It was 1981, and David J.A. Jenkins who is a British-born University Professor in the department of Nutritional Sciences at the University of Toronto, along with his student Thomas Wolever, published research showing the effects of various carbohydrates on the body’s blood sugar levels. This research was compiled into a list, and as you might’ve guessed they called it the Glycemic Index (shortened to simply GI). It is composed of a scale ranging from 0 to 100, with glucose being the baseline of 100 (although some carbs do go above 100).
Glycemic Index Of Foods
The scales purpose was to determine how much of a glycemic response (the conversion of a carbohydrate to glucose in the body) occurred when an individual ate 50 grams of a certain carbohydrate after an overnight fast. Described more simply, a food with a value of 0 will have no impact on your blood sugar levels and the higher a food is on the scale, the more your blood sugar spikes. A few examples of popular carbohydrate-rich foods and their GI ratings include: Coca Cola® with a 63, oatmeal with a 55, ice cream with a 62, an apple with a 36, and Fruit Roll-Ups® with a 99. In a 50 gram serving out of all the mentioned examples, Fruit Roll-Ups® will give your body the highest blood sugar spike (literally one degree less than pure glucose), while an apple will spike it the least (a little more than a third of what glucose would).
As most of us already know, we don’t want an excess of blood sugar (used interchangeably with glucose) in the blood stream for a number of reasons:
- Your body performs best when your blood sugar is kept relatively constant (if it isn’t around exercise). If your blood sugar drops too low, you become lethargic and/or experience increased hunger. And if it goes too high, your brain signals your pancreas to secrete more insulin. Insulin brings your blood sugar back down by shuttling the glucose into your cells, but primarily by converting the excess blood sugar to stored fat (again, if not around exercise).
- The greater the rate of increase in your blood sugar, the more chance that your body will release an excess amount the hormone insulin, and drive your blood sugar back down too low3. For the healthy individual the worst thing that can come out of a constantly shifting blood glucose level is a cycle of increased energy while your blood sugar is high, followed by a crash when your blood sugar goes back to baseline. If this happens multiple times throughout the day on a chronic level it can cause fat gain, a lethargic mood and an increase in hunger (usually for high GI sweets, which only starts this cycle over again).
A lesser utilized version of the GI takes into account the amount of carbs in the 50 gram serving. This newer rating system is called the Glycemic Load and simply multiplies a foods GI number by the amount of carbohydrates that is in a food and that is then divided by 100. This makes it possible for a food like watermelon to have a high glycemic index (of 72) but low glycemic load (of 4). These numbers can be impacted by the amount of fat or fiber that is in a food, and they can be impacted further still by the size of the portion consumed1.
If you compare two foods such as popcorn and potato chip, the GI rating tells you they both equal 55. However, if you compare their Glycemic Load of 7 for popcorn and 12 for potato chips, we know the potato chips will have a greater impact on blood sugar than the popcorn. “While the Glycemic Index is a good way of making food choices, the Glycemic Load helps to work out how different sized portions of different foods compare with each other in terms of their blood glucose raising effect”2. As such, both have their place when choosing food and meals.
How The GI Helps Diabetics
Although increased fat storage may sound bad enough, individuals with diabetes (diabetes mellitus, types 1 and 2) have an even worse problem. Their body’s inability to secrete or process insulin causes their blood sugar to rise too high, leading to a host of additional medical problems. Living with diabetes makes the individual five times more likely to suffer from a cardiovascular disease, such as a stroke or heart attack. Diabetes is also responsible for most cases of kidney failure and lower limb amputation. A lesser known but just as serious health problem is chronic loss of vision to varying degrees and even complete blindness.
Preventing diabetes can be helped by exercising regularly, staying at a healthy weight, not smoking, and eating a balanced diet with mostly low GI foods. Because having low blood sugar is so important for people living with diabetes, the GI is extremely beneficial for them to control what they eat. For example a white potato has a GI rating of 82 and would spike blood sugar levels to the roof, causing all sorts of issues for the sufferer while a yam has a lower GI rating of 54, making it easier for the sufferer to control their blood sugar.
When High GI Food Are Beneficial?
Everything I’ve said so far has most likely lead you to believe that a diet full of only low GI foods is much superior to one of a combination of both. Which is true if you have diabetes, but healthy individuals who exercise regularly and are at a healthy weight can actually benefit from strategically adding high GI carbs to their diet. Strategically is the key word here, because when high GI carbs are arbitrarily added to your diet on a daily basis it can and will lead to fat gain, insulin resistance and in extreme cases will develop diabetes. And as we’ve already discussed, diabetes is currently incurable and a very detrimental condition to have to live with.
In this new low-carb age we live in, insulin is labeled as the bad guy who does nothing but get you fat, which is far from its main function. It is true that eating a lot of high GI carbs on a daily basis will cause your body’s insulin to store the extra glucose in your blood stream as fat, but insulin is also responsible for bringing that glucose into your cells, replenishing glycogen (the stored form of glucose in our cells that we use for energy) and repairing muscle. You see, our muscles need carbs as much as they need protein. The insulin response associated with a high carb meal after a workout will shuttle all the nutrients into your muscles to replenish your depleted glycogen stores from said workout, rather than storing the glucose as fat. It’s when our body’s stores of glycogen are already filled that glucose gets stored as fat. Conversely when an individual is on a low-carb diet and depriving themselves of carbs, their glycogen stores run dry and that is when our body resorts to burning body fat and muscle which is known as gluconeogenesis (but that’s a topic for another day)4.
If I could tell you to remember one thing from all the information I just laid out, it would be that high GI carbs can indeed be healthy, if you know how to use them correctly, by centering them around your workouts when you are depleting your glycogen stores. In fact there are supplements you might’ve heard of including Dextrose, Maltodextrin, and Waxy Maize Starch which all have a GI rating of over 100. They are designed to be eaten/drank with protein or amino acids and spike your blood sugar, which is when your pancreas secretes insulin to replenish your glycogen and repair your muscles faster and more efficiently than if you only ate your post-workout protein with low GI carbs.
Take Home Message
It’s easy in our culture to hear something negative and automatically assume it to be true, and in the case of insulin being the bad guy along with carbs, this can’t fit the situation better. The Glycemic Index is a misunderstood beast, originally classifying healthy foods as “low GI” and unhealthy foods as “high GI”, which simply isn’t the case. The GI is simply used to determine how much your blood sugar raises with 50 grams of that carb heavy food, which isn’t an indication of healthfulness. If you are diabetic you most likely are already very aware and familiar with the GI, but if not, I hope you learned at least a little bit about this whole process.
Yes the GI is important, but not to distinguish what foods you should stay away from, but when you should be eating them. Making sure to consume high GI foods around your workouts, effectively replenishing your glycogen at an increasing rate and increasing your overall recovery time for the better. Also keep in mind to stay away from high GI carbs if you live a sedentary life without exercise, opting for whole grain and brown carbs over white (whether that be potatoes or sugar) to keep your insulin resistance down and prevent the development of health conditions such as diabetes. Thank you avid reader for pushing through to the end and once again I really hope you got a little smarter from reading this article! And as always, train smart, get a solid eight hours a night and continue to fuel your ambition!