GLYCINE

The amino acid glycine is conditionally essential during pregnancy. Usually, we are able to make enough of it ourselves to meet our basic survival needs; during pregnancy, however, it must be obtained from food. It is the limiting factor for protein synthesis in the fetus, and thus almost certainly a limiting factor for fetal growth.⁵⁵

The fetus can obtain glycine from two sources: the placenta transports glycine from the mother’s blood, and it uses folate to manufacture it from another amino acid called serine. The mother can obtain glycine primarily from collagen- rich foods such as skin and bones or bone broths (see Figure 8).⁵⁶

Glycine is depleted in the detoxification of excess methionine, another amino acid. Eggs and meat are the main sources of methionine—it not only constitutes a greater percentage of their total protein but these foods are also higher in total protein than plant foods (see Figure 9).⁵⁶ It is important, therefore, for the expectant mother to liberally match her eggs and muscle meats with glycine-rich skin and bones and folate-rich liver, legumes and greens.