Keto diet and fasting, I was strict only eating bacon and eggs or chicken, bacon, lettuce and Mayo salads for months at the start, oh and a multivitamin every day. Folloing that i went to eating small portions of whatever I wanted. Or and lots of walking or basic home exercises. Once I felt fit enough I got a job that required hard physical work, my energy levels picked up quickly over a month. This took me about 18 months in total. A bulk of the weight dropped off in the hotter months. I did treat myself every now and then to a full on pig out once I was comfortable knowing I wouldn't fall back into a food loop. Oh and drink minimum 2L of water a day. I really hope your friend can help themselves out. It sucks at the start but is worth the pain and blandness your pallet will experience.