Is My Rat Too Fat? A Guide To Proper Weight And Size

If you’ve not kept rats before, it can be hard to work out whether they’re the right weight and size. Fortunately, it’s not too complicated to keep an eye on your pets and keep them happy and healthy. This guide will walk you through everything you need to know.

Is my rat too fat? A guide to proper weight and size includes an examination of the different conditions of rats from too thin to obese. Then we examine how you can help an obese rat lose weight through a program of diet and exercise. Finally, we take a very brief look at rats that are too skinny too.

How To Tell If Your Rat Is Too Fat

It is absolutely right, as a pet owner, to be concerned about your rat becoming overweight. Just as with human beings, obesity in rats can be a genuine problem.

Believe it or not there is an official score for rat body weight which helps you to define the condition of your rat:

Condition Of The RatDiagnostic Approach
Your rat is emaciated (that means the rat is too thin)The spine will be very prominent or even visible through the furThere will be almost no flesh over the rat’s dorsal pelvis
Your rat is under conditioned (this means your rat is not fit enough)The spine will be very prominent or even visible through the furThe flesh on the dorsal pelvis will be thin with almost no subcutaneous fatThe caudal vertebrae (the ones at the tail) will segment easily with a little pressure
Your rat is exactly the way you want them “well-conditioned”The spine is properly segmented and not visible through the furThere is a bit of subcutaneous fat over the pelvis The caudal vertebrae are not segmented
Your rat is over conditioned (not fat but not exactly right either)The vertebrae can be segmented with a little pressureThere is plenty of fat over the pelvisThe caudal vertebrae are covered in a thick layer of fat
Your rat is obese (that’s definitely too fat)The spine may appear to be a continuous column because of fat stores over itThere is a large amount of fat over the pelvis which is not at all palpableThere is a large amount of fat over the caudal vertebrae which are not palpable

Now, it’s important to note that you are not to blame if your rat is obese. It’s actually very hard to come up with a standard approach to feeding rats because, just as with humans, they may have varying metabolisms and varied potential sizes too. Male and female rats also have different nutritional needs.

The average house rat is between 9” and 11” long and while 2” doesn’t sound like a large difference – in this case that’s nearly 20% of the whole length of a rat.

To put that in human terms – a 5 foot tall person who ate the same diet as someone 6 feet tall would likely be much fatter than the taller person after a few months.

So, don’t be distressed if you find that your rat is obese. However, you must take action to help your rat lose weight.

How To Help Your Rat Lose Weight

Give Your Rat A Smaller Plate

Oddly, this is a top tip for human beings trying to go on a diet too. If you put the food on a smaller plate, when all the food is gone there is a visual message to the brain that the meal is over which may (or may not) trigger the sense of being “full”.

So, portion control is one of the first things to try when slimming your rat down. Get a smaller food bowl, add a smaller amount of food than usual and let them eat.

Just make sure that the new bowl won’t tip over easily (because food spilled over the floor is not great to eat) and try not to use plastic bowls because rats have been known to chew on them.

Now, this isn’t to say that a fat rat won’t still feel a little hungry after a smaller meal but that’s not really all that important – after a few meals, they will get used to the idea of smaller portions and they will no longer feel hungry.

The Food That You Provide Should Be Fortified

When a rat is getting fat, it’s a good idea to make sure that you’re feeding them the best possible diet and that diet is always a fortified custom designed rat food. Now, there’s nothing wrong with feeding a rat of a healthy weight a little treat every now and again but when they’re become obese – it’s time to stop.

You can find fortified rat foods easily in any pet store, on Amazon, or via your local vet. They come in both pellet/seed form and in blocks. You can mix the two together for the best results, if you like.

You should be giving them no more than 3 tablespoons in any 24 hour period to help them lose weight.

Don’t buy the usual “rodent formula” but seek out fortified rat foods, instead. The standard formulae can often be a little light on protein content which makes the rats hungrier and therefore more unhappy while they’re trying to lose weight.

Time To Cut Down On Treats

Rats won’t die without treats. It’s perfectly reasonable to cut out all treats until your rat is a healthy weight and if you decide to opt for this – that’s fine. Don’t feel bad about it, even if your rat tries to guilt trip you into changing your mind.

However, if you must give treats in this period. Stick to vegetables which are both low in fat and low in sugar. You should offer no more than a single tablespoon of chopped vegetables in any one 24-hour period while they’re dieting.

You should place the treats in a different bowl from the standard food bowl and you should clean this bowl on a daily basis too.

Never give your rat a sticky food as a treat, think peanut butter, because these foods can represent a serious choking hazard for rats.

Once a week, you should give a rat a hard treat such as a small dog biscuit because this helps to keep their teeth in healthy condition.

Work With Your Rat’s Natural Cycle

Rats aren’t daytime animals. In fact, given a choice, rats would prefer to sleep during the day and be active in the evenings and nighttime. Wild rats, of course, are completely nocturnal but pet rats are a little more flexible, you can find out more about pet rats sleeping habits here.

The best time for you to feed your rats is going to be early in the evening. Think of it like a human being starting the day with a good breakfast – you’re giving your rat the most opportunity to burn off any calories that they take on.

Plus, your rat will be nice and alert at this point in the day and it will probably enjoy its food more than it would when it’s half asleep in the middle of the day.

If your rat is getting too much food, it might actually try to hide some of it in the corners of the cage, so watch out for these little stashes and if you find them, you should start to cut down on the amount of food you put out for your rat.

What you absolutely should not do is try to force your rat into an intermittent fasting practice (e.g. skipping some meals) because while this may work for humans, it’s likely to turn your rat into an anxious depressed mess.

Keep Things Clean And Healthy Looking

One other thing that you ought to do for your rat at each mealtime is to give their food bowl a good clean. We don’t think that there’s any link between rodent obesity and a dirty food bowl, but we do think that you don’t want to make your rat sick and one way to ensure good health for your pet is to pay attention to hygiene.

Ideally, you should scrub the food bowl out completely with a cleaning sponge or even a wire brush. You should only use warm, soapy water with no additives to clean the bowl. Then give it a thorough rinse to remove all traces of soap before you air dry it.

When you return the food bowl to the rat’s cage – we’d recommend that you place it on the opposite end of the cage from their litter. You wouldn’t want to eat in your toilet because of the health risks, so, it’s best to ensure that your rat doesn’t either.

Give Your Rat A Visual/Physical Inspection – Weight Gain Isn’t Always Due To Overeating

Before you assume that your rat is fat because it’s stuffing too much food down in each meal or because it’s not running around enough; you should make sure that there is no other cause for the sudden appearance of obesity.

The number one cause of a swollen belly in female rats, for example, isn’t getting fat – it’s getting pregnant. You definitely don’t want to start cutting down on what you feed a pregnant rat because it might damage the babies.

Sadly, there are some less happy reasons that your rat might be bulking up too and they include:

  • Tumors in the belly/abdomen. The bulk of the tumor can cause the rat’s belly to begin to swell and it’s possible for a tumor elsewhere in the digestive system to trap fluid which then builds up to swell out the abdomen too.
  • Diseases of the liver and kidneys. These can cause fluid retention in the abdomen which leads to a swollen appearance.
  • Megacolon. This is an unusual condition of rat’s nervous systems. The nerves in the large intestine fail to send the correct message to expel poop from the rat’s system. As you might expect – if a rat isn’t pooping, things are going to get backed up in there and swelling ensues.
  • Bladder/Urinary tract problems. If a rat can’t pee, then the rat’s bladder is going to swell up like an unpleasant water balloon and this too can lead to a fat looking abdomen.

If you suspect that you rat has any of these problems, don’t put them on a diet, take them to your vet at once because rats are so small, any minor issues can quickly become major issues and you don’t want them to suffer.

Avoid Cancer Causing Foods

Now that we know that tumors can be linked to the appearance of obesity in rats, we have to ask, can we help prevent tumors in rats? The answer to that is, yes, sort of.

There are no guarantees that any animal won’t develop tumors, of course, in the same way that you can’t guarantee that a non-smoking person won’t get lung cancer. However, you can dramatically reduce the chances of your rat getting a tumor by removing carcinogenic foods from their diet these include:

  • Beets
  • Celery
  • Collards
  • Cucumber
  • Dried Corn
  • Eggplant
  • Lettuce
  • Radish
  • Spinach
  • Turnip Greens
  • Any moldy or spoiled food stuffs of any description

All of these food stuffs have been linked to liver cancer in rats. Now, please don’t panic if your rat has had a little bite of one of these things in the past but do try and ensure that you don’t feed them to your rat moving forward from here.

Get Your Rat Working Out To Get In Shape

Another way to help your rat ditch the extra pounds (or ounces, this is a rat after all) is to help it get a thorough physical workout each day. The good news is that your rat definitely won’t resent you for this (as larger humans might) because they enjoy mental and physical stimulation.

So, make sure that they have:

  • Tunnels to run through, rats are voracious tunnellers in the wild and they absolutely love tunnels
  • Ropes and ladders to climb, rats are also some of the finest climbers in the animal kingdom and the more they can climb the better
  • Chew toys, rats enjoy chewing on things and if you provide something hard like a dog biscuit for this – it can also help to keep their teeth clean and healthy

Rat toys don’t cost a fortune though some of them will wear out over time. We recommend that you have a monthly budget for toys to keep your rat moving around and entertained. They’re much less likely to bulk up if they’re moving around a lot.

Consider Getting Them An Exercise Wheel

Please don’t buy an exercise ball. These devices will cut the rat off from being able to smell its surroundings which can confuse it and cause severe distress.

An exercise wheel, however, is open on all sides and is just like a treadmill for humans. Make sure that the wheel has no rungs or crossbar that it can get tangled up in though, a plain surface is what you need.

Unfortunately, we can’t guarantee that your rat will love the exercise wheel – some will just sleep on it.

Make Sure To Play With Your Rat Each And Every Day

You can also take you rat out of his cage on a daily basis and ensure that you allow him time to play. We’d recommend a minimum of an hour a day while you pet him, allow him to explore, etc. just make sure there are no ways for your rat to get out of your room while he runs about.

Make Some Toys For Your Rat

You can even make your own toys from household objects for your rat to play with, just make sure they’re not using anything dangerous to rats – cardboard and PVC are great materials for rats to play with. A kitchen paper tube can be the perfect makeshift tunnel for your rat, for example.

Is My Pet Rat Too Skinny?

If your rat is emaciated, then you have other problems to worry about. Run the diagnostic at the top of the page and if you conclude that your rat is too skinny – you should speak to a vet.

Rats are obsessed with eating. It’s their primary goal in life and unless you’re not feeding them enough (if all their food is gone every time – try increasing their feed levels slightly until they gain weight) then the odds are that if they’re too skinny, they’re not well.


We hope that “Is my rat too fat? A guide to proper weight and size” has been helpful to you so that you can now identify whether a rat is overweight or underweight. The good news is that in most cases a change in diet and exercise can help an obese rat become thinner.

However, if your rat is emaciated or your obese rat is showing symptoms of bloating rather than over-eating, you should contact your vet immediately to get their input and put a stop to any suffering that your rat may be undergoing.

Relate Questions

Can rats eat cat food, why not find out more in this other article we recently wrote about rats eating cat food.

Darren Black

I'm Darren Black, the owner, and author of I am from Scotland, United Kingdom and passionate about sharing useful information and tips about properly caring for an animal's wellbeing.

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