Mackerel, sardines and salmon often top the list of good-for-you foods, but what is it that makes oily fish so good for us? Health experts recommend two portions of fish a week and specifically advise that one of these should be an oily variety. Unfortunately, few of us are eating that much. Figures from the most recent National Diet and Nutrition Survey show that adults aged 19 to 64 manage, on average, just over a third of a portion of oily fish each week. Older adults eat more but still fail to get close to the recommended amounts. And teenagers are even more oily fish-averse. They eat just one portion every 10 weeks.