In this paper, we sought to understand the biological mechanisms of Attention Deficit Hyperactive Disorder (ADHD), so that we could learn how to benefit those with ADHD. Previous research has found that ADHD symptoms can be mediated by variables such as body mass index (BMI), consumption of refined sugar and polyunsaturated fatty acids (PUFA). In our first (correlational) study, we tested the strength of these relationships by examining naturalistic daily changes in their variables longitudinally over a one-week period. We measured weight and BMI by using a weight scale, as well as a standard BMI calculator. We tracked food intake, refined sugar intake, and PUFA intake through the MyFitnessPal application. We measured ADHD symptoms using the Adult ADHD Self-Report Scale. Based on the strength of correlation found between PUFA and ADHD symptoms in our correlational study, we then conducted a second (experimental) study to test for a causal relationship between these two variables. Over a one-week period, we randomly assigned participants each day to either a placebo condition or a PUFA supplement condition using a double-blind procedure and measured the effect this manipulation had upon ADHD self-report symptoms using the Adult ADHD Rating Scale. Data pooled across participants in our correlational study failed to show significant correlations of BMI, sugar intake, and PUFA intake with ADHD symptoms. However, data pooled across participants in our experimental study showed that PUFA intake significantly reduced ADHD Self-Report Scale scores. This data suggests that PUFA supplementation is beneficial in the reduction of ADHD symptoms, both on their own and in conjunction with stimulant medication.