You're Eating Protein and Still Deficient. Here's the Genetic Reason.

The MTHFR enzyme catalyzes one of the most critical reactions in your body: the conversion of folate into its active form (methylfolate), which then powers the methylation cycle. Methylation is required to convert serine into glycine, and to activate the cofactors that drive glycine synthesis. Without proper MTHFR function, your methylation cycle stalls, and your body cannot manufacture glycine efficiently, even if you eat all the serine you need.

The MTHFR C677T variant, carried by roughly 40% of people with European ancestry, reduces enzyme activity by 40 to 70 percent. The A1298C variant is less severe but still impairs function. When you have either variant, your cells cannot convert dietary folate into the active methylfolate needed to power glycine synthesis. This means your glycine production drops significantly, regardless of how much protein you consume.

You may notice poor sleep quality, slow wound healing, joint discomfort, and weak connective tissue. Your skin may lack elasticity, and your nails and hair may be brittle. These are all signs that your body is struggling to manufacture collagen, which requires abundant glycine. Brain fog and mood instability are also common, because methylation powers neurotransmitter synthesis as well.

The COMT enzyme breaks down dopamine, norepinephrine, and epinephrine, the catecholamines that drive focus, motivation, and stress response. This breakdown process consumes methyl groups from your methylation cycle. The COMT Val158Met variant (commonly called the slow COMT or warrior gene variant) reduces enzyme activity, meaning catecholamines accumulate in your brain and body, and fewer methyl groups are consumed in the process. The fast COMT variant (Met158Met) increases enzyme activity, meaning catecholamines are broken down very rapidly, but this consumes methyl groups at a much faster rate.

Roughly 30 to 40% of the population carries at least one copy of the slow COMT variant. If you have a slow COMT, catecholamines accumulate, which compounds methylation demand at a time when your methylation cycle may already be sluggish. If you have a fast COMT, you burn through methyl groups rapidly, leaving fewer methyl donors available for glycine synthesis and collagen production. Either way, your methylation cycle is competing for the same limited methyl pool.

You may experience anxiety, insomnia, or emotional sensitivity if you have a slow COMT. If you have a fast COMT, you may feel energy crashes, mood swings, or restlessness. Either pattern reduces the methyl groups available for glycine synthesis, worsening joint pain, skin elasticity, and wound healing.

The SOD2 enzyme (superoxide dismutase 2) is your cell’s primary antioxidant defense system inside mitochondria. It converts dangerous superoxide radicals into hydrogen peroxide, protecting your cells from oxidative damage. This process is essential for healthy energy production and for the stability of the enzymes that synthesize glycine. When SOD2 is impaired by a genetic variant, oxidative stress accumulates in your mitochondria, damaging the very enzymes responsible for converting serine into glycine.

The SOD2 Ala16Val variant, carried by roughly 40% of the population, reduces enzyme activity and increases mitochondrial oxidative stress. High oxidative stress in your mitochondria impairs the conversion of serine to glycine, creating a functional glycine deficiency even when serine intake is adequate. Your cells are literally too stressed (at the molecular level) to manufacture glycine efficiently.

You may experience persistent fatigue, slow exercise recovery, and chronic joint or muscle pain. Your connective tissue may be slow to heal, and you may notice premature aging of skin. These symptoms reflect the dual problem: your mitochondria are under oxidative stress, and your glycine production is compromised as a result.

The VDR receptor is the lock on your cells that receives the vitamin D signal. Vitamin D is far more than a bone health nutrient; it is a hormone that regulates gene expression throughout your body, including genes involved in glycine metabolism and collagen synthesis. When your VDR receptor is functioning normally, vitamin D signals flow freely into your cells, turning on the genes that manufacture glycine and build collagen. When a VDR variant is present, your cells become resistant to vitamin D signaling, even when blood levels are normal.

The VDR BsmI, FokI, and TaqI variants are carried by roughly 30 to 50% of the population, depending on ancestry. These variants reduce your cells’ sensitivity to vitamin D, meaning you may have adequate blood levels of vitamin D but insufficient cellular uptake and gene expression. Your cells are literally not hearing the vitamin D signal that should be telling them to manufacture glycine.

You may experience poor bone density, weak connective tissue, slow wound healing, and persistent joint discomfort. Your immune system may be sluggish, and you may notice seasonal mood changes. These are all signs that your cells are not responding properly to vitamin D, and as a result, the genes controlling glycine synthesis are not being activated.

The FADS1 enzyme is a fatty acid desaturase that converts short-chain omega-3 and omega-6 fatty acids (from plants and seeds) into long-chain forms (EPA, DHA, and arachidonic acid). These long-chain fatty acids are essential for cell membrane structure, inflammation regulation, and the proper function of enzymes throughout your body, including those that synthesize glycine. Your cell membranes are made of fatty acids; when they are built from the wrong fatty acid ratios, the enzymes embedded in those membranes function poorly.

The FADS1 rs174537 variant, carried by roughly 30 to 40% of the population, reduces delta-5 desaturase activity, impairing the conversion of plant-based omega-3 to EPA and long-chain forms. This means your cell membranes may lack the correct balance of long-chain omega-3 fatty acids, destabilizing the enzymes that manufacture glycine and weakening your structural proteins. You are eating omega-3 rich foods, but your body cannot convert them efficiently into the forms it needs.

You may notice joint stiffness, inflammation, slow wound healing, and weak connective tissue. Your skin may lack elasticity and radiance. Your mood and cognition may suffer, because EPA is essential for brain health. These symptoms reflect the dual problem: your membranes are built from suboptimal fatty acids, and as a result, the glycine-synthesis enzymes embedded in those membranes function poorly.

The HFE gene encodes a protein that regulates hepcidin, a hormone that controls how much iron your intestines absorb and how much your body stores. Iron is an essential cofactor for dozens of enzymes throughout your body, including several involved in amino acid metabolism and collagen synthesis. When HFE function is disrupted, iron either accumulates (in the case of the C282Y variant) or becomes insufficiently available (in the case of the H63D variant or other genetic patterns). Either excess or deficiency impairs the iron-dependent enzymes that convert serine into glycine.

The HFE H63D variant, carried by roughly 15 to 20% of people with European ancestry, is associated with mild iron dysregulation and reduced iron absorption. The C282Y variant (when homozygous) causes iron overload, a serious condition. When iron levels are suboptimal, the iron-dependent enzymes responsible for glycine synthesis lose catalytic activity, slowing glycine production even when all other pathways are intact. You may have adequate dietary iron, but your body cannot utilize it efficiently.

You may experience fatigue, weak connective tissue, slow wound healing, joint discomfort, and poor exercise recovery. Your hair and nails may be brittle, and your skin may be pale or lacking radiance. If you have iron overload (C282Y), you may experience joint pain, organ damage, and metabolic dysfunction. In both cases, the glycine synthesis machinery lacks the cofactor it needs to function.