Increased fatigue can be one of the signs indicating low iron content in the body. Due to low iron, the blood cannot carry adequate oxygen to various body parts, keeping the cells recharged. Lack of sufficient oxygen causes fatigue and stress and even increases the amount of lactic acid in the muscles. People who do heavy physical activities and pregnant women need to have a good iron intake in their diet. Adding foods rich in iron with the correct and herbal iron supplements helps to increase the iron content in the body. The blood can carry more oxygen and keep the person full of energy.