Nectarines are luscious and juicy fruit that have a smooth skin. It is very similar to a peach, in fact they are the same species, even though they are regarded commercially as different fruits.
We absoulutely love nectarines and when in season, love to have them in our house fruit bowl.
So if we can eat them, can guinea pigs eat nectarines, and if they can how much can they eat?
Lets take a look at their nutritional data, in particular at their calcium, phosphourus, acidic, sugar, and fat content.

Energyt165 kJ (39 kcal)
Carbohydratest9.54 g
– Sugarst8.39 g
– Dietary fibert1.5 g
Fatt0.25 g
Proteint0.91 g
Vitamin A equiv.t16 μg (2%)
– beta-carotenet162 μg (2%)
Thiamine (vit. B1)t0.024 mg (2%)
Riboflavin (vit. B2)t0.031 mg (3%)
Niacin (vit. B3)t0.806 mg (5%)
Pantothenic acid (B5)t0.153 mg (3%)
Vitamin B6t0.025 mg (2%)
Folate (vit. B9)t4 μg (1%)
Cholinet6.1 mg (1%)
Vitamin Ct6.6 mg (8%)
Vitamin Et0.73 mg (5%)
Vitamin Kt2.6 μg (2%)
Calciumt6 mg (1%)
Iront0.25 mg (2%)
Magnesiumt9 mg (3%)
Manganeset0.061 mg (3%)
Phosphorust20 mg (3%)
Potassiumt190 mg (4%)
Sodiumt0 mg (0%)
Zinct0.17 mg (2%)
Fluoridet4 µg
(source: Wikipedia)
As you can see nectarines contain a small amouont of phosphorus, a hint of calcium and fat, they are quite acidic and are quite sweet.
Based on this information, guinea pigs can eat nectarines, but only only once or twice a week in small amounts.
However, do cut it up and throw away the stone. They can also eat the skin which is lovely and soft.