Eat well while you’re young, and you’ll set up healthy habits for life – a good idea in theory, though trickier in the offing.

While the mainstays of a good diet apply no matter your age – everything in moderation, eating whole foods wherever possible and choosing from a wide range of ingredients – certain decades of life and the changes they bring, be they hormonal or lifestyle-based, can require us to sharpen our focus on particular areas...