Orangutans adjust their diet according to the season, researchers have found.

The team from Rutgers University documented the critically endangered apes in the rainforests of Indonesia and Malaysia and found that their nutrient intake and behaviour change according to food availability.

Erin Vogel, Henry Rutgers Term Chair Professor in Anthropology at Rutgers, said: ‘These findings show how wild Bornean orangutans adapt to changes in their environment by adjusting their nutrient intake, behaviour and energy use.

‘The work highlights the importance of understanding natural dietary patterns and their impact on health, both for orangutans and humans.'

The study was published in Science Advance and shows how the animals maintain balance and avoid obesity, unlike many humans on modern diets.

The research claimed that orangutans consume fruit when abundant for energy-rich carbohydrates and fats, and switch to leaves, bark, and other protein-rich foods when fruit is scarce.

During low-fruit periods, they conserve energy by resting more, travelling less, and reducing social interaction, a strategy comparable to intermittent fasting in humans.

Researchers said they collected daily dietary data and urine samples to study how orangutans metabolise energy, revealing that they switch between fat and protein stores when needed.

Prioritising consistent protein intake helps them maintain muscle and overall health despite fluctuating food sources.

Erin added the importance of conserving orangutan habitats, such as the 764,000-acre Tuanan Orangutan Research Station in Central Kalimantan, to support both species' survival and ecosystem health.

He said: ‘Understanding these adaptations can help us learn more about how humans can manage their diets and health.'