1 December 2006

Food for Thought

Going with the WHOLE grain
Grains are the seeds of cereal plants and include amaranth, barley, buckwheat, bulgur, maize (corn), millet, oats, quinoa, rice, rye, spelt and wheat. These staple foods are the most concentrated source of carbs in our diet, provide us with protein, are low in fat, packed with essential vitamins and minerals and rich in fibre when you eat the wholegrain varieties. Studies around the world show that eating plenty of wholegrain cereals reduces the risk of certain types of cancer, heart disease and type 2 diabetes. In addition, a higher fibre intake, especially from whole cereal grains, is linked to a lower risk of cancer of the large bowel, breast, stomach and mouth. Although all wholegrains are healthy, nutritious foods, it’s only the low GI ones that reduce your blood glucose and insulin levels throughout the day and increase your sense of feeling full and satisfied because they are the ones that slowly trickle glucose into your bloodstream. We like to say that your body is doing the processing, not the manufacturer.


By the way, GI Group, I've got a question for you. How would you explain this ‘contradiction’? Both wholemeal bread and sweet corn contain lots of insoluble fibre but the GI of wholemeal bread tends to be high while sweet corn's GI is relatively low. Why do you think this happens?

Why do some ‘wholegrains’ have a low GI and not others? Prof Jennie Brand-Miller explains
Some people use ‘wholegrain’ and ‘low GI’ as though they are interchangeable terms. That’s not the case at all. Wholegrain foods can be high or low GI, and it’s essential to understand this and know what’s low and what’s not to manage your blood glucose levels. In fact many processed wholegrain foods such as wholemeal bread have a high GI. Why? It all comes down to the physical state of the fibre and the starch in the food. When wheat fibre has been finely divided as it is in wholemeal bread, it does little for either constipation or blood glucose levels. That’s why we say to choose your carbs carefully, and if your favourite wholegrain food has a high or moderate GI, combine it with a low GI food to reduce the glycemic load of the meal or snack. Just for the record, here are five factors that can slow digestion of those nutritious wholegrain carbs. (For tips on reducing the GI of your diet see November GI News.)

Jennie Brand-Miller

  1. Starch gelatinisation
    The starch in raw food is stored in hard, compact granules that make it difficult to digest. During cooking, water and heat expand these starch granules to different degrees – some actually burst freeing the individual starch molecules inside. If most of the starch granules have swollen and burst during cooking, we say that the starch is fully gelatinised. These swollen granules and free starch molecules are very easy to digest. The less gelatinised or swollen the starch is after cooking, the slower the rate of digestion.

  2. Physical entrapment
    The fibrous coat around foods like beans, chickpeas, lentils, barley and seeds acts as a physical barrier. It slows down access of the digestive enzymes to the starch inside and thus slowing digestion. That’s why we say to look for lots of grainy bits when buying bread.

  3. How much amylose starch there is in the food
    Amylose and amylopectin are two types of starch found in foods, but the ratio of one to the other varies considerably. Here’s how it works. Amylose is a straight chain molecule, like a string of beads. These tend to line up in rows and form compact clumps. The more amylose a food contains, the less easily the starch is gelatinised and the slower its rate of digestion. Legumes have lots of amylose as does basmati rice. Amylopectin on the other hand is a string of glucose molecules with lots of branching points, such as you see in some sorts of seaweed. Amylopectin molecules are larger and more open and the starch is easier to gelatinise and digest. So if a food has more amylopectin than amylose, it’s going to be moderate or high GI.

  4. Particle size
    The larger the particle size, the lower the GI. When you eat a starchy food in ‘nature’s packaging’ – whole intact grains like barley that have been softened by soaking and cooking – the food will have a lower GI value. It’s the grinding or milling of cereals that reduces the particle size that makes it easier for water to be absorbed and enzymes to attack during digestion. That is why cereal foods made from fine flours like many breakfast cereals tend to have a high GI value.

  5. The type of fibre
    The effect of fibre on the GI value of a food depends on the type of fibre (soluble or insoluble). Soluble fibres are the gel, gum and often jelly-like components of foods like oats, legumes and apples. By slowing down the time it takes for food to pass through the stomach and small intestine, soluble fibre can lower your body’s glycemic response to a food.
    Insoluble fibres are dry and bran-like and often referred to as roughage. All cereal grains and products made from them that retain the outer coat of the grain are sources of insoluble fibre. But not all foods containing insoluble fibre are low GI. Why? Insoluble fibres will only lower the GI of a food when they exist in their intact, original form, for example in whole grains of wheat. Here they act as a physical barrier, delaying access of digestive enzymes and water to the starch within the cereal grain.


Anonymous said...

Does instant oatmeal have a low glycemic effect or do I have to buy the regular long-cooking kind?

Anonymous said...

Is there any bread that is o.k. to eat?

gi group said...

Re oatmeal: The instant porridge oats that have been tested have a moderate to high GI depending on the brand. Check out the GI database on www.glycemicindex.com (and click on database in the menu to the left of the page). To lower the GI of your diet you need to buy traditional porridge oats such as rolled oats. You can use them to make porridge or as a base for muesli.

Re bread: If you live in Australia, look for the GI symbol on the pack as many breads have been GI tested. If you live in the UK or US or Canada, choose a really grainy 'multigrain' bread - one with lots of visible grainy bits not just on the outside, but right through the loaf. Other low GI options include: soy and linseed, sourdough and fruit breads, and pumpernickel. For the lowdown on the best breads to buy and why, check out a copy of Low GI Eating Made Easy which has the top 100 low GI foods. Or pick up a copy of the latest Shopper's Guide to GI Values 2007.

patlevee said...

What about grits? Are they high glycemic index.

Wilfrid said...

Thank you for describing processing details and components in wholemeal grains but something is missing.

I'm now interested in choosing Low GI wholegrain but this is not clearly presented in your article.

Succinct recommendations would provide positive guidance in my choice of dietary habits.

gi group said...

Looking for low GI wholegrains? Check out the database at www.glycemicindex.com or pick up a copy of The Shopper's Guide to GI Values 2007, or Low GI Eating Made Easy which tells you all about the top 100 low GI foods including cereal grains.

GI Group said...

Grits haven't been tested so we don't know their GI. If you enjoy grits, keep your portions moderate and combine it with fruits or berries to lower the GI.

Anonymous said...

Great Article, thanks! I'll now start preferring those grains/products with more roughage.
Does that mean that "Tempeh" is better than "Tofu"?
I understand tempeh is the more original form of tofu - you can actually see outlines of the tofu-beans in tempeh, while tofu is all smooth throughout.
Both are consumed by perhaps billions of people...

Howard Rossman, SYDNEY

gi group said...

Tofu (soybean curd) contains very little carbohydrate so it doesn't have a GI. The same goes for tempeh which is made from fermented cooked soybeans. They are both protein-rich foods derived from soybeans and as such are in the legume family not the cereal grains one. They are important foods in vegetarian and vegan diets. All canned and dried legumes (beans, chickpeas, lentils) apart from broad beans have a low GI. If you are looking for recipes using low GI grains along with tofu or tempeh, check out The Low GI Vegetarian Cookbook.

Anonymous said...

Can you please tellme what grits are.

Anonymous said...

Grits are a southern United States food. They are basically used as an addition to breakfast instead of potatoes. It is a roughly ground corn meal that is boiled and server with butter.

Anonymous said...

Grits are hominy -corn treated with lye, then dried and ground to make grits. My guess is grits are fairly high GI as corn is and the particle size of grits is fairly small. They are however very good, especailly with cheese and jalapeno paeppers.

Curious Voyager--low gly southerner USA

gi group said...

Thanks for the information about grits - and the serving suggestion. It would be good to see them tested so we will put them on the list. FYI, sweet corn on the cob (or the canned kernels) has a low GI. That's why we sometimes add corn to recipes or suggest it as an accompaniment - it lowers the overall GI of the meal. But hold the butter.

Anonymous said...

Another question about porridge oats. I understand the difference between instant porridge and rolled oats and why rolled oats are better.
But should rolled oats be only lightly cooked since their GI will be lowered by cooking them for too long?
Thank you.

Ed said...

The GI database shows the GI for low-amylose corn muffins to be 102. I checked with some manufacturers of the corn meal mix sold in the grocery stores and asked if it is high-amylose or low-amylose. They said low-amylose. Does that mean I should not eat corn meal muffins since I am a type 2 diebetic?

gi group said...

Cooking porridge: When testing a food, we prepare it according to the manufacturer's instructions on the packet, sticking to the cooking times suggested like a typical consumer. We haven't done a GI test comparison of lightly cooked and overcooked oats.

gi group said...

Most baked products like pancakes, cakes, muffins and cookies are going to have a high GI because the flour they contain is a finely milled product which is rapidly digested. In our recipes we incorporate other ingredients such as oatbran, whole grains, fruit, milk and juices that will reduce the GI of these items. If you enjoy eating a corn muffin as a snack, try making the one on page 83 of The Low GI Vegetarian Cookbook by Jennie Brand-Miller et al.

beruang said...

sorry if you have covered this in another page but i'm just wondering if any of Lean Cuisine products have been tested for GI? thanks

gi group said...

Hi Beruang, LEAN Cuisine (some Australian products which had been GI tested) were covered in June 2006. Here's a handy tip for next time you wonder if we have covered a topic. GI News has a great google search feature (on the right-hand side near the top of the masthead. Just type in the key words as you would using google. We use it ourselves when we want to find stories from past issues in a hurry.