In addition to three Doshas that form the physiological constitution, Ayurveda recognizes three psychic energies or Gunas that governs the mind and determines your psychological characters. When the three Gunas are balanced they keep the mind and, the body healthy. However, an imbalance can produce mental and physical disorders. This understanding helps in determining which food to consume for a healthier psyche.
The Gunas are the subtlest principles in all form of energies. Every form of energy, physical or mental, will have the Gunas in a particular ratio. The Doshas are grosser energies (slower vibrations) that make up the physical body. This understanding paves a path in the understanding that each Dosha will have all the three Gunas in some proportion. These Gunas are present in all things and beings in the world. Together they make and create the entire existence. The Gunas are higher vibrations that amalgamate and form the five basic elements (earth, water, fire, air, and ether) and these five basic elements form the three Doshas. All other forms of energies are derived from the Gunas. These are subtle energies which cannot be perceived by our senses but can only be understood by its effect, the impact they have on our body. Despite having opposing qualities they coexist at all time.
The Gunas are three in number, namely, Sattva, Rajas, and Tamas. Sattva translates to pure. The quality of Sattva is calm, quiet, focused and centered, pure, essence, nature, vital energy, clean, conscious, strong, courageous, true, honest and wise. Rajas translate to active. It possesses qualities of restless, hyperactive, agitated, passionate, moving, and emotional. Tamas translates to subdued. The qualities of Tamas is sleepy, lazy, lethargic, dark, destructive, spoiled, ignorant, stale, inertia, unripe, unnatural, weak and unclean. Rajas and Tamas are not bad; they are just qualities that everyone possesses in different proportions. You wake up in the morning from the effects on Rajas on your mind and Vata on your body. When you want to sleep, it is the Tamas that acts on your brain and Kapha that acts on your body.
Food influences the three Gunas. The foods you eat possess certain energies that get transferred and makes an impact on your mental Gunas as well as physical Doshas, which are the ethereal energies that make you tick. Change your food and you can change your mind. That is why yogis advise only the Sattvic (related to Satva) food, which increases your Sattva. Depending on your body type the Sattvic food may vary. Some Satvicc foods better for Vata type, while others may be better for Pitta people or Kapha people.
Sattvic diet is meant to include food and eating habit that is pure, essential, natural, vital energy containing, clean, and conscious. These include seasonal foods, fruits, dairy products, nuts, seeds, oils, ripe vegetables, legumes, whole grains, and non-meat based proteins. Easier access to meditation is provided by predominance on Sattvic food in life. Rajasic (related to Rajas) food provokes mental restlessness, aggressive and dominating thoughts. This energizes and develops the Manipura (navel) chakra and body but does not promote advancement in higher chakras. Rajasic food balances out the excess of Tamas in the mind. So people who possess an excess of Tamas should initially start out with Rajasic food and eventually move onto Sattvic food. Rajasic food includes coffee, caffeinated tea,
fermented foods, certain grains and legumes, garlic, onions, sour fruit, spicy or salty foods, meat, and eggs. The Rajasic tastes are hot, bitter, sour, dry, or salty. Eating in a rush is considered Rajasic as well. Tamasic food promotes dullness and passivity. Tamasic food stimulates and strengthens the lower two chakras but will not assist in the beneficial development of the higher chakras. Tamasic foods include processed foods, frozen or microwaved meals, alcohol, refined sugar, blue cheese, fertilized eggs, tobacco, bread, and pastries. The produces (mushroom, yeast) that grow in the dark or underground are considered Tamasic as well. These foods make you feel heavy after consumption and should usually be avoided. Overeating and consuming leftover food is considered Tamasic as well.
To summarize, food that promotes purity of mind, peace, intelligence and the right decision is Sattvic food. Food that gives us motivation, but eventually keeps us attached to the ego, creates desires and suffering is Rajasic food. Food that clouds the mind, increase susceptibility to diseases and promotes negative emotions is the Tamasic food.