The wild orangutans (Pongo pygmaeus wurmbii) of Indonesia have developed a unique strategy for survival in an environment where food availability constantly fluctuates: they gorge on calorie-rich fruits during the season of abundance to accumulate fat reserves that allow them to face periods of scarcity.
The finding, published in the journal Science Advances, offers a new perspective on the metabolic adaptation of primates in the wild and provides insights into how humans have evolved to overconsume energy-dense foods.
The change of “fuel” in nature
The research explains that when food sources are scarce, some species resort to a change of “fuel”: the body shifts from digesting external nutrients (exogenous) to processing internal nutrients (endogenous).
An example of this mechanism is ketosis, a metabolic state in which, in the absence of carbohydrates, the organism begins to burn endogenous fats to obtain energy. This process, known in humans, is now also confirmed in wild orangutans.
“Food sources fluctuate in nature, and orangutans have developed a flexible metabolic response to survive,” notes the research team.
Fifteen years of observation in Indonesia
The study was led by anthropologist Erin Vogel from Rutgers University (USA) and was based on 15 years of observation of orangutan behavior in the Mawas nature reserve, Indonesia.
Between 2004 and 2017, researchers conducted periodic urine analyses to assess metabolic changes during periods of fruit abundance and scarcity.
- In times of abundance: orangutans excessively consumed calorie-rich fruits, accumulating fat reserves.
- In times of scarcity: they resorted to endogenous fat and amino acids for energy, maintaining a constant protein intake.
The analyses showed that when fruit was scarce, the urine reflected an internal conversion of glycerol to store it as fat and later use it in gluconeogenesis.
Tendency to overeat
The study confirms that wild orangutans tend to overeat when food is abundant, especially calorie-rich fruits. This behavior allows them to prepare for periods of scarcity, ensuring sufficient energy reserves to survive.
The total caloric intake during times of abundance was much higher than normal, although protein intake remained constant at all stages.
Implications for human health
The study’s authors argue that this finding offers an analogy with the current global pandemic of obesity and metabolic diseases in humans.
Chronic overexposure to ultra-processed, energy-dense foods with low protein content mimics a pattern similar to that observed in orangutans, but without the adaptive function it serves in nature.
“This behavior in wild orangutans helps us understand how humans have evolved to overconsume calorie-rich foods,” concludes Vogel.
The study on wild orangutans in Indonesia demonstrates that metabolic flexibility is a key evolutionary tool for surviving in environments with fluctuating resources.
The tendency to accumulate fat during times of abundance and rely on internal reserves during times of scarcity reveals an ancestral mechanism that also helps explain the human propensity to overeat.
This finding not only provides insight into primate biology but also offers clues to understanding the current challenges of human health, such as obesity and metabolic diseases, in a world where the abundance of processed foods has disrupted the natural balance of the diet.
