Fatigue is one of the most common presenting complaints in primary care. When thyroid dysfunction, anaemia, and sleep disorders are excluded, the remaining majority of cases are attributable to dietary and lifestyle factors. In adults over 35, these dietary contributors are often multiple and compounding: blood sugar instability producing afternoon crashes, iron insufficiency below the anaemia threshold, magnesium deficiency impairing ATP production, B12 deficiency causing neurological fatigue, and chronic systemic inflammation producing the sickness behaviour response that the brain interprets as exhaustion.
The Blood Sugar Contribution
A refined carbohydrate-dominant diet produces recurring cycles of glucose elevation and reactive hypoglycaemia that generate a predictable fatigue pattern: energy that spikes briefly after eating and crashes two to three hours later. The body responds to the glucose drop with cortisol, which temporarily restores blood glucose but at the cost of interrupted sleep, muscle catabolism, and continued HPA axis stimulation. Eliminating this cycle by switching to whole food meals with protein, fat, and fibre at every meal often resolves unexplained fatigue within two to three weeks.
Micronutrient Contributions to Energy
- Iron: tissue iron depletion (ferritin below 30) impairs oxygen delivery and mitochondrial enzyme function; confirm by testing ferritin specifically
- Magnesium: required for ATP synthesis in every mitochondrion; the most common micronutrient deficiency associated with fatigue
- Vitamin B12: neurological fatigue from demyelination is a classic B12 deficiency presentation; may develop slowly over years on low-animal-food diets
- Vitamin D: deficiency produces musculoskeletal fatigue and mood-related fatigue through multiple pathways; supplement from October to March in all northern hemisphere locations