Jolly fat rats? The effects of diet‐induced obesity on territorial fighting

In experiment 1, pairs of young male rats became obese on a palatable and complex diet high in fat, sucrose, and protein. The obese pairs exhibited greater within‐group weight variability and, when tested as adults, were significantly more aggressive toward an unfamiliar conspecific than chow‐fed controls. The increased aggressivity of obese males was not due to the relatively larger resident‐intruder weight disparities in these pairs, since weight‐matched pairs of unfamiliar animals were as aggressive toward each other as pairs not matched in body weight (experiment 2). The complex and calorically dense diet may have accelerated the development of the experimental animals, producing subjects whose aggressivity was comparable to that of much older animals.