A pet food labelled "complete" supplies everything the animal needs; one labelled "complementary" does not. "Organic" is defined in law, but "natural", "premium" and "holistic" are not.
Grain-free and raw diets have no proven health advantage, cats cannot safely be fed without meat, and overfeeding is the most common dietary problem.
The shelves of a pet shop offer hundreds of foods described as natural, premium, grain-free, organic or raw. Few of those words have a legal meaning. What matters for the animal is whether the food is complete, whether it suits its age and health, and how much of it is fed.
Under the feed law that applies in the United Kingdom and the European Union, a complete food provides all the nutrients an animal needs when fed as its only food. A complementary food does not, and has to be combined with others; treats, mixer biscuits and many toppers fall into this group. The statement appears on every label and is the first thing to check.
Complete wet and dry foods are both adequate. Dry food is convenient and keeps well once opened; wet food contains more water, which benefits cats in particular. Many owners feed a mixture.
Raw meat diets, bought frozen or made at home, are popular with some dog owners. Veterinary bodies point to two risks: bacteria such as salmonella and campylobacter, which can infect people in the household as well as the animal, and nutritional imbalance in home-made recipes. Commercial raw foods labelled complete address the second but not the first, so strict kitchen hygiene is needed.
Organic is the one term defined in law: the ingredients must come from certified organic farming and the product is certified by an approved body. It describes how the ingredients were produced, not the nutritional quality of the food.
Natural, premium, holistic and human-grade have no fixed definition.
Grain-free foods replace cereals with potato, peas or lentils. Dogs digest cooked grains well, and true grain allergy is rare. In the United States, regulators investigated a possible link between some grain-free diets rich in pulses and a form of heart disease in dogs; no cause was established, but there is no health reason to avoid grains in a healthy animal.
Hypoallergenic is used loosely. Food allergy is diagnosed by a strict elimination diet under veterinary supervision, not by switching brands.
Dogs are omnivores, and the British Veterinary Association has accepted since 2024 that a dog can be fed a plant-based diet provided it is nutritionally complete and balanced, while noting that long-term evidence is limited. Cats are obligate carnivores and need nutrients found naturally only in animal tissue; veterinary organisations advise against meat-free diets for cats. Foods using insect protein are sold as a lower-impact alternative for both species.
Puppies and kittens need food formulated for growth, and large-breed puppies a version that controls the rate of growth to protect their joints. Senior foods have fewer calories. Diets prescribed by a vet for kidney disease, urinary problems, allergies or weight loss are fed only on veterinary advice.
Around half of dogs and cats seen by British vets are judged to be overweight, which shortens life and causes arthritis and diabetes. Food is weighed, treats are kept to about a tenth of the daily calories, and portions are reduced if the ribs become hard to feel. Changes of diet are made gradually over a week.
Chocolate, grapes and raisins, onions and garlic, the sweetener xylitol, macadamia nuts, alcohol and cooked bones are dangerous to dogs, and most of them to cats. Details for each species are given under feeding a cat and preparing a home for a puppy.
Dry food keeps best in its original bag, rolled shut, inside a clean airtight container in a cool place; the bag carries the batch number needed if a product is recalled. Opened tins and pouches are covered, refrigerated and used within a day or two. Bowls are washed after every meal, and hands after handling any pet food.