Doesn't seem that farfetched. I mean there are well known genetic conditions which cause you to become mentally retarded, if not death, if you eat certain foods (eg PKU). Then there's protective genetic conditions like gilbert's syndrome, mutations which give lactose tolerance for life, hereditary haemochromatosis...

It should be obvious by now that subtle genetic differences can hold a huge influence in regards to what a "healthy" diet for someone is. IMO, there isn't enough research being done on such matters.