It's been actually researched, that eating too much and for prolonged period of time (an average American is eating during an 18-hour window daily!) creates a traffic jam in mitochondria, and that means they literally incapable of making energy. On top of that, eating junk food greatly affects your microbiome. The bacteria in your gut lives off the food you consume, so by making the wrong nutrition choices, you're not only causing the good bateria to die off, but also contribute to the growth of the bad agents.

Out gut talks straight to our brains, and even to our other organs. That's why it's called our second brain (some scientists claim that soon it'll become to be known as our first brain!) We all should be eating for the gut :)