This post is by Sheryl Canter, an online writer and editorial manager at Environmental Defense Fund.

Want to know how your lifestyle impacts the environment? Yahoo Green's Lifestyle Calculator (data provided by EDF) estimates your carbon footprint based on factors like the size of your home, and how much you drive and fly. The H₂O Conserve Water Use Calculator asks questions about your habits to assess your water usage (see why saving water saves energy)

But what about the food you eat? Bon Appétit Management Company has a new Low Carbon Diet Calculator that can tell you. It has a very entertaining interface, but how good is it? We asked Lisa Moore, Ph.D., a scientist at Environmental Defense Fund, to check it out.

Lisa found no glaring errors, but she noted two caveats:

• The calculator is specific to Bon Appétit's recipes, cooking
  processes, and supply chain.
• Most of the numbers are underestimates (for example, it doesn't include emissions from all recipe ingredients, and it omits nitrous oxide emissions from fertilizer use).

Still, the calculator can give you a sense of which foods have higher emissions than others. For example, it says that beef has higher emissions than pork, pork more than chicken, and chicken more than vegetables. This is the same order as our own analysis, but the magnitudes are different.

Bottom line: The calculator is good for comparisons, but not exact numbers.