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Coping with feast and famine: Integrated behavioral and metabolically flexible responses of wild orangutans to ecologically driven dietary variation

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Jan 21, 2025 version files 1.69 MB

Abstract

Diet and nutrition are critical factors influencing energetics and health. Laboratory studies show that organisms adjust to changes in nutrient intake through flexible metabolic responses. While the physiological effects of nutrient balance in humans have been studied, data from closely related species living in nature are lacking. We integrate macronutrient regulation and metabolic flexibility to elucidate how wild Bornean orangutans are buffered against natural fluctuations in nutrient intakes. We found that orangutans regulate protein and regularly switch between exogenous and endogenous nutritional substrates as preferred food availability declines. When total caloric, lipid, and carbohydrate intakes decline, orangutans drew on fat and endogenous amino acids for energy. This strategy is beneficial only in the context of alternating periods of fruit scarcity and abundance. Our findings provide a direct analog for the current global obesity pandemic, which has arisen in parallel with transitions in human diets towards energy-dense, protein-dilute foods.