Data from United Nations agencies such as the World Health Organization indicate at least 1.1 billion people get too few calories to ward off hunger and another 1.1 billion or more take in too many calories. The rest of humanity gets enough calories and enough exercise but lacks enough vitamins and minerals. People in this middle group are in the best place, but many of them are still far from optimal health.
Of 2.1 million Americans who died in 1987, a poor diet was associated with the cause of death in two-thirds of the cases. Diet is implicated in perhaps a third of cancers, particularly of the digestive organs.
Conventional dietary advice takes no account of individual differences. If you have good genes you can eat almost anything in moderation. The most risk is from diseases which your family have suffered from and these can be traced and specifically managed by "genetic nutrition".