Your husband should be able to safely juice fast up to ten days unsupervised for cleansing purposes. Any weight he loses will be quickly regained when he resumes eating.
Of course he could try a shorter (3 day, 5 day) cleanse to see how it works for him, and any weight loss will be negligible.
If he is pretty toxic I highly recommend he eat a cleansing diet for a few days to a week prior to beginning the fast to avoid those traditional first week detox crises! I ate this way for 30 days before a 60 day cleansing fast, and was glad I did:
Fresh fruit and natural yogurt smoothie
Raw veggie salad dressed with good oil and lemon juice
Homemade vegetarian vegetable soup
All the fresh juices you like, fruits am, veggies pm
Drink LOTS of pure water! If you drink caffeine, DO NOT STOP! TAPER OFF over about 3 days. I have broken this rule and suffered -- there is nothing like a caffeine headache!
Plan to do a colon cleansing routine every fasting day. I have posted this information many times on this forum, you should be able to google it.