and starch in the nutritional management of diabetes mellitus. American Journal of Clinical Nutrition, 2003; 78(supp): 858S-864S