Eating healthy food is as important to our four-legged friends as keeping an eye on doughnut intake is to humans, veterinarians say. 'Diets have been proven to have an effect on an animal's health. As early as 1939, a veterinarian in the United States showed that a specific diet helped a dog suffering from kidney disease,' says Jane Gray, chief veterinary surgeon at the Society for the Prevention of Cruelty to Animals. Gray says three of the most common ailments related to a dog's diet are obesity, joint problems and kidney disease. Obesity can lead to other problems such as diabetes, breathing difficulties and heart disease. 'In pet shops, you can buy [dog food] for weight loss, but there are 'stronger' diets that you can only get from a vet. It's like taking a drug, so they should only be taken under veterinary supervision.' Gray says obesity in animals should be treated with exercise and a healthy, calorie-reduced diet. She says a well-balanced diet is essential. 'If you feed a growing dog a pure-meat diet, such as pork or beef, without any nutritional supplements, it may have abnormal bone development.' A meat-only diet can cause a dog's bones to become brittle and prone to breaks. 'I've seen an extreme example of a puppy breaking its legs just by jumping from the sofa,' Gray says. She recommends mid- to premium-range pet food. 'Most [dog food] from [companies such as] Hill's, Royal Canin, Iams, Applaws are good quality, but there are many more now available in Hong Kong. The higher-priced brands generally spend millions of dollars on nutrition centres, veterinarians and science.' She says that cheaper brands often don't have stringent quality control standards and are not as nutritionally balanced. She says cats are generally fussier about their food, so they need to enjoy what they eat. Obesity and kidney disease in cats can also be caused by diet. Obesity is a major problem, as most cats get limited exercise, and kidney disease is one of the top killers of cats in Hong Kong, so a change to a cat's diet can prolong its life, she says. Veterinarian Brad Easton agrees some diseases are clearly diet-related, such as obesity and dental disease. 'For other conditions, such as kidney disease, diet can be one of several factors. If a dog or cat is already predisposed to the disease, excessive protein would mean the kidneys would be more likely to fail.' Easton says owners should 'definitely' invest in mid-range to premium quality pet food. 'Most people don't appreciate the research and testing that has gone [into making quality dog food],' he says. '[Companies] will spend a lot of time on research, feeding dogs and tracking their health before [releasing their products].' Cheaper pet-food brands only formulate their food on paper without testing them on animals, Easton says. If your cat or dog is sick, Easton stresses the importance of consulting your own veterinarian. 'If your animal has renal failure, a pet shop has no medical training to advise [you] what to buy. For diets that treat disease, there are prescription diets that are only available from a vet, who can make sure the diet is right for your dog or cat.'