The Truth About Glycemic Index

What is it?

Simply put, it is the rate at which the body converts carbohydrates into energy (blood sugar). Foods are given a rating of 0-100. Pure glucose being the reference point on 100. Glycemic index values are determined by feeding humans a fixed portion of food (after an overnight fast) then measuring samples of their blood at specific intervals.

Some Surprises:

It’s believed that all simple (junk) sugars digest very quickly and cause a “spike” in blood sugar. But this is not always the case. While many sweet and sugary foods have a high Glycemic Index (G.I), some starchy foods like potatoes and white bread score even higher than honey or even table sugar (sucrose).

Why is the Glycemic Index Important?

The body performs best when blood sugar is kept relatively constant. If your blood sugar drops too low, you become lethargic and/or get hungry. And if it goes too high, your brain signals your pancreas to produce more insulin. Insulin brings your blood sugar back down, but by primarily converting excess sugar to fat. Also, the greater the rate of blood sugar increase, the more chance the body will release an excess amount of insulin and drive blood sugar back down too low.

It must be mentioned here that excess insulin and or high GI foods don’t make you fat, excess calories do. You can’t store fat if you don’t have excess calories, period. So don’t read between the lines and think that high GI foods make you fat and low GI foods make you lose weight. (more on this later)
Therefore, when you eat foods that cause a large and rapid glycemic response, you may feel an initial elevation of energy and mood as your blood sugar rises, but this is followed by the cycle of lethargy and more hunger

Another problem is individuals with diabetes. There body’s inability to secrete or process insulin causes their blood sugar to rise, leading to a host of additional medical problems. The theory behind the glycemic index is simple- To minimize insulin-related problems by identifying and avoiding foods that have the greatest effect on blood sugar.

Bodybuilders have been eating low GI for decades. When dieting for competition and you on a limited calorie “budget”, you want to get, what I call, the best gas mileage off your calories. In other words you want the food to last you as long as possible as your next meal may be hours away. Low GI foods seem to be the best choice

Should all High GI Foods be Avoided?

For non-diabetics there are times when a rapid increase in blood sugar (and the corresponding increase in insulin) may be desirable. For example, after strenuous exercise, insulin helps move glucose into the muscle cells where it adds to tissue repair. This is the theory behind sports drinks during and after exercise, to speed up recovery. Professional bodybuilders take insulin injections and eat straight after a workout to increase muscle growth.

Glycemic Load

Although most sweets have a relatively high GI, eating a small sweet will result in a relatively small glycemic response.

Why? Well simply because your body’s glycemic response is dependent on both the type and amount of carbohydrates consumed. This concept is known as the glycemic load and was first popularized in 1997. GL = GI/100 X net carbohydrates.

Therefore you can control your glycemic response by consuming low GI foods and or by restricting your intake of carbohydrates.

The table below shows values of GI for the common foods. GI’s of 55 or below are considered low, 70 or above are considered high

Glycemic Myths:

This next section is not going to make me popular, but your deserve to know the truth. Many diet books and renowned authors and dietitians alike would have you believe that GI is all that matters when selecting which foods to eat. (I wish it were that simple) . In reality, diet is a more complex issue and I do agree that GI is a marvelous tool for ranking carbohydrates (and much better than the old “simple” vs. “complex” carbohydrate designations).

However, there are also many limitations to GI which are explained in the next section. Consider this the warning that those diet books and diet authors didn’t tell you.

  1. Scarcity of GI data…Only about 5% of all foods have GI values. It is impossible to estimate GI values by simply looking at the food type
  2. Wide Variation in GI Measurements…The table above shows the GI value for each food. In reality, measurements are not so precise. GI values in fruit rises as the fruit ripens. Different tests measured potatoes at a GI of 56 and then 111. Since values are calculated on humans, there may be other factors skewing the results.
  3. GI Values affected by Preparation Methods….How you prepare food, how long you cook food for, all affect the GI values. The longer you cook it, the higher the GI value goes. Food processing, such as grinding, will elevate GI values for certain foods, because it makes those foods quicker and easier to digest
  4. GI Values Affected by Combination with Other Foods…While test on GI are usually done on individual foods eaten alone, we often consume those foods in combination with other foods. The addition of other foods that contain fiber, protein and or fat reduces the GI value of the entire meal
  5. Individual Differences in Glycemic Response..The rate at which different people digest food (carbohydrates) also varies, so there are some individual differences in glycemic response from person to person. Individual response may also vary from one time of the day to another. And finally, different people have different insulin responses (I.E. produce different levels on insulin), even with identical glycemic response.
  6. Reliance on GI and GL can lead to Over Consumption..It’s important to remember that GI is only a rating of a foods carbohydrate content. If you use GI and GL as a sole factor in determining your diet, you can easily end up eating too many calories.

Take a look at the following example:


Size  GI Cals
 Apple 1 cup  38  72
 Peanuts 1 cup  14  872

Based on GI, the peanuts would look like the better choice, but trust me the extra 800+ calories are not going to do you any good. (Unless you starving to death, which I don’t think you are)

The low GI craze reminds me of other fad diets that blame a single food or concept for all our weight problems. These are the blood group diet, the Atkins diet, just to name a few. If there was one diet that would work it would be the “eat less exercise more diet”. I am shocked to see how many supposed experts in our industry are embracing a concept and basing their entire profession on a theory that is still unfounded. These professionals should rather be teaching our overweight nation to eat less and exercise more. Trying to get people follow a diet has never worked and never will.

Is Low Carbohydrate the Answer?

Now that you can see why carbohydrates have gotten a bad name over the years. (It is the carbs that make you fat etc etc).

Following are some problems associated with low carb diets.

  1. Deficiency of essential Nutrients. If your diet is low in fruits and vegetables, you may not be consuming enough Vitamin A, C and fiber and other essential nutrients
  2. Potential Risks Associated with High Fat Consumption. Low carb diets usually contain large amounts of fat and protein. High consumption of fat increase your risk of heart disease and other ailments
  3. Hypoglycemic effects of Minimized Carbohydrate Consumption. Your brain requires glucose to operate. In the absence of carbs your brain is forced to synthesize glucose from digested or stored fats and protein. This somewhat inefficient process results in a lower than optimal blood sugar levels, which leads to a feeling of lethargy un-alertness and confusion.
  4. Boredom or Cravings Resulting from the Elimination of Carbohydrate-Rich Foods. Any diet that greatly restricts our food selection can lead to increased cravings for the eliminated foods or boredom with the allowable food choices
  5. Added Expense of Specific foods A lot of grocery stores have jumped onto the band wagon. At Woolworths you can buy a wide selection of low GI foods. These foods are more expensive that their normal counterparts. Even food manufacturers are making low carb versions of their foods (low carb bars etc.)
  6. Vegetarians. If you consider yourself a vegetarian, you’ll find it very difficult to follow a low carb diet since nearly all low carb meals focus on the consumption of meats and other animal proteins

What about Satiety (feeling of fullness)

Another reason why the low carb diets are popular is because it is a know fact that protein based foods satiate you better. Most of these low carb diets are high in protein to help control your appetite.

In 1995 researchers performed an interesting study in which they compared the satiating effects of different foods. The results are their study were published in the European Journal of Clinical Nutrition, September 1995 called “The Satiety Index of Common Foods”. In the study researchers fed human subjects fixed calories portions of 38 different foods, and then recorded the subjects “perceived” hunger following each feeding.
The results of this study clearly indicate that certain foods are much better than others for satisfying hunger. The researchers used white bread as the reference point and arbitrarily assigned it a “Satiety Index” of 100. Foods that did a better job at satisfying hunger were given proportionately higher values, and foods that were less satisfying were assigned lower values. Among the satisfying foods they tested were plain boiled potatoes (which is a no-no based on the low GI diet), fruits, fish and lean meats. Subjects that consumed the prescribed portions of these foods were less likely to feel hungry afterwards. Foods that did the poorest job at satisfying hunger include croissants, donuts and, candy bars and peanuts (which by the way has a low GI value)

Outcome of Study

Even though the study was limited to a very small amount of foods (38), researchers noted one very important observation. All foods had a high weight to calorie ratio. In other words, these foods these foods contained a greater amount of bulk for each calorie. They helped make you feel full by literally filling your stomach
This suspected relation between bulk and satiety may seem obvious and trivial, but it opens the door to a very powerful theory – that it may be possible to predict satiety by knowing the nutrient composition of the food. And if that is true, some sort of satiety index could prove to be more flexible for assessing diet than the glycemic index.

Fullness Factor

The above observation has introduced another concept called the fullness factor. This is beyond the scope of this article but it can be calculated based on the foods nutritional value. Bodybuilders have always been aware of the fullness factor. When dieting for competition, you would slowly replace certain foods that had more bulk. For example, I would eat steak for my protein, but as I approached competition date and inevitable became hungrier, I would switch to fish. I could eat almost twice as much fish (grams) as steak for the same caloric value. This was previously explained by literally filling up your stomach. I would also throw in a big bowl of sugar free jelly for only 40 calories.


If you still with me, you would think I am opposed to low GI. Definitely Not. As I mentioned before, it’s a small piece of the puzzle. But to base your entire diet on low GI is naïve and potentially unhealthy. There is a lot more to nutrition than just GI. I will probably make a few enemies with this article, but you deserve to know the truth.

Depending on your goals, I can give you a few obsoletes, and one is eat in moderation, probably less than you eating now and exercise more. Now that you can take to the bank. No one is arguing that fact.


compliments of MH.


About Shaun That Awesome Guy

Husband to the most beautiful woman, Man of honour, Gym enthusiast, Artist, Man of Steel, That Awesome Guy.
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2 Responses to The Truth About Glycemic Index

  1. Pingback: High/Low Week of June 27, 2013 | Chasing Lows

  2. Pingback: The dietitian | So Your Diabetic

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