If you have ever kept guinea pigs, then you will know that all they seem to do is eat and sleep. They may play for a few minutes in between, but basically their life is all about eating, and then eating some more. Considering that they are so small, it is difficult for some people to understand why they have to eat so much, but the explanation is simple.
They have a high metabolism, and so burn energy quickly. They process food through the digestive tract quickly, usually it takes around 20 hours from mouth to bottom. Most of what they eat is fiber, and so has no health benefits at all, apart from keeping their digestive system working.
A guinea pig must have food constantly passing through it. If a guinea pig struggles to eat, then their digestive system will slow down, and can result in gastric stasis. When this happens, the guinea pig’s life is on the line. This is why ill guinea pigs need to see a vet quickly, and be syringe fed if they are not eating, so that digestion continues.
So, can a guinea pig eat too much food? The answer is no. It may appear to us humans that they must have a huge stomach, but food passes quickly into the lower intestine, usually in 1-2 hours. For their size though, they do actually have a large stomach. One thing that they do have in common with humans is that they get the same sensation of fullness as we do, and that prevents them from overeating.
So a guinea pig can be put in the garden, and graze on the grass until it is full, and this may take a while. It will then sleep for 1-2 hours, wake up, and then start eating again. It is a hard life for guinea pigs, all that eating and sleeping. It is a good job they do not have to go out to work, as they would not have the time!