Modern diets tend to be rich in saturated fats and hydrogenated oils, and are lacking in essential fatty acids. The two most important ones are omega-3 and omega-6 essential fatty acids, also known as alpha-linolenic acid and linoleic acid respectively. Omega-3 fatty acid is one of the most deficient of the essential fatty acids in our diets. It is found in flax, hemp, nuts and seeds, dark green leafy vegetables, and fish. Dietary deficiency of omega-3 plays a central role in many diseases such as cardiovascular and neurological disease. Supplementation of omega-3 essential fatty acids is usually recommended in the form of fish oil, which is also naturally high in vitamin D, another common deficiency. The recommended dose is usually 1-2 teaspoons daily, and must be kept refrigerated.