Why if you have chicken legs you should eat chicken legs (and feet): The Glycine Gap
The Forgotten Amino Acid That Plant-Based Warriors Don't Want You to Know
While soy enthusiasts are busy perfecting their quinoa-tempeh combinations and tofu smoothies, convinced they've cracked the protein code, there's one amino acid that's laughing at their carefully calculated macros from the sidelines: glycine.
We often hear about lysine deficiency in grains and methionine deficiency in legumes, which is why nutritionists recommend combining these protein sources. The irony? The famous soy-rice combination that plant-based advocates swear by doesn't actually improve soy protein quality—it increases methionine but decreases lysine, making lysine the new limiting amino acid. So much for that "complete protein" theory.
However, there's one amino acid that's consistently overlooked despite being deficient in grains, legumes, and dairy products: glycine.
Chicken feet, common in Chinese cuisine, are extremely rich in glycine.
Our Evolutionary Heritage
The high glycine requirement in human skin and muscles has deep anthropological-evolutionary roots. Primitive humans didn't consume only muscle meat—they also consumed the skeletal parts. Bones were boiled and released high amounts of glycine, completing the amino acid profile of meat to make it suitable not only for muscles but also for collagen regeneration.
Why Glycine Matters More Than You Think
Glycine is present in decent quantities in meat, fish, and eggs, though still less than what's found in human muscle composition. This is one reason why animal proteins have superior quality compared to casein and whey proteins, despite what supplement sellers might claim.
Many protein quality assessments are flawed because they ignore non-essential amino acids like glycine. These indices assume that deficiencies will be compensated by endogenous production from other amino acids, completely ignoring the actual biochemical conversion processes involved.
The Flawed Science Behind Protein Rankings
The belief that whey and casein are superior proteins stems from fundamentally flawed research methodologies:
The Rat Study Problem: Many protein quality assessments originated from nearly absurd experiments measuring weight gain in rats. These studies ignored a crucial fact: rats have a significantly higher conversion rate for transforming threonine and serine into glycine compared to humans. This led to the creation of the worthless PER (Protein Efficiency Ratio) index.
Incomplete Assessment Methods: Current protein quality indices like PDCAAS and DIAAS are rushed and irrational. They completely ignore non-essential amino acids (those that can be synthesized from other amino acids), assuming that any deficiencies will be automatically compensated by endogenous production from other amino acids.
The Critical Flaw: These assessment methods completely ignore the actual biochemical conversion formulas and metabolic costs involved in amino acid transformation. They assume unlimited conversion capacity without considering the enzymatic limitations and energy requirements of these processes.
The Collagen Connection
This glycine deficiency becomes even more critical when we consider not just muscle repair and growth from training, but also human collagen formation. Collagen contains extremely high percentages of glycine, making it essential for:
Skin health and elasticity
Joint function and mobility
Connective tissue repair
Wound healing
The Modern Disconnect
Today's eating patterns have shifted dramatically from our ancestors. We consume primarily muscle meat while discarding the glycine-rich parts that our bodies evolved to utilize. This creates a nutritional gap that can impact:
Skin aging and elasticity
Joint health and recovery
Overall connective tissue function
Optimal muscle development
Practical Solutions
To bridge this glycine gap, consider incorporating:
Bone broth: Rich in glycine from dissolved collagen
Chicken feet: Extremely high in collagen and glycine
Organ meats: Often contain higher glycine levels than muscle meat
Gelatin supplements: Concentrated collagen-derived glycine
Whole animal consumption: Following ancestral eating patterns
Glycine supplements: 3-5 grams of glycine per day (also seemingly good for sleep)
The Bottom Line
If you're serious about optimizing your protein intake for both muscle development and overall health, don't ignore glycine. Our bodies evolved with specific nutritional expectations based on consuming whole animals, not just select muscle cuts.
The next time you see chicken legs (both the walking kind and the eating kind), remember that this overlooked amino acid might be the missing piece in your nutrition puzzle.