Women are twice as likely to be hit with the nutritional double-whammy of a combined iron and folic acid deficiency, especially during the summer, say Harvard researchers. Increased physical activity combined with the physical stress of adapting to heat and humidity can drain your body's stores of these energizing nutrients. The result: Mental fatigue, brain fog and trouble concentrating. To prevent brain drain, eat more meat, poultry and eggs -- top sources of an iron-folic acid combo, say Harvard researchers. Getting enough of the iron-folic blend daily can pump up your mineral stores (and mental energy) within three weeks. Try it: Dig into a four-ounce burger or toss two hard boiled eggs or a cup of diced chicken into your salad.