Hello waterbug,
a series of shorter fasts can be used and has been used very successfully in not only losing weight, but also in resolving health issues, but the re-feeding periods in between need to be highly nutritious, and for at least an equal number of days as the fast itself, to replenish food reserves.
Once an ideal weight has been achieved, and also for the re-feeding period/s, a properly combined diet will ensure that any excess weight is avoided and an ideal weight is maintained thereafter.