Sort of. Not every food is unique enough to encourage a radically different combination of bacteria--most fruit is biologically pretty similar, for example, lots of fructose and fiber. And not every species of gut bacteria has evolved the same ability to affect the human brain in the same way. Plus, nothing happens in a vacuum; even as one species starves, another thrives to fill the niche. What we're just now figuring out is what
other things these bacteria do for us. Some bacteria that thrive on high-fiber diets, for example, have
recently been discovered to release substances that help modulate our immune systems. Without fiber, they never grow, and your immune system maybe doesn't get everything it needs. But just like tending a garden, you have to consistently eat fiber every day for the colony to thrive--fruit once in awhile will get you a dose of vitamins, which is good, but it will not keep the bacteria going. You are what you eat.