The health experts that US News & World Report consults really don't 
like our diet. Again it gets ranked last:

http://health.usnews.com/best-diet/best-overall-diets

Their summary of it:

Experts took issue with the diet on every measure. Regardless of the 
goal--weight loss, heart health, or finding a diet that's easy to 
follow--most experts concluded that it would be better for dieters to 
look elsewhere. "A true Paleo diet might be a great option: very 
lean, pure meats, lots of wild plants," said one expert--quickly 
adding, however, that duplicating such a regimen in modern times 
would be difficult.

More info: http://health.usnews.com/best-diet/paleo-diet