What is protein? How much protein do we need? Is it possible to eat too much protein? These are important questions for people following a low-carb way of eating, who usually are replacing part of their carbohydrate intake with protein.
What is protein?
Protein is one of the basic building blocks of the human body, making up about 16 percent of our total body weight. Muscle, hair, skin, and connective tissue are mainly made up of protein. However, protein plays a major role in all of the cells and most of the fluids in our bodies. In addition, many of our bodies' important chemicals -- enzymes, hormones, neurotransmitters, and even our DNA -- are at least partially made up of protein. Although our bodies are good at “recycling” protein, we use up protein constantly, so it is important to continually replace it.Proteins are made up of smaller units called amino acids. Our bodies can manufacture most of the needed amino acids, but nine of them must be gotten from our diets. Animal proteins such as meat, eggs, and dairy products have all the amino acids, and many plants have some of them.
How much protein do we need?Our protein needs depend on our age, size, and activity level. The standard method used by nutritionists to estimate our minimum daily protein requirement is to multiply the body weight in kilograms by .8, or weight in pounds by .37. This is the number of grams of protein that should be the daily minimum. According to this method, a person weighing 150 lbs. should eat 55 grams of protein per day, a 200-pound person should get 74 grams, and a 250-pound person should eat 92 grams. (The top calculator on this page can compute a range of the recommended dietary protein for you. The lower number in the range is the minimum.)
Another way to compute protein needs has to do with lean body mass, rather than total body weight (based on the idea that our fat tissue needs less protein to support it). This method is discussed in the Zone Diet and Protein Power books. The second calculator on this page can help you compute this number. To do this, you will also need to know your body fat percentage. (Body Fat Calculator here)
Do athletes need more protein?Yes. People engaging in endurance exercise (such as long distance running) or heavy resistive exercise (such as body building) can benefit from additional protein in their diets. The current recommendation is for these athletes to consume 1.2 to 1.7 grams of protein per day for each kilogram of body weight.
Do pregnant women need more protein?Yes. The Institute of Medicine recommends that the minimum protein consumption for pregnant women be about 10 grams per day more than usual, though this is not as crucial in the first half of the pregnancy.
But shouldn’t protein intake be a percentage of total calories?Quite a few programs and nutritionists quote percentage of calories, usually in the range of 10 percent to 20 percent, as a way to figure out how much protein a person needs to consume daily. This is a rough estimate of a person's minimum protein needs. It works because typically, larger and more active people need more calories, so the more calories they need, the more protein they will get.
Where this falls down is when people are eating diets that are lower in calories for any reason, conscious or not. People who are ill or losing weight, for example, do not need less protein just because they are eating fewer calories -- so anyone on a weight loss diet should not go by the "percent of calories method" for calculating protein needs.
What happens if we don’t eat enough protein?Unlike fat and glucose, our body has little capacity to store protein. If we were to stop eating protein, our body would start to break down muscle for its needs within a day or so.
Is it OK to eat a lot more protein than the minimum recommendations?This is an important question for people on diets that are higher in protein than usual, as low-carb diets tend to be. In a review of the research, the National Academy of Sciences reported that the only known danger from high-protein diets is for individuals with kidney disease. After careful study, they recommend that 10 percent to 35 percent of daily calories come from protein. They point out that increased protein could be helpful in treating obesity. There is also accumulating evidence that extra protein may help prevent osteoporosis.
Extra protein can be broken down into glucose in a process called gluconeogenesis. On low-carb diets, this happens continually. One benefit of obtaining glucose from protein is that it is absorbed into the bloodstream very slowly, so it doesn’t cause a rapid blood sugar increase. However, some diabetics do find that too much protein causes an excessive blood sugar rise, and low-carbers sometimes find that as time goes on they do better with a moderate protein intake right than eating large amounts of protein.
Can Too Much Protein Cause Bad Breath?Yes, actually, it can. If this is happening suddenly after a dietary change, excess protein could be the cause of bad breath.
What foods have the most protein?Meat, fish, eggs, dairy products, legumes, and nuts all have substantial amounts of protein. This information can help:
- Calculate Your Protein Requirement
- List of High-Protein Foods, with amounts of protein listed
- Protein Sources That Are Low in Saturated Fat
- Low-Carb Vegetarian Protein Sources
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005), Food and Nutrition Board, National Academy of Sciences.
Lemon, PWR. (1996). “Is increased dietary protein necessary or beneficial for individuals with a physically active lifestyle?” Nutrition Review 54:S169-S175.Nutrition During Pregnancy: Part II. Institute of Medicine. (1990)