Non-human primates are often used to research diet induced obesity models because of their genetic and physiological similarities with humans.  It has been observed that in macaques obesity can occur spontaneously, both in controlled and uncontrolled settings.  It should be noted that like with humans measuring body fat percentage rather than body weight is a better method of determining obesity in macaques. Research done on rhesus macaques showed that fat gain was primarily found in the abdominal region, similar to fat distribution in obese humans. There is also evidence that the same factors that an influence obesity in humans (stress, social status, feeding behaviors) also influence obesity in macaques.[1]

  1. ^ Bauer, Sharon A; Arndt, Tara P; Leslie, Ken E; Pearl, David L; Turner, Patricia V (2016-11-16). "Obesity in Rhesus and Cynomolgus Macaques: A Comparative Review of the Condition and Its Implications for Research". Comparative Medicine. 61 (6): 514–526. ISSN 1532-0820. PMC 3236694. PMID 22330579.