There has been a resurgence of diets emphasizing increased protein intake to promote weight loss or to improve health, so the topic of protein and its role in a healthy diet is worth reviewing.
There are nine essential amino acids: histidine (essential for children), isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids must be supplied by food; the body cannot make them. There are also 12 nonessential amino acids, which are important, but called nonessential because the body can make them from the essential amino acids.
Proteins come from plant and animal sources. Animal proteins more closely match the amino acid composition of human proteins, however people who do not consume animal foods can get all of the protein needs from plant sources, (they just need a larger amount of plant protein versus animal protein to fulfill the body’s requirement for protein).
According to the Food and Nutrition Board of the National Research Council (who establish dietary recommendations for the population), the body’s need for protein is met when protein intake is at .8 grams of protein per kilogram of body weight. (Divide your body weight in pounds by 2.2 to get the equivalent in kilogram weight). This meets the needs of about 90% of the population of adults. For men, this translates to about 63 grams of protein per day, and for women, it is about 50 grams of protein per day.
Protein needs increase for growing children, nursing mothers, severally injured or seriously ill people, and athletes. Athletes, in particular, pay special attention to their protein intake and often supplement with protein powders. In fact, the typical diet consumed in industrialized countries already contains more than enough protein to cover the needs of most athletes and any additional protein above the body’s needs is either used for energy or converted to body fat. A typical diet should contain between 10-20% of calories as protein. What athletes and others expending great amounts of physical energy need are additional calories, (in the proper balance of fat, protein, and carbohydrate, not just protein).
So, if we already get enough protein, why are high protein diets like the Atkins diet so popular right now? In the past few years, there has been a swing towards hatred of carbohydrates, and carbohydrates are being blamed for the obesity problem. The option on low-carbohydrate diets is to increase fat and/or protein in the diet to make up for a low-carbohydrate intake. What’s wrong with this is that high protein, high fat diets severely limit sources of carbohydrates that provide essential vitamins, minerals and other protective factors against serious diseases such as cancer, heart disease, and high blood pressure. And, at very low levels of carbohydrate intake, the body produces ketones, which is a potentially dangerous condition. Beside the dangers of a low carbohydrate intake, a high protein intake produces waste products containing nitrogen that require a lot of water to flush out of the body. Excess protein taxes the liver and kidneys, and does nothing to increase muscle mass because the excess that is not used for energy is converted to fat.
The fact is, the body needs all of the nutrients that supply energy: fats, proteins, and carbohydrates. Each have a unique purpose and are essential in the right amounts, and taxing to the body in the wrong amounts. Too much of any of these nutrients will lead to an increase in body fat.
For people who are following a reduced calorie to lose weight, the protein intake should be at least 75 grams per day. This is a higher protein level than the typical intake of a diet that supplies calories to maintain weight. This is because when energy balance is negative (i.e. fewer calories taken in than are needed, causing weight loss), the body’s nitrogen requirement is greater to maintain nitrogen balance when other sources of energy (fat and carbohydrate) are not enough to provide energy balance. This amount of protein can be adequately supplied with a reduced calorie diet (of more than 1000 Calories) comprised of 15-20% of calories as protein. Therefore, protein intake above 20% of calories is not necessary for a properly reduced calorie diet and has no additional health benefits.