English to Russian Art/Literary Medical (general) survival medicine

Although you can live several weeks without food, you need an adequate amount to stay healthy. Without food your mental and physical capabilities will deteriorate rapidly, and you will become weak. Food replenishes the substances that your body burns and provides energy. It provides vitamins, minerals, salts, and other elements essential to good health. Possibly more important, it helps morale. The two basic sources of food are plants and animals (including fish).
... укрепляет/возвращает нам веру в свои силы/поднимает настроение.