Over the past few years, two major areas of misinformation about nutrition have been gradually clearing up in the public mind and people don’t look at me like I’m crazy when I give talks about these subjects. Most people are now aware that “good” fats (oils, mayo, nuts) are actually good for you and are aware that we need some sun exposure to make vitamin D.
There is another urgent topic that will probably make it into the media and into our doctors' attention in a few years, and that is our need for animal products to get vitamin B12. We can get protein and iron from beans, but vitamin B12 is found reliably only in animal products such as meats, eggs and milk. Vegan sources such as tempeh and seaweeds can’t be counted on for B12. If you don’t get enough you’ll be okay for a few years, but then your nerves will start dying, and your legs, arms, and brain won’t work very well.
I found a great source for information on this topic on the VeganHealth.org website. This is written by Jack Norris, a Registered Dietician, President of Vegan Outreach, and apparently a thoughtful reader of the scientific literature. If you are a vegan, take supplements or eat fortified foods.