Dr. Yevgeny Belousov, a gastroenterologist, stated that the oxalic acid found in spinach may aggravate existing kidney diseases, and that plant proteins may cause allergies.
Dr. Belousov warned that the oxalic acid in spinach may bind to calcium in the body, forming insoluble calcium oxalate crystals, which form the basis of most kidney stones.
Dr. Belousov said: "People with urinary tract stones, hyperoxaluria, and other kidney diseases should limit their consumption of spinach or eat it only cooked, as cooking reduces the oxalic acid content by between 30 and 87 percent."
He also warned of the risk of developing a spinach allergy, especially in people with hypersensitivity to plant proteins, which may manifest as itching, swelling and nausea, although rare.
Despite the warnings, spinach remains a healthy food for most people, as it is one of the best sources of lutein and zeaxanthin , two types of carotenoids that accumulate in the retina and help protect it from ultraviolet rays, and may reduce the risk of developing cataracts and age-related macular degeneration, which are common causes of vision loss in older adults.
Each 100 grams of spinach also contains approximately 2.2 grams of dietary fiber , which helps maintain normal bowel function, prevents constipation, and promotes beneficial gut bacteria. Fiber also slows glucose absorption, which is beneficial for people with insulin resistance or type 2 diabetes.
