I fear this might cause some controversy because it contradicts some of our long-held assumptions/beliefs (the world is not flat?), but I've been questioning some of our "givens" (questioning minds never stop) and did some research in the USDA and other databases regarding a couple of nutrition issues. I found no where that the oxalates in spinach or any other food blocks the absortion of the calcium contained in any other food. I also tried to confirm that animals (humans included) have been known to get vitamin A toxicosis from vegetables and found nothing. To confirm or refute my findings, I emailed a Phd in nutrition. Below is our exchange:

My inquiry:

I rehabilitate squirrels, and certain issues about their diets have come up. My questions are

1) Do the oxalates in spinach block calcium absorption from any other foods or only the calcium in the spinach itself?
2) Can an animal (human even) get Vitamin A toxicosis from eating vegetables high in vitamin A? I read about some mountain climbers getting vitamin A toxicosis from eating a diet consisting primarily of bear liver (of all things), but veggies?

Her response (my bold):

Oxalates reduce the absorption of the minerals in the food itself (calcium and iron primarily) because they chemically bind the mineral in the food so it’s not absorbed. Other food sources without oxalates will not be affected.

The active form of Vitamin A is found in animal products like liver… polar bear liver has the most but regular old beef liver has 6580 micrograms/3 oz and upper tolerable level (to avoid toxicity) is 3000. The RDA for humans is 700-900. The plant version is a precursor form of Beta Carotene. There is no possibility of toxicity with plant sources because the liver will not convert it fast enough to be toxic and the excess carotene is stored in the fat cells under the skin and causes the skin to become “orangy”.