Does Your Dog or Cat Need A Diet?

Most people land on a page like this after noticing a quiet change: a dog that no longer springs into the car, a cat that can’t quite reach to groom, a belly that seems to hang lower each month. Weight creep is common, easy to miss, and it matters—because extra body fat is linked with arthritis, diabetes, surgical risk and a shorter, less comfortable life.

The useful question isn’t “Should my pet go on a diet?” so much as “Is their body condition healthy, and if not, what’s the safest way to change it?” A good plan starts with a simple hands-on check, then moves to measured food, treat limits, and gentle, regular activity—often with your vet’s help.^{1, 2}

Quick check: does your dog or cat actually need to lose weight?

Body weight alone can mislead. A stocky breed, a fluffy coat, or age-related muscle loss can hide what’s happening underneath. Vets rely on a Body Condition Score (BCS), usually on a 9-point scale, because it tells you more than kilograms ever will.^{1, 3}

At-home signs that suggest weight gain

• Ribs are hard to feel without pressing firmly, or you can’t feel them at all.
• No clear waist when you look from above.
• No “tuck” behind the ribs when viewed from the side (the belly line looks straight or rounded).
• Less mobility: slower on walks, reluctance to jump, difficulty with stairs, tiring quickly.
• Breathing looks harder than it should for the effort (especially in warm weather).
• In cats: reduced grooming, especially along the back and around the tail base.⁴

Don’t confuse overweight with underweight

Visible ribs and spine usually point to being underweight, not overweight. Sudden weight loss, loss of appetite, vomiting, diarrhoea, or a pot-bellied look in a thin animal need veterinary attention rather than a home “diet”.²

Why a healthy weight matters (beyond appearance)

Extra weight is not just “a bit cuddly”. In dogs and cats, obesity is associated with a range of diseases and complications, including arthritis, diabetes and increased risk around anaesthesia and surgery, along with reduced quality of life and lifespan.^{2, 5}

What “a diet” should mean for pets

For dogs and cats, a good diet plan usually means:

• measuring daily intake (including treats, table scraps, dental chews and “tastes”)
• aiming for a steady, safe rate of loss, not a sudden drop
• feeding a complete and balanced food appropriate to life stage
• adjusting based on results (weight trend + BCS), not guesswork.⁵

Treats: the quiet calorie leak

In weight management guidelines, the consistent advice is to keep “extras” (treats and other non-core foods) to no more than 10% of your pet’s daily calories, so the main diet stays nutritionally balanced.⁵

Feeding basics that actually work

Start with a BCS and a target weight

Ask your vet to record your pet’s BCS and muscle condition, then agree on a realistic target. On a 9-point BCS scale, each step above 5 is roughly 10–15% overweight—enough to matter, but also enough to improve with steady changes.^{3, 6}

Measure food properly

Use kitchen scales or a standard measuring cup and stick to one method. “A scoop” varies wildly from day to day. Recheck your pet’s weight and BCS regularly and adjust portions gradually if progress stalls.⁵

Choose a complete and balanced diet (and be cautious with DIY)

Commercial foods labelled as complete and balanced are designed to meet nutrient requirements when fed as directed. Home-prepared diets can work, but they’re easy to unbalance without professional formulation—especially during weight loss, when the margin for nutrient shortfalls narrows.^{5, 7}

Dogs vs cats: key differences during weight loss

Dogs

Dogs often do well with portion control, fewer high-fat treats, and predictable daily exercise. The trick is consistency—small, daily overfeeding adds up, especially in middle age and after desexing when energy needs can drop.⁸

Cats

Cats need a more careful approach. Rapid or severe food restriction can be dangerous; overweight cats are at risk of hepatic lipidosis (fatty liver disease) if they stop eating or lose weight too quickly. Any cat that isn’t eating, or is losing weight unexpectedly, should be seen by a vet promptly.⁹

Transitioning to a new diet without upsetting the gut

Sudden food changes can trigger vomiting or diarrhoea. A slow transition is usually gentler:

• Days 1–2: 75% current food, 25% new food
• Days 3–4: 50/50
• Days 5–6: 25% current food, 75% new food
• Day 7 onwards: 100% new food

If your pet has a sensitive stomach, your vet may suggest stretching this change over 10–14 days.²

The role of exercise (and what “enough” looks like)

Movement helps, but exercise alone rarely outpaces extra calories. Think of activity as the support beam: it preserves muscle, helps joints, and improves fitness while the food plan does the heavy lifting for fat loss.⁵

Keep it appropriate to your pet’s age, breed and health. If your dog is overweight and stiff, start with shorter, more frequent walks and build slowly. For cats, short bursts of play across the day (chasing toys, climbing, food puzzles) are often more realistic than one long “workout”.^{1, 8}

Common feeding mistakes that lead to weight gain

• Free-feeding (a full bowl all day), especially indoors and for desexed pets.
• Counting meals but not treats, table scraps, dental chews and “training snacks”.
• Feeding to the label only and not adjusting based on your pet’s BCS and lifestyle.
• Multiple people feeding without realising it—double breakfasts happen quietly.
• Using food for every reward when praise, pats, play or a toy would do.⁵

When to seek professional help

Weight management is straightforward for many pets, but it’s time to involve your vet if you notice:

• weight gain or loss that’s rapid or unexplained
• exercise intolerance, coughing, heavy breathing, or fainting
• signs of pain (stiffness, reluctance to jump, limping)
• vomiting, diarrhoea, or appetite changes during a diet change
• a cat that stops eating, even briefly—this is urgent.

Your vet can check for underlying disease, set a safe calorie target, and track BCS and muscle so weight loss doesn’t come at the cost of strength.^{1, 9}

Final thoughts

A pet “diet” doesn’t need to be harsh. It’s usually a quiet recalibration: a measured portion, treats that stay small and accounted for, and movement that fits the animal in front of you. With regular checks and a steady hand, many dogs and cats return to a healthier shape—and keep their joints, heart and lungs working with less strain.^{2, 5}

References

1. World Small Animal Veterinary Association (WSAVA) – Global Nutrition Guidelines
2. RSPCA Pet Insurance – Health concerns for dogs and cats (guide)
3. UC Davis School of Veterinary Medicine – Nutritional Management of Weight
4. RSPCA Pet Insurance – How to spot signs of pet obesity
5. American Animal Hospital Association (AAHA) – 2021 Nutrition and Weight Management Guidelines for Dogs and Cats
6. US FDA – Helping Pets Live Healthier, Thinner Lives (summary of AAHA nutritional assessment, BCS scales)
7. AAHA – Feeding plans for healthy, appropriate-weight cats and dogs
8. AAHA – Prevention of obesity
9. FOUR PAWS in Australia – Countermeasures to pet obesity (cat rapid weight loss caution)