The best food for guinea pigs is unlimited timothy hay, which should make up 85 to 90 percent of their diet. The rest comes from one cup of fresh vegetables and one tablespoon of fortified pellets per day. Getting this balance right keeps their teeth worn down, their digestion running smoothly, and their vitamin C levels where they need to be.
Why Hay Is the Foundation
Guinea pigs need constant access to hay, and timothy hay is the gold standard for adults. It contains 32 to 34 percent crude fiber, 8 to 11 percent protein, and moderate calcium at 0.4 to 0.6 percent. That fiber content is critical for two reasons: it keeps the gut moving (guinea pigs have a fermentation-based digestive system that stalls without it), and it grinds down teeth that never stop growing.
Guinea pig teeth are “hypselodont,” meaning they grow continuously throughout life. The tiny abrasive particles embedded in hay, called phytoliths, wear down the tooth surface as your guinea pig chews. Without enough of this long-strand fiber, the molars overgrow and misalign, leading to painful dental problems that often require veterinary intervention. You simply cannot replicate this effect with pellets or vegetables.
Unlike pellets, you can’t overfeed hay. Keep a generous pile available at all times and refresh it daily. Orchard grass (34 percent fiber, 10 percent protein) and meadow hay (33 percent fiber, 7 percent protein) are good alternatives if your guinea pig is picky, and rotating between types can keep them interested.
Alfalfa Hay: Only for Young or Pregnant Pigs
Alfalfa hay has 13 to 19 percent protein and 1.2 to 1.4 percent calcium, roughly double or triple the calcium in timothy hay. That extra nutrition helps growing babies and nursing mothers, but it’s too rich for healthy adults. The high calcium content contributes to bladder stone formation, one of the most common urinary problems in pet guinea pigs. Most bladder stones in guinea pigs are made of calcium carbonate, so keeping dietary calcium in check matters. Switch from alfalfa to timothy hay once your guinea pig reaches about six months of age.
Fresh Vegetables: One Cup Per Day
Your guinea pig needs at least one cup of fresh vegetables daily, and the centerpiece should be bell pepper. An eighth of a bell pepper (any color, though red has the most vitamin C) gives a significant boost toward their daily nutritional needs. Pair it with a rotating selection of leafy greens.
Vegetables safe to feed every day include cilantro, tomatoes (ripe red ones, not green), and zucchini with the skin on. These are low enough in calcium and oxalates that they won’t cause problems with regular feeding.
Other popular vegetables should be limited to one or two servings per week at most:
- Kale and spinach: nutrient-dense but high in calcium and oxalates
- Broccoli and cauliflower: can cause gas and bloating in large amounts
- Collard greens and turnip greens: high calcium content
- Brussels sprouts: another gas producer
- Basil, dill, and watercress: fine as occasional additions
Variety matters. Rotating through different vegetables prevents any single mineral from building up to harmful levels while giving your guinea pig a broader nutrient profile. Wash everything thoroughly before serving.
Vitamin C Is Non-Negotiable
Guinea pigs, like humans, cannot manufacture their own vitamin C. A healthy adult needs 20 to 25 milligrams per day, and pregnant guinea pigs need 30 to 40 milligrams. Without enough, they develop scurvy: rough coat, swollen joints, reluctance to move, and eventually serious illness.
Bell peppers are the single best vegetable source of vitamin C for guinea pigs. A daily slice, combined with other vitamin C-containing vegetables and fortified pellets, usually covers the requirement. If your guinea pig is recovering from illness or seems run down, you can supplement with a vitamin C tablet designed for guinea pigs. Avoid adding vitamin C to the water bottle, though. It degrades within hours of contact with water and light, so your pig may get very little of it, and it can change the taste enough that they drink less.
Choosing the Right Pellets
Pellets play a supporting role: one level tablespoon per guinea pig per day. They’re a convenient way to deliver stabilized vitamin C and fill any nutritional gaps, but overfeeding them leads to obesity and reduces how much hay your pig eats.
Look for plain, timothy-based pellets specifically formulated for guinea pigs with added vitamin C. Check the ingredient list carefully and avoid pellets containing corn products, seeds, nuts, beet pulp, rice bran, or animal-derived ingredients. Skip anything with colorful bits, dried fruit pieces, or food dyes. Those “gourmet” mixes with seeds and yogurt drops are essentially junk food. Freshness matters too, since vitamin C degrades on the shelf. Buy in smaller quantities and check the manufacturing or expiration date.
If you have guinea pigs under six months old, alfalfa-based pellets provide the extra protein and calcium they need for growth. Transition to timothy-based pellets as they mature.
Fruit: A Treat, Not a Staple
Fruit is high in sugar and should be offered in small amounts, no more than a few times per week. Think of it as a treat for bonding and enrichment, not a dietary staple. Guinea pigs are prone to obesity and can develop diabetes-like metabolic issues when sugar intake is too high.
Particularly sugary fruits to limit carefully include banana, mango, figs, pineapple, grapes, and melon. Moderately sugary options like strawberries, blueberries, and small apple slices (seeds removed) are fine in thumbnail-sized portions a couple of times per week. One or two cherry tomatoes per day are an exception, since they’re low enough in sugar and high enough in vitamin C to count more as a vegetable in practical terms.
Water Needs
Each guinea pig drinks 80 to 100 milliliters of water per day, roughly a third of a cup. Always provide fresh water in a clean bottle or heavy bowl, changed daily. Guinea pigs that eat lots of fresh vegetables may drink slightly less, but water should always be available. If you notice a guinea pig drinking significantly more or less than usual, that can signal a health issue worth paying attention to.
Foods That Are Dangerous or Toxic
Some common household foods are genuinely toxic to guinea pigs. Avocado contains a compound called persin that can be fatal. Chocolate and caffeine are poisonous. Onions, garlic, and chives can cause a life-threatening form of anemia. Rhubarb damages the kidneys.
Less obvious dangers include apple seeds, peach pits, and cherry pits, all of which release cyanide when chewed. Raw beans contain compounds that damage the gut lining. Potato leaves, tomato leaves, and unripe green tomatoes belong to the nightshade family and cause neurological and digestive problems. Nuts of any kind are too high in fat and can trigger digestive shutdown. Dairy products cause severe gastrointestinal distress since guinea pigs are completely lactose intolerant. Iceberg lettuce has almost no nutritional value and commonly causes diarrhea.
Also keep guinea pigs away from ornamental flowers like lilies, daffodils, and oleander, many of which contain compounds toxic to the heart or liver. Wild mushrooms and unwashed foraged greens carry additional risks from pesticides and natural toxins.
Putting It All Together
A good daily feeding routine looks like this: unlimited timothy hay available at all times, refreshed morning and evening. One cup of mixed fresh vegetables (always including bell pepper) split into one or two servings. One tablespoon of plain, timothy-based, vitamin C-fortified pellets. Fresh water changed daily. Fruit two or three times a week in small pieces as a treat.
The single most important thing you can do for your guinea pig’s diet is make sure they’re eating plenty of hay. If your pig turns up their nose at hay but devours pellets, reduce the pellet portion slightly to encourage more hay consumption. A guinea pig that eats mostly hay, with vegetables for vitamin C and variety, is set up for a healthy digestive system, good dental wear, and a longer life.