Most people who fast report that same "clearheadedness".

Try intermittent fasting. It's easy. It gives your gut a chance to rest. For me it helped with weight control and slightly improved my overall well being. Later I also eliminated sugar from my diet and reduced caffeine intake to minimum by replacing coffee with reasonable amounts of quality tea. That in turn improved my mood, made me less angry and emotional. I also started exercising a bit. All of that combined increased my energy levels, made me calmer, nicer and a bit more optimistic and happy.