I am not sure that this is true. Many countries in northern Europe such as Iceland, Sweden, and Norway eat quite healthy.

Using body mass index as a (arguably quite bad) proxy for a healthy diet we find [0] that many of the southern countries such as Spain, Greece and Portugal are more overweight than many countries farther north.

[0] http://apps.who.int/bmi/index.jsp

Sure, thats why I said generally. The UK and Germany don't have especially healthy diets in my opinion and have a lot more people than the Scandanavian countries that you mentioned.

Agreed. However, Germany is typically not regarded as a part of Northern Europe. Although that can be argued since there is no formal definition if Northern Europe.