Regarding the formal diet, you need to be on the exclusion diet for 8 weeks before attempting to reintroduce foods. This takes about one year to do properly. You will still experience unexplained flare ups. I would not suggest attempting the fodmap diet in the UK without speaking to a nutritionist first. You will need a go referral.
The AMT is the excess of the tentative minimum tax over the regular tax. Thus, the AMT is owed only if the tentative minimum tax is greater than the regular tax. The tentative minimum tax is figured separately from the regular tax. In general, compute the tentative minimum tax by:
Some deductions have a floor which is higher under AMT than under the regular tax system. For instance, the floor for medical expenses under the regular tax system for taxpayers at least 65 is 7.5%, but 10% under the AMT system. Furthermore, none of the elements of the AMT are indexed for inflation.