Understanding why plant-eating mammals like antelopes and sheep are far less likely to die of cancer than carnivores may help protect us from cancer too
22 December 2021
Mammals that live on meat are more likely to die of cancer than those that only eat plants, according to a study of tens of thousands of zoo animals from around the world.
Orsolya Vincze at the Centre for Ecological Research in Hungary and her colleagues analysed post-mortem records for 110,148 animals from 191 mammal species that died in zoos to determine their risk of dying from cancer.
They found that carnivorous mammals were much more likely to die of cancer than mammals that rarely or never eat animals. The artiodactyls, a mostly herbivorous group that includes antelopes, sheep and cows, was the least cancer-prone order of mammals.
The most cancer-prone species was the kowari (Dasyuroides byrnei), a small, carnivorous, Australian marsupial, with 16 of the 28 post-mortem records available for the species stating cancer as the cause of death.
In contrast, none of the 196 blackbucks (Antilope cervicapra) or the 213 Patagonian maras (Dolichotis patagonum) were recorded as having cancer when they died. Blackbucks are grass-eating antelopes native to India and the Patagonian mara is a large, grass-eating rodent found in Argentina.
The findings challenge the common belief that bigger animals with longer lifespans are most at risk of getting cancer, since they have more cells that can mutate and there is more time for mutations to occur. Instead, cancer risk appears to be heavily influenced by diet, although more research is needed to confirm whether the relationship seen in captive mammals is also found in wild populations, say the researchers.
One reason why carnivores may be more prone to cancer is that raw meat can contain viruses that have the potential to cause cancer when ingested, says Vincze. For example, cancers in some captive lions have been found to be related to papillomavirus in cow carcasses they ate, she says.
Another reason may be that carnivores are more exposed to pollutants that become increasingly concentrated in animals further up the food chain, says Beata Ujvari at Deakin University in Geelong, Australia, who was also involved in the study. Moreover, carnivores have high-fat, low-fibre diets and less diverse gut bacteria than plant-eaters, which are factors that have been associated with cancer risk in people, she says.
The finding that meat-eating mammals are more susceptible to cancer doesn’t necessarily mean that people who eat meat are also more at risk, since we have different lifestyles to other mammals and don’t tend to eat raw meat, says Ujvari. However, some human studies have linked meat consumption with increased cancer risk, she says.
At this stage, it is unclear why artiodactyls seem to be unusually resistant to cancer, but a better understanding of this could help protect us from cancer too, says Ujvari. Their low-fat, fibre-rich plant diet may be a factor, or they may have evolved natural anti-cancer defences to compensate for the extra cancer potential caused by their large size, she says.
Species like the blackbuck and the Patagonian mara are of particular interest due to their exceptionally low cancer mortality rates, says Vincze. “Understanding how they defy cancer may help us to develop cancer treatments.”
Journal reference: Nature, DOI: 10.1038/s41586-021-04224-5
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