One change in the American diet is the introduction of seed oils in the 20th century. The highest source of omega 6 fats are seed oils. The percentage of fat in people’s bodies that is omega 6 fats keeps increasing, so that change in diet is still having effects.
Many experiments found that omega 6 fats increase weight and cause cancer.
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Foods contain more vitamin a than we need.
Milk sellers threatened by the government add vitamin a to skim milk.
Wonder bread, floride in the water, vitamin D fortified whole milk, etc - a list much longer than any grocery list.