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Human digestive tract

Diet is an important modifiable lifestyle factor which can influence risk of cancer, particularly cancers of the digestive system. It has been suggested that carbohydrate intake is one aspect of diet that might affect cancer risk, but research findings are mixed. This is not surprising considering that carbohydrates are found in a wide range of foods and drinks which differ in their nutritional value, dietary fibre content and glycemic impact.

The reasons proposed for the link between carbohydrates and cancer risk include impacts on blood glucose levels, insulin and insulin-like growth factor-1 (IGF-1). IGF-1 is a growth factor which can play a role in cancer growth, and studies have shown a positive association between IGF-1 levels and various types of cancer, including colorectal (large intestinal) cancer. Considering the impact of dietary glycemic index (GI) and glycemic load (GL) on blood glucose and insulin levels, many studies have looked at the association between GI, GL and cancer risk.

In 2019, a group of Chinese researchers published a meta-analysis of 44 studies (26 cohort and 18 case-control studies) looking at the association between glycemic index, glycemic load and digestive system cancers (1). This included oesophageal, stomach, colorectal (colon and rectum), liver and pancreatic cancers. The researchers found a significant association between dietary GI and risk of digestive system cancers – those with the highest GI diets had a higher risk of cancer of the digestive system compared to those with the lowest GI diets, although this finding only reached statistical significance for the cohort studies. They also observed a significant dose-response association, meaning that the higher the GI of the diet, the greater the risk. However, there was no association between total carbohydrate intake or dietary glycemic load and digestive system cancers.

These findings are similar to those of another systematic review and meta-analysis published in the same year, looking at the association between glycemic index, glycemic load and a wide variety of different cancers (2). In this review, a small but statistically significant association was seen between high GI diets and risk of colorectal cancer. Again, there was no association with GL.

Overall, these studies suggest that the types of carbohydrate foods you eat, rather than the total amount, might impact your risk of developing digestive system cancers. And this is consistent with research showing that higher intakes of wholegrains and dietary fibre (other markers of carbohydrate quality) are associated with a lower risk of colorectal cancer.

Read more:

  1. Cai and colleagues. Dietary carbohydrate intake, glycaemic index, glycaemic load and digestive system cancers: an updated dose-response meta-analysis. Br J Nutr. 2019.
  2. Turati and colleagues. Glycemic Index, Glycemic Load and Cancer Risk: An Updated Meta-Analysis. Nutrients. 2019.

Dr Kate Marsh is an is an Advanced Accredited Practising Dietitian, Credentialled Diabetes Educator and health and medical writer with a particular interest in plant-based eating and the dietary management of diabetes and polycystic ovary syndrome (PCOS).

Contact: Via her website