The nutrient deficiency most commonly associated with fatigue is iron deficiency, resulting in reduced hemoglobin levels and inadequate oxygen transport to cells. This leads to feelings of weakness and tiredness during physical and mental activities. Additionally, vitamin D and B vitamin deficiencies can also contribute to fatigue. Addressing these deficiencies through diet or supplementation can help restore energy levels and improve overall functioning. Eating a balanced diet rich in nutrient-dense foods plays a crucial role in preventing deficiencies and promoting sustained energy and vitality.