Using processed foods, or for that matter, fast foods too, are a personal choice. Many choose to avoid nitrates, artifical sweeteners and preservatives, soybean oil, etc for health reasons, but they are not prohibited on Atkins (or they could never sell their bars or frozen meals).

Not everyone experiences the "Atkins Flu", here is a description and tips to avoid it: http://www.atkins.com/Program/Phase...AT-BURNING.aspx