Should Lifters Pay Attention to the Glycemic index?

The glycemic index is a relative ranking of carbohydrate-rich foods that’s used as a proxy to determine their relative impact on an individual’s blood sugar levels. Over the years, the glycemic index has creeped into fitness circles as a means to maximize recovery and muscle growth, but is it really something the average fitness enthusiast needs to be concerned with?

Let’s discuss...

What is the Glycemic Index?

The Glycemic Index (GI) is a measure of how much and how quickly glucose appears in the blood (a.k.a. Blood sugar) after eating a particular food. The rating system uses a scale of one to 100, with foods having a GI value of 55 or classified as low glycemic, meaning they do not create a very large and sudden spike in blood glucose levels.

Foods such as fruits, veggies, and whole grains are typically considered low GI while processed and refined carbohydrates generally speaking are high GI foods.

In other words, the glycemic index is a numerical value that represents how high your blood sugar rises after you eat a specific food in isolation.

Foods like white bread, white rice, and refined sugar are have some of the highest glycemic index values, and, as such are used as the “standard” to measure foods against as they create some of the quickest and sharpest spikes in blood sugar.

The reason this is concerning is that when an individual’s blood glucose levels are chronically elevated (hyperglycemia), they can become toxic, leading to such consequences as type 2 diabetes, metabolic syndrome, blindness, kidney failure, or increased cardiovascular disease risk.

This is why many in the nutrition and medical professions advocate the consumption of foods that are on the lower end of the glycemic index as they provide a more steady and sustained release of glucose into the bloodstream.

A slower release of glucose also tends to keep more balanced hunger and energy levels as well.

The reason certain foods have lower glycemic indices than others is due to its macronutrient composition (proteins, carbohydrates, and fats) as well as its fiber content. The more fiber, protein, and/or fat a certain food has, the slower it digests, meaning the body has to work hard to break it down, and as a result it provides a more sustained release of sugar (glucose) into the bloodstream.

Now, keep in mind that the glycemic index only accounts for the impact a food has on an individual’s blood sugar levels when it is eaten in isolation, not in combination with other foods as you would typically consume then in the context of a normal meal.

How Do You Determine the Glycemic Index of Food?

GI values of foods were determined by feeding 10 or more people each 50 grams of the same carbohydrate source (rice, pasta, cereal, etc.). Following ingestion of the test food, scientists then measured each person's blood glucose response two hours after ingestion.

The results were plotted on a graph and researchers then measure the area under the curve (AUC) of their group’s collective glucose response.

On a separate day, the same group of individuals returned for testing and ingested 50 of pure glucose (the reference food). Again, researchers measured the subjects’ blood sugar levels two hours after ingestion and plotted the results.

From this, researchers calculated the GI value of the food by dividing the glucose AUC for the test food by the glucose AUC for the pure glucose solution for each individual.

The final GI value of each food is an average of all the individual GI values calculated for that particular food.

Glycemic Index Chart of Common Foods

Problems with the Glycemic Index

While an interesting concept, and one that holds some merit, the glycemic index isn’t without its own limitations and faults.

For starters, the GI values were based off an individual consuming a food that yielded 50 grams of digestible carbohydrate. However, 50 grams of digestible carbohydrate isn’t necessarily a one-size-fits-all portion size.

For instance, 50 grams of carbohydrate from white rice is a considerably smaller portion size than 50 grams of carbohydrate from air popped popcorn.

Additionally, an individual’s response to ingesting 50 grams of digestible carbohydrates in isolation is highly individualistic, which means two individuals can have wildly different glycemic responses to ingesting that amount of carbohydrate.

For example, a person who has relatively low body fat and exercises regularly will handle the 50 grams of carbohydrate much better than someone who is sedentary and overweight.

Moreover, there is significant variation in the GI values that are assigned to the same food depending on the source of information. One source may list a boiled russet potato with GI of 56 while another source may list it as over 100.

The reason for this is that GI values of foods aren’t static. They can vary depending on how the food was prepared (baked vs boiled vs refrigerated and then reheated), the degree of processing, and the ripeness of a food.

For example, a ripe banana will have a significantly higher GI value than an unripened banana due to the fact that the ripe banana will have had more of it starch content converted to sugar.

Further still, as we mentioned earlier, the glycemic index values were tabulated when the food was eaten in isolation. When most of us eat a meal, it contains a variety of foods, not a whole bunch of a single food (such as white rice).

Like we stated above, the glycemic effect of a food will change when it is consumed in the presence of other foods or if it has higher amounts of protein, fats, and fibrous carbohydrates.

What this means is that a mixed food meal (such as salmon, brown rice, and broccoli) will have a vastly different GI value than if you just consumed an entire plate of brown rice or even a plate of only broccoli.

Finally, just because a food has a lower GI value does not necessarily mean that it is “healthier”. For instance, a candy bar and a cup of brown rice have roughly the same GI value (~55), but you’d be hard pressed to find any dietitian who says that both pack the same nutritional value.

Now, this brings us to the main focus of the article…

Should Lifters Pay Attention to the Glycemic Index of Foods?

Since its inception, the glycemic index has been used by bodybuilders, elite athletes, and recreational fitness enthusiasts alike to optimize athletic performance, recovery from exercise, and muscle growth.

The reason for this is two-fold:

There are two main reasons why it was used:

1. Following exercise the body is very insulin sensitive, meaning it is primed to utilize a high dose of carbohydrates (glucose) to support glycogen replenishment and recovery.
2. Foods with high GI values spike insulin which supports muscle building as insulin plays a primary role in shuttling nutrients (carbs and protein) into muscles.

Now, we’ll all agree on the first point that exercise (really of any kind) helps boost insulin sensitivity and consuming a high amount of carbohydrates post workout will raise blood sugar levels, thereby support glycogen resynthesis and facilitate recovery.

However, the glycemic index of a singular food is not really what you should be focusing on, so much as you should be focused on how much total carbohydrate you are consuming.

There is no conclusive body of evidence noting that consuming high glycemic foods post workout leads to better muscle growth. This is especially true if you are only working out once per day.

The individuals that need to be concerned with ingesting high GI, low fiber carbohydrates and fast-digesting protein immediately post workout are those top-tier competitive field sport athletes that engage in multiple bouts of training or competition each day with only a couple of hours between each engagement.

When faced with this type of situation, maximizing nutrient replacement (especially carbohydrates) is a must.

But, for the rest of us that only train once per day, it’s not worth the extra mental stress and effort to focus on the GI index of the foods we’re eating.

Additionally, the belief that insulin is “anabolic” isn’t 100% accurate. It’s more truthful state that insulin is an anti-catabolic hormone rather than an anabolic one, meaning it helps limit muscle protein breakdown as opposed to directly stimulated muscle protein synthesis.

And, as we said above, the main focus should be on hitting your overall macronutrient targets each day, not stressing about whether to eat brown rice or white rice with your post workout meal. Their impact on recovery and muscle growth will likely be the same.

Plus, remember that we don’t eat foods in isolation, we eat them in combination with other foods, which basically renders the whole GI value as a null proposition.

Therefore, focus on hitting your macros each day and consuming enough high quality whole food sources, not so much on whether or not to have some high GI carbs post workout.

The Bottom Line on Lifters and the Glycemic Index

By and large the glycemic index is an outdated concept that doesn’t hold up for the individual.

Additionally, there is little evidence that adhering to the glycemic index as any tangible benefit for muscle growth or recovery.

What this means is that instead of spinning your wheels worry about whether or not that serving of white rice is going to spike your blood sugar and ruin your fat loss results, focus more on meal prepping, consuming the right amount of calories, and training your butt off in the gym.

Those three things will have a profoundly larger impact on your performance and physique than whether or not you had white or brown rice with your meals.

References

1. Atkinson, F. S., Foster-Powell, K., & Brand-Miller, J. C. (2008). International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care, 31(12), 2281 LP – 2283. https://doi.org/10.2337/dc08-1239