Higher glycemic index linked to higher lung cancer risk

 Background: In this study, researchers examined whether people who follow higher-GI or higher-GL diets have different risks of developing lung cancer. They used data from 101,732 adults in the U.S. National Cancer Institute's Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial cohort who filled out a detailed diet questionnaire when they joined the study (1993–2001). These adults were followed for about 12 years to see who developed lung cancer. The researchers then compared people with the highest GI and GL to those with the lowest, accounting for smoking and other factors.

What This Study Found:

• Glycemic index: People who ate diets with the highest glycemic index had a higher chance of lung cancer than those with the lowest glycemic index — about 13% higher overall — including higher risks for both non–small cell and small cell lung cancer.

• Glycemic load: People who ate diets with the highest glycemic load had a lower chance of lung cancer than those with the lowest glycemic load — about 28% lower overall — and the pattern was similar for non–small cell lung cancer. There was no clear link for small cell lung cancer.

Implications: Diets that contain fewer amounts of high glycemic index foods and higher amounts of high-quality carbohydrates, such as vegetables, fruits, and whole grains, may be linked to lower lung cancer risk.

Dietary Glycemic Index, Glycemic Load, and Risk of Lung Cancer: a Population-Based Cohort Study  

The dietary glycemic index (GI) is a rating system for carbohydrate-containing foods based on how quickly they raise blood sugar (glucose) levels after eating, compared to a reference food (usually pure glucose). 

Understanding the Glycemic Index

The GI ranks foods on a scale of 0 to 100, categorized into three ranges: 

• Low GI: 55 or less
• Medium GI: 56 to 69
• High GI: 70 or higher 

Foods with a high GI are quickly digested and cause a rapid spike in blood sugar, while low GI foods are digested more slowly, resulting in a gradual and lower rise in blood glucose and insulin levels. 

Foods that are primarily fat or protein (e.g., meat, fish, oils) do not contain carbohydrates and are not assigned a GI value. 

Factors Affecting a Food's GI

A food's GI value is not static and can be influenced by several factors: 

• Processing: Minimally processed, whole foods generally have a lower GI than refined or instant versions (e.g., steel-cut oats vs. instant oatmeal).
• Fiber, Fat, and Protein Content: The presence of these nutrients slows down digestion and absorption, which lowers the overall GI of a food or a meal.
• Cooking Method and Time: Longer cooking times can break down starches, increasing the GI (e.g., al dente pasta has a lower GI than soft-cooked pasta).
• Ripeness: As fruits ripen, their sugar content increases, raising their GI (e.g., an unripe banana has a lower GI than an overripe one). 

Glycemic Load (GL)

A related and often more accurate measure is the Glycemic Load (GL). While the GI indicates how quickly a carbohydrate is converted to glucose, the GL accounts for both the speed of digestion (GI) and the actual amount of carbohydrate in a standard serving size. 

The GL calculation is: (Glycemic Index × grams of available carbohydrate per serving) / 100. 

GL values are also categorized: 

• Low GL: 10 or less
• Medium GL: 11 to 19
• High GL: 20 or more 

For example, watermelon has a high GI (72), but a standard serving size contains little carbohydrate, giving it a low GL (around 4), which is a more realistic picture of its effect on blood sugar. 

Health Implications

Following a low-GI or low-GL diet may offer health benefits: 

• Diabetes Management: Helps people with type 1 and type 2 diabetes manage blood sugar levels and improve glycemic control.
• Weight Management: May help with short-term weight loss and appetite control by promoting a feeling of fullness.
• Reduced Disease Risk: Diets with a high GI and GL are positively associated with a higher risk of developing type 2 diabetes, coronary heart disease, and certain cancers. 

While the GI is a useful tool, it is best used as part of an overall healthy eating pattern that focuses on a variety of nutrient-dense foods, portion control, and general dietary guidelines. You can use resources like the University of Sydney's GI database or the American Diabetes Association guidelines to learn more.