Can carbs' glycemic index help you fine-tune your meals?
If you’re wondering where your favorite foods fall on the Glycemic Index there’s a new chart out, but wait before you delve into it
Carbs have been demonized. Understandably, it’s much easier to target an entire major nutrient group than to understand the intricacies of how our body interacts with the multitude of foods out there, so some lump all carbs in the to-minimize category, whether they’re an apple or a sugary drink.
But when it comes to how our body works, the quality of a food is what matters. We’ve been there before with blanket warnings about fat, only to realize that you just can’t view them all as the same thing, and you can’t develop a sensible food philosophy that aims to replace one entire macronutrient – of which we have just three. This is nutrition reductionism to the point of silliness.
To better understand carb quality people may look at the dietary fiber content of the food and to the “added sugar” in it. Another indicator is the Glycemic Index, which measures how a food raises blood sugar. The glycemic index used to be reserved to diabetes management but it's now part of several popular weight-loss programs (South Beach, Zone) and disease prevention plans. The low glycemic index health claim is also a selling point advertised on food labels.
What is the glycemic index?
The glycemic index ranks carb-containing foods on how they affect blood glucose levels when eaten in isolation. The glycemic index charts were developed by testing people’s blood sugar after ingestion of 50 grams – almost 2 ounces – of carbs from the food tested.
Carbs that break down quickly, like white bread and potatoes, have a high glycemic index. Those that release sugar into the bloodstream more gradually, like fruit, have a low glycemic index. Foods are scored on a scale of 0 to 100; a glycemic index of ≥70 is high, 56–69 is medium, ≤55 is low.
Is the glycemic index absolute?
As you can imagine, since there are so many foods in the world, since food varies in its nutritional composition depending on cultivar and growing conditions, since foods are not eaten in isolation, because different labs are doing the testing, and due to people’s unique physiology, glycemic indexes are not and exact science.
The glycemic index also measures the response to 50 grams of carbs. Eating 50 grams of carbs from white bagels is commonplace. But although watermelon has the high glycemic index of 80 you’d have to eat almost 2 pounds of watermelon to load yourself up with 2 ounces of carbs, and therefore watermelon’s high glycemic index is irrelevant for most. To guess blood sugar responses you’d also have to take into account the glycemic load, which tallies the amount of carbs consumed.
On top of that, although the type and proportion of sugar or starch in a food affects glycemic index, so do a lot of other factors in the meal — the way the food’s been cooked, the presence of fiber, protein, fat, alcohol or acid in the meal will all affect the glucose response. Exercising and activity around a meal will affect it, too.
Your own glycemic response will change from day to day.
The new glycemic index charts
Since the glycemic index’s popularity and usage are rising, and previous data is incomplete and inconsistent, a refresh of the information is overdue.
A new study in The American Journal of Clinical Nutrition looked at the glycemic index studies published to see if the older tables could be improved upon from the 2008 table. The authors reviewed published and unpublished studies and tabulated the glycemic index of about 4000 foods, more than double that of the previous table.
To generalize the 4000 results with a very broad brush:
Fruit, legumes, pasta and dairy products have low glycemic indexes that are pretty consistent across countries.
Cereal and cereal products, however, show a very wide variation in glycemic index, depending on the grain processing (whole grain has a lower glycemic index) and the preparation.
Potatoes, generally a high glycemic food, varied from 84, all the way down to 49, depending on the origin and cooking method. Such was the case with the glycemic index of rice: from 73 for white rice, to 65 for brown rice.
These detailed tables will no doubt serve researchers and clinicians, as well as the general public. The glycemic index can be useful as there are studies linking low glycemic index diets to better management and prevention of diabetes, to weight loss, and the prevention of other illnesses.
But rather than relying on a 4000 item glycemic index chart, understanding its basic themes can help us develop a healthy lifestyle pattern – no tedious counting and reference checking needed.
What the glycemic index chart teaches us is that whole plant-based foods are better, fruits and vegetables are excellent, and that lack of processing really matters. Naturally occurring carbohydrate foods also supply fiber, which is very important for health – it lowers the glycemic index, helps with satiety and promotes a healthy microbiome. Bread and rice – and even potatoes – won’t necessarily spike blood sugar if they’re eaten in moderate amounts and combined with other healthy foods.
For the non-diabetic, it’s much easier to follow the well-proven guidelines of limiting added sugar (sugary drinks are especially harmful), eating more plants and whole grains, and minimizing hyper-processed foods.
These dietary principles yield a low glycemic diet as an added bonus.
Dr. Ayala
“Follow the well-proven guidelines of limiting added sugar, eating more plants and whole grains, and minimizing hyper-processed foods”