I went on a week long fast in Thailand.

It's quite reasonable but the flights can cost a bit.

Then you can pretend it's a holiday, maybe have a week in a nice hotel after the fasting for a treat.

Most people lose a pound a day and keep the weight off for a year.

https://www.healthoasisresort.com/

Otherwise do keto.

And men can get in shape easier by working out than women so you should get him lifting and doing small amounts of hitt (if you do sensible "moderate" exercise you just tend to eat more). Make it a competition somehow. https://thesixpackrevolution.com/transformations/