Guinea pigs may be herbivores, but that doesn’t mean they can eat everything. Unfortunately, many foods cause your guinea pigs distress. You should never feed these things to your guinea pigs, though it’s not an exhaustive list.
For details on specific vegetables, check out this other post.
Grass clippings may seem like a tasty guinea pig snack, and you have a lot of them over summer. However, you have no way to know what’s on the grass clippings. It could be pesticides, insects, or even the exhaust from your mower. That’s why it’s one of the things you should never feed guinea pigs.
Potatoes developed a toxin to prevent most critters from eating them. Humans handle this through the cooking process. Guinea pigs do not have that option, so never feed your guinea pigs any form of potato.
All guinea pigs should be fed vegan foods. Their digestive system simply did not develop the gastrointestinal tract for animal products. If you give them animal products, the best-case scenario is that your guinea pig is uncomfortable. More likely, your guinea pig will experience distress, require a veterinarian, or even die.
Cooked and Processed Human Food
Again, guinea pigs simply do not have the digestive tract for cooked and processed. That means you should never feed guinea pigs these things, regardless of how tasty you think they are.
Garlic, shallots, and anything else with a bulb is dangerous for guinea pigs. Everything in that family is poisonous. Even if your guinea pig survives, they will have lifelong complications relating to their blood.
Guinea pigs did not evolve in a location with access to evergreens. Therefore, their digestive tract did not develop to handle it. Any evergreen from shrubs to trees is poisonous to your guinea pigs, so never feed it to them.
Guinea pigs are small, and micro-chemical traces affect them. That includes pesticides, which are incredibly dangerous for your guinea pigs. They just don’t have the body mass to mitigate even a small amount, and it has consequences.
Pretty much anything that might give a guinea pig gas is a risk to feed them. That includes beans and cruciferous vegetables like broccoli. While some guinea pigs can handle small quantities, it’s best never to feed these items to guinea pigs. It’s simply a risk you do not need to take since there are so many things guinea pigs can have without issue.