top of page

The 5 Most Common Myths About Glycemic Index

There are several misconceptions or half-truths concerning the Glycemic Index. Let's just say it's not a black and white topic. Generalized comments will make it difficult for you to make the right decision.

The Glycemic Index is a quantitative way to assess how a given diet increases blood sugar on a scale of 0 to 100. Easy right? Yeah ... the understanding of what you can eat as a result of this calculation is where the shades of grey come in.

Myth 1: Watermelon has a high glycemic index, so it's bad for you.

The answer to this question is yes and no. Well, watermelon does have a high glycemic index of 72, but this topic has more. The glycemic index tests a certain amount of carbohydrates, i.e., 50 grams. This will equal to around 4 or 5 cups of watermelon that you actually won't eat. Now there is the glycemic load that calculates the glycemic index for the quantity of food you are consuming and score it from 0 to 20. So one cup of watermelon (a fair quantity to eat) comes with a glycemic level of seven, which renders it low in glycemic index. With a high watermelon nutrient content, you wouldn't want to remove it from your diet for any reason!

Myth 2: All foods that are low in GI are healthy for you.

No, it's not true. Low glycemic only tests how rapidly the blood sugar is boosted by a diet. Good eating is more than just one definition. Peanut M&M and certain sodas, for instance, are medium glycemic ... this would not mean that it's safe to consume or drink every day. Sugar also has a detrimental effect on wellbeing in several respects. Don't chuck what you know about safe eating away. The Glycemic Index is just a piece of the whole puzzle.

Myth 3: You've seen multiple glycemic index levels for the same stuff, so one source has to be incorrect.

No! Glycemic index measurement is not a straightforward task. Usually, 10 participants are checked for the same quantity of food. For a span of two hours, their blood is expected to develop a blood sugar reaction curve. This is then compared to a reference item like table sugar. The average reactions for each measure are the glycemic index of the product. -- an individual can have a slight shift in their reaction to food, because if two different laboratories examine the same product, you may find some minor variations. Basically: the variations are so tiny that they won't matter: a high GI product always ends up with high GI.

Myth 4: Plain, simplified carbs are fast, and complex carbs are slow.

No! A 2003 analysis found that the perceived meaning of the GI is significantly inaccurate. The research study measures the glucose kinetics of a low-GI cereal breakfast (bran cereal) and a high-GI (corn flakes) breakfast, each with 50 g of the available carbohydrate. The GI of corn flakes was much more than twice as high as that for bran cereal, considering the fact that the amount of glucose present within the bloodstream of the two foods did not vary substantially during the 180-minute examination. In other words, for corn flakes and bran cereal, the amount of glucose entry into the bloodstream was the same.

However, the presence of insulin in the bloodstream was slightly higher and quicker compared to corn flakes following the ingestion of bran cereal. The release of insulin is not used in the GI, and insulin is used to withdraw excess glucose from the bloodstream and transfer it into muscle and liver cells. Twenty minutes after eating bran cereal, the concentration of insulin was 76 percent higher participants, contributing to a 31 percent higher blood glucose disappearing rate in comparison to corn flakes. The lower GI of bran cereal is, however, not due to slower glucose production in the bloodstream. Instead, the amount of glucose production in the bloodstream of the two foods is similar. The distinction was that glucose from the bran cereal was absorbed more easily from the bloodstream and the overall increase of glucose was also lower than that of the maize flakes.

It's so abstract that I will repeat it with a more tangible reference. Think of the bloodstream, like a bath that has a faucet that pours water (blood sugar) into the bath and a drain, which removes it from the bath (insulin concentrations). Only imagine two bathtubs parallel to each other. The water pours out of the outlet into the bathtub at the same time for both tubs. The drain is mostly blocked in the first tub, but the drain is wide open in the second tub. The overall rise in the water level in the first bathtub continues to rise and go as long as the water is drained until only a limited quantity trickles from the drain. In the second bathtub, the water is quickly flowing out of the bottom at the same time as the water is coming out of the faucet, and the water level does not go much high. Just by comparing the overall increase of the water level, you will never see that the water entry rate is the same, simply that the total increase is much higher with the first bath relative to the other.

The overall increase in the amount of water (blood glucose) is what the GI tests. The high fiber bran cereal in this study induced a stronger insulin reaction, which drained glucose more easily from the bloodstream and triggered a lower overall blood glucose rise, thus the low GI classification. It has little to do with the level of metabolism, absorption, or blood glucose. Glucose from the purest and basic sugar-sweetened corn flakes reached the bloodstream at the same pace as glucose from the more complex bran cereal.

This data cannot be applied to all foodstuffs from these experiments without the execution of glucose kinetics tests on all foodstuffs. The results of these tests, however, fully disprove the idea that GI represents glucose entry-speed into the blood flow. It is also entirely untrue that basic carbohydrate products are high GI foods that more easily go into the bloodstream than more complicated low-GI carbohydrates.

Myth 5: All foods with a low GI are rich in fibers.

Most of the time, this is valid, but not always. Fiber usually helps slow digestion and can be a low-glycemic component in a meal, although this is an over-generalized argument. A Russet baked potato, for example, is rich in fiber but has a rich glycemic load. Any white bread products aren't fiber-rich but have a low glycemic load. For those with diabetes who may be more susceptible to a spike in blood sugar, such differentiation is significant. Finding foods that are both low in GI and high in fiber is the method to go!

The Bottom Line:

Study findings offer a deeper look into the effects of a low glycemic diet on your wellbeing. When you mainly eat low glycemic food, you will increase your glucose regulation, feel healthier, boost your heart's health, lower the risk of stroke, and even regulate the food cravings—only lookout for these general statements and broad conclusions.