The Glycemic Index Revisited
"Diets rich in high-glycemic index foods, which cause quick and strong increases in blood sugar levels, have been linked to an increased risk for diabetes, heart disease, and [becoming] overweight, and there is preliminary work linking high-glycemic diets to age-related macular degeneration, ovulatory infertility, and colorectal cancer. Foods with a low glycemic index have been shown to help control type 2 diabetes and improve weight loss."
– The Nutrition Source (Harvard School of Public Health)
I'm sure that you can appreciate the importance of optimizing your blood sugar levels; not only for the quest of a lean, muscular physique but, as the opening quote illustrates, the pursuit of good health and a longer life.
But considering that walking around with a glucometer and sticking ourselves after every meal just isn't practical – or polite – a more efficient method of measuring the effect of carbohydrates on blood sugar levels needed to be determined.
Unfortunately, what athletes, bodybuilders, and TNation readers find scientifically relevant usually doesn't find its place on the National Institute of Health's "Top 10 Research Programs to Give Funding To" list.
Sometimes though, we get lucky, and while it wasn't with the NIH, the British Diabetic Association and the Medical Research Council decided in the late 1970s to find out more about the differing effects of carbohydrate-based foods on blood sugar.
Fast forward to 1981, and the Glycemic Index (GI), a method of ranking the effects of different carbohydrate based foods on blood sugar, was born.
The GI of a food is measured in a two-step process. Researchers will give a person 50 grams of pure glucose and then measure their blood glucose levels over the course of several hours. This pure glucose serves as the control, as theoretically, nothing can be digested faster than pure glucose.
Next, researchers give the same person 50 grams of the food in question (like carrots, rice cakes, or black beans), and measure their blood glucose levels for several hours afterwards. As the diagram on the right and the following technical definition of the GI shows, the blood sugar responses for the two foods are then compared.
"...the area under the blood glucose response curve for each food expressed as a percentage of the area after taking the same amount of carbohydrate as glucose."
One key component to how the GI is measured has to do with amount. The amount of food used is always the same, 50 grams. As a result, the GI only takes into account the type of carbohydrate and not the amount. This is a point of criticism that many GI critics often bring up; for example, how practical is the GI when 50 grams of carbs from rice can be ingested with ease while 50 grams from carrots would require Bugs Bunny-like dedication?
The Glycemic Load
To make the GI more real world applicable – as no one eats food in 50-gram increments – scientists came up with the Glycemic Load (GL). The GL is a carbohydrate/blood sugar rating that accounts for both type and amount of carbohydrate.
It's defined by this equation:
Glycemic Load = (Glycemic Index x Amount of Carbohydrate in Grams) / 100
Here's an example of how the GL works versus the GI:
|Food||Standard Serving Size||Glycemic Index||Glycemic Load|
Traditionally, the much-maligned carrot is vilified by GI disciples because they have a higher GI than most vegetables (one study found the GI of carrots to be 90 but these findings were never replicated), but as you can see the average GI for carrots is only 47 – which actually makes carrots a low GI food – and when you take into account the amount most non-hares would normally eat, the GL for carrots is really very low.
The GI is a property of a food, just like the amount of protein or fat in a food, while the GL refers to the composition (type of carbohydrate) and size of your meal (amount of carbohydrate).
Dr. Wolever, an Oxford trained physician, nutrition PhD, and world leading expert on the Glycemic Index, hammered this point home repeatedly in a seminar I attended recently. This is an important designation, as it makes a food's GI rating applicable across different populations.
The Insulin Index
You might have heard about a study published over a decade ago talking about the Insulin index. Like the GL, the idea behind the Insulin Index is that scientists wanted to quantify the effects that different foods had on insulin levels.
But one problem with the Insulin Index is that the insulin response can vary tremendously between individuals, thereby requiring a lot of extra data on the effects of different foods in a variety of populations to have a standardized version of the Insulin Index.
To further complicate matters, the Insulin index concept never really took off in the scientific community – at the time of writing this article, there were 22 times more scientific papers in PUBMED about the GI compared to the Insulin Index.
Now that we've established the various indexes, let's see how you can best apply them to your physique pursuits. Here are two important points:
1. Glycemic Index versus Glycemic Load is more of an academic debate than practical one
I always stress this point with clients when we discuss carbohydrates, blood sugar, and the Glycemic Index. Generally (and practically) speaking, foods with a low GI will also have a low GL.
Green leafy vegetables have a low GI, and while you can eat a large volume of these foods, the actual gram amount of carbohydrate that you're consuming will also be low (making the GL low as well), while foods with a higher GI are usually more carbohydrate dense (meaning that if you eat a large volume of these foods, you'll also be eating a lot of carbohydrates).
Long story short: Meals with low glycemic carbs will naturally have a lower GL and meals with higher glycemic carbs will naturally have a higher GL. Why make it more complicated than it has to be?
2. High Glycemic Foods versus Low Glycemic Foods is what really matters to You
Another point of criticism regarding the GI is consistency. While the measuring of a food's GI is supposed to be a standardized procedure, different labs have calculated different GI's for the same food. While this might sound like a problem, it really isn't. Why?
As you can see by the chart below, when using the GI to categorize foods, three main categories are used: High, medium, and low.
High: GI > 70
Medium: GI = 55-69
Low: GI < 55
|High GI Foods||Medium GI Foods||Low GI Foods|
|Shredded Wheat||Apricots||Green Vegetables|
|Bagel||Long Grain Rice||Nuts|
|White or Whole Wheat Bread||Pita bread||Apples|
If you follow my recommendations and use the GI as a tool to improve your carbohydrate choices, high versus low GI is what really matter. When researchers combined discrepancies found between laboratories and published studies, low GI foods were always low GI foods and high GI foods were always high GI foods.
Jasmine rice and rice cakes don't suddenly become low GI foods simply because two labs can't agree on a score.
The Glycemic Index of Foods Can Change
Remember when I mentioned above that the GI of a food was a property of the food? After reading that, you might've thought that means that the GI rating of a food always stays the same. Unfortunately, that's not always the case due to some interesting food science – and more recently, the unrelenting efforts of food companies to get 'whole grains' into our diets.
There are three common ways that the GI of a food can change: processing, ripeness, and cooking. Let's take a look at how cooking can influence the GI.
The Potato Story
This is where it gets really cool. Let's say you take a potato; prepare and eat it two different ways and it'll have two different GI ratings.
Raw potatoes, cooked potatoes, and potatoes that are cooked and then cooled all have different GI ratings due to the potato's unique starch make-up. Certain types of potatoes, like red potatoes, contain high levels of amylose. When cooked, amylose is released, mixes with water molecules and forms a gel like substance. By letting the potatoes cool, you're giving the gel a chance to solidify into a state that's more resistant to digestion. If you eat it while it's still hot, the gel is still gelling, and it will get digested faster.
Lest you think this is the spud-inspired version of splitting hairs, think again: according to one researcher I talked, to the difference between eating a warm potato versus waiting for it to cool and then eating it can be a GI rating of 75 versus 40!
Who would have thought that potato salad could be better for you than a steaming baked potato?
Here's a muscled-up version of potato salad for you to try:
- 3 medium red potatoes
- 1/2-cup olive oil mayonnaise
- 5 chives, minced
- 2 strips turkey bacon (not the processed Jennie-0 stuff that looks like play-dough pressed into a bacon form – try Applegate Farms)
- 1/2 medium onion, diced
- 1 stalk celery, diced
- 1 Tbsp yellow mustard
How to Prepare:
Place the potatoes in a medium-sized pot with boiling water. Cook for ~15 minutes, until the potatoes are fork tender. While the potatoes are cooking, cook the turkey bacon in a nonstick frying pan over medium heat. Once the potatoes are cooked, remove them from the pot and let cool.
Next, dice up the turkey bacon and place in a bowl with the mayonnaise, chives, onion, celery, and yellow mustard. When the potatoes have cooled, cut them up into 1-inch cubes. Add to the bowl and mix thoroughly. Add salt, pepper, and Frank's Red Hot to your desired taste. Makes 2 servings (see nutrition facts below).
Enjoy this with a roasted chicken breast or grilled flank steak for a great post training meal.
Protein and Carbohydrate Affects on Glycemic Index & Glucose Response
Another criticism of the reliability and effectiveness of the GI is that it ranks foods by themselves, when in reality, when we eat carbohydrate-based foods, we eat them together with protein and fats.
Another factoid I frequently hear bandied about is that "adding protein and fats to a meal reduces the GI of rice/potato/Pop Tarts/etc."
However, as stated earlier, one of the important points about the GI rating is that it's a property of the food, so adding fat and protein to a meal containing white rice for example doesn't change the GI of rice, it only will reduce the rise in blood sugar...or will it?
In 2006, Dr. Wolever published a study that was the first to systematically examine the 'mixed meal' question. In this study, participants received shakes containing glucose (50 grams), protein (0, 5, 10, or 30 grams), and fat (0, 5, 10, or 30 grams).
The researchers found that gram-for-gram, protein had almost a three times greater effect than fat at reducing glucose response to the meal. They also found that the effect of protein was linear across the protein dosages (0 grams to 30 grams), so that the more protein that was in the shake, the greater the reduction in glucose response.
Dr. Wolever cautioned against taking these findings out of context, as the study used liquid shakes and not whole food meals. But as a TNtaion reader who probably has a second pantry dedicated to tubs of Metabolic Drive, this research is especially relevant to you.
To further explore the 'mixed meal' question, Dr. Wolever ran another study, this time using whole food meals. The meals contained 0-18 grams of fat and/or protein and 16-79 grams of carbohydrates (with GI's ranging between 35-100).
They found very different results than the previous smoothie study: when using whole foods, the protein and fat content of the meals had a negligible effect on glucose levels. The total carbohydrate content of the meal and the GI of the foods in the meal were able to predict glucose response with almost 90% accuracy.
While they might have found different effects at higher protein dosages, when these two studies are taken together the message is pretty clear: if you're having a shake, then adding protein to that shake is a good way of controlling your blood sugar response.
If you're having a whole food meal, then eating low glycemic carbs and reducing your total carb intake (which can be done by eating low glycemic carbs) is the best way to control your blood sugar response.
Glycemic Index, Nutrition Timing, and Your Diet
What's the best way to use glycemic index in your diet? You can use the glycemic index to optimize the nutrient timing of your diet.
|Hypertrophy Phase||High + Medium GI carbs||Mainly High GI carbs||Low & Medium GI carbs|
|Maintenance Phase||Low + Medium GI carbs||Mainly High GI carbs||Low GI Carbs|
|Fat Loss Phase||Low GI carbs||Mainly High GI carbs||Low GI carbs|
The Glycemic Index Wrap Up
• The Glycemic Index has been around for three decades and isn't going away anytime soon.
• Eat raw or lightly cooked oats to maximize the blood sugar lowering effects of beta-glucan.
• When having a shake, adding additional protein is a very effective way of controlling your blood sugar response.
• When having a whole food meal, eating less carbs and lower GI carbs is the best way to control your blood sugar response.
• You can use GI to easily optimize the nutrient timing of your diet.