Page 20 - Fall2012

A better enough folate or vitamin B to properly handle these nutrients. Randomized, placebo-controlled
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way to the methionine they are obtaining from muscle trials have shown that two weeks' supplementa-
meats.
tion with choline or six weeks' supplementation
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improve the As shown in Figure 2, once our needs with betaine lowered homocysteine levels both
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1-3
balance of for methylation are met, we use vitamin B and in the fasting state and after consuming a large
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glycine to glycine to convert any additional methionine in dose of methionine. In a similar study, three
months' supplementation with vitamin B made a
our diet to glutathione, which is the master anti-
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methionine oxidant and detoxifier of the cell as well as a key small improvement in homocysteine levels after
would be regulator of protein function. The conversion of a large dose of methionine. 5
to replace a methionine to glutathione is not instantaneous, There are, unfortunately, very few nutri-
however, and our liver requires a buffer system tional studies using glycine because scientists
substantial to protect itself against excessive methylation have not considered it an “essential” amino acid.
proportion of and the accumulation of homocysteine. Although our bodies can synthesize glycine,
This buffer system is comprised primarily primarily from the amino acid serine, one group
muscle meats of three nutrients: glycine, which is found most of scientists recently estimated that our ability
in the diet abundantly in bones and other connective tis- to produce glycine may fall short of our needs
with bones sue (Table 3); choline, which is found primarily for this amino acid by up to ten grams per day. 1
and skin. in liver and egg yolks (Table 4); and betaine, This is roughly the equivalent of an ounce of bone
meal each day. These authors pointed out that
which we can either make within our own bod-
ies from choline or obtain directly in our diets markers of glycine deficiency appear in the urine
from spinach, wheat, and beets (Table 5). Muscle of vegetarians, people consuming low-protein
meat provides its own vitamin B , but provides diets, children recovering from malnourishment,
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relatively little glycine, choline and betaine. In and pregnant women. They further suggested
order to safely use extra methionine from muscle that most of us adapt to a subtler degree of glycine
meat to support our antioxidant defenses and de- deficiency by decreasing our own turnover of
toxification systems, we therefore must balance collagen, which may lead to the accumulation of
muscle meat with liver and egg yolks as well as damaged collagen with age, thereby contributing
with soups, gravies, sauces, or other creative to arthritis, poor-quality skin, and many of the
dishes made from bones and other connective other negative consequences of aging. Indeed,
tissue, including skin. As useful adjuncts to while some studies have shown that restricting
these foods, some people may also benefit from dietary methionine lengthens the lifespan of rats
incorporating spinach, wheat or beets into their and while these have generated a great deal of
diet. interest, a similar study recently showed that the
Several studies support the relevance of same effect can be achieved by supplementing
these pathways to human nutrition. In one such the diet with extra glycine.
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study, a large dose of methionine increased the Some authors have recently suggested that
excretion of a metabolic byproduct of glycine, a vegan diet would lengthen lifespan because
choline and betaine in the urine, suggesting that of its naturally low methionine content. If me-
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excess methionine causes the irreversible loss of thionine restriction primarily increases lifespan

Table 3. PROPORTION OF TOTAL PROTEIN AS GLYCINE IN SELECTED FOODS 23

Chicken Breast 5%
Chicken Skin 16%
Bone 31% (estimate)

Glycine makes up only five percent of the amino acids in typical muscle meats, but is much richer in proteins such as
collagen and elastin, found in connective tissues like skin and bone. Most of the protein in bone is collagen, which is about
one-third glycine, making any dishes made from bone, including soups and sauces, excellent sources of this amino acid.
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