A recent study published in the Annals of Family Medicine highlights the role of carbohydrates, one of the main macronutrients in Indian diet, in determining lung cancer risk. Interestingly, it is not just the quantity of carbohydrates that matters, but the type of carbohydrate.

Considering that lung cancer is the leading cause of cancer-related deaths worldwide, with 25 lakh new cases reported in 2022 alone, and India accounting for 5.9 per cent of all cancers and 8.1 per cent of cancer-related deaths, the disease poses a significant public health challenge.

What did the study find?

Researchers analysed data from the US National Cancer Institute’s Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial cohort. The study followed thousands of older American adults over a median of 12.2 years, tracking diet, lifestyle habits, and health outcomes. During this period, 1,706 participants developed lung cancer, including 1,473 cases of non–small cell lung cancer (NSCLC) and 233 cases of small cell lung cancer (SCLC).

Unlike previous studies that only looked at total carbohydrate intake, the researchers focused on two measures. The first is Glycemic Index, or GI, which indicates how quickly a food raises blood sugar levels. The second is Glycemic Load, or GL, which measures the total impact of both the quantity and quality of carbohydrates in a food.

The study found that individuals consuming high-GI diets had a higher risk of developing lung cancer, including both NSCLC and SCLC. Specifically, participants in the highest GI intake group had a 13 per cent higher risk of lung cancer compared to those in the lowest group. Interestingly, participants with higher GL diets, meaning they consumed more carbohydrates overall but not necessarily high-GI carbohydrates, showed a lower risk of lung cancer, particularly NSCLC, with a 28 per cent reduced risk.

High-GI foods can cause rapid spikes in blood sugar and insulin. Over time, this may lead to hormonal changes involving insulin-like growth factor-1 (IGF-1), which promotes cell growth. Scientists believe that long-term alterations in this pathway could encourage the growth of cancer cells. However, consuming more carbohydrates overall, as long as they are low-GI, did not show the same increase in risk.

Despite these findings, smoking remains the most significant driver of lung cancer, responsible for up to 85 per cent of cases in developed countries. Diet plays a supporting role, but quitting smoking and reducing exposure to pollution remain the most effective prevention strategies.

The researchers highlighted an important takeaway that not all carbohydrates are equal. Choosing whole grains, legumes, fruits, and vegetables over refined, high-GI foods may not only help manage diabetes and heart health, but, may also contribute to lowering lung cancer risk. They concluded that diets causing sharp blood sugar spikes could increase lung cancer risk, whereas higher-quality carbohydrate diets may offer some protection.

In their own words, “In this large prospective analysis adjusting for lung cancer risk factors, we found that GI was linked to greater risks of lung cancer, NSCLC, and SCLC, whereas GL was inversely associated with lung cancer and NSCLC risk. Though replication in diverse populations and further mechanistic studies are needed, our findings suggest that low-GI and high-GL foods (eg, vegetables, white meat) might offer lung cancer prevention benefits.”

The study also noted that “the observational nature of this study limits the ability to determine causality and eliminate residual confounding from unmeasured variables.”

What does it mean for India?

Lung cancer is a growing concern in India. According to the Globocan 2022 India Fact Sheet, lung cancer is the second most common cancer among Indian men, with 58,970 new cases, constituting 8.5 per cent of all male cancers.

Previous studies have also suggested links between high carbohydrate intake and increased cancer risk, indicating that dietary GI, alongside other lung cancer risk factors, may independently influence lung cancer development.

Dr Gaurav Jaswal, Director and Consultant Radiation Oncologist at TGH-Onco Life Cancer Centre, Maharashtra, highlighted the relevance of this study in the Indian context. He noted that the Indian diet is predominantly carbohydrate-heavy and low in protein compared to Western diets, which are richer in non-vegetarian protein sources. “Since the Indian population consumes more carbohydrates, this can increase the risk of an inflammatory state in the body. Chronic inflammation is linked to several diseases, including cancer,” he explained.

In fact, an ICMR-INDIAB study revealed that the average Indian diet comprises approximately 62 per cent carbohydrates, one of the highest proportions globally. Much of this intake comes from refined sources, such as white rice, milled grains, and added sugars, which are typically high-GI foods.

Commenting on lung cancer risk, he added, “Many patients ask why they develop lung cancer despite never smoking. Studies like this substantiate the fact that, apart from smoking, a high inflammatory state in the body can contribute to lung cancer, along with other factors like pollution.”

On dietary recommendations, Dr Jaswal emphasised avoiding high-GI foods. “We should limit refined sugars, white rice, processed foods, and items like ketchups that have high sugar content. These foods increase insulin and insulin-like growth factors, which can elevate inflammation in the body,” he said.

He suggested focusing on whole grains, legumes, traditional grains like millets, and natural sources of sweetness. “Maintaining a healthy weight and including a good amount of fruits in the diet can also help reduce risks,” he advised.

Also read: What’s on your plate? Study links Indian diet to diabetes and obesity  

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