No. Your pet will actually benefit from spaying or neutering, because he or she will lead a healthier and longer life. Pets become fat and lazy as a result of overeating and a lack of exercise, not from spaying or neutering. Furthermore, spaying a female eliminates the possibility of her developing uterine and/or ovarian cancer and greatly reduces the chance of breast cancer. Neutering a male eliminates the risk of testicular cancer.