Why a cat has to lose weight slowly

The instinct with an overweight cat is to cut the food sharply and get on with it. In a cat specifically, that instinct can kill.

The reason cats are different

When any animal takes in far less energy than it burns, the body mobilises stored fat and sends it to the liver to be processed. In cats, the liver’s capacity to handle that flood is limited, and fat can accumulate in the liver faster than it can be used.

That is hepatic lipidosis, and it can be fatal. It is most strongly associated with overweight cats that stop eating altogether, which is why the two most dangerous things you can do are to cut the ration drastically and to switch abruptly to a food the cat then refuses.

A dog that skips three days of food is usually hungry. A fat cat that skips three days of food may be in serious trouble, and the risk goes up with how overweight it was to start with.

The safe rate, and what it implies

The pace generally considered safe is half a percent to one percent of body weight a week.

For a 6 kg cat that should weigh 4.5, that is 30 to 60 g a week, and the whole plan runs for something like four to six months. That timescale is the normal one. An owner who expects a visible change in a fortnight will either conclude it is not working or push harder, and pushing harder is the actual danger.

Feed to the target, not below the floor

The calculation that matters starts from the ideal weight rather than the current one. Work out the resting requirement for the cat the cat should be, then feed somewhere around 80% of that figure for weight loss.

For a cat whose target is 4.5 kg, the resting requirement is about 216 kcal, so a reduction plan lands near 170 kcal a day. The cat calorie calculator will give you both figures, the maintenance number and the resting number, which is the pair you need to set a sensible floor.

The floor matters as much as the target. Taking a cat much below its resting requirement is where the risk sits, and it is not the kind of thing to improvise. A reduction plan for a seriously overweight cat belongs in a conversation with a vet, who can also check that the weight is what you think it is rather than fluid or something else.

Protein and volume make it bearable

Cats on a reduction plan are hungry, and hunger is what makes owners give in.

Two things help. Higher protein diets preserve lean mass during weight loss and tend to satisfy better, which is why prescription weight management foods are built that way. And wet food delivers the same calories in a much bigger bowl, because so much of it is water, so the cat eats what looks like a proper meal.

Splitting the daily allowance into four or five small meals also helps more than it sounds like it should. The total is unchanged, but the gaps are shorter, and most of the difficult behaviour is about gaps rather than quantity.

Measure the cat, not the bowl

Weigh the cat every two weeks on the same scale, at the same time of day, and write it down. Baby scales work well, as does weighing yourself holding the cat and subtracting, though that method is noisier than most cats will tolerate twice.

If nothing is moving after a month, the adjustment is small. Ten percent off the ration, not thirty. If the cat is losing faster than one percent a week, that is the signal to feed slightly more, which is counterintuitive enough that people ignore it.

And if the cat stops eating for more than about a day, that stops being a diet question. In an overweight cat it is a reason to call a vet rather than to wait and see whether appetite returns.