Here's the most important thing you'll read about guinea pig care: guinea pigs, like humans, cannot synthesize their own vitamin C. Every other pet — dogs, cats, rabbits — makes its own. A guinea pig that doesn't get enough vitamin C develops scurvy, which shows up as limping, swollen joints, poor appetite, and bleeding gums. And it happens faster than you'd think, often within 3-4 weeks of a deficient diet.
So the question "what can my guinea pig eat?" isn't just about variety — it's about survival. Get the diet right and your piggy can live 6-8 years. Get it wrong and you're looking at avoidable vet bills and heartbreak. This guide covers the daily staples, the safe vegetables, the absolute no-gos, and how much of everything to actually feed.
The 80/10/10 Rule of Guinea Pig Diet
Think of the diet in three layers, by volume:
80% hay. Unlimited, always-available timothy or orchard grass hay for adults (alfalfa is too rich for adults — it's for babies and pregnant sows). Hay grinds down their continuously growing teeth and keeps the gut moving. A guinea pig should eat a pile of hay roughly the size of its own body every day.
10% fresh vegetables. About one cup of fresh veggies per pig per day, split across two feedings. This is where most of the vitamin C should come from.
10% pellets. A high-quality, timothy-based pellet — about 1/8 cup per pig per day. That's roughly one to two tablespoons. Not more.
The Daily Vitamin C Requirement
An adult guinea pig needs about 10-30 mg of vitamin C per day (more for pregnant or young pigs). Since they can't store it, they need it every single day — no skipping.
Good daily sources: bell peppers (especially red — one slice covers most of the day's need), kale, parsley, broccoli. Bad sources: oranges and citrus in large amounts (too acidic, and the sugar content is high). A tiny wedge of orange once in a while is okay, but it shouldn't be a daily staple.
Pellets fortified with vitamin C lose potency within about 90 days of manufacturing, so check the date on the bag and buy fresh. If you're unsure whether your piggy is getting enough, we've reviewed the best vitamin C supplements for guinea pigs — or grab a vet-recommended vitamin C drop for a direct solution — drops, tablets, and treat-based options.
The Safe Vegetables List (Daily Rotation)
Rotate these so your pig gets variety and doesn't get bored — or worse, picky:
Daily staples: romaine lettuce (not iceberg — it's mostly water and nearly nutrient-free), bell peppers (any color), cilantro, cucumber (small amounts).
2-3 times a week: kale, parsley, broccoli, zucchini, carrot tops (not the carrot itself — too sugary), celery, green beans, cherry tomatoes.
Occasional treats: a slice of apple or pear (seedless), a blueberry or two, a small strawberry, a baby carrot. Treats are for bonding, not nutrition — keep them to a thumbnail-sized piece.
Foods That Will Hurt Your Guinea Pig
This list is non-negotiable. Some of these are toxic; others just cause problems. Either way, don't feed them:
Never: chocolate, caffeine, avocado, onion, garlic, leeks, chives, potato (especially green parts and sprouts), rhubarb, iceberg lettuce as a staple, bread, pasta, crackers, cereal, seeds, nuts, beans, corn (even "guinea pig corn treats" sold in pet stores are bad — corn kernels are a choking hazard and nutritionally empty), dairy, meat, sugar, salty snacks, anything moldy.
Careful with: high-sugar fruit (banana, grapes — tiny amounts only), cabbage and broccoli-family veggies in excess (gas and bloating — guinea pigs can't burp, so gas is genuinely dangerous for them), and anything from the nightshade family other than ripe tomatoes and peppers.
The House Rabbit Society (which covers guinea pig nutrition too) emphasizes that a sudden change to a new vegetable can cause digestive upset — introduce new foods one at a time, in small amounts, and watch for soft stool.
What About Pellets — and Which Ones?
Not all pellets are created equal. Avoid the muesli-style mixes with colorful bits, seeds, and dried fruit — guinea pigs will pick out the sugary pieces and leave the nutrition. You want a plain, uniform, timothy-hay-based pellet with no seeds, no nuts, and no added sugar.
Look for: timothy hay as the first ingredient, 15-18% crude fiber, and stabilized vitamin C. A good plain pellet is the boring-looking one — and boring is exactly what you want. For more on choosing the right food, our guide to the best guinea pig food, and a plain timothy pellet like this one is the boring-but-right choice breaks down the top pellet brands by ingredient quality.
Water: The Forgotten Fourth Layer
Fresh water must be available 24/7 — ideally from a bottle (bowls get tipped and soiled). Change it daily, and clean the bottle nozzle weekly because it grows biofilm. Guinea pigs drink more than you'd expect: roughly 100 ml per kg of body weight daily, so a 1 kg pig drinks about a cup of water a day.
If your pig suddenly stops drinking, that's an emergency red flag — it usually signals dental disease or illness, and guinea pigs hide illness until it's severe.
How Much to Feed: A Daily Schedule
Here's a concrete daily routine that works:
Morning: top up hay, fresh water, 1/2 cup veggies (include a vitamin C source), 1 tablespoon of pellets.
Evening: fresh water, another 1/2 cup of veggies (different ones than morning), check hay supply.
Weekly: weigh your pig. A stable adult weight is the single best health indicator — sudden weight loss is usually the first sign of illness.
Baby, Senior, and Pregnant Guinea Pigs
Babies under 6 months and pregnant sows need alfalfa hay (calcium-rich) mixed with timothy, and more pellets. Seniors often need softer veggies and may need vitamin C supplements more aggressively. Pregnant sows need almost double the vitamin C — talk to your vet about a supplement schedule.
FAQ: Guinea Pig Diet Questions
Can guinea pigs eat carrots? Yes, but sparingly — they're high in sugar. A baby carrot a couple times a week is fine; carrot tops are better and can be daily.
Can guinea pigs eat tomatoes? Ripe tomatoes, yes — a small cherry tomato 2-3 times a week. Never feed green tomatoes or the plant itself (toxic).
Can guinea pigs eat bananas? Occasionally, a thin slice — bananas are sugar bombs. Some pigs love them as treats; keep it rare.
Can guinea pigs eat apples? Yes, seedless, a small slice occasionally. The seeds contain trace cyanide — always remove them.
How long can a guinea pig go without food? Never let it happen. Guinea pigs can't go more than about 12 hours without eating — they develop GI stasis, which is often fatal. If your pig stops eating for even a few hours, that's a vet emergency.
Is hay really that important? It's the most important thing in the cage. Hay keeps teeth worn down and digestion moving. A guinea pig without unlimited hay will develop painful dental disease and gut problems.
The Bottom Line
Unlimited timothy hay, one cup of rotating veggies (with a daily vitamin C source), and a tablespoon of plain pellets. No seeds, no sugary treats, no dairy, no iceberg as a staple. Weigh your pig weekly, introduce new foods slowly, and treat "not eating" as an emergency. Get those basics right and your guinea pig will outlive most of the care myths floating around the internet — and stay healthier doing it.