First, the warning that matters most
PetMD puts it above everything else: talk to your veterinarian before putting your cat on a diet, because rapid weight loss can be very dangerous. In cats, severe food restriction can trigger hepatic lipidosis — fatty liver disease.
That single fact shapes the whole plan. Weight loss in cats is a math problem you run slowly, not a willpower problem. If your cat ever stops eating during a diet, that's an immediate vet visit (PetMD).
Know your starting point
- Overweight means 10 to 20 percent above the expected body weight; obese means more than 20 percent (PetMD).
- The measurement is body condition score — can you see the ribs, is there a waist, can you feel the spine and hips without padding? Your vet assigns a score and a target weight from it (PetMD).
- Obesity is a disease, not a look. It raises the risk of diabetes, certain cancers, metabolic disease, heart and respiratory problems and joint discomfort (PetMD).
The numbers, without guesswork
PetMD's formula for resting energy requirement: 70 × (body weight in kg)0.75 = RER. Feeding around 80 percent of RER produces the target rate.
The speed limit is just as important: cats should not lose more than 1 to 2 percent of body weight per week. Weigh weekly. Losing faster than 2 percent means adding 10 percent more calories (with your vet); slower than 1 percent means trimming 5 to 10 percent (PetMD).
Measure the food, don't eyeball it — a gram scale is the most accurate, a measuring cup second best (PetMD). And log treats: snacks count against the daily calorie budget, not alongside it (PetMD).
Food, movement, and the boring middle
- Pick the food with your vet. High fiber/low fat diets add bulk and satiety; high protein/low carbohydrate diets delay stomach emptying. Wet food's water content adds volume without calories (PetMD).
- Make the cat work. Scheduled play with wand toys or a laser pointer, vertical space for jumping, puzzle toys and treat balls. Meals on an elevated surface, harness walks and even a cat wheel all count (PetMD).
- Control the schedule. Timed feeds or an automatic feeder help; slow-feeders stop the two-minute inhale (PetMD).
- Transition slowly. Any food change runs over 7 to 10 days to avoid stomach upset (PetMD).
- Keep score. Weekly weigh-ins, honest portions, regular vet review — and patience with the plateaus, which PetMD notes are normal. Weight control after the loss is a lifelong habit, not a finished project.
Frequently asked questions
How fast should my cat lose weight?
No more than 1–2% of body weight per week, per PetMD. Faster loss can trigger fatty liver disease (hepatic lipidosis) in cats. Your vet sets the calorie target; you set the scale.
How many calories should a cat eat to lose weight?
The starting math is the resting energy requirement: 70 × (body weight in kg)^0.75. Feeding about 80% of that number typically produces the 1–2% weekly loss (PetMD). Your vet refines it with your cat's condition score and adjusts based on weekly weigh-ins.
Is my cat overweight or obese?
Overweight is 10–20% above expected body weight; obese is above 20% (PetMD). The hands-on version: ribs should be palpable under a thin fat layer, with a visible waist from above.
My cat stopped eating on her diet. Is that OK?
No — have her examined. PetMD lists a cat that stops eating during weight loss as an immediate vet-visit trigger, since food refusal in an overweight cat can lead to fatty liver disease.