The Glycemic Index (G.I.), like all things within the fitness industry, is a highly controversial topic.
Some groups consider the G.I. an essential tool to achieve all goals related to health and fitness, while others view it as more or less an arbitrary piece of information.
Per usual, the radical incongruence among beliefs most likely stems from poorly conducted and misinterpreted research, the mainstream media, and the inability of individuals to disassociate between their viewpoints and ego.
Before we examine the research behind the G.I. to determine how useful it may or may not be, it’s necessary to have a basic understanding of what the G.I. is and how it’s used.
What is the Glycemic Index?
“A food’s Glycemic Index (G.I.) is the measure of its ability to raise blood sugar.” Generally speaking, consuming higher G.I. foods will result in a more rapid spike in blood sugar than foods ranked lower on the G.I. scale.
The Glycemic Index is established through ingesting roughly 50g of carbohydrates in a test food following an overnight fast. Blood samples are taken pre and post consumption and are used to measure the blood sugar response. Results are then compared to the effect of standard dietary glucose, which has a G.I. of 100, and finally given a rank corresponding to the degree that blood sugar was raised.
The table presented below outlines the classifications and rankings of the Glycemic Index, as well as several examples of certain foods that fall into each classification.
|Low Glycemic||Score: 55 and below||Brown Rice, Apples, Lentils|
|Moderate Glycemic||Score: 56-69||White Rice, Pumpernickel, Full Fat Ice Cream,|
|High Glycemic||Score: 70 and above||White Bread, Watermelon, Dates|
The Glycemic Index: Common Beliefs and Associations
Some groups commonly reference the Glycemic Index as a means to determine how “healthy” a certain food may (or may not) be, with lower-GI foods by and large representing the healthiest options.
Following this train of thought, certain professionals believe lower-GI foods are inherently superior to foods ranked higher on the GI scale for achieving and maintaining a lean physique.
Both of these claims tend to be made under the assumptions that high-G.I. foods will:
- Cause a rapid increase in the hormone insulin, thus inhibiting lipolysis (the breakdown of fat)
- Be far less satiating than lower-G.I. foods, making weight/fat loss far more difficult
Another common belief which will be touched upon in today’s article is the idea that lower-GI foods are naturally better than high-GI foods for optimizing athletic performance.
This assertion is generally made under the impression that the decline in blood sugar following a high-GI meal will result in decreased energy causing a negative effect during training or competition.
As you now have a basic understand of the Glycemic Index and some of its commonly associated beliefs, let’s see what the research has to say.
The Glycemic Index and Body Composition
As outlined above, many individuals believe lower-GI foods are inherently better than high-GI foods for achieving and maintaining a lean physique.
This belief is largely due to misunderstanding the relationship between the Glycemic Index, insulin, and The Energy Balance Equation.
Let’s have a look at all three, shall we?
In healthy individuals, insulin is a hormone used within the body to regulate the amount of sugar in ones blood. Following a meal, insulin is secreted by the pancreas and used to transport glucose from the blood into the necessary tissues and organs such as muscle, liver, and fat cells.
As I discussed in this article, insulin is known to inhibit the breakdown of fat. Since insulin has been shown to rise following the ingestion of carbohydrates, some professionals have stated a minimal-carbohydrate diet will eliminate insulin spikes thereby creating the optimal environment for fat loss.
While in theory this appears to be a valid hypothesis, upon examining the research we begin to find some gaping holes in this argument, such as:
- Protein stimulates insulin secretion too, which means insulin alone cannot be the sole cause of fat gain
- Assuming the individual is in good health, insulin will not stay chronically elevated following meals. As long as the individual remains in energy balance (equal ratio of calories in vs. calories out), the net balance of fat gain/loss will be equivalent. James Krieger does a great job of explaining this here.
Given that the Glycemic Index is a measure of a foods ability to raise blood sugar and insulin is used to transport those sugars into surrounding tissues, some individuals have concluded the G.I. and insulin have a linear correlation.
That is to say: as a foods G.I. goes up, the insulinemic response will also go up.
Conversely, as a foods G.I. goes down, the insulinemic response will also go down.
Logically this seems to make perfect sense; however, upon examining the research we find this hypothesis doesn’t hold water.
For example: in this study, milk products with a low G.I. produced surprisingly high insulinemic responses, coming close to what was produced by white bread (one of the highest G.I. foods).
Furthermore, as Alan Aragon outlines here, options such as baked beans, cheese, beef, and fish are all relatively low glycemic yet exhibit insulin responses analogous to various carbohydrate sources.
While other factors such as macronutrient composition play a major role in the total insulin response to a meal, a major concept to grasp from this section is: The Glycemic Index is not an accurate predictor of subsequent insulin secretion following a meal.
That’s it. Plain and simple. The G.I. of individual foods cannot predict how much insulin will be released.
More to the point, even if the G.I. did appropriately calculate the subsequent insulin response to a meal, in regard to healthy individuals it would be more or less irrelevant seeing as studies show“reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize.”
I’d note I’m in no way condemning low-carb/ketogenic diets or any other form of dieting which manipulates macro-nutrient composition. I am very well aware that each and every individual has different preferences and needs which must be taken into account when choosing the optimal diet for them.
That being said, assuming an individual has sufficient protein intake and an adequate caloric deficit, it’s important to realize that “diets differing substantially in glycemic load induce comparable long-term weight loss”
In the simplest terms possible, assuming an individual is in good health, the G.I. of specific foods is an arbitrary piece of information regarding body composition.
I don’t know about you…but if someone tries convincing me that watermelon will eventually make me fat because it has a high G.I. of 72, I just might bleed through my eyes.
The Glycemic Index and Hunger
A common argument made by numerous professionals is low-G.I. foods provide a great deal more satiety than high-G.I. foods.
Needless to say, for individuals looking to lose weight this is a highly relevant concern.
Beyond recommending a diet largely consisting of whole and minimally processed foods, it’s hard to recommend the ideal diet for satiety as what specifically reduces hunger varies from person to person. However, I thought it was worth noting in this study potatoes (a very high-GI food) were easily the most satiating food of the six categories tested.
Other studies have shown low-G.I. foods to be better for overall satiety while others have shown high-G.I. foods are better. My best recommendation would be to experiment with different combinations and find what works best for you.
The Glycemic Index and Athletic Performance
A common and valid concern regarding the G.I. of a meal (specifically pre-workout/competition) is the possibility of compromised athletic performance.
To be honest, the research on G.I. and athletic performance is rather diverse with outcomes all over the spectrum. Some say high-G.I. prior to training negatively effects performance while others say it has no effect whatsoever.
Recently, in Alan Aragon’s monthly Research Review, he broke down a study via Jarmurtas AZ, et al. which compared the effect of high and low G.I. meals on exercise performance and beta endorphin responses.
In this study the authors concluded “…ingestion of foods of different glycemic index 30 min prior to one hour cycling does not result in significant changes in exercise performance, beta-endorphin levels as well as carbohydrate and fat oxidation during exercise.”
Needless to say, this study is clearly limited as it only tested the results of cyclists, whereas much of my readership is devoted to individuals looking for improved anaerobic performance (i.e. lifting heavy ass weight).
I think the most important concept to take from the current body of research surrounding the G.I. and athletic performance is to experiment and find what works best for you.
If eating a high-G.I. meal prior to training makes you fatigue earlier and feel like crap, stick to a lower-G.I. meal.
Likewise, if you notice the G.I. of your meal prior to training has no effect on your mood or performance, eat whatever leads you to perform at your best while making sure to get an adequate amount of protein and carbohydrates.
Based on the current body of knowledge surrounding the G.I., I think it’s relatively safe to assume the majority of healthy individuals don’t need to worry about it.
In today’s world it’s entirely too easy to get caught up in the minutia, trying to control each and every aspect of our lives. Unfortunately, this may to lead to neuroticisms and unhealthy relationships, not only in training and nutrition, but in all facets of life.
The best advice I can give is, stick to the basics!
The basics work. They’ve been proven to work. And they will continue to work.
Rarely does complicating and meticulously accounting for each and every variable ever work out to our overall advantage.
Play around, experiment, and find what works for you. When you eventually find the most productive system…use it!
Never Minimal. Never Maximal. Always Optimal