Chronic low-level deficiency in specific nutrients affects mood, motivation, and energy in ways that don't feel like a deficiency — they feel like "being tired lately". Ten nutrients where the evidence is strong enough to warrant paying attention, with the most effective food sources for each.

1. Vitamin D

Deficiency correlates with depressive symptoms. Sunlight is the best source; supplementation if latitude or lifestyle makes sun inadequate. Test before dosing; 1,000-4,000 IU is a typical therapeutic range.

2. B12

Essential for nervous-system function. Deficiency is common in vegetarians and older adults. Sources: meat, eggs, dairy, fortified cereals.

3. Iron

Low iron produces fatigue that feels like mood. Test ferritin levels, not just haemoglobin — you can be iron-deficient with normal hemoglobin. Sources: red meat, lentils, spinach, fortified cereals.

4. Omega-3 (EPA + DHA)

Supports brain function and mood. Evidence particularly strong for depressive symptoms. Sources: fatty fish twice a week, or 2-3 g/day of a quality fish-oil supplement.

5. Magnesium

Low magnesium correlates with anxiety, poor sleep, muscle tension. Glycinate or citrate forms absorb best. Sources: leafy greens, nuts, seeds, dark chocolate.

6. Zinc

Supports immune function and neurotransmitter synthesis. Sources: oysters, beef, pumpkin seeds, chickpeas.

7. Folate

Methylation pathway; deficiency linked to mood disorders. Sources: leafy greens, legumes, citrus.

8. Protein (full amino-acid profile)

Neurotransmitter precursors. A chronically low-protein diet depresses mood reliably. Aim ~1 g/kg minimum.

9. Choline

Memory and cognitive function. Most people underconsume it. Sources: eggs, liver, fish.

10. Adequate carbohydrates

Chronic very-low-carb dieting produces mood changes in a large subset of people. Fibrous carbs — fruit, oats, whole grains — keep serotonin synthesis supported.

The order of operations

Don't supplement blindly. Test for D, B12, and ferritin. Fix food first where possible; supplement where diet genuinely can't cover it. Most "I feel low lately" becomes "I feel normal" within four to six weeks of correcting the one or two nutrients that were actually missing.