Guava is a fruit that measures between 4 to 12 cm long and are round or oval in shape.
They come from Mexico, Central America, and northern South America. However they are now cultivated and naturalized throughout the tropics and subtropics in Africa, South Asia, Southeast Asia, the Caribbean, subtropical regions of North America, Hawaii, New Zealand, Australia and Spain.
They smell similar to lemons but are not as sharp as them.

They have a rough skin and its flesh has a taste which varies in taste depending on the species. This taste can vary from bitter to soft and sweet.
They are often eaten raw, cut into quarters or indeed eaten whole.
So if we can eat guava, then can guinea pigs eat guava, and if they can how much of it can they eat?
Lets take a look at their nutritional data to get under the skin of guavas and get to know them a little better.
As per usual, we’ll take a look at their calcium, acidic, sugar, phosphorus, and fat content which is most pertinent as far as guinea pigs are concerned.
Energyt285 kJ (68 kcal)
Carbohydratest14.32 g
– Sugarst8.92 g
– Dietary fibert5.4 g
Fatt0.95 g
Proteint2.55 g
Vitamin A equiv.t31 μg (4%)
– beta-carotenet374 μg (3%)
Thiamine (vit. B1)t0.067 mg (6%)
Riboflavin (vit. B2)t0.04 mg (3%)
Niacin (vit. B3)t1.084 mg (7%)
Pantothenic acid (B5)t0.451 mg (9%)
Vitamin B6t0.11 mg (8%)
Folate (vit. B9)t49 μg (12%)
Cholinet7.6 mg (2%)
Vitamin Ct228.3 mg (275%)
Vitamin Kt2.2 μg (2%)
Calciumt18 mg (2%)
Iront0.26 mg (2%)
Magnesiumt22 mg (6%)
Manganeset0.15 mg (7%)
Phosphorust40 mg (6%)
Potassiumt417 mg (9%)
Sodiumt2 mg (0%)
Zinct0.23 mg (2%)
Lycopenet5204 µg
(source: Wikipedia)
As you can see guavas contain some phosphorus and sugar, a hint of calcium and fat, but are a quite acidic.
However, their vitamin c content is absolutely huge which is very good news for guinea pigs.
So guava is a very good food for guinea pigs and a great addition to their diet. However, they can only be eaten one to two times a week due to their phosphorus, sugar and acidic content.