Nectar-feeding bats (Glossophaga soricina) have a high sugar diet and consequently high blood sugar levels. Despite their sweet tooth, these bats do not suffer detrimental sugar-related health effects as would other mammals, including humans, and they are especially long lived – about five times longer than a similar sized rodent. Detlev Kelm, at the Leibniz Institute for Zoo and Wildlife Research, and a team of German researchers were curious as to how these bats regulate their blood sugar during rest and flight, wondering how they avoid the adverse effects of a high sugar diet. Their fascinating findings were published in a recent issue of PNAS.
The team first measured the bats’ blood glucose levels at rest during a meal similar to that consumed in the wild. Interestingly, the bats’ blood glucose levels after the meal far exceeded normal values for mammals of similar size and were among the highest ever recorded in mammals. The researchers speculate that the bats have evolved a physiological tolerance to glucose, avoiding the damaging effects of a high sugar diet and the shorter life span usually associated with it.
Next, the researchers set out to determine the role exercise has on regulating blood glucose by using three different exercise regimes after consuming either one big meal or several smaller meals. Overall, flying reduced the severity of blood glucose peaks seen in the resting bats. Moreover, the bats that spent more time flying after a meal had lower blood glucose peaks and their blood glucose returned to pre-feeding values faster. This suggests that bats use flight as a strategy to prevent blood glucose from rising to extremely high and potentially damaging levels.
In the wild, nectar-feeding bats spend up to 12 h a night feeding, flying about 60% of the time. As Kelm and his colleagues suggest, flying helps the bats not only to regulate blood glucose levels but also to devote more energy to searching for roosts or new food sources, perhaps providing a selective benefit to bats that spend more time flying between meals.
Lastly, the researchers wanted to know how high the bats’ blood glucose concentrations were over a longer period of time (weeks) whilst being fed a diet similar to that found naturally. Blood glucose irreversibly reacts with haemoglobin in the blood to form glycated haemoglobin depending on the amount of glucose in the blood and on the lifetime of the red blood cells. Kelm took blood samples from bats and measured the amount of glycated haemoglobin. The nectar-feeding bats had normal levels of glycated haemoglobin in their blood in comparison to other mammals. Thus, the bats had low blood glucose levels over long periods of time and consequently were not chronically exposed to high blood sugar levels and their damaging effects.
Although the nectar-feeding bats’ secret to a long life was not entirely revealed, Kelm and his colleagues used elegantly designed experiments to figure out how the nectar-feeding bats use flight to take advantage of a high sugar diet and avoid its harmful effects. So perhaps we can all eat our cake, as long as we run a marathon right after.
