Ultra processed food is everywhere in modern society and may contain multiple ingredients that affect the way participants' bodies store energy. Some studies have shown that eating a diet high in ultra processed foods leads to weight gain, but these foods have not been studied enough to understand why. Recently, the gut microbiome has become a potential way to measure energy balance in the human body; this is done by measuring how many calories are in the stool. The investigators propose to test a very high ultra-processed food diet where 80% of calories are coming from ultra processed food and a low ultra processed food diet where 20% of the calories are coming from ultra processed food. This study will compare stool sample energy content of the two diets.