The Walnut is the nut of the the walnut tree in the genus Juglans. It is a food that is used after it is processed whilst it is green for pickled walnuts or after it is fully ripened for nutmeat.

They are rounded, single-seeded stone fruits. After they are fully ripened, removing the husk unearths a wrinkly walnut shell which is usually found in two segments. When they are ripening, the husk becomes brittle and the shell hardens and encloses the meat or the kernel which is made up of two halves separated by a partition.

There are two types of walnuts that are grown for their seeds which are the Persian or English Walnut and the Black Walnut. They are used in all kinds of culinary dishes around the world or just eaten as a snack.

So can guinea pigs eat walnuts at all?

Lets take a look here and their nutritional data, in particular their acidic, phosphorus, calcium, sugar, and fat content is of particular interest as far as guinea pigs are concerned.

Energy 2,738 kJ (654 kcal)
Carbohydrates
13.71
Starch 0.06
Sugars
lactose 2.61
0
Dietary fiber 6.7
Fat 65.21
Saturated 6.126
Monounsaturated 8.933
Polyunsaturated 47.174
Protein 15.23
Vitamins
Vitamin A equiv.
beta-carotene
lutein zeaxanthin
(0%) 1 μg
(0%) 12 μg
9 μg
Vitamin A 20 IU
Thiamine (B1) (30%) 0.341 mg
Riboflavin (B2) (13%) 0.15 mg
Niacin (B3) (8%) 1.125 mg
Pantothenic acid (B5)
(11%) 0.570 mg
Vitamin B6 (41%) 0.537 mg
Folate (B9) (25%) 98 μg
Vitamin B12 (0%) 0 μg
Vitamin C (2%) 1.3 mg
Vitamin D (0%) 0 μg
Vitamin D (0%) 0 IU
Vitamin E (5%) 0.7 mg
Vitamin K (3%) 2.7 μg
Trace metals
Calcium (10%) 98 mg
Iron (22%) 2.91 mg
Magnesium (45%) 158 mg
Manganese (163%) 3.414 mg
Phosphorus (49%) 346 mg
Potassium (9%) 441 mg
Sodium (0%) 2 mg
Zinc (33%) 3.09 mg
Other constituents
Water 4.07
Alcohol (ethanol)
0
Caffeine 0
source wikipedia

As you can see, walnuts contain a huge amount of phosphorus, acidic content, and fat and a lot of calcium.

This means that guinea pigs cannot eat walnuts at all. They are just too bad for their tummies and will make them ill if they are eaten. They just cannot handle their acidic and fatty content.

So as a food for guinea pigs, they are best avoided.

Image “3 walnuts” by J.Dncsn – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons – https://commons.wikimedia.org/wiki/File:3_walnuts.jpg#/media/File:3_walnuts.jpg