You’re not consuming enough iron
An iron deficiency can leave you feeling sluggish, irritable, weak, and unable to focus. “It makes you tired because less oxygen travels to the muscles and cells,” says Goodson. Boost your iron intake to reduce your risk of anemia: load up on lean beef, kidney beans, tofu, eggs (including the yolk), dark green leafy vegetables, nuts, and peanut butter, and pair them with foods high in vitamin C (vitamin C improves iron absorption when eaten together), suggests Goodson. Note: an iron deficiency may be due to an underlying health problem, so if you’re experiencing these symptoms of iron deficiency, you should visit your doc.