Ojas is said to be the pure substance that is accumulated from properly digested, nourishing food. It gives life and energy to the cells in the body. Non-sattvic foods, like meat, processed foods, oily foods, reheated foods and foods that aren't freshly prepared, are close to impossible for the body to convert into ojas.
The opposite of ojas is ama, which is thought to be a toxic residue in the cells that promotes disease. It is created by consuming non-sattvic foods and harboring destructive habits or emotions. An individual can counteract ama by repairing their ojas.
Signs of plentiful ojas are feeling rested, having a radiant complexion, a healthy-colored tongue, feeling centered and balanced, having easy digestion, a clear mind, rarely getting sick, and feeling light and energized.