Prof Jennie Brand-Miller answers your questions.
Why doesn’t cheese have a GI value? Other dairy foods like milk and yoghurt and even ice cream do.
The glycemic index (GI) is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood glucose levels after eating. Only foods that are sources of carbohydrate can be GI tested. Milk and yoghurt are good sources of carbohydrate (and protein, too). For example, here in Australia a 200g/7oz tub of low fat plain yoghurt contains around 12g each of carbohydrate and protein. The carbohydrate comes from the milk sugar, lactose. (However, if the yogurt is sweetened, then it will contain other sugars in addition to lactose.) Cheese on the other hand is a good source of protein but has almost no carbohydrate because cheese is made from milk solids (curd); the lactose-rich whey has been drained off during the early stages of processing which is why people who are lactose intolerant can enjoy cheese but not milk.
Other foods that contain no carbohydrate, or so little that their GI can’t be measured, are meat, chicken, fish, eggs and nuts (well most nuts). If you come across a website that gives you a GI value for cheese (or meat, chicken, fish and eggs), then you know the testing has certainly not followed the international standard method and was probably done in a test tube (in vitro).
Following the international standard method, the GI value of a food is determined by feeding 10 or more healthy people a portion of the food containing 50 grams of digestible (available) carbohydrate and then measuring the effect on their blood glucose levels over the next two hours. For each person, the area under their two-hour blood glucose response (glucose AUC) for this food is then measured. On another occasion, the same 10 people consume an equal-carbohydrate portion of glucose sugar (the reference food) and their two-hour blood glucose response is also measured. A GI value for the test food is then calculated for each person by dividing their glucose AUC for the test food by their glucose AUC for the reference food. The final GI value for the test food is the average GI value for the 10 people.
Latest GI values from Fiona Atkinson at SUGiRS.
Yoghurt, naturally low GI.
Yogurt’s low GI values are thanks (mainly) to the combination of acidity and high protein and of course the fact that lactose, the sugar in milk, has a naturally low GI. Here’s why. Lactose is a disaccharide (double sugar) that needs to be digested into its component sugars before our bodies can absorb it. In our bodies, glucose and galactose, the two component sugars that make up lactose, compete with each other for absorption. Once absorbed, the galactose is mainly metabolised in the liver and produces very little effect on our blood glucose levels. The remaining sugar, glucose, is present in a small enough amount not to cause a spike in blood glucose.
Did you know that even if you are lactose intolerant, you can enjoy yoghurt? This is because the micro-organisms added to milk to make yoghurt are active in digesting lactose during passage through the small intestine, in other words, the ‘bugs’ help do the job of lactose digestion for you.
Yoplait Petit Miam: SUGiRS recently tested Yoplait Petit Miam 100g tubs – a calcium-rich, creamy tasting snack or dessert for babies (they say 1+ years on the label), toddlers and young children with 87 calories (364kJ), 14g available carbs and 3g protein in a tub. No arguments over who got the biggest serving because everyone gets their own little pot of yoghurt.
GI testing by an accredited laboratory
- Fruit Salad GI 41
- Strawberry & Banana GI 39
- Banana GI 39
- Strawberry GI 43
- Blueberry GI 43
- Mixed Berry GI 43
- Vanilla GI 38
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 Canada
Phone +1 416 861 0506
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022