When my weight hit 80kg and I was most definitely slap bang in the middle of the overweight band on a BMI diagram, it was time to do something about it. I had some while before flirted with the trendy 5:2 diet but struggled to stick with it. Recently I investigated the alternate fasting day diet, essentially an earlier incarnation of the far more well-known 5:2. Both diets ultimately originate from research into increased longevity as a result of calorie restriction and so that was the original motivation behind it all rather than weight loss per se.
Never one to read just one book on a subject, I bought both The Every Other Day Diet by Krista Varady and this one by James Johnson. Both books have their differences. Varady doesn't really go into the underlying science in depth, in contrast to Johnson. Varady asserts that the 25% of calories on the fasting day optimises weight loss by minimising muscle loss; Johnson by contrast says that total food abstinence on each fasting day would be optimal in maximising the effects of the SIRT1 gene, but the 25% is a concession to the fact that no-one would be able to stick to such a diet, and it still has a sufficient effect. Varady seems to make no concession to extra calories on a fast day if your are exercising, whilst Johnson allows increasing from 500 to 1000. Varady argues that the dieter should step on the scales every day, Johnson says once a week.
Personally I have not been calorie counting on the fasting days but just having one meal in the evening and trying to exercise a certain amount of portion control (and definitely no 'extras', e.g. wine). I think I have been finding this easier to maintain than 5:2 because of the establishment of a routine with every other day - with 5:2 you get back into normal eating for a few days then think "Oh God I've got to fast again" when the next fasting day comes around. Combined with my normal gym routine I have been losing around 1kg per week so far as expected.