Obesity Obesity is the most common, completely preventable health problem that rats can have. An obese rat will live a shorter life, being much more prone to heart and respiratory problems. It's also very uncomfortable for them and greatly hampers their ability to move. Your rats will be much happier and healthier if you keep them at a trim healthy weight. The female on the left is a trim healthy weight of 13.2 ounces. The female on the right is an obese 16.7 ounces. An ideal weight for a female rat is usually between 10 and 14 ounces, unless she is a particularly large sized female. An ideal weight for a male rat is usually between 18 and 23 ounces, unless he is a particularly large sized male. Females should look slender and sleek, where as males tend to have a slightly more chunky appearance. Males do have a chunky appearance, however it is obvious that this male is grossly overweight. Although fat rats can be quite adorable and squishy, it is cruel to let them get like this if you can help it. To keep your rats at a trim healthy weight simply give them lots of exercise, a healthy core diet, and be very sparing with the treats (and pick low fat healthy treats.) Once a rat becomes fat, it is very hard to get them to loose the weight, so it is critical that you don't indulge them with too many treats. This can be hard when they look at you with those cute little faces begging for food, but it's for their own good. If you have fat rats, cut down on or completely cut out their treats and hopefully they will lose some of that extra weight. Do not tamper with your rats' core diet though. A rat's core diet should consist of free access to rat blocks along with a serving of fruit/veggies each day. Sometimes, even if you're strict with your rats treats, you can still end up with a fat rat. Don't despair. Some rats are just genetically prone to being fat and there is nothing you can do. As long as you're giving your rats exercise, a healthy core diet, and few treats, your doing things right.