Does Your Dog or Cat Need A Diet?

By Sophie Kininmonth · 25 Nov 2025 (updated 21 Jul 2026) ·6 min read

Weight creep in dogs and cats is easy to miss. It usually shows up as a quiet change: a dog that no longer springs into the car, a cat that cannot quite reach to groom, a belly that hangs a little lower each month. The good news is that body condition is one of the most fixable things about a pet's health, and small, steady adjustments do most of the work. It matters because extra body fat is linked with arthritis, diabetes, higher surgical risk and a shorter, less comfortable life. The useful question is not "should my pet go on a diet?" but "is their body condition healthy, and if not, what is the safest way to change it?"^{1, 2}

Quick check: does your pet actually need to lose weight?

Body weight on its own can mislead. A stocky breed, a fluffy coat, or age-related muscle loss can hide what is 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 cannot 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

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

A pet diet is rarely harsh restriction. For dogs and cats, a good 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 plus BCS), not guesswork.⁵

Treats are the quiet calorie leak. Weight management guidelines consistently advise keeping "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 to 15% overweight, which is 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 are easy to unbalance without professional formulation, especially during weight loss, when the margin for nutrient shortfalls narrows.^{5, 7}

Dogs and cats need different approaches

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 is not 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, so a slow transition is usually gentler:

Days 1 to 2: 75% current food, 25% new food
Days 3 to 4: 50/50
Days 5 to 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 to 14 days.²

The role of exercise

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, so 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 is time to involve your vet if you notice:

weight gain or loss that is 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, which is urgent.

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

The Bottom Line

A pet "diet" does not need to be harsh. It is 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

Sophie Kininmonth

Dog lover and writer at My Pets Australia, sharing practical breed guides and care advice for Australian pet owners.