I have to give my husband credit for this post.  He's been doing an intense exercise program for the past 6 months and complained that he's "not getting any stronger" and wondered about how much protein he should be eating.  Good question, I said!Protein is one of the four macronutrients in our diets and provides 4 calories per gram.  Carbohydrate also provides 4 calories per gram and fat provides 9 calories per gram.  Alcohol, thought not really a "nutrient" does give you 7 empty calories per gram, meaning, lots of calories, but little if any, nutrients.Protein is known as a "building" nutrient as it's needed for muscle strength and recovery.  Skin, hair and nails are all technically made out of protein.  Your body also needs protein to make hormones, enzymes, blood cells and other structures in the body.  Protein is needed for normal growth and development and for healing the body under times of stress such as surgery, infection or trauma such as a car accident.  Protein also aids with satiety, the feeling of fullness you get between meals.  Adding protein to meals may aid weight weight reduction as it impacts appetite.Protein is made up of amino acids.  Essential amino acids are those that cannot be made by the body from other amino acids.  Complete proteins are foods that provide all the of the essential amino acids needed by the body.   In general, eggs or other animal foods (beef, poultry, pork, dairy products) are complete proteins, while plant-based foods such as beans and rice offer some amino acids, but not all in one food. Combining beans with rice provides a complete protein.  It was once thought that these foods needed to be eaten at the same time, but this is not true.  If you have rice at lunch and beans at dinner, your body will assimilate essential amino acids from them.  Beans, lentils, nuts, seeds, tofu, peas, and  peanut butter also provide protein in plant-based form.Protein needs vary based on age, weight and physical activity.  Infants and toddlers have higher protein needs per weight for growth and pregnant women also require more protein for a healthy pregnancy.  Active men and women (such as long distance runners or weight lifters) have higher protein needs to help with muscle growth and recovery.Most healthy adults require approximately .8 grams of protein per kilogram body weight.  There are 2.2 lbs in 1 kilogram, so a 220 lb man weighing 100 kg would require 80 grams per day.  (220/2.2 = 100 kg).  Athletes may require between 1.0 to 1.5 grams of protein per kg depending on how active they are.  In my husband's case, I suggested 1.2 grams of protein per kg body weight to build more muscle.  He is exercising at high intensity and using weights five days per week for at least an hour.Finally, to spare protein from being broken down for calories, you've got to eat enough food to meet calorie needs.  Consider this- if you've not got enough food to fuel your workout, you won't be able to exercise as intensely, and your body may eat up muscle for energy, thus lowering metabolism.  You can't argue with science.