A question about today's foods and peoples health?!

It seems in recent decades there has been a big increase in mysterious illnesses like ibs, chronic fatigue syndrome, heart disease, sickness etc. Could it be that the food we eat today is full of ingredients that are not good for you? For thousands of years people ate natural foods, no chocolate bars, no fast food take aways etc. At one time milk would go sour in a few days, but now milk can last quite some time. What are they putting in these foods? Why don't animals get the same kind of sicknesses as humans? Could it be that animals eat more healthy? Let me give you an example...

Suppose someone has 2 bars of chocolate, five days a week, for work. 2 chocolate bars a day doesn't seem much, but that's 10 bars a week, 40 bars a month, 480 bars a year. Bad bacteria loves to feed on sweet foods. And then we have the fatty milk, all the dairy products, the fast foods etc. All these things combined together is just not good. For thousands of years people would not eat these kings of foods. Why is it that in recent decades ibs has incresed and many other mysteries illnesses? Do you believe it is food related?