Fatigue and nutrition
A persistent feeling of exhaustion that can stem from identifiable nutritional deficiencies, chiefly iron, vitamin B12 or vitamin D, but whose causes go well beyond diet.
Fatigue is one of the most common reasons for a medical consultation, and diet is only one cause among many. Sleep, stress, physical activity, illnesses and medicines weigh at least as much. That said, a few deficiencies produce a characteristic tiredness and can be corrected.
The first is iron deficiency, with or without anaemia. It is worth stressing this: stores can be empty while haemoglobin remains normal, and the fatigue is already there. Only a ferritin test reveals it. Next come vitamin B12 deficiency, common on a strict plant-based diet or with certain treatments, and vitamin D deficiency.
Blood sugar fluctuations are the most ordinary and most neglected cause. A meal very high in fast-release sugars causes a rise then a drop in blood glucose, felt as a slump that is often blamed on digestion. Meals better balanced in fibre, protein and fat smooth out these swings.
Two questionable reflexes deserve a mention. “Anti-fatigue” multivitamin supplements only work if there is a genuine deficiency: without one, the extra intake does nothing. And fatigue that persists beyond a few weeks warrants a medical check-up rather than self-medication, since non-nutritional causes are the most numerous.