Why Is My Hamster Fat All Of A Sudden? Everything You Need To Know

Hamsters are small and fragile. They have obesity issues because of hereditary factors. Moreover, they are prone to overeat and hiding food inside their mouth. 

So it’s no wonder if you ask, why is my hamster fat all of a sudden? Well, there are a number of possibilities. Your hamster is a female and is pregnant, or maybe your hamster is suffering from an internal tumor. Or it could be as trivial as your hamster just overeating.

But how to spot the problem behind my hamster’s overweight? Do not worry, we shall discuss all the necessities below.

Why Is My Hamster Fat All Of A Sudden?

As we have briefly discussed, there could be a number of possibilities. Like us humans, hamsters gain weight during pregnancy and after pregnancy due to hormonal changes. 

Hamsters also gain weight simply, just like us, due to overeating which is simply called obesity. And could be easily fixed by tweaking the diet of your hamster. Or maybe the problem isn’t so trivial. And maybe your hamster is suffering from gastric problems or has tumors.

Why Is My Hamster Fat All Of A Sudden

The symptoms of any of these issues are straightforward. So does the solution, which we will talk about later in this article. All that is needed for the well-being of your hamster is a bit of your honest effort.

Ideal Weight For Your Hamster

There are a lot of breeds of hamsters, as many as 19 breeds in total. Although only 9 breeds of hamsters are more commonly petted in households. Nevertheless, different breeds of hamsters have different sizes, shapes, and ideal weights. 

Ideal Weight For Your Hamster

Here is a chart to better understand the ideal weight of your hamster’s breed.

Name Size Ideal Weight
Roborovski Hamster(4.5 to 5) cm (1.8 to 2) inch(20 to 25) g(0.7 to 0.8) oz
Dwarf Winter White Russian Hamster(6.8 to 9) cm(2.7 to 3.5) inch(70 to 90) g(2.5 to 3.2) oz
Dwarf Campell’s Russian Hamster(5 to 10) cm(2 to 4) inch(40 to 60) g(1.4 to 2) oz
Syrian Hamster(13 to 18) cm(5 to 7) inch(145 to 170) g(5 to 6) oz
Ciscaucasian Hamster(23 to 28) cm(9 to 11) inch(60 to 105) g(2 to 3.7) oz
European  Hamster(20 to 35) cm(8 to 14) inch(220 to 460) g(7.8 to 16) oz
Chinese Striped Hamster(7 to 12) cm(2.8 to 4.6) inch(20 to 35) g(0.7 to 1.2) oz
Chinese Hamster(5 to 13) cm(3.2 to 5) inch(30 to 45) g(1 to 1.6) oz 
Armenian Hamster(8.4 to 12) cm(3.3 to 4.7) inch(30 to 60) g(1 to 2) oz
Eversmann’s Hamster(13 to 15) cm(5 to 6) inch(65 to 75) g(2.3 to 2.6) oz
Lesser Long-Tailed Hamster(8.6 to 13.5) cm(3.4 to 5.3) inch(35 to 50) g(1.2 to 1.7) oz
Ladak Hamster(9 to 13) cm(3.5 to 5) inch(35 to 45) g(1.2 to 1.6) oz
Greater Long-Tailed Hamster(10 to 15) cm(4 to 6) inch(40 to 55) g(1.4 to 2) oz 
Gansu Hamster(13 to 15) cm(5 to 6) inch(65 to 75) g(2.3 to 2.6) oz
Mongolian Hamster(13 to 15) cm(5 to 6) inch(65 to 75) g(2.3-2.6) oz 
Tibetan Hamster(9 to 11) cm(3.5 to 4.4) inch(35 to 45) g(1.2 to 1.6) oz
Romanian Hamster(15 to 18) cm(6 to 7) inch(80 to 115) g(2.8 to 4) oz
Turkish Hamster(13 to 18) cm(5 to 7) inch(145 to 170) g(5 to 6) oz

How To Know If My Hamster Is Overweight?

The first sign is getting chubbier. Hamsters are pretty fluffy creatures, even then, the sudden gain is usually very visible. 

If your hamster suddenly gained by a bit much, measure his weight on a weighing scale. 

How To Know If My Hamster Is Overweight

Since hamsters have very low weight, it is recommended to use a weighing scale accurate to 0.1g

If your hamster has exceeded the upper limit of his recommended weight by a few grams, it is recommended to start taking accurate measures.

Hamster Pregnancy Relating To Overweighing

Female hamsters gain weight very quickly after mating. They only keep the babies in the womb for only about 18 to 30 days, depending on the breed. 

Hamster Pregnancy Relating To Overweighing

But the main problem is post-pregnancy. The mother can become lazy and obese. However, you need to determine that her overweight issue is because of her pregnancy. 


  • Changes in behavior
  • Nest building 
  • Drinking and roaming a lot more
  • Moving slower than usual


  • Take care well of the pregnant mother by giving her nutritious meals and separate space

Here’s a video of how to take care of a pregnant hamster;

  • Once she reaches post-pregnancy, encourage her to play more

Hamsters Reaching Alarming Obesity

Obesity in hamsters is nothing unusual or new. The equation to obesity is simple, your hamster is intaking more calories than he can burn. So technically, you have a lazy hamster.

Hamsters Reaching Alarming Obesity


  • Sudden increase in body weight 
  • Inactivity of your hamster


  • Encourage your hamster with new toys to play with, mainly encourage your hamster to use the hamster wheel. Running around is a survival instinct for hamsters. Once the mental barrier of laziness fades, your hamster would run regularly on a hamster wheel
  • Restrict excessive intake of carbohydrates

Your Hamster Has Health Problems

There are many major health problems among hamsters that contribute to a sudden increase in body weight. Some of them are extremely fatal health problems and need immediate attention.

Your Hamster Has Health Problems

Gastric Problems 

Hamsters, just like us, too have gastric problems. Such problems arise due to digestion problems. Giving repetitive meals or meals with high fiber that your hamster cannot digest could lead to such problems


  • Weakness 
  • Rear Smells
  • Loss in Appetite


  • Decrease repetitive high-fiber meals
  • Decrease excessive food intake
  • Encourage to drink more water
Your Hamster Has Health Problems


Another health problem that leads to increase in weight is a tumor. Tumors in hamsters have significant mass as well as bloat the body.


  • Lethargy
  • Droppings contain blood
  • Moves very slowly


  • Contact a vet and take professional treatment 
If you’re concerned about your hamster’s behavior and health, you may find our articles on why your hamster is running around like crazy and whether hamsters have a good memory helpful. Our article on why your hamster is running around like crazy explores the potential reasons behind this active behavior and how to keep your hamster safe while they play. Meanwhile, our article on whether hamsters have a good memory discusses the current scientific understanding of hamster memory and learning abilities.


Down below, we shall answer the most frequently and commonly asked questions to ease your doubts.

Q: Is obesity in hamsters a bad thing?

Yes, as with us humans, obesity affects our health and livelihood. Not only does obesity decrease the life expectancy of your hamster. But it will also make your hamster prone to many diseases that he previously was not susceptible to.

Q: What are the foods that make hamsters fat?

Mainly foods that contain a lot of sugar. A common example would be commercial hamster treats.

Q: Do fruits make my hamster obese?

Yes. As previously discussed, sugar helps in obesity and fruit is no exception. Even though fruits contain a lot of other essential minerals, excess intake will however result in obesity.


We have discussed thoroughly the topic of why is my hamster fat all of a sudden. Let’s do a quick review so that you don’t forget. A number of things could lead to sudden weight gain in hamsters. Something so trivial as obesity or pregnancy but also something life-threatening such as a tumor.

So it is essential to take a pet only when we are responsible enough to take good care of it. Just because our pets cannot express their problems and suffering as we can, doesn’t mean they cannot feel anything.

Lisa G

Meet Lisa G, the founder and author of RodentsFact.com. With over 3 years of experience studying and observing various species of rodents. Lisa has established herself as a credible expert in the field. Her passion for these often-overlooked animals shines through in her in-depth articles and engaging writing style. Follow her blog to learn fascinating facts and gain a new appreciation for the furry creatures that share our world.

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