Study explores the link between diet, blood glucose, and cancer risk

By Dr. Liji Thomas, MDReviewed by Benedette Cuffari, M.Sc.Mar 19 2025

A large-scale comparative study exploring the role of blood sugar levels, diet composition, and domestication in vertebrate cancer risk.

Study: The relationship between diet, plasma glucose, and cancer prevalence across vertebrates. Image Credit: Wirestock Creators / Shutterstock.com

A recent study published in Nature Communications explores the relationship between diet, blood glucose levels, and cancer incidence across vertebrate species.

Glucose levels in birds

For humans and organisms with human-like glucose metabolism, increasing blood sugar levels can lead to oxidative stress, DNA damage, protein glycation, and inflammation, all of which are risk factors for cancer.

Birds often lack the glucose transporter 4 (GLUT4) protein, which allows glucose to enter cells. As a result, birds have higher energy expenditures and are more reliant on fatty acids as an energy source, rather than glucose.

As blood glucose levels rise, birds produce larger clutches, which similarly increases their risk of developing cancer. Despite this association, birds have the highest average blood glucose concentrations among all vertebrates while being the least likely to die from cancer as compared to reptiles and mammals.

What is the relationship between diet, plasma glucose levels, and cancer across vertebrates, and could it help explain why birds get less cancer?”

About the study

The current study investigated the relationship between diet, blood glucose levels, and cancer incidence across vertebrates. To this end, diet was categorized by its trophic level, of which included herbivore, invertivore, primary carnivore, and secondary carnivore diets, as well as the percentage of each type of food consumed in the diet.

Differences in blood glucose unrelated to diet

The researchers identified significant differences in blood glucose concentrations across vertebrates, with the lowest levels of 1.2 mmol/L observed in the Burmese python as compared to 21.1 mmol/L in the blue-bellied roller bird.

Amphibians and birds had the lowest and highest average blood glucose concentrations, respectively, at two and 15 mmol/L, respectively, Mammals had a mean blood glucose of 6.7 mmol/L.

Trophic levels failed to show correlations with blood glucose levels. Likewise, the percentage of fruit, invertebrates, plants, seeds, vertebrate ectotherms, vertebrate endotherms, and animal products did not correlate with blood glucose levels.

Both animal- and plant-based diets were associated with similar blood glucose concentrations, as carnivores, herbivores, and omnivores did not exhibit significantly differences in their blood glucose levels.

Blood glucose unrelated to cancer prevalence

We show that there is a negative correlation between cancer prevalence and mean plasma glucose concentration across vertebrates but not within birds, mammals, or reptiles.”

Blood glucose levels did not predict cancer prevalence in any of these classes after accounting for other cancer risk factors such as body mass, lifespan, length of pregnancy, domestication, and trophic level. This adjustment was crucial, as body mass is negatively associated with blood glucose levels.

For both benign and malignant tumors, cancer prevalence was most accurately predicted by both domestication and trophic level, with blood sugar having no effect.

Primary carnivores were associated with a greater cancer prevalence than herbivores after adjusting for domestication. This difference was not observed after accounting for the difference in blood glucose levels.

The increased cancer risk among primary carnivores may be due to toxin accumulation with rising trophic levels, their relatively high proportion in the study, and the higher oxidative stress and DNA damage associated with red meat consumption.

Domestication reduces genetic diversity and suppresses natural selection against carcinogenic or harmful gene variants. Domesticated bovine species have lower blood glucose levels as compared to their wild counterparts, which may increase the risk of cancer among these animals.

Conclusions

Plasma glucose levels were not predictive of cancer prevalence across vertebrate species. Moreover, diet type was not correlated with blood sugar levels across species.

Domesticated primary carnivores had the highest risk of cancer. However, most primary carnivores in the current study were mammals or reptiles, which may account for the relatively lower cancer prevalence in birds.

A notable limitation of the current study was the inability to determine absolute correlations of various outcomes with mean blood glucose levels due to the lack of individual tracking. Blood glucose levels can also be affected by variations in health status at the time of collection, stress, and dietary status. The number of species for which required data was available was also low, which can be addressed with the currently available millions-strong cancer death databases like Species360.

Future studies are needed to elucidate the mechanisms that contribute to the low cancer prevalence in birds, as these findings could support the development of more effective cancer prevention strategies in humans.