Carbohydrates have been getting a lot of ‘hate’ in recent years. Wanna lose weight? Avoid that carbohydrate! Wanna prevent cancers? No more carbohydrates. But what if we tell you that not all carbohydrates are equal?
Indeed, carbohydrate is a class of macronutrients that consists of various sub-types. Instead of seeing carbohydrate as an individual component that we avoid altogether, we should look at their glycemic index (GI).
Rank your carbohydrate: Glycemic Index (GI)
The glycemic index (or GI) is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar (glucose) levels after eating. Scientists do not rest on these numbers arbitrarily – they measure the glucose-raising potential of the carbohydrate content inside a food to a reference food (generally pure glucose). Low-GI foods have a rating of 55 or less, and foods rated 70-100 are considered high-GI foods. Medium-level foods have a glycemic index of 56-69.
Foods with a high GI are those which are rapidly digested, absorbed and metabolised and result in marked fluctuations in blood sugar (glucose) levels. If you consume high-GI foods, it can cause a sharp increase in blood sugar concentration (a.k.a postprandial blood glucose level) that declines rapidly afterwards. This is why some people might feel extremely sleepy after eating too full.
On the other hand, low-GI foods are digested more slowly, prompting a more gradual rise in blood sugar. This may help you feel fuller for longer and help control your appetite.
Image credit: http://www.glycemicindex.com/about.php
Here are some examples:
|
Food |
GI (Pure glucose = 100) |
|
High-Carbohydrate Foods |
|
|
White wheat bread |
75 ± 2 (low-GI alternatives are available) |
|
Chapatti |
52 ± 4 |
|
White rice, boiled |
73 ± 4 (low-GI alternatives are available) |
|
Brown rice, boiled |
68 ± 4 |
|
Fruit and Fruit Products |
|
|
Apple, raw |
36 ± 2 (on average) |
|
Apple juice |
41 ± 2 |
|
Banana, raw |
51 ± 3 (on average) |
|
Vegetables |
|
|
Potato, boiled |
78 ± 4 |
|
Vegetable soup |
48 ± 5 |
The complete list of the glycemic index and glycemic load for more than 1,000 foods can be found in the article "International tables of glycemic index and glycemic load values: 2008" by Fiona S. Atkinson, Kaye Foster-Powell, and Jennie C. Brand-Miller in the December 2008 issue of Diabetes Care, Vol. 31, number 12, pages 2281-2283.
Many factors can affect a food’s glycemic index (GI), including the following:
-
Processing: Grains that have been milled and refined—removing the bran and the germ—have a higher GI than minimally processed whole grains.
-
Physical form: Finely ground grain is more rapidly digested than coarsely ground grain. This is why eating whole grains in their “whole form” like brown rice or oats can be healthier than eating highly processed whole grain bread.
-
Fiber content: High-fiber foods don’t contain as much digestible carbohydrate, so it slows the rate of digestion and causes a more gradual and lower rise in blood sugar.
-
Ripeness: Ripe fruits and vegetables tend to have a higher GI than un-ripened fruit.
-
Fat content and acid content: Meals with fat or acid are converted more slowly into sugar.
-
Protein content: Milk and other dairy products have a low GI because they are high in protein and contain fat.
For these reasons ,it is important to remember that not all low-GI foods are healthy choices – most chocolates, for example, have a low-GI because of their fat content, which slows down the absorption of carbohydrates.
Glycemic load
One thing that a food’s glycemic index does not tell us is how much digestible carbohydrate – the total amount of carbohydrates excluding fiber – it delivers. That is why scientists developed a related way to classify foods that takes into account both the amount of carbohydrate in the food in relation to its impact on blood sugar levels. This measure is called the glycemic load (GL). A food’s glycemic load is determined by multiplying its glycemic index by the amount of carbohydrate the food contains. Watermelon, for example, has a high glycemic index (80). But a serving of watermelon has so little carbohydrate that its glycemic load is only 5.
In general, a glycemic load of 20 or more is high, 11 to 19 is medium, and 10 or under is low.
Low glycemic load (10 or under)
-
Apple
-
Orange
-
Carrots
-
Lentils
-
Watermelon
Medium glycemic load (11-19)
-
Brown rice: 3/4 cup cooked
-
Oatmeal: 1 cup cooked
-
Whole grain breads: 1 slice
High glycemic load (20+)
-
Baked potato
-
French fries
-
Refined breakfast cereal: 1 oz (approx. 28g)
-
Sugar-sweetened beverages: 12 oz (approx. 340g)
The bottom line? Using both GI and GL to plan your diet can be a good place to start.
Fact: High-GI/GL diet is linked to type 2 diabetes and cardiovascular diseases.
The nasty effects of consuming high GI/GL food are more than just feeling sluggish after eating a lot of them. Consuming high GI/GL food in large quantities for long-term is linked with higher risk of developing type 2 diabetes mellitus. A recent updated analysis of three large US cohorts indicated consumption of high-GI/GL foods was associated with a risk of developing type 2 diabetes that was increased by 20-44%.
Why? Scientists think the reason could be this: if you consistently have high blood sugar level after every meal (an effect of eating high-GI/GL foods), your pancreas would produce insulin excessively to deal with those blood sugar. Over time, this exhausts the pancreas (poor pancreas!) and damage the β-cells in the pancreas– they are the factories that produce insulin in your body. As a result, this can lead to type 2 diabetes, and you might have to take medications to control your blood sugar or inject insulin for the rest of your lives.
For these reasons, major diabetes organisations around the world (e.g. the American Diabetes Association; Canadian Diabetes Association and Diabetes UK) now advise people with diabetes use the GI or GL as part of the nutritional management of their condition. High-GI/GL diet is also linked to higher risk of cardiovascular diseases, especially among overweight women.
Fact: Eating low-GI/GL diet reduces your risk of diabetes and cardiovascular diseases.
It sounds like we are repeating ourselves, but because we genuinely care about your health so it is worth the hassle.
Not only scientific evidence has shown that a high-GI/GL diet is bad for your health, but a low-GI/GL diet is good for you, especially with respect to diabetes and cardiovascular risks. A meta-analysis published in 2013 found that eating a low-GI diet results in significantly lower risk of diabetes. A systematic review and meta-analysis of randomised controlled trials showed that eating a low-GI/Gl diet can even lower total and LDL- cholesterol, a.k.a the ‘bad’ cholesterol. Another meta-analysis found that high-GI/GL diets were significantly associated with cardiovascular diseases in women but not in men. Further scientific studies are required to examine the relationship between GI/GL with cardiovascular diseases in men.
Myth: High-GI/GL diet increases risk of cancer...or does it?
Scientific evidence that high-GI or -GL diets are related to cancer is inconsistent. A recent meta-analysis of 32 case-control studies and 20 prospective cohort studies found modest and non-significant increased risks of hormone-related cancers (breast, prostate, ovarian, and endometrial cancers) and digestive tract cancers (esophageal, gastric, pancreas, and liver cancers) with high-GI/GL diet. The only cancer that is significantly linked to high-GI/GL diet is colorectal cancer. Yet, meta-analyses published in earlier years did not see the link between high-GI/GL diet and colorectal cancer. Well, we need more studies in the future to look into how high-GI/GL diets can affect one’s cancer risk.
Myth: GI and GL are all that matters!
When you have a disease, you can almost be certain that the medicine prescribed by your doctor is going to cure you, or at least makes you feel better. Modern medicine advancement has raised our collective expectations of medical treatments. However, when it comes to nutritional choices, things are not that clear-cut.
Yes, some low GI foods, such as wholegrain foods, fruit, vegetables, beans and lentils, are foods we should eat as part of a healthy, balanced diet. However, using GI and GL to decide whether foods or combinations of foods are healthy can be misleading. Like we mentioned earlier, watermelon are high GI foods, but when served in normal servings, it has low GL and is packed with many awesome vitamins and antioxidants. On the other hand, foods high in fat tend to have lower GI because the fat slows down the absorption of carbohydrates.
We should see our food as a whole, not individual macronutrients.
If you focus only on the GI of foods, without looking at other aspects, your diet could be unbalanced and high in fat and calories, which could lead to weight gain and increase your risk of heart disease.
If you have diabetes, it can be beneficial for you to follow the principle of low-GI diet. But like we mentioned, GI should not be the sole focus. The total amount of carbohydrate you eat has a bigger effect on blood glucose levels than GI alone. Hence, the most important thing to do is get your portion size right – once you do this, you will get an added bonus for choosing low-GI alternatives.
