At a BBQ last weekend, a friend and fellow sushi-lover mentioned that sushi-grade tuna is basically a myth, one that regularly prompts me -- and many other suckers -- to spend top dollar for a cut of fish.

"It's meaningless," she told me. "I read about it in this great article about sushi in this month's Vanity Fair. You have to read it."

"I don't know," I hedged. "Those tell-all food articles really get under my skin. And I love sushi too much to let an article ruin it forever."

Okay, okay... ignorance is bliss until it wrecks your health. Considering that I eat sushi at least once a week, I decided to find out if I actually have anything serious to worry about -- even if it means risking the bliss that generally accompanies a spicy tuna roll.

As it turns out, the article, Letter from Tokyo written by Nick Tosches really is a fun trip through Tsukiji, Japan's largest fish market, the frenetic sushi business, and the story of how raw fish caught on in the United States.

While the article is as colorful, irresistible, and long as a rainbow roll, I am happy to report that it hasn't forever dissauded me from going to a sushi restaurant.

Still, I'm now aware of the various reasons that sushi probably isn't quite as healthy as I once believed. And I'm glad to know this, so that the next time I grab lunch at my local natural foods store, I can decide if I really want those premade sushi rolls -- or if I'd rather opt for the salad bar instead.

Here are some of the eye-opening things I learned:

• Tuna grade may be based on cat food grade, which is what blue fin tuna used to become in this country. That rich crimson color may be due to being gassed with carbon monoxide, which causes the fish to retain its healthy color.
• Sushi contains hidden sugar. It goes into sushi rice, pickled ginger, and it even goes into a thick, delicious sauce that causes us crave something as unpalatable as broiled eel.
• Wild wasabi -- reputed to be healthier and more intense than conventional wasabi -- is difficult to find in the U.S. The wasabi paste that's commonly served is often American horseradish, hot mustard, and a dash of green food coloring. Purists in search of real wasabi can start at Chow.com.
• Chances are that super-fresh mouthful of tuna is several days old, caught near Massachusetts, shipped to the Tokyo fish market, and then flown back to New York or other parts of the United States. And it's fresh taste? Chalk it up to the fact that it was instantly frozen and transported in something called -- ugh! -- a "tuna coffin."
  

For whatever reason, the article didn't go into the most obvious danger related to regular sushi consumption -- the high levels of mercury and PCBs that are often found in certain types fish.

To keep track of which fish are safe, check out the Monterey Bay Aquarium and Natural Resources Defense Council have comprehensive lists of which fish are safest.