Please keep in mind that humans have spread to all parts of the globe over thousands of years because we are capable of getting nutrition from a wide variety of foods. Before the days of airplanes and trucks, people ate what was available to them. People on the coasts ate fish. People who lived far from water ate whatever meats they could catch. People who earned to recognize nutritious foods from poisonous ones ate local vegetation.
As for the list of foods that your friend said to avoid, please point your friend to an atlas, where she might contemplate the wide varieties of diets in the various parts of the world.
The peoples in South America have thrived on corn for thousands of years. They learned to use lime to release its vitamin B1 and other nutrients, but they obviously have no difficulty digesting it.
Some populations of people around the world have lost the ability to digest animal milk as adults, but others do just fine. Certain groups of nomads travel with dairy animals and get a large portion of their nutrition from it.
Eggs are an important part of the diet of lots of people around the world. If you are poor, then you can get a lot more use from one chicken by feeding it a bit of cheap food for a few years, enjoying its eggs, then slaughtering it for dinner when it gets too old to make eggs anymore.
Beans are a fine food for supplying protein. There are millions of people around the world who have thrived for many generations by eating a vegetarian diet.
The peoples in the frozen northern parts of North America eat almost no vegetables. They eat the fish and animals that they catch.
Im sure that you can come up with lots more examples. There are lots of foods that are nutritious for humans. Nowadays in the western world we are blessed with so many options that we have a choice about what kind of diet we choose to eat. Then we declare that our choices are the "right" ones for everybody. We can declare this on religious grounds or "ancient humans ate XXX foods" or Dr. Atkins says such-and-such or whatever. But all of this is silly logic (because humans all over the world eat healthy on a wide range of diets) and dangerous as well (because it is too easy to wave your magic wand and declare that a specific diet is the best without knowing anything about your particular body's needs).
My personal view on one reason why many people in the western world get Type 2 Diabetes is that we have diets that are far removed from the simple unrefined foods
of our ancestors. Our diets are too filled with white flour and modified corn sugars and a long list of processed foods which our bodies are struggling to get nutrition from.
I'll step down from my soap box now.