Three different kinds of food sit on this page and they aren't interchangeable. Light versions of ordinary complete foods, veterinary weight diets sold over the counter, and prescription lines meant to be used under your vet's direction. Most dogs need the first.
Which of the three you actually need
Light versions of normal food. Lower in fat, usually higher in fibre so the dog feels fuller on less. The right answer for a dog carrying a bit too much and otherwise well. Ferguson, Ramsay Originals, Beta, James Wellbeloved and Green Pantry sit here.
Veterinary weight diets you can buy without a prescription. Hills Science Plan Perfect Weight, Royal Canin Light Weight Care, Eukanuba Daily Care and Pro Plan. Formulated for weight loss rather than steady maintenance, and dearer for it.
Hills Prescription Diet and Royal Canin Veterinary. Metabolic, r/d and Satiety. Despite the name, these don't need a prescription and you can buy them here without one. Prescription is part of Hills' brand name, not a legal requirement.
What they are is food formulated for a dog with a diagnosed problem, often one alongside the weight. So speak to your vet before you start rather than after, and stick with what they suggest. If you're already feeding one on your vet's advice, buying it here is straightforward. Our veterinary dog food range covers the rest of these lines.
Neutered dogs are a separate group
Several foods here are made specifically for neutered dogs: the Royal Canin Neutered range, Pro Plan Light / Sterilised, Eukanuba Overweight Sterilised. Manufacturers build these as separate lines because a dog's energy needs change after the operation.
If your dog has put weight on in the months after being neutered and nothing else changed, that's the group to look at first.
Before you change the food at all
Most overweight dogs are overweight because of the total going in, not the food in the bowl. Treats, chews, the end of somebody's toast. Adding those up is usually more useful than switching brand.
Weigh the food rather than scooping it. Scoops are generous and portions creep.
Ask your vet to body condition score your dog before you start. It takes two minutes at any appointment and gives you something to measure against later. If your dog is only slightly over, a light version of the food they already eat is a smaller change than moving to a weight diet, and it costs less.
When to speak to your vet
Book an appointment if your dog has gained weight without any change in what they're fed, if the weight won't shift after a couple of months on a reduced diet, or if they're being treated for anything else. Weight gain can be a symptom rather than a habit, and that's worth ruling out before you spend on food.
Where to start
For most dogs it's a light version of an ordinary complete food, not a veterinary diet. Our own Ferguson Scottish Salmon Adult Light is the cheapest way into that, and the Acana Grain Free Light & Fit if you'd rather stay grain free.
Older dogs are the common case, because they slow down before their portions do. Several foods here cover both, and our senior dog food range has the rest.