Q & A Month: why does yoghurt have a low GI?
Posted by kathryn in Carbohydrates and Q & A Thursday
Paul has asked the question – why do yoghurts that contain sugar still have a low GI?
Most yoghurts have a GI of between about 14 and 40. Despite the variety of scores, this puts yoghurt in the low GI category. Even the ones that contain sugar have a low GI.
In the pre-GI days of nutrition, carbohydrate foods were separated into two categories: simple and complex. This distinction was solely based on the stucture of the carbohydrate itself. It was believed complex carbohydrates were harder to breakdown and therefore better for you – because they kept you fuller for longer.
What affects the GI of a food?
However, research into the GI has shown it’s more complicated. Carbohydrate breakdown is less about the structure of the carbohydrate itself than the physical state of the carbohydrate in a particular food.
This can be seen when you compare the GI response of jasmine vs basmati rice.
The GI of a food can be affected by a number of factors including:
- the size of the carbohydrate particles
- the type of fibre in a food
- whether the food also contains fat
- how starch is stored in the food
What about yoghurt
Yoghurt contains carbohydrate, so it does impact blood sugar levels. However, it also contains other nutrients and has properties which slow down this glycemic response:
- yoghurt is slightly acidic
- yoghurt contains protein
- most yoghurt contains some fat
All these factors impact yoghurt’s GI, because they alter the rate at which your stomach empties food into the small intestines.
The GI is affected by the rate of digestion
After chewing and swallowing food, it travels down your oesophagus and hits your stomach. Your stomach is primarily concerned with breaking down proteins. Very little happens to carbohydrates in the stomach.
Instead it’s in the small intestines that carbohydrate absorption occurs. So any food which is held up in your stomach and only released slowly into the small intestines, will have a slower glycemic response.
The acidity of yoghurt, combined with it’s protein and fat, ensures a slow release into your small intestines. So yoghurt’s carbohydrate is broken down slowly and it has a low GI.
Yoghurt picture by Noranna under the terms of a creative commons license.
28 February, 2008
Comments
Hi Kathryn,
If it’s not too late, I’d like to add a question to your list for Q&A Month!
February has been the month that I overhauled my diet. I’ve managed to drastically reduce the amount of meat/carb heavy meals that I’m eating, upped my fruit and veg, and embraced legumes, whole grains and nuts. Combined with regular exercise, I’m feeling terrific and losing weight.
I’m now facing a new problem. And, like most nutritional topics, I doubt there’s a simple answer!
My boyfriend gets very little calcium in his diet, but appears fit and healthy. I fear that this is something that will bite him later in life, and without knowing where the goal posts are I could well be neglecting some areas of my own diet.
A quick look over the contents of my multi-vitamin tells me that there are vitamins and minerals I know nothing about. This suggests that there are probably important aspects of my nutrition that I am neglecting.
What vitamins and mineral requirements should we REALLY be striving to meet on a daily basis? Which ones are easily overlooked, and which are the most challenging to fulfill?
Your blog has been a godsend in terms of teaching me how to include more of the good stuff in my diet, but I sometimes feel like I’m navigating the big picture without a map!
I hope this isn’t too broad a question, as I know it’s at the very core of what you’re all about. I’m sure my more varied approach to food is helping me cover my bases, but mostly I’m just feeling really clueless!
Hi there Elizabeth. You’ve asked an excellent but HUGE question. And it’s not something I can cover in one post. But it could make an excellent series of posts – I’ll just need to think about how to approach and how to present the information.
So keep tuned and I’ll get to this big, BIG topic!
I should also let everyone know I’m not taking any more Q & A Month questions. Q & A Month has already turned into Q & A 2-Months and I still have four more questions to answer.
The response to Q & A Month has been wonderful, but I do feel the need to move onto other topics.
I still want to include a regular Q & A session on Limes & Lycopene. However, changes to my working life this year mean I need to think about how often I do this and what form it takes – so stay tuned.
Back to the yogurt and GI question, I think this question highlights one of the real difficulties in using concept in a practical way. The evidence seems to be building that GI has even more of an effect on health than we initially thought BUT it is really difficult to look at a food and ‘guess’ what its index might be – it isn’t intuitive so you really have to know, or have it marked on the label. I’ve worked in GI testing for a while and even I find it difficult to remember!
Agreed Sophie – while there are a few basic guidelines we can use, particularly when choosing bread (grains and sourdough, etc), overall much of it’s counter-intuitive. And you’re right, you just have to know.
Here in Australia, the GI group at Sydney Uni have established a GI logo to go on food labels. But at the moment it’s primarily found on breakfast cereals and not much else.
Thanks Kathryn and Sophie! Much, much appreciated. Breads, rices, ok, but the GI rating of yoghurt has always stumped me! So I guess it carries the same effect as I’ve heard with vinegar on chips? Sorry I’ve been a bit slow in coming back to respond. Have a great weekend everyone.
Paul – yes vinegar would lower the GI of chips. But chips would be lower in GI than straight boiled potatoes because of the fat content. Again it slows down stomach emptying. A classic example of why the GI can’t be used in isolation!
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