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Why You Should Not Use the Glycemic Index Alone for Your Cancer Prevention Diet

Choosing a healthful diet is very important to reduce your risk of many types of cancer, but choosing a food solely based on its glycemic index is not necessarily a good idea.


The Glycemic Index (GI) is a numerical ranking of carbohydrates according to how much they raise blood sugar after eating. Foods higher on the scale are rapidly digested and absorbed and make blood sugar rise higher and faster than foods on the lower end.

Obviously, blood sugar control is critically important for the health of diabetic patients. Other research suggests that unhealthy blood sugar levels and the resultant rise in hormones such as insulin could promote the development of some types of cancers. However, the AICR warns against using GI as a sole determinant of your food choices for a cancer prevention diet.

An analysis of 19 different studies has found that there is no link between breast cancer risk and diets high in GI beyond what could occur by chance. Even glycemic load – which takes into account portion sizes – showed no significant link.

Most often, foods lower on the glycemic index are healthier choices because they contain other nutrients that help slow down digestion – such as fiber or protein. Foods higher on the scale are usually higher in sugar or are more processed/refined which could lead to a spike in blood sugar levels. But not every food falls into this “neat” category.

For example, a whole apple (with the peel) scores a low 36 on the GI scale. Peanut M&M’s score a 33. On the other end, watermelon (rich in nutrients such as lycopene) scores a 76 – considered a high GI food. Somewhere in the middle, French fries are just about equal in GI to a banana.

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Here is something else to keep in mind: glycemic index is affected by many factors, including processing – a plain boiled potato is high in the 80s while those fries are much lower at 64.

GI is also affected by the foods you eat in combination with the chosen food – eating potatoes as a part of a meal with meat and a vegetable as opposed to eating the potato alone will affect how your body processes that food. Portion size is also quite important – a large portion of a “low GI” food could end up raising blood sugar as much as a small portion of a “high GI” food.

You may also be surprised to learn that there is a wide day-to-day variation – the same person can eat the same food at different times over a three month period and the blood sugar effect can range as much as 20%!

The Bottom Line: For a healthy, cancer prevention diet, it is important to choose a food based upon many factors, including nutrient value and how it fits into your overall meal plan. Do not choose or avoid a food based upon GI alone.

American Institute for Cancer Research
Harvard Medical School

Photo Credit:
By Raysonho @ Open Grid Scheduler / Grid Engine - Own work, CC0, via Wikimedia Commons