RDA for Amino Acids

Posted by Blog Thursday, April 7, 2011

Figuring out the RDA for amino acids gets complicated, because you really need to know two things: How much protein you need, and then how much of that protein should be made up of each of the nine essential amino acids. Bear with us as we work it out.

First, the protein. How much do you really need? Probably a lot less than you're getting. The RDA for protein is figured using a very complicated formula, but it basically comes down to this: You need 0.36 grams of protein for every pound of body weight. So, if you're that mythical 130-pound woman, you need about 47 grams of protein (130 × 0.36) every day.

To put your protein needs in a different way, you need to get about 10 to 15 percent of your daily calories from protein. A gram of protein has about 4 calories, so our imaginary 130-pound woman gets about 188 calories a day from protein.

Let's get real with these numbers. There's about 28 grams in an ounce. A quarter-pound hamburger has about 14 grams of protein; a baked chicken leg has about 30 grams. In an average American diet, you reach your daily protein quickly. In fact, you probably go way over it every day.

Now let's look at the amino acids. Animal proteins, such as meat, eggs, and milk, contain all nine of the essential amino acids, along with some of the nonessential ones. Nutritionists call these “high-quality” or “complete” proteins. The protein in eggs is such high quality that eggs are used as the standard to measure other proteins by (see the chart for the breakdown). So, the proportions of the essential amino acids in an egg set the standard for how much of each essential amino acid you need. Looking at the egg chart, you can see that you need relatively little tryptophan, for example, compared to leucine.

Amino Acids in an Egg

Amino Acid               Amount in mg
Arginine                          377
Cysteine                          146
Histidine                          149
Isoleucine                         343
Leucine                            537
Lysine                              452
Methionine                       196
Phenylalanine                    334
Threonine                         302
Tryptophan                        76
Tyrosine                           257
Valine                               383

Now let's combine what we know about protein and what we know about amino acids. We know you need 0.36 mg of protein for every pound of your body weight. We know that protein needs to contain the different essential amino acids in roughly the same proportions as those found in an egg. Based on that, we can then figure out how much of each essential amino you need to get every day.

The breakout is shown in the chart in terms of milligrams per each pound of your body weight. Checking the chart, you can see that a 130-pound woman needs to get 1,040 mg (130 × 8), or almost exactly 1 gram, of leucine every day. To put that in perspective, there's close to 2 grams of leucine in a quarter-pound hamburger.

Adult Requirements for Essential Amino Acids

Amino Acid               Requirements in mg/Ib
Histidine                          5–7
Isoleucine                        6
Leucine                           8
Lysine                             7
Methionine                      8
Phenylalanine                  8
Threonine                       4
Tryptophan                     2
Valine                             6


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