I'm a former decently competitive D1 runner who gave up the sport entirely after graduating in 2013 for about 5 years. Last summer, I started running again and have slowly built up my mileage to about 50 mpw, have shed 20 pounds of extra weight, and am now eyeing some summer road races and perhaps a fall marathon.
However, as a result of a highly demanding job in public accounting, I've been doing all of my running in the early morning before work. I also do all of them in a fasted state with nothing in my system except a small cup of coffee and some water, but I do eat a carb-rich breakfast post run. From a scheduling perspective, this works out well and I generally feel great on morning runs and have no issues waking up to do them. Once I get to work around 9 am, though, things go south. On mornings that I run anything harder than a light jog, I feel completely exhausted during the work day and have trouble concentrating on my work, as well as just not feeling as mentally sharp or motivated as I normally do. Previous to getting back into running, I was absolutely excelling at my job and was one of the higher-rated people in my firm at my level, but I can tell that since then my work performance has definitely taken a significant dip. I have noticed that this does not occur if I do my runs in the evening or afternoon, but due to my erratic work schedule it is simply not possible to schedule my runs after work.
Has anyone else had this problem and found a solution? Is it to simply take all my runs during the work week easy, and save the hard workouts for the weekend? Is there something nutritionally I should consider fixing like laying off the caffeine? I'm open to any and all suggestions as I'm getting pretty frustrated with my fatigue and lack of alertness at work off of what I used to consider moderate mileage (50 mpw).