You feed them the same. They’re walked together, they’re the same age, they came from the same litter. One is a comfortable shape and the other has been on a diet since March.
Owners get told to feed less and walk more, which is true as far as it goes and doesn’t explain why two dogs on identical rations end up different sizes. Part of the answer is in the intestines.
The uncomfortable numbers
Somewhere between forty and sixty per cent of dogs in the UK are overweight, depending on which survey you read. Most of their owners don’t think they are.
That last part is the difficult bit. Overweight has become normal-looking, and a dog at a genuinely healthy weight now gets comments about being too thin.
Excess weight shortens life measurably and worsens arthritis, breathing, heat tolerance, diabetes risk, anaesthetic risk and pancreatitis risk. It is, by a distance, the most common preventable health problem in dogs.
Where the gut comes into it
This is newer science and it’s genuinely interesting rather than marketing.
Research in several species, including dogs, has found consistent differences between the gut microbiomes of lean and overweight individuals. The populations differ in composition and in diversity.
The proposed mechanisms are plausible. Different bacterial populations extract different amounts of energy from the same food – some are simply better at it, which means two dogs eating an identical bowl absorb slightly different numbers of calories from it. Gut bacteria also influence appetite and satiety signalling, and they affect the low-grade inflammation associated with fat tissue.
The honest position: the association is well established, the direction of causation is still being untangled, and nobody has yet shown that changing a dog’s microbiome makes him lose weight. It is not a shortcut and it isn’t a replacement for the maths.
Where it does matter practically is during weight loss, because a dog on a reduced ration with more fibre in it is a dog whose digestion is being asked to work differently. A Dog Gut Health Supplement through that period supports the population while the diet shifts, which is worth doing for the same reason you’d support it through any other change.
Assessing your dog honestly
Forget the scales for a moment and use your hands.
Ribs. You should feel them easily under a thin layer of covering, like the back of your hand. If you have to press, there’s too much. If they’re visible from across the room, too little.
Waist from above. Standing over him looking down, there should be a visible narrowing behind the ribs.
Tuck from the side. The belly should rise from the ribcage towards the back legs rather than running level.
That’s the body condition score system in three checks. Vets score it out of nine, with four to five being ideal.
Then weigh him, and write it down. Most practices have scales in reception and won’t mind you using them. A number you record monthly is worth more than an impression.
Why “feed less and walk more” often fails
Not because it’s wrong, but because it’s incomplete.
Nobody weighs the food. A scoop is not a measurement. The same scoop of two different kibbles can differ by a fifth in calories, and most people over-fill it.
The treats aren’t counted. This is the big one. Training treats, chews, dentasticks, the crust off a sandwich, something from the grandparents. Ten per cent of daily calories from treats is a reasonable maximum and plenty of dogs are well past thirty.
The guide on the bag is generous. It’s a starting point for an average dog, and neutered dogs in particular typically need noticeably less than it suggests.
Exercise does less than people think. A dog walk burns fewer calories than most owners assume. Weight loss is won at the bowl and maintained by activity.
The dog is hungry and the household caves. Four weeks of a dog staring at you at six o’clock is the actual reason most diets fail.
Doing it properly
Weigh the food. Kitchen scales, every meal, for the whole period. This single change fixes a great many stalled diets.
Cut by about ten per cent to start rather than slashing it, then reassess in a fortnight.
Bulk the bowl out with fibre. Green beans, carrot, a little pumpkin. The bowl looks the same, the calories drop, and the dog feels fuller. This is the single most useful trick there is.
Keep the protein up. A dog losing weight needs adequate protein to hold onto muscle. Crash dieting produces a thin dog with poor condition, not a fit one.
Take treats out of the daily ration rather than adding them to it. Set the day’s food aside in the morning and use it.
Aim for one to two per cent of body weight per week. Slower than people want. Considerably more likely to stay off.
Weigh him monthly, same scales, same time of day.
Working out what he actually needs
The number on the bag is a starting point and not much more.
A rough calculation most vets use: work out his resting requirement, then multiply by a factor for his circumstances. For weight loss the target is usually based on his ideal weight rather than his current one, which is the step people miss – feeding a fifteen per cent reduction of what an overweight dog is currently eating just makes him a slightly less overweight dog.
Your vet or a veterinary nurse will do this properly in a five-minute appointment, and most practices run free weight clinics with nurses who are genuinely good at it. It’s one of the more underused services in veterinary medicine.
Neutered dogs typically need somewhere around twenty to thirty per cent fewer calories than entire ones of the same size, and almost nobody adjusts the food when it happens. If your dog started gaining a few months after neutering, that’s very likely the whole explanation.
Activity level matters less than people assume unless the dog is genuinely working. A pet dog getting an hour a day is not burning as much as his owner imagines.
The plateau
Almost every weight loss programme stalls somewhere around week eight, and it’s the point most owners give up.
Some of it is metabolic – a lighter dog needs fewer calories, so what was a deficit becomes maintenance. Some of it is drift, because portions creep and treats reappear once the initial resolve fades.
The fix is to recalculate rather than to despair. Reweigh, work out the new requirement for the new weight, and adjust down slightly. And do an honest audit of everything going in for a week, written down, including anything given by anyone else in the house.
If the numbers are genuinely right and nothing has moved in a month, that’s the point to ask about thyroid testing rather than cutting further. A dog on a genuinely restricted ration who isn’t losing weight has something else going on.
When it isn’t the food
Some dogs genuinely don’t respond, and at that point it’s worth investigating rather than cutting further.
Hypothyroidism. Weight gain despite normal food, lethargy, coat changes, sometimes a tragic facial expression. A blood test finds it and treatment is straightforward and effective.
Cushing’s disease. Weight gain with a pot-bellied appearance, increased drinking and urinating, thinning coat, panting.
Neutering genuinely reduces energy requirements, often by a fifth or more, and most owners don’t adjust the food afterwards.
Some medications, steroids in particular.
Age. Older dogs need less, and often get the same.
If you’ve been genuinely rigorous for eight weeks with no movement, ask for a thyroid panel before you cut the food again.
The multi-dog household problem
Two dogs, one needs to lose weight, the other doesn’t.
Feed them in separate rooms with the doors shut. Not at opposite ends of the kitchen – separate rooms. The dog who needs to lose weight is invariably the faster eater and will finish and move on to the other bowl.
Pick bowls up when the meal’s over rather than leaving them down. Feed the slower dog somewhere the fast one can’t get to. And if one is on a prescription diet, make sure the other isn’t eating half of it, which happens constantly and quietly undermines the whole plan.
Digestion during weight loss
Expect some changes and don’t read them as failure.
More fibre usually means more volume and sometimes more wind for the first fortnight while the population adjusts. Stools may soften briefly with any diet change.
Introduce the fibre gradually rather than all at once, keep the gut support running, and give it a fortnight before judging.
If stools stay genuinely loose beyond two weeks, the change was too fast or the food doesn’t suit him. Back off a step rather than abandoning the whole thing.
The part nobody says out loud
Feeding a dog is how a lot of people express affection, and being told to stop is heard as being told to be less kind.
It helps to substitute rather than subtract. A five-minute training session, a snuffle mat with his own kibble in it, a chew, a walk somewhere new, ten minutes of scent games in the garden. Dogs value attention at least as much as food, and a scattered handful of his own dinner in the grass is received as a treat rather than as a ration.
Get the whole household to agree, including the person who thinks a bit of toast doesn’t count. It does, and it’s usually the reason the numbers don’t move.