Mushrooms are good for you! Adding four to five medium sized mushrooms (100 g) to your diet provides important vitamins and minerals, essential for a healthy body and active lifestyle.
Mushrooms are a source of:

B Complex Vitamins – Mushrooms are a good source of B vitamins such as niacin, riboflavin, and panotothenic acid. These B vitamins help to provide energy by breaking down proteins, fats, and carbohydrates. B vitamins also play an important role in the nervous system.

Minerals – Mushrooms are a source of important minerals such as selenium, copper, and potassium. Minerals are necessary for the proper function of the human body and play different roles from making healthy red blood cells to protecting body cells.

Fibre – Mushrooms contain both soluble fibre and insoluble fibre, which helps to maintain good bowel health.

Vitamin D – Vitamin D works with Calcium and Phosphorus to make strong bones. Mushrooms are the only source of vitamin D in the produce aisle and one of the few non-fortified food sources.

Mushrooms are low in:

Fat
Carbohydrates
Sodium
Cholesterol
Sugar

Some easy ways to add more mushrooms and nutrients into your diet:

Add ½ cup white button mushrooms to your omelet or scrambled eggs. Benefit: one 1 extra gram of fibre.
Mix 1 cup of diced portabella mushrooms into pasta or pasta sauce. Benefit: three 3 extra grams of fibre.
Include 1 ½ cups sliced crimini (brown) mushrooms in risotto or other rice dishes. Benefit: five 5 extra grams of fibre.

Source: Mushrooms Canada