Bhagavad Gita 17.8

Foods that increase life, clarity, strength, health, happiness, and love—which are juicy, naturally oily, stable, and agreeable—are dear to the sattvic mind.

आयुःसत्त्वबलारोग्यसुखप्रीतिविवर्धनाः ।
रस्याः स्निग्धाः स्थिरा हृद्या आहाराः सात्त्विकप्रियाः ॥

ayuh-sattva-balarogya-sukha-priti-vivardhanah |
rasyah snigdhah sthira hrdyah aharah sattvika-priyah ||

Foods that increase life, clarity, strength, health, happiness, and love—which are juicy, naturally oily, stable, and agreeable—are dear to the sattvic mind.

This classical verse perfectly describes the modern nutritional psychology we just explored. Notice that it specifically praises foods that are Snigdha (naturally oily or rich in healthy fats, like the Omega-3s) because good fats are part of a diet that supports the brain. A calm, steady ( sattvic ) mind requires stable, nourishing physical food. However, there is a hard medical boundary. A healthy plate of food is the foundation that can support your nervous system through a difficult week. But food is not a magical cure for a broken biological engine. A good diet cannot replace thyroxine if your thyroid is failing, it cannot replace insulin if you have diabetes, and it absolutely cannot replace an antidepressant when a licensed doctor indicates your brain needs one.