I read it in a German sociology magazine. The two countries compared where Germany and France (because with this issue, you could never compare Scotland with Turkey or somewhere like that, because of the different climate, but in this study the two countries had similar climate).
Basically, the Germans introduce food generally at six months, and only like one per week, and mostly pureed foods. Potato, carrot, apple, pear, beef, pasta, tomatoes and chicken is as adventurous as we go. no spice, low salt, low sugar. Tastes all the same, really
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The French introduce at four months, they let their babies nibble on chicory, duck, rooster in red whine sauce, garlic soup, asparagus, etc.
And the incidents of allergy, asthma and eczema in France are WAY lower than in Germany. Also, the kids are not as picky, and not as overweight or unhealthy, life expectancy is higher, too.