A high-sugar diet increases metabolic health risks for humans, contributing to conditions like diabetes, heart disease, stroke, and even cancer. However, certain bats thrive on a diet that includes consuming nearly twice their body weight in sugary nectar or fruit daily. Now, we have uncovered how “sweet-toothed bats” have adapted their metabolism to consume large amounts of sugar, with potential implications for millions of Americans living with metabolic syndrome. The findings, published on August 28, 2024 in Nature Eco Evo, point to adaptations in the bat body that control blood sugar. 

This study started as a collaborative effort between bat biologists at Cali, Colombia (Andrea, Oscar) and my team at the Stowers Institute (Valentina, Pedro, Nick). Together, we studied the relationship between blood glucose levels after a sugar meal to the evolution of the bat duodenum, which absorbs sugar into the bloodstream. We discovered that the duodenum of fruit bats and nectar bats, compared to that of insect-eating bats, is longer, has additional intestinal cells and higher microvilli density. Our data also show that glucose transporter regulation contributes to acute increases in blood sugar. These changes in the duodenum’s morphology and function contribute to extreme post-feeding hyperglycemia (>750 mg/dL within 10 minutes). 

The stress imposed on the body by high levels of circulating glucose can cause damage to various tissues and the pancreas plays a crucial role in lowering blood sugar by producing insulin. Our data show that fruit bats are very effective at quickly lowering their blood sugar via insulin, which prevents damage. However, nectar bats do not effectively lower their blood glucose levels, a condition similar to humans with type 2 diabetes. Our study suggests that the duodenum may play a role in promoting insulin sensitivity in fruit bats and insulin resistance in nectar bats. However, the exact causes and mechanisms behind these drastically different evolutionary adaptations to high-sugar feeding and metabolism are still not fully understood.

This research is very exciting because it brings together ecology, evolution, and biomedical research in a new way. It lays the foundation for future studies to identify how evolution has solved problems of metabolic syndrome in a long-lived mammal. If confirmed, nectar bats can offer insights into enhancing human health and treating type 2 diabetes and obesity, as they do not experience issues such as insulin overproduction, excess visceral fat, atherosclerosis, blindness, chronic inflammation, or cancer. Furthermore, as we delve into their biology, we might uncover new therapeutic targets to prevent the onset of type 2 diabetes and obesity among the one in three Americans who are prediabetic.