Here is a cool interactive tool where you can explore how diets (both worldwide and by specific country) have changed in the past few decades.
Here is an article summarizing the overall worldwide trend, best summarized in this quote:
"The increase in homogeneity [of diets] worldwide portends the establishment of a global standard food supply, which is relatively species-rich in regard to measured crops at the national level, but species-poor globally". Incidentally, according to the first link, this "global standard food supply" would look much like the average diet in Colombia, which is pretty diverse, consisting in a wide range of tubers, fruits, vegetables, and grains, in accordance with its wide range of climatic zones.
Let me translate the above quote into layman's terms. Imagine if the world consisted in 100 people, each of whom ate only one crop (species or variety) not eaten by any others. In total, there would be 100 crops eaten in the world, presumably each uniquely suited to the specific ecology where it grew, and each crop giving rise to a human cuisine and culture distinct from any other. Over time, let's say that ten of those crops came to predominate, such that by the end of a transition phase, each of the 100 people in the world would eat the same diet consisting in 10 crops. For each individual, their diet has become more diverse, which is a good thing. But for the world as a whole, the diversity of human culture, crops, and ecological adaptation will have decreased drastically, with 90% of crop varieties going extinct.
So the news is mixed. Most people in the world are now eating a more diversified (read healthier) diet than they used to, but we are losing biodiversity, and diversity of cuisine and culture, which is bad.