Both flax and hemp are nutritious, high-fiber seeds that have only recently gotten their due in mainstream health circles. Each contains a high amount of precious omega-3 fatty acids that we tend to lack in our diet, instead consuming high amounts of omega-6s. While both foods are versatile, each are used in different ways.
One of the main differences of flax seed and hemp powder is that hemp can be used healthfully in baking. Flax seeds can be ground into a meal that can be added to soups, salads and smoothies. While flax meal is used for baked goods as well, Jane Heimlich in her book, "What Your Doctor Won't Tell You," advises only cooking with flax seed at low temperatures, noting that heat destroys omega-3 fatty acids, which are higher in flaxseed than hemp powder.
Hemp powder can be widely used in a variety of recipes, and author Steven Winkler notes in his book, "Wholesome Gourmet: The Art of Gluten-Free Cuisine," that you can substitute one-fourth of the amount of flour called for in a recipe with hemp flour to add a slight nutty flavor to the recipe.
Flax seed is more susceptible to rancidity than hemp powder. Though both contain omega-3 oils that can easily be damaged by heat, the amount of oil is reduced when hemp is made into a powder, which allows it to be stored for longer periods of time than flax seeds. Winkler recommends always purchasing flax seed that is refrigerated, and refrigerate it once you bring it home. Hemp powder can be stored for up to a year in a cool, dark cupboard.
Flax seeds may help improve waste transit time through the body, whereas hemp powder is not known to help with digestion issues. Paul Pitchford, in his book, "Healing with Whole Foods" notes that flax seeds help to lubricate the intestines and are therefore helpful in dealing with constipation. Although hemp powder is an easily-digestible protein and may help to bulk up waste for removal since it contains fiber, it's not associated with relieving constipation.
Hemp powder is often used as a protein supplement, while flax seed is considered more of a nutritional supplement. In her book, "The Gorgeously Green Diet," author Sophie Uliano recommends hemp powder as among the best of the protein powders available on the market, noting it is generally organic, contains a high ratio of amino acids and is high in protein. One serving size of hemp powder normally contains 11 to 13 g of protein. Flax seed, while high in fiber, essential fatty acids and B vitamins, has a lower protein content, usually around 7 g in a 1/4 cup.