How much protein should we eat daily?
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The RDA for protein for adults is set at 0.8 g of protein per kg body weight. This works out to about 54 to 60 g for most men and about 44 to 50 g for most women. You can estimate basic protein needs based on % of total calories, where by 12-15% will give you approximately the same level. This level of protein merely compensates for normal daily body protein loss; however it is not an optimal level of protein in various situations such as weight loss, exercise, and illness. In these situations a protein level of 25% of calories is more appropriate. Higher protein needs in these situations are discussed more in Dieting and Exercise/Fitness, |
Are high protein diets dangerous?
At one time there was a belief that higher intakes of protein can be problematic to health. Today we know that for most people this isn’t the case. In fact, diets with a higher level of protein then the RDA are encouraged for athletes as well as people during weight loss. Two areas of health have are often the target for concern regarding higher protein intakes. The first is kidney health. It was long believed that since higher intakes of protein leads to the formation of more nitrogen-based compounds such as urea, this work become detrimental to the kidneys. However we now know that this isn’t the case unless a person has a special situation related to the kidneys and receiving guidance from his or her physician.
The second area of concern with higher protein intakes was in relation to to body calcium and bone health. Some research efforts have determined that when diet protein levels increase, so too does the level of calcium in the urine. This lead to the conclusion that high protein diets cause a loss of calcium from bones, rendering a person more prone to osteoporosis. However, follow up research has shown that the higher protein intake also increases calcium absorption, thus leading to a corresponding increase in calcium in the urine. So, like kidney dysfunction, the notion that a high protein intake, such as 25% of calories for weight loss or maintenance leads to osteoporosis has not been shown to be true.
What are essential amino acids?
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From a nutritional standpoint, only ten of the twenty amino acids found in protein are essential to the diet. These amino acids present us with the same situation as do the other essential nutrients. We simply cannot make them or at least not in the amounts necessary to promote growth, development, and health throughout the lifespan. As a result, these amino acids must be provided by our diet. As listed in Amino Acids Table, arginine and histidine are noted as essential during periods of growth and maybe at an advanced age but not at other times. |
The easiest way to remember the essential amino acids is by the acronyms TV-TILL-PM-AH. These are the first letters of the essential amino acids tryptophan, valine, threonine, isoleucine, leucine, lysine, phenylalanine, methionine, and the two semi-essential amino acids arginine and histidine. Other acronyms include PVT TIM HALL or VP MATT HILL where PVT is the abbreviation for the military rank of private.
What are nonessential amino acids?
The remaining amino acids used to make protein in our body are called nonessential. That’s because they can be made in our body by using essential amino acids and/or other molecules. It should be understood that dietary essentiality or nonessentiality by no means is meant to imply biological essentiality or nonessentiality. All 20 amino acids must be present in cells to make proteins which support the health of those cells and our body in general. Further, if a problem exists in making a nonessential amino acid, as is the case in some genetic anomalies, then that amino acid would also become a dietary essential for that person as well. This is the case with some individuals who lack the ability to produce the appropriate enzyme to convert phenylalanine (essential amino acid) to tyrosine (nonessential amino acid). In these cases (i.e., phenylketonuria [PKU]), tyrosine becomes an essential amino acid.
What are“complete” proteins?
The goal of protein nutrition is fairly simple – to provide our body with food protein that closely resembles our own protein and in adequate amounts. Furthermore, since the nonessential amino acids can be made in our body, it is desirable for food protein to provide the essential amino acids, in proportion to human protein. Food sources with levels of essential amino acid content similar to our essential amino acid requirements are considered more “complete” and sometimes referred to as higher biological value. Those that don’t measure up to the standard are considered incomplete.
- Complete Protein Sources: Animal based protein sources from such as beef, pork, fish, poultry, eggs, milk, and milk products are among the more complete protein sources. In addition, soy, quinoa, amaranth, buckwheat and spirulina are complete or nearly complete plant based protein sources.
- Incomplete Protein Sources: Plant-based foods such as wheat, corn, fruits and vegetables are considered incomplete or lower biological value as the levels of essential amino acid within their protein does not match our essential amino acid needs as closely.
How can incomplete protein foods be combined to form a complete protein?
When we compare the essential amino acid composition an incomplete food, we find that one or more of these amino acids are in a limited quantity relative to our protein (see Figure 6.4). These amino acids are referred to as “limiting amino acids” because our cells ability to make new protein will be limited to the level in that protein. This is analogous to building a brick wall with alternating rows of red, white and blue bricks. If there is only enough red bricks to build the wall 4 feet tall that is as tall as wall can be build even if there are abundances of blue and white bricks.
What does it mean to “complement protein”?
Because the limiting amino acids within plant foods varies, strategic combinations of different plant foods will provide adequate quantities of all the essential amino acids. This practice is called “complementing” proteins (see Table 6.4). For example, we could combine cereals (i.e., oats, wheat, rice, rye) or nuts and seeds (walnuts, cashews, almonds, pecans and sunflower, pumpkin and sesame seeds) which are low in lysine but a good source of methionine, with legumes (beans, peas, lentils, garbanzos (chick peas)) which are low in methionine but a good source of lysine. While considered a complete protein source, soy is limited in lysine as well and often used in a complementing scheme. The practice of complementing proteins may be best served within the same or adjacent meals for strict vegetarians with lower daily protein intakes (e.g. below RDA); however, for less restrictive vegetarians complementing within the same day is fine.
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