Actually, I think it would be fine to do this program, with some modifications.
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This program, and I emphasize program (not diet - as diets don't work), can be a healthy lifestyle change for anybody.
Its really about deciding to make a change and eating healthfully. If your choice is to use Medifast meal replacements to help you, then go for it.
I would suggest, however, as Alpha was alluding to, that you not follow the 5 & 1 as your wife may be doing. You may want to do a modified maintenance style program that includes 3 medifast replacements and 2 lean and greens.
Kudos to you for wanting to support your wife.