Whether you prefer chowing down on a well-marbled steak or tossing back a few handfuls of nuts, many of your favorite foods contain both protein and fat. Although you don't need to have both nutrients in the same meal, you need protein to burn fat. Your body uses proteins to transport fats to your cells, while within your cells, enzymes made of proteins help to metabolize, or burn, those fats for energy.
As implied by the expression "oil and water don't mix," fats are not water-soluble. To reach your cells, they must be transported through your bloodstream attached to proteins, called lipoproteins. Your cells take up these fats, in the form of triglycerides, and burn them to produce energy. Triglycerides that aren't needed immediately are stored in fat cells for later use as fuel. Fats released from storage are transported as free fatty acids bound to another protein called albumin.
Once fats are taken up by your cells, they are metabolized to provide energy. That process takes place within organelles in your cells known as mitochondria, sometimes referred to as the powerhouses of the cells. A compound called carnitine, which is formed from amino acids derived from proteins, helps to shuttle fats into the mitochondria. That process, as well as each step of fat metabolism within the mitochondria, is catalyzed by enzymes, which are also formed from proteins.
Transport proteins and enzymes can be re-used many times. However, like all proteins in the body, they are eventually broken down into their individual building blocks, nitrogen-containing amino acids. Your cells can use most of those amino acids to form new proteins, but some nitrogen is lost from your body every day. For your cells to build all the proteins they need, you need to replenish your supply of amino acids each day by eating protein-containing foods.
The U.S. Department of Agriculture's My Plate guidelines recommend that adult women consume five one-ounce equivalents of protein per day. A one-ounce equivalent of protein could be one ounce of meat, poultry or fish, one egg, half an ounce of nuts or seeds or a quarter of a cup of cooked beans. The USDA suggests getting your protein from a variety of sources, including seafood. The agency also notes that vegetarians can get sufficient protein if they include a variety of foods such as nuts, seeds and beans in their diet.
- Nutrition for Sport and Exercise; Marie Dunford and J. Andrew Doyle
- USDA Choose MyPlate.gov: Protein Foods
Joe Miller started writing professionally in 1991. He specializes in writing about health and fitness and has written for "Fit Yoga" magazine and the New York Times City Room blog. He holds a master's degree in applied physiology from Columbia University, Teacher's College.