Have you heard someone tell you that, “A slice of whole wheat bread raises your blood sugar more than a Snickers bar?” Or possibly one of the variants for whole grain bread? …or maybe you’ve heard “two slices of wheat bread”? I’ve been trying to dig up the research everyone keeps talking about, and the best that I could come up with is this article from The American Journal of Clinical Nutrition. In it, the authors provide a table measuring the Glycemic Load and Glycemic Index for a variety of foods. The full details behind the table are in the article, but I’ve made a composite image from the pertinent sections of the table below. Have a look:
If we compare Glycemic Index for an American (sorry for the bias) Snickers bar at 68/97, we see that it has a higher GI than all varieties of Whole Wheat bread in the study, and is higher than both common varieties of Whole Grain bread found in America. So it would appear that the apocryphal reports are NOT correct, except in the case of 2 slices of bread.
The authors also indicate the Glycemic Load for all these foods, and by that measure, the Snickers bar clearly carries a higher load.
So what’s that mean? Well, Glycemic Index
“is a measure of the effects of carbohydrates in food on blood sugar levels. It estimates how much each gram of available carbohydrate (total carbohydrate minus fiber) in a food raises a person’s blood glucose level following consumption of the food, relative to consumption of glucose. [...] Glycemic index is defined for each type of food, independent of the amount of food consumed.(source)”
Glycemic Load, on the other hand,
“is a number that estimates how much the food will raise a person’s blood glucose level after eating it. One unit of glycemic load approximates the effect of consuming one gram of glucose.  Glycemic load accounts for how much carbohydrate is in the food, and how much each gram of carbohydrate in the food raises blood glucose levels. Glycemic load is based on the glycemic index (GI). Glycemic load is defined as the grams of available carbohydrate in the food x the food’s GI / 100.” (source)
So it appears that while whole grain or whole wheat bread is not the health food it is marketed as, the oft reported comparison is not true, unless you compare to 2 slices of wheat or whole grain bread. If you want to compare gram for gram glycemic responses between Snickers and the breads, you’d look at Glycemic Load and see that the Snickers bar clearly has a higher value than the other two. The trouble is, both of these values (Glycemic Load and Glycemic Index are calculated…which is often a fancy way of “guessing by formula”). A more interesting (and perhaps more informative) value would be direct measure of blood glucose response to these foods, or even the respective Insulin Index values for each. Until that comes along, this is apparently the best we can do…
Lastly, it is worth noting that there are many breads that a single slice of which will raise your blood sugar more than a US Snickers bar (which has a GI of 68/97)…if the Glycemic Index can be believed. You can browse the table yourself to see. I’ve included some of the more interesting ones below.
Breads that have a higher Glycemic Index than a Snickers bar:
- Bagel, white, frozen (Lender’s Bakery, Montreal, Canada)
- Baguette, white, plain (France)
- Kaiser rolls (Loblaw’s, Canada)
- Melba toast, Old London (Best Foods Canada Inc, Etobicoke, Canada)
- White flour (Canada)
- White flour (USA)
- White flour (Sunblest; Tip Top Bakeries, Australia)
- White flour (Dempster’s Corporate Foods Ltd, Canada)
- White flour (South Africa)
- Wonder, enriched white bread
- Stay Trim, whole-grain bread (Natural Ovens, USA)
- “International table of glycemic index and glycemic load values: 2002” (American Journal of Clinical Nutrition, August 2006 vol. 84 no. 2 354-360)