Originally published in The Ottawa Citizen March 4, 2003
Original Title: Sugar by the numbers
Last week’s column reviewed how what we eat can influence blood insulin levels. Diets high in carbohydrates (sugar) result in elevated insulin levels or hyperinsulinemia. This in turn may lead to obesity, insulin resistance and type 2 diabetes.
Diets like he popular Atkin’s diet restricts carbohydrate intake. Weight loss occurs because the body taps its fat stores to fulfill its daily energy requirements. Through biochemical processes, fats convert into glucose (sugar). Glucose is the main fuel that provides the energy for the body’s metabolism.
Carbohydrates are sugar molecules that come in two types: simple and complex. Sugars like glucose, fructose and others link together like a chain to form complex sugars.
Fruits, milk and milk products, vegetables and refined products such as candy, table sugar, syrups (not including natural syrups such as maple) and regular sodas contain simple sugars. Starchy vegetables, legumes, rice, pasta, cereals and bread contain complex sugars.
The body will absorb and convert simple and complex carbohydrates into glucose at different rates. Blood sugar levels depend upon this glucose production rate and the amount of sugar within the food.
A ranking system of these rates for over 750 carbohydrate-containing foods exists (available at http://diabetes.about.com/library/mendosagi/ngilists.htm ). This system uses two measurements, the glycemic index (GI) and the glycemic load (GL).
The glycemic index measures the speed that a carbohydrate (for three hours after a meal) is turned into glucose. A value of 55 or less is low, 56 to 69 is medium and 70 and above is high. These rates are set against glucose that has a value of 100.
Fibre is a carbohydrate that comes in two types. Fruits, vegetables and legumes contain soluble fibre that slows the rise in blood glucose after a meal. Whole-wheat bread and brown rice among other foods contain insoluble fibre. Insoluble fibre promotes regular bowel movements and has little effect upon blood sugar levels.
The glycemic load tells you how much carbohydrate (minus the fibre content because it does not contribute to glucose production) is available in a particular food. A glycemic load of ten grams or less per serving is low, 11 to 19 is average and 20 or greater is high.
Both the glycemic index and glycemic load are necessary to determine whether the food provides too great a sugar load.
Indeed many a healthful diet contains foods that are low in fat content yet may not be appropriate for diabetics and people on weight-reducing diets.
Scanning through the list reveals that rice and cereals have some of the greatest glycemic indices and loads. This data goes against the grain (pardon the pun) of our assumptions. A Russet potato has a greater glycemic index than table sugar. Pumpernickel has a glycemic load half that of white bread.
There are differences within food groups. A 250 millilitre serving of Allen’s(r) apple juice has a GI of 40 and a GL of 12 grams. Compare this to the same quantity of Ocean Spray(r) Cranberry Cocktail with a GI of 68 and GL of 24 grams. The body produces glucose from the cocktail’s carbohydrate 70 per cent faster than it does for the apple juice. The cocktail also has double the sugar content of the apple juice leading to more glucose production.
A 120-gram apple has a GI of 34 and a GL of 5 compared to 60 grams of raisins with a GI of 64 and GL of 28 grams.
A 30-gram serving of Kellogg’s Corn Flakes(tm) has a GI of 86 and GL of 22, Cheerios(tm) 74 and 15 and Kellogg’s All-Bran(tm) 51 and 9.
The list provides a means to choose foods with a low to average glycemic index and low glycemic load to minimize insulin spikes and potential weight gain over time.
There is another list of very low glycemic index foods known as free foods (http://www.mendosa.com/freefoods.htm). These foods, like celery or tomatoes, have little to no effect upon glucose and insulin levels. They are guilt-free foods.
Does this mean everyone should avoid or reduce their carbohydrate consumption to manage their weight? The indices are useful as a guide but should not be the sole measure of a healthful diet. Indeed, most diets should include lots of fruits and vegetables, high-fibre foods and foods low in saturated and hydrogenated fat. Diabetics must also be wary of excess protein in their diets. Regular exercise should be part of any weight loss or maintenance program.
Mars Bar lovers take note. It has a GI of 65 and GL of 26. Ice Cream aficionados seem to have the better treat: a GI from 38 to 61 and GL of 5 to 8. Bragging rights are short-lived once you account for all the extra fat. There is no free ticket. C’est la vie.