The Glycemic Index and the Glycemic Load

What happens when we eat carbs?

Some foods make our blood sugars spike really quickly and others, not so much. The foods that have an effect on blood glucose contain carbohydrates. When you eat foods containing carbs they break down to their basic component, glucose or sugar, in the intestine and glucose gets into the bloodstream. As a result, your blood glucose goes up. In response, your pancreas secretes a hormone called insulin that helps sugar get out of the blood and into your body cells that need sugar. Glucose is actually the main fuel for your brain and muscles.

However, when lots of glucose comes in at the same time, your pancreas secretes a lot of insulin at once resulting in a quick drop of your blood glucose. When your blood glucose goes down that quickly, you feel hungry and, as a result, eat again, leading to potential weight gain. Another thing that happens when there’s too much glucose that comes in at once is that your muscle cells start to resist storing the extra glucose. This extra sugar gets stored as fat and also contributes to weight gain.

There are carbohydrates that break down really quickly into glucose- so eating too much of those types of carbohydrates quickly causes your blood glucose to spike quickly, causing all this havoc.

David Jenkins and colleagues from the University of Toronto created a system that ranks carbohydrate foods based on how quickly they break down to sugar. This is known as the Glycemic Index. They compared the impact of different foods on blood glucose to the impact of standard foods like pure sugar on blood glucose. Pure sugar was given a Glycemic Index (GI) of 100.

Foods that have a GI of less than 55 are considered to have a low GI or low impact on blood glucose, 55-69 is a moderate GI and a GI of greater than 70 is considered high.

For example, black beans have a GI of 30. This means that they boost blood sugar 30% as much as pure glucose.

Although GI offers some useful information, it’s not the whole picture. For example, carrots have a GI of over 70. Carrots do have sugar that’s highly absorbable but the total amount of sugar is very small and therefore has very little effect on blood glucose. Luckily, there’s something called the Glycemic Load.

The Glycemic Load (GL) was developed by Walter Willett and colleagues at the Harvard School of Public Health and considers the total amount of carbs in a food as well as the GI. A GL of less than 10 is low, 11-19 is medium and more than 20 is high.

The Glycemic Load of carrots is 5.

Although most health experts, including Marion Nestle and Walter Willett, call GL and GI useful tools, they caution to not build your diet around it. Marion Nestle says she ignores the long lists of foods and their GI and GL values (I included one of those lists below) because not only do the numbers vary depending on the source, but they also vary depending on preparation and cooking methods. It all gets very confusing.

Not only that but if you add butter and cheese on top of a potato, the Glycemic Index will be lower (fat and proteins have no GI because they have no carbs) but calories and saturated fats increase. So just because a food or a meal has a low GI or a low GL, doesn’t mean it’s necessarily a good choice!

What you should focus on is how much food you’re eating and choosing less processed starchy foods (that usually have high GI and GLs anyway).

Health Benefits of choosing low Glycemic Index and Glycemic Load foods

In both the large Nurse’s Health Study and Health Professionals Follow-up Study, it was found that people who ate low fibre cereals and high Glycemic Load foods more than doubled their risk of type 2 diabetes.

Other research has shown that the excess sugar and insulin that comes from eating high GI and GL foods contribute to other chronic conditions like heart disease, breast cancer, colon cancer and polycystic ovarian syndrome.

Now, I haven’t read any of these studies (yet) but just summarizing from Willett’s book. However, it seems to me that people who eat higher fibre and lower GI and GL foods (like whole grains, legumes, vegetables) are those that are most likely to have healthier lifestyles- eat healthier, exercise more, don’t smoke, not overweight etc. than those that are eating low fibre and high GI/GL foods. So is it just the higher intake of high GL/GI foods that are contributing to these health conditions or is it a less healthy lifestyle?

Mike- hope this answers some of your questions. There'll be more to follow.

Glycemic Index and Load of foods: http://www.ajcn.org/cgi/reprint/76/1/5

Sources:

Nestle, Marion. What to Eat. 2006

Willett, WC. Eat, Drink, and Be Healthy- The Harvard Medical School Guide to Healthy Eating. Free Press 2005.

Rice-a-rific!

Rice is a staple food for at least 2/3 of the world's population. However, there are so many different types of rice that it could get a bit confusing.

Here’s a bit of an overview.

Rice is a member of the grass family. The plant is native to tropical and subtropical southern Asia and Southeastern Africa.

There are different types of rice, categorized based on processing, size and variety.

Processing

Brown rice undergoes the least amount of processing. The first step in milling of the rice plant is the removal of the outer husk and the product after this step is brown rice. The bran stays intact therefore brown rice contains more nutrients and 4 times the fibre found in white rice.

The Glycemic Index (GI) is a scale that ranks foods by how much they raise blood glucose compared to a standard food. A glycemic index off 55 or below is considered low and 70 or above is high. Brown rice falls in between with a GI of ~66.

Converted or Parboiled rice has been soaked and then steamed under pressure before milling. This actually forces some of the nutrients into the remaining portion of the grain so that some are retained during processing. As a result, this rice falls between brown and white rice in terms of nutrient content but actually has the lowest GI with a GI of 48.

Enriched rice has had the B vitamins (thiamin, niacin) and iron added after milling to replace some of the nutrients lost when the bran layer is removed.

Instant white rice has been milled and polished, fully cooked and then dehydrated. It is usually enriched but does not have the superior taste and texture of regular rice.

Size

Long-grain rice is four to five times longer than it is wide. When cooked the grains are fluffy and dry and stay separated. It’s ideal for salads. Long-grain rice (unconverted) has a medium GI of ~57.

Medium-grain rice is about twice as long as it is wide and cooks up moister and more tender than long-grain. It is popular in some Asian and Latin American cultures, and is the type of rice most commonly processed to make cold cereals.

Short-grain rice is oval or round in shape. Of the three types of rice, it has the most starch that makes it sticky, or clump together, when cooked. It is ideal for dishes such as sushi. Short grain rice has a high GI of >70.

Variety

Arborio: A starchy white rice, almost round in shape. Traditionally used for cooking Italian risotto. It also works well for paella and rice pudding. Arborio absorbs up to five times its weight in liquid that results in grains of a creamy consistency. This type of rice has a high GI of ~70.

Aromatic rice: Primarily long-grain varieties that have a toasty, nutty fragrance

Basmati: The most famous aromatic rice is grown in India and Pakistan. The grains elongate much more than they plump as they cook. Can be substituted for regular white rice in any recipe. You can also purchase brown basmati rice. Basmati rice is a long-grain variety. Basmati rice has a medium GI of 58.

Glutinous, sticky or sweet rice: Long-grain rice with a very high starch content. Suitable for Chinese dishes of shaped rice, such as rice balls or sticky rice cakes. This type of rice has a very high GI of ~98.

Jasmine, perfumed or Thai fragrant: A traditional long-grain white rice grown in Thailand. It has a soft texture and is similar in flavour to basmati rice. It is also grown in the United States where it is available in both white and brown forms. Jasmine rice has a very high GI of ~109.

Sources:

http://www.lesliebeck.com/ingredient_index.php?featured_food=18
http://en.wikipedia.org/wiki/Rice
http://freecookbooks.a1nethost.com/001/04/25.htm
http://images.google.ca/imgres?imgurl=http://www.bernas.com.my/images/ricegrain.jpg&imgrefurl=http://www.bernas.com.my/process.htm&h=282&w=360&sz=84&hl=en&start=4&um=1&tbnid=6VQ17F4VyxtItM:&tbnh=95&tbnw=121&prev=/images%3Fq%3Drice%2Bgrain%26um%3D1%26hl%3Den%26sa%3DN
Foster-Powell, K; Holt, S; Brand-Miller, JC. International table of glycemic index and glycemic load values. American Journal of Clinical Nutrition. 76(1) 2002. http://www.diabetes.ca/files/Diabetes_GL_FINAL2_CPG03.pdf
http://www.abingredients.com/products/rice_starch/images/rice_varieties.jpg