My guinea pig's too fat how should I put it on a diet ?

Why do you think it is too fat ? Pigs vary in size and are supposed to be a nice chunky handful - they can be anywhere between 2lb and even over 3.5lb when fully grown and of varying levels of daintyness and chunkiness ! Personally, I would be more concerned if my guinea pig was underweight than overweight as when they are poorly they drop weight so quickly, a little extra won't hurt - it is really only if they are obesely fat that I would worry about health implications - and then I would want a vet to tell me that it had got to that stage rather than me taking the matter in to my own hands !

One of the first things I think of when asked this question is whether the pig is female and whether it has had access to a male, either in it's home, or if it is a new pig, at the petshop/previous home - if so then there is every possibility that she could be pregnant and that is why she is getting fat. A visit to a vet could confirm this.

If there is no possibility of pregnancy / or the pig is male then I'd still feel unsure about whether a pig really was overweight. Don't forget, males are often a little heftier than the females - this is normal so just because a male piggy of yours is bigger than a female piggy it doesn't mean he is overweight. However, if you have had it confirmed that your pig is officially overweight and needs to lose weight for the sake of it's health then the first thing I would do would be to increase her exercise - lots more floor-time, plus some new tunnels etc in the cage to stimulate activity - perhaps even get a bigger cage with plenty of room to move around - the C&C cages are a good option as you can build very large one's for a reasonable amount of money. Make sure you don't feed any sugary 'pet' treats or molassed feed mixes. What type of feed mix are you feeding ? Is it a mix which your pig is selectively feeding from - eating all the fattening elements and leaving the pellets ? Is it a high fat mix containing nuts [which you shouldn't be feeding as nuts can be considered a choking hazard as well as having a high fat content] ? You can discuss this with your vet but it might be an idea to very gradually switch your pig over to a nutritionally complete pelleted feed such as Oxbow Cavy Cuisine which is regarded as a very good Timothy hay based cavy pellet. Remember to always switch food gradually so as not to cause digestive problems. Do not feed more than a small piece of fruit a day to reduce her sugar intake for now. Keep feeding plenty of hay and veggies and a nice handful of dry mix a day, to cover the bottom of the bowl. Hopefully the extra exercise, the first course of action, will resolve any weight issues your pig may have within a few weeks without having to interfere with her diet.