The so-called “freshman fifteen” is a term often said on college campuses that illustrates how dining plans that emphasize high calorie foods with little nutritional value (such as easy to prepare fried foods) contribute to a noticeable weight gain among incoming students. This should be no surprise, as foods like pizza, fried chicken and sweets that are provided in an “all-you-can-eat buffet” style at dining halls have been shown to contribute significantly to freshmen weight gain.

The effects of a poor diet, however, extend far beyond your short-term physical health. Inside your gut there is an immense number of microorganisms that make up what scientists call a microbiome. While some of these microorganisms can be harmful, the vast majority are either benign or helpful in breaking down food, providing chemical signals and even aiding in immune responses.

This bacterial, fungal and viral system inside your gut (often called the gut-brain axis) has a profound effect on your immune system, brain health and can even influence your weight. One such study found that microbiomes can have an impact on depression. It is no wonder some health professionals call the gut a “second brain.”

Since microbiota are made up of bacteria and other microorganisms, the prevalence of specific healthful or harmful organisms depends on and can reinforce your diet. By eating junk food, you promote microorganisms that love sugary, high calorie foods. These microorganisms can secrete chemical signals that are sent to your brain, which are interpreted as a desire to consume more junk food. This cycle repeats, as increased junk food consumption promotes the proliferation of these junk food organisms. This pushes out other organisms that would promote the consumption of fruits, meats and vegetables as your microbiome sets up a path for obesity and health complications. This really does prove the point of “you are what you eat.”

There is a way to fight and reverse these effects, and that is by promoting a healthier microbiome through healthier eating. Meats, fruits and vegetables can all influence and promote a healthier and more diverse microbiome. By switching up your diet to one that avoids processed and junk food, you are setting yourself up for a better life. An improved diet that influences a better microbiome will help your physical health and can stave off the effects of some cancers and even Parkinson’s disease. It can also help your mental health by preventing depression, anxiety and elevated stress levels.

It may seem impossible at first to get started on the healthy eating track, especially if you have been consuming junk food for a while. After all, it takes discipline and effortful habit building to take the first steps to a healthier life. But even the smallest step, like eating single serving of yogurt or a banana (both of which have probiotic factors that improve your microbiome), is a step in the right direction toward a healthier and happier life.