The glycemic index of a food in a measure of how it affects blood sugar. Foods that cause rapid increases in blood sugar have high glycemic indices, and food that cause very low increases in blood sugar have low glycemic indices. The references for this scale are pure glucose (which is what blood sugar is) and any food that causes no increase in blood sugar. A glycemic index of 100 is defined as the increase in blood sugar caused by consuming pure glucose. In theory, this is the highest glycemic index, because glucose requires no time or energy to be broken down, because it is already glucose. Every other form of energy (for the most part) must be broken down into glucose to be useful to the body. Counterintuitively, there are a few foods that have a higher glycemic index than glucose, though the reason is not well understood.
Glycemic index is important in measuring the impact a food may have on health. For diabetics, glycemic index determines what they can and cannot eat, and how much insulin they will need before or after eating it. Most non-diabetic people do not worry about blood sugar and thus do not care about glycemic index. They should.
Having chronically high blood sugar can lead to type 2 diabetes. Type 2 diabetes is caused by something called insulin resistance. I have been asked how this works by people who were confused about how sugar could become resistance to another chemical. The confusion was the result of a misunderstanding of what insulin is and how it works. Insulin does not directly control sugar levels by reacting with it. Insulin is a hormone. It sends messages to the cells. The cells respond by absorbing glucose from the bloodstream. It is not the sugar that becomes insulin resistant; it is the cells. The process is mildly complex, but the result is that chronically high blood sugar will make cells less responsive to insulin after about 25 years (give or take 5-10). The timing and severity of the effect is different for each person, but the trend seems to be that people with a significant diet of high glycemic index foods tend to start showing symptoms of pre-diabetes at around 25 to 35 years old and actually get type 2 diabetes around 35 to 45, if they do not change their diets. So far, it is not known if there is any way to reverse this. In other words, once you have pre-diabetes, you had better stay on a good diet, or you will pick up where you left off. (Note that eating high sugar foods occasionally does not seem to have any lasting effect of insulin resistance.)
Really everyone should care about glycemic index. A few hundred years ago, most people did not live more than 40 to 60 years anyhow, so even those with the money to maintain high sugar diets would be unlikely to see the long term effects of it before dying of something else. Now, most people live into their 70s or 80s, and sugar is much more accessible. Given that it takes 20-30 years for a high sugar diet to cause diabetes, and we tend to live two to three times that long, we need to care about this problem. Some people do not care about their health. I have occasionally heard people tell other that this is their own life and their own body, and they are the only ones being hurt by their poor decisions. This is a lie. If you have parents, children, friends, a job, or really any other long term relationships with other humans, dying at 40 or 50 affects a lot of other people. If you die at 50 instead of 80, you could be hurting five generations of family or more. If your job is important and you are hard to replace, you could be hurting all of your coworkers, your managers, your subordinates, the stockholders of your employer, and even the customers of your employer. Just dealing with the emotional stress of well managed diabetes could be a strain on your family and friends, even if you do not die early. If you seriously think that your health decisions have no impact on others, you should probably get counseling for depression, because only very seriously depressed people think that no one else cares about them.
So, how should you deal with this blood sugar issue? There is always the option of stabbing yourself multiple times daily to check your blood sugar, but unless you have been diagnosed with pre-diabetes, you probably do not need to do this far. Glycemic index does not account for the volume of a food that you consume, so there is no real measure of how much glycemic index you should consume in a day. For that, look into glycemic load, which adjusts glycemic index based on amount consumed. Using glycemic index alone, reduce consumption of foods with a high glycemic index, and increase consumption of foods with a low glycemic index. For instance, if you drink a lot of normal soda, which is sweetened with high fructose corn syrup, drink less and consider replacing it with a soda sweetened with table sugar (sometimes advertised as cane sugar). High fructose corn syrup has a glycemic index around 88, which is fairly high, while table sugar has a glycemic index around 68, which is considered medium. Corn syrup will make your blood sugar spike and then drop. If you constantly consume it, it will keep your blood sugar constantly high. Table sugar will cause a smaller spike, and your blood sugar will drop more slowly, because it takes longer to break down. You may even have an easier time drinking less of the table sugar sweetened soda, because it will take longer for your blood sugar to drop to a point where you feel like you need more energy. There is one problem with adjusting your diet based on glycemic indices of food. Where do you find them? I just gave you two that I found by doing a lot of research into the differences of high fructose corn syrup and table sugar. While these two were not difficult to find, you may find it impossible to find reliable numbers for the foods you eat every day.
There are some places you can find information on glycemic index of foods. In most cases, treat them as estimates, because glycemic index can be affected dramatically by things that seem trivial. For instance, Russet potatoes have a glycemic index that is higher than glucose when cooked (this is one of the strange ones). When they are not cooked, their glycemic index is much lower. Most other varieties of potatoes have much lower glycemic indices. Some potato-like root vegetables even have extremely low glycemic indices. Sweet potatoes and yams range between 15 and 20, which is very low. When looking for the glycemic index of a food, be very specific. The more specific the result, the more likely it is to be accurate for the variety and cooking method you are using. Sadly, no amount of search will find every food you might eat. The glycemic indices of most very commonly eaten foods can be found easy with a few internet searches. Generic brands or less common foods will be much harder to find, if they are even available. And do not trust that the glycemic index for a name brand will be the same as the glycemic index for a generic brand. Preparation techniques can have a substantial impact of glycemic index.
Now that you know all about the glycemic index (well, sort of), I want to make a suggestion. I think that glycemic index should be considered as important as any other nutritional information. The FDA should add glycemic index to the list of nutritional information that is required on labels. We have Vitamin C listed, even though very few cases of scurvy have been seen in a century. We have fat listed, which is ironic, given that studies have found sugars have a larger effect on weight gain and loss than fat (even though fat has a higher energy density). The listing of sugars says almost nothing. High fructose corn syrup is a mixture of molecular glucose and fructose, table sugar is made of composite molecules of fructose and glucose, and fructose is an entirely different basic sugar molecule. High fructose corn syrup has a glycemic index of 88, sucrose (table sugar) has a glycemic index of 68, and fructose has a glycemic index of about 19. All three of these are listed under "sugar" on labels. This means that an apple, with a glycemic index of 39 (an average) might have the same amount of sugar as a shot of soda with a glycemic index of 88, even though they both could have the same volume of sugar. A label would list both under "sugar," implying that the impact is the same for both. (Fruits contain primarily fructose, which makes most fruits low glycemic index foods, even though they taste sweeter than higher glycemic index foods).
Some countries have a "low glycemic index" stamp that can be used on products with a low glycemic index (Australia seems to be one). The U.S. does not have any requirement for disclosing the glycemic index of foods. Companies might claim that it is expensive, but it should be no more expensive than getting the nutrient profiles required on product labels. In fact, glycemic indices are obtained by having people eat the food, then measuring the impact on blood sugar over time. Since blood sugar measurements are fairly cheap to take, determining glycemic indices should be far cheaper than the chemistry required to profile nutrients. A sample of 50 people (a reasonable sample for getting an average) could go through the testing for 2 hours. If they were paid $10 an hour (not bad for getting free food) and blood sugar was tested 4 times during that time (maybe even a bit excessive), it would cost only $750, if each test cost $1.25 (lower end test strips can be obtained for less than $1 a strip now). That is extremely low for a regulatory requirement. If each food only needed to be tested with the process changed, the long term cost per sale would not be enough to count. Even if each product had to be tested yearly, the cost would not be enough to justify raising the price of the product. It would probably cost more to add the glycemic index to the label than it would to figure out what the glycemic index was.
Anyhow, the point of this is that glycemic index has become a more important measure of nutritional value than most of the other information on product labels. It is great to have a lot of nutritional information, but most people can figure out what foods are high in fat and what foods have more vitamins and minerals (fruits and vegetables are more nutritious, greasy foods have more fat, etc...). Fiber content is often harder for people to guess, and calories are obviously important to list. None of this is very useful, however, if the real primary factor on weight gain or loss is how blood sugar is affected. Even listing the weight of sugar in a product does not tell us anything about how that sugar will affect people. Some organizations even try to claim that different types of sugar have the same effect (the Corn Refiners Association claims that high fructose corn syrup and table sugar affect the body in exactly the same way). This is such an important health concern that it should be mandatory to include the average glycemic index of foods on the labels, just like we do with other nutritional information.
Just for the record, putting the glycemic load of one serving of a product would be even better than putting the glycemic index on food labels. The problem here is that glycemic load is less well known, and is more likely to be misinterpreted. For instance, Altoids have a low glycemic load around 7, because the serving size is very small. Tomato juice has a glycemic load of 27, for a 6 oz serving. If a person forgot to consider serving size, and most people do forget, this might be interpreted to mean that eating a box of Altoids in one sitting is much healthier than drinking a glass of tomato juice, because the glycemic load of tomato juice is 4 times that of the Altoids. Instead, drinking the glass of tomato juice is the same as eating 12 Altoids, while eating the whole box of Altoids would be like drinking 6 and a half cups of tomato juice. Note that I am ignoring any nutritional value besides the effect on blood sugar. That said, I would be happy with glycemic index, glycemic load, or both on labels. Besides helping people to be healthier, it would also more clearly reveal the lies about how the body handles different sugars.
Our biggest health problem right now is not about getting the right nutrients or even about eating too many calories. It is about managing blood sugar. As such, we should be putting a higher priority on informing people about how their food affects their blood sugar than anything else. (Of course, with the FDA's practical worship of Monsato, I do not expect it to do anything about this without very strong public pressure or even government intervention.)
Australian web site with advice on swapping high glycemic index foods with lower glycemic index foods:
http://www.gisymbol.com/
Lower sugar diets reduce weight, high sugar increases weight:
http://www.bmj.com/content/346/bmj.e7492
This article is about a lawsuit over the claim that high fructose corn syrup is the same as sugar. It discusses a small part of the chemical process. It also discusses the opinion of some nutritionists that while there are differences, they are not significant. Notice that no one mentions the substantial difference in glycemic index. One PhD., near the end of the article, is quoted as saying that the only difference is the ratio of glucose to fructose. This is a filthy lie. In corn syrup, the sugar molecules are separate, which allows the body to absorb them very quickly. In table sugar, the body cannot absorb the molecules directly, because they are bound together. They must be broken apart before they can be absorbed. Note that this is also the same difference between sugars and starches. Starches are long molecular chains of sugars, which cannot be absorbed until they are broken apart. Even better, fiber is also composed of sugar chains, but the chains are organized such that the body cannot break them down. Claiming that high fructose corn syrup is identical to table sugar is like saying that glucose is identical to most starches and fibers, because they are composed of the same molecules. The body can tell the difference. Most starches have a low glycemic index, because it takes time for them to break down. Fiber has a glycemic index of 0, because it does not break down at all. I am not impressed by the PhD. of a person that spouts lies. (Note that this is not strictly in the realm of medicine anyhow. This question should really be addressed by a nutritionist, though most of them seem to hold to the claim that it does not matter, because we should be consuming less sugars regardless of molecular composition. This is also a lie, given that most Americans do not eat enough fruit.)
http://abcnews.go.com/Business/corn-syrup-versus-sugar-legal-fight-court/story?id=15969618
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