Diet and exercise have a great effect on the body both physically and mentally. Being honest with yourself, the more you appreciate what the mirror is showing you, the better you will feel. Scientifically, we could delve into the body releasing endorphins and heart health and studies that prove certain diets and exercise produce a higher level of energy throughout the day.
Finding time for exercise is certainly difficult, which is why I am a big fan of High Intensity Interval Training (HIIT). If time is what's preventing you from exercising, I recommend HIIT workouts. They are interval workouts that typically last 15-25 minutes. They produce the same anaerobic response as lifting weights, thus enabling burning calories throughout the day.
To conclude, I believe in diet and exercise to support you physically and mentally which in turn will help your work performance. If timing is the issue, there are a number of reputable HIIT coaches free on YouTube with no equipment necessary. Everyone can find 15 minutes! I hope this brings you some value!