Glycemic Load and OA

As we've shown elsewhere on our site, sugars can bind with the proteins in our joints, causing browning and stiffening--the process of glycation. This is part of our new understanding about osteoarthritis. So, the question is, what are the effects of eating carbohydrate-rich foods that are broken down to the same simple sugars by our digestive process? In other words, can a high carb diet trigger glycation of joint proteins in the same way as a diet high in simple sugars? In order to answer this, we have to look at two measures of carbohydrate in the diet: glycemic index and glycemic load.

Glycemic Index (GI) is a measure of the degree to which a carbohydrate is likely to raise your blood sugar (glucose) levels. The scale is 0 to 100 (based on either white bread or glucose), with 0 being low and 100 being high. The GI compares equal quantities of carbohydrate and provides a measure of carbohydrate quality but not quantity. Glycemic indices can be misleading because they have been developed using fixed amounts of food that do not accurately reflect what people actually eat.

In 1997, Harvard University scientists introduced the concept of glycemic load (GL). This measure gives a more accurate reflection of the blood sugar effects of a standard portion of food. In short, the GL of a typical serving of food is the product of the amount of available carbohydrate in that serving and the glycemic index of that food.

In practical terms, the higher the GL of a food, the greater the expected rise in blood glucose and the greater the adverse insulin effects of the food. Foods with a GL of 10 or below would be presumed to be less detrimental to health, while those with a GL of 20 and above would have more detrimental affects. Long-term consumption of foods with a high glycemic load appears to be linked to a greater risk to obesity, diabetes, and inflammation. These, in turn, now appear to have negative effects on inflammation related to the joints that we are only beginning to understand.

Glycemic Load of Common Foods

The table below contains a representative sampling of the glycemic load of some common foods.[i] It immediately becomes clear that foods like potatoes, pasta, bagels, rice, and soft drinks stand out as high glycemic foods. Conversely, fruits and nuts stand out as low glycemic foods.

FOOD	SERVING SIZE (g)	GLYCEMIC LOAD (GL)
DRINKS
Coca Cola®, average	250	15
Cranberry juice cocktail (Ocean Spray®)	250	24
GRAINS
White rice, average	150	23
Bagel	35	25
Macaroni, average	180	23
Macaroni and Cheese (Kraft)	180	32
Baked russet potato, average	150	26
FRUIT
Grapefruit	120	3
Grapes, average	120	8
Orange, average	120	5
Peach, average	120	5
Pear, average	120	4
Apple, average	120	6
NUTS
Cashews, salted	50	3
Peanuts, average	50	1

The complete list of the glycemic index and glycemic load for 750 foods can be found in the article "International tables of glycemic index and glycemic load values: 2002," by Kaye Foster-Powell, Susanna H.A. Holt, and Janette C. Brand-Miller in the July 2002 American Journal of Clinical Nutrition, Vol. 62, pages 5–56. <http://www.ajcn.org/cgi/content/full/76/1/5>

Glycemic Load and General Inflammation

We now know that the glycemic load of the diet can affect general inflammation. For instance, in a recent study published in the Journal of the American Medical Association, 244 healthy women were tested to see how their glycemic load (the intake of high or low glycemic foods) affected an inflammation chemical called CRP (C-reactive protein). One way to view the glycemic load is that it is the amount of carbohydrate that is easily broken down into simple sugars. In this study, women with high glycemic diets had average CRP values of 5.0, while those with low glycemic diets had CRP levels of only 1.6. The highest CRP levels were in women who were overweight. Elevation of these inflammatory compounds is problematic for joints, since high CRP values are associated with other inflammatory changes known to affect ligaments, cartilage, and tendons.

We also know that simple sugars may fuel free radical stress, which threatens the fatty acids that make up our cell membranes. For example, when 21 people were given the amount of sugar in two soft drinks (75 grams of glucose), the free radical products of damaged fatty acids, called isoprostanes, rose by 34 percent in only 90 minutes.[1] A separate study showed that people with impaired glucose tolerance had a significant increase in blood levels of other inflammation chemicals such as TNFα and IL-6 after a simple sugar load. The sugar load also depleted one of the body's protective antioxidants—glutathione. These were studies of simple sugars, which we now know increase inflammation and free radical stress.

If simple sugars fuel free radical stress, a logical question is whether high glycemic diets also trigger free radical stress. A team at the University of California at Berkeley, led by Younqing Hu and Gladys Block, looked at 292 healthy people, comparing glycemic load/index to blood markers of oxidative stress—isoprostanes and malondialdehyde (MDA). MDA is another footprint of damaged fatty acids. Dr. Hu’s group found that “MDA concentrationsincreased from 0.55 to 0.73 µmol/L as glycemic load increased from the lowest to the highest quartile,” implying that as the intake of high glycemic foods increases, there is a commensurate increase in damage to fatty acids. They also concluded, “A low-GI diet…appears to be beneficial in reducing oxidative stress.”[ii]

These studies and others like them seem to suggest that diets high in high glycemic carbohydrates have the potential to increase inflammation and increase free radical stress. Both are conditions that do not favor healthy joints. On a positive note, it appears to add one more measure within our control that may help to preserve joint health. More precisely, a low glycemic load diet could be another tool to support healthy joints. We believe the evidence supports this view.

In summary:

- High sugar diets appear to fuel inflammation and free radical stress

- High glycemic diets appear to fuel inflammation and free radical stress

[1] Subjects in this study suffered from diabetes. Other studies show that overweight people with impaired glucose tolerance show elevations in inflammatory compounds and free radical products, though not quite as dramatic as in diabetes.

[i] Holt, SHA, Brand-Miller, JC. International tables of glycemic index and glycemic load values. Am J Clin Nutr 2002;62: 5–56.

[ii] Hu, Y, Block, G, Norkus, EP, et al. Relations of glycemic index and glycemic load with plasma oxidative stress markers. Am J Clin Nutr 2006;84(1):70-76.

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