summarize: Why is protein so important? One clue lies in the name, which is derived
from the Greek word proteios, meaning “primary.” Protein and amino acids
are the essential building blocks of life. Without them, we simply cannot
build or maintain the lean muscle mass that we need. As we saw in chapter
11, this is absolutely critical to our strategy, because the older we get, the
more easily we lose muscle, and the more difficult it becomes to rebuild it.
Remember the study we discussed in chapter 11 that looked at the effect
of strength training in sixty-two frail seniors? The subjects who did only
strength training for six months gained no muscle mass. What I didn’t
mention there was that another group of subjects was given protein
supplementation (via a protein shake); those subjects added an average of
about three pounds of lean mass. The extra protein likely made the
difference.
[*7]
Unlike carbs and fat, protein is not a primary source of energy. We do not
rely on it in order to make ATP,
[*8] nor do we store it the way we store fat (in
fat cells) or glucose (as glycogen). If you consume more protein than you can
synthesize into lean mass, you will simply excrete the excess in your urine as
urea. Protein is all about structure. The twenty amino acids that make up
proteins are the building blocks for our muscles, our enzymes, and many of
the most important hormones in our body. They go into everything from
growing and maintaining our hair, skin, and nails to helping form the
antibodies in our immune system. On top of this, we must obtain nine of the
twenty amino acids that we require from our diet, because we can’t synthesize
them.
The first thing you need to know about protein is that the standard
recommendations for daily consumption are a joke. Right now the US
recommended dietary allowance (RDA) for protein is 0.8 g/kg of body
weight. This may reflect how much protein we need to stay alive, but it is a far
cry from what we need to thrive. There is ample evidence showing that we
require more than this—and that consuming less leads to worse outcomes.
More than one study has found that elderly people consuming that RDA of
protein (0.8 g/kg/day) end up losing muscle mass, even in as short a period as
two weeks. It’s simply not enough.
On a related note, some of you may have the impression that low-protein
diets are helpful for longevity purposes. Certainly, a number of mouse studies
have suggested that restricting protein can improve mouse lifespan. I am not
convinced that these results are applicable to humans, however. Mice and
human beings respond very differently to low protein, and numerous studies
suggest that low protein in the elderly leads to low muscle mass, yielding
greater mortality and worse quality of life. I am more persuaded by this
human data than I am by studies in mice, who are simply not the same as us.
How much protein do we actually need? It varies from person to person.
In my patients I typically set 1.6 g/kg/day as the minimum, which is twice the
RDA. The ideal amount can vary from person to person, but the data suggest
that for active people with normal kidney function, one gram per pound of
body weight per day (or 2.2 g/kg/day) is a good place to start—nearly triple
the minimal recommendation.
So if someone weighs 180 pounds, they need to consume a minimum of
130 grams of protein per day, and ideally closer to 180 grams, especially if
they are trying to add muscle mass. This is a lot of protein to eat, and the
added challenge is that it should not be taken in one sitting but rather spread
out over the day to avoid losing amino acids to oxidation (i.e., using them to
produce energy when we want them to be available for muscle protein
synthesis). The literature suggests that the ideal way to achieve this is by
consuming four servings of protein per day, each at ~0.25 g/lb of body
weight. A six-ounce serving of chicken, fish, or meat will provide about 40 to
45 grams (at about 7 grams of actual protein per ounce of meat), so our
hypothetical 180-pound person should eat four such servings a day.
Most people don’t need to worry about consuming too much protein. It
would require an overwhelming effort to eat more than 3.7 g/kg/day (or
~1.7 g/lb of body weight), defined as the safe upper limit of protein
consumption (too much stress on the kidneys, for one). For someone my size,
that maximum amount would be nearly 300 grams per day, or the equivalent
of seven or eight chicken breasts.
How much protein you need depends on your sex, body weight and lean
body mass, activity level, and other factors, including age. There is some
evidence that older people might require more protein because of the
anabolic resistance that develops with age—that is, their greater difficulty in
gaining muscle. Unfortunately, there’s no CGM for protein, so it becomes a
bit of a process of trial and error. I try to consume enough to maintain muscle
mass as I train. If I find that I’m losing muscle mass, then I endeavor to eat
more. Older people in particular should try to keep track of their lean mass,
such as via a body-composition-measuring scale (or better yet, DEXA scan),
and adjust their protein intake upwards if lean mass declines. For me and my
patients, this works out to four servings, as described, with at least one of
them being a whey protein shake. (It’s very difficult for me to consume four
actual meals. Typically, I will consume a protein shake, a high-protein snack,
and two protein meals.)
Now, a word on plant protein. Do you need to eat meat, fish, and dairy to
get sufficient protein? No. But if you choose to get all your protein from
plants, you need to understand two things. First, the protein found in plants is
there for the benefit of the plant, which means it is largely tied up in
indigestible fiber, and therefore less bioavailable to the person eating it.
Because much of the plant’s protein is tied to its roots, leaves, and other
structures, only about 60 to 70 percent of what you consume is contributing
to your needs, according to Don Layman, professor emeritus of food science
and human nutrition at the University of Illinois Urbana-Champaign, and an
expert on protein.
Some of this can be overcome by cooking the plants, but that still leaves
us with the second issue. The distribution of amino acids is not the same as in
animal protein. In particular, plant protein has less of the essential amino
acids methionine, lysine, and tryptophan, potentially leading to reduced
protein synthesis. Taken together, these two factors tell us that the overall
quality of protein derived from plants is significantly lower than that from
animal products.
The same is true of protein supplements. Whey protein isolate (from
dairy) is richer in available amino acids than soy protein isolate. So if you
forgo protein from animal sources, you need to do the math on your protein
quality score. In truth, this can get pretty complicated pretty quick, because
you get wrapped around the axle of something called the Digestible
Indispensable Amino Acid Score (DIAAS) and the Protein DigestibilityCorrected Amino Acid Score (PDCAAS). These are great if you have the
time to comb through databases all day, but for those of us with day jobs,
Layman suggests focusing on a handful of important amino acids, such as
leucine, lycine, and methionine. Focus on the absolute amount of these amino
acids found in each meal, and be sure to get about three to four grams per day
of leucine and lycine and at least one gram per day of methionine for
maintenance of lean mass. If you are trying to increase lean mass, you’ll need
even more leucine, closer to two to three grams per serving, four times per
day.
Multiple studies suggest that the more protein we consume, in general, the
better. A large prospective study called the Healthy Aging and Body
Composition Study, with more than two thousand elderly subjects, found that
those who ate the most protein (about 18 percent of caloric intake) kept more
of their lean body mass over three years than those in the lowest quintile of
protein consumption (10 percent of calories). The difference was significant:
the low-protein group lost 40 percent more muscle than the high-protein
group.
You could make the case that protein is a performance-enhancing
macronutrient. Other studies have found that boosting protein intake even
moderately above the RDA can slow the progressive loss of muscle mass in
older people, including patients with heart failure and cachexia (wasting).
Adding thirty grams of milk protein to the diet of frail elderly people, in
another study, significantly improved their physical performance.
Beyond its role in building muscle, protein may have beneficial effects on
our metabolism. One study found that giving elderly people supplements
containing essential amino acids (that is, mimicking some effects of
increasing dietary protein) lowered their levels of liver fat and circulating
triglycerides. Another study in men with type 2 diabetes found that doubling
their protein intake from 15 to 30 percent of total calories, while cutting
carbohydrates by half, improved their insulin sensitivity and glucose control.
Eating protein also helps us feel satiated, inhibiting the release of the hungerinducing hormone ghrelin, so we eat fewer calories overall.
In case my point here isn’t clear enough, let me restate it: don’t ignore
protein. It’s the one macronutrient that is absolutely essential to our goals.
There’s no minimum requirement for carbohydrates or fats (in practical
terms), but if you shortchange protein, you will most certainly pay a price,
particularly as you age.