This thread has been derailed pretty hard on the whole diet subject so I thought WTH.
The healthiest diet for each person has a lot to do with their personal genome and what part of the world their ancestors evolved in. The suggestion that people eat a lot of omega-3 fatty acids was based on a study done of the Inuit people who had evolved to derive as much nutrition from their particular
diet as possible. Based on this, nutritionists were suggesting everyone get lots of fish oil in their diets. But not everyone's body processes it the same way.
A similar thing occurs with milk. People who can digest lactose in adulthood get more nutrition from dairy than people who are lactose intolerant. It's actually very healthy for someone with lactase persistence to consume lots of dairy but not so much for other people.
This
article sums it up pretty nicely: "We will be better adapted to something eaten by our ancestors over millions of years than to, say, margarine, which we first encountered only 100 years ago. Or take a food like wheat, to which some populations (those in the Fertile Crescent) have been exposed for 10,000 years, and others (Pacific Islanders) for only 200 years. Is it surprising that Pacific Islanders have the greatest prevalence of obesity in the world (higher even than in the United States)? And should we really tell them to switch to a Mediterranean diet, heavy on grains, pulses, and dairy, to which they've had no evolutionary exposure whatsoever?"