Place · Level 3 · Supplement
Glycine
最小的氨基酸 · 条件必需每日缺口 ~10 g · 一分子 5 命运 (胶原/GSH/肌酸/血红素/神经) · 3 g 改善睡眠
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Chapter 1
Conditionally essential
Conditionally essential
Glycine (Gly, G) is the smallest of the 20 proteinogenic amino acids — its side chain is just a hydrogen atom. This makes it structurally unique, able to fit anywhere a protein needs 'very little space + high flexibility', most famously at the inner turns of the collagen triple helix.
Classic textbooks list glycine as a 'non-essential amino acid': the body can synthesize it from serine via SHMT enzyme + 5,10-methylene-THF, feeding into one-carbon metabolism.
Meléndez-Hevia 2009 J Biosci re-counted daily glycine demand:
Collagen synthesis: ~10-20 g new collagen/day in adults, containing ~3-7 g glycineGSH synthesis: ~5-10 g GSH turnover/day, containing ~1-2 g glycineCreatine synthesis: ~1.5-2 g creatine/day, containing ~0.5 g glycineHeme synthesis: red cells turn over daily; each porphyrin ring contains 4 glycines, ~0.2 g/dayPurine bases + bile acids + neurotransmitters: ~1 gTotal demand: ~10-15 g/day
Endogenous capacity: the SHMT pathway from serine produces ~2.5-3 g/day. The gap is ~10 g/day, which has to come from diet. A typical Western diet supplies 1.5-3 g/day (eggs / meat / legumes / gelatin), still well below the requirement.
Meléndez-Hevia's conclusion: glycine isn't 'non-essential' — it's conditionally essential. The body makes some, but not nearly enough for daily use, so dietary intake is required.
This is the Atlas's first systematic treatment of the 'conditionally essential' concept in nutrition. It also applies to glutamine, arginine, cysteine, and tyrosine — a third category beyond the textbook 'essential vs non-essential' split.
Classic textbooks list glycine as a 'non-essential amino acid': the body can synthesize it from serine via SHMT enzyme + 5,10-methylene-THF, feeding into one-carbon metabolism.
Meléndez-Hevia 2009 J Biosci re-counted daily glycine demand:
Collagen synthesis: ~10-20 g new collagen/day in adults, containing ~3-7 g glycineGSH synthesis: ~5-10 g GSH turnover/day, containing ~1-2 g glycineCreatine synthesis: ~1.5-2 g creatine/day, containing ~0.5 g glycineHeme synthesis: red cells turn over daily; each porphyrin ring contains 4 glycines, ~0.2 g/dayPurine bases + bile acids + neurotransmitters: ~1 gTotal demand: ~10-15 g/day
Endogenous capacity: the SHMT pathway from serine produces ~2.5-3 g/day. The gap is ~10 g/day, which has to come from diet. A typical Western diet supplies 1.5-3 g/day (eggs / meat / legumes / gelatin), still well below the requirement.
Meléndez-Hevia's conclusion: glycine isn't 'non-essential' — it's conditionally essential. The body makes some, but not nearly enough for daily use, so dietary intake is required.
This is the Atlas's first systematic treatment of the 'conditionally essential' concept in nutrition. It also applies to glutamine, arginine, cysteine, and tyrosine — a third category beyond the textbook 'essential vs non-essential' split.
Where Gly comes from in food
Dietary glycine content (per 100 g protein):Gelatin / collagen / bone broth: ~25-30 g, by far the highest (collagen itself is 33% Gly)Egg white: ~3 gChicken breast / red meat / fish: ~3-5 g (mostly in connective tissue and muscle membrane collagen)Soy / legumes: ~4-5 gWhey protein: ~1.5-2 g, very lowGrain / vegetables: ~3-4 g
Practical implications:
1. If you eat only lean meat / chicken breast / whey protein, even with very high total protein (common in fitness diets), a glycine deficit can persist
2. 'Whole animal + connective tissue' eating patterns (traditional cuisine / whole chicken / bone broth / tripe / chicken feet / fish skin) supply lots of Gly
3. Strict vegan + high-protein diets (soy / pea protein powders) usually fall short on Gly
For cooking: eating a whole chicken (with skin + bone broth) provides 3-5× more Gly than just chicken breast. Consciously add collagen sources to your diet: gelatin powder (5-15 g stirred into water), bone broth, fish skin, chicken wings, tendons. Or supplement plain glycine powder — one of the cheapest amino acids on the shelf, ~$0.05-0.10/g, 5-10× cheaper per gram of Gly than collagen peptides.
Note: this is not a 'fitness muscle-building' supplement; it's a multi-purpose adjunct for connective tissue repair, GSH maintenance, and sleep improvement.
这笔缺口账是怎么算出来的
身体自己确实能造甘氨酸: 从丝氨酸 (serine) 出发, 由 SHMT 酶 (丝氨酸羟甲基转移酶) 转过来, 顺带接进 1-碳代谢。所以能不能造从来不是争点, 争点是造得够不够。把收支两边摆开:
内源合成 (SHMT 通路从 serine 出发) 每天只造 ~2.5-3 g胶原、GSH、肌酸、血红素、神经递质这些用途加起来每天要 ~10-15 g典型西方膳食再补 1.5-3 g/天 (鸡蛋、肉 / 豆、明胶), 仍然填不平这 ~10 g/天 的缺口
Meléndez-Hevia 那篇文章的论证到此为止: 它没有发现甘氨酸的新用途, 只是把已知的用途逐条加起来, 发现供给端对不上。条件必需这一类之所以要存在, 就是因为一个氨基酸可以既造得出来、又不够用, 而必需 / 非必需的二分法里没有放这种情况的格子。
Chapter 2
Metabolic hub
Metabolic hub
Glycine isn't 'just another amino acid' — it's a hub node on the body's metabolic map, directly feeding at least five independent pathways.
1. Collagen synthesis (largest consumer)
The triple helix's Gly-X-Y repeat puts a Gly at every third residue — collagen is ~33% Gly. Adults synthesize 10-20 g of collagen per day, consuming 3-7 g of Gly. This is the chemical root behind the collagen-peptides/identity scene in the Atlas: 'why is collagen so Gly-rich?' is the mirror image of 'collagen synthesis drains the Gly pool'.
2. GSH (glutathione) synthesis
GSH = γ-Glu-Cys-Gly, with glycine as the third amino acid. The GSS enzyme (glutathione synthetase) joins γ-Glu-Cys + Gly → GSH (this is step 2 in the NAC L4 animation). Although Cys is the rate-limiting raw material in the NAC story, chronic low Gly can become a secondary bottleneck.
3. Creatine synthesis
Creatine is made in two steps:
AGAT (kidney): Gly + Arg → guanidinoacetate (GAA) + ornithineGAMT (liver): GAA + S-adenosylmethionine: The body's main methyl-group donor — it tags DNA, neurotransmitters, and more with methyl groups. → creatine + SAH
Glycine donates the carbon backbone for creatine, which is why vegans and vegetarians often have low baseline creatine (low Gly intake + no dietary meat creatine). Supplementing creatine bypasses this endogenous bottleneck.
4. Heme synthesis
The first step of porphyrin-ring synthesis (covered in the iron/heme-synthesis L4) is ALAS (mitochondrial), condensing Gly + succinyl-CoA → δ-aminolevulinic acid (ALA) + CO₂. Each porphyrin ring contains 4 glycines. The body makes ~2 million new red cells per second, continuously drawing Gly into the heme-production line.
5. Inhibitory neurotransmitter + NMDA co-agonist
In the spinal cord and brainstem, Gly is a classic inhibitory neurotransmitter (similar to GABA), binding the GlyR chloride channel and inhibiting motor neurons. Tetanus toxin works by blocking Gly release, producing muscle rigidity. In the cortex, Gly is simultaneously a mandatory co-agonist at NMDA receptors (both glutamate and Gly required to open the channel), participating in learning, memory, and neural plasticity. Gly receptor activation also contributes to sleep regulation in the spinal cord and brainstem — the next scene covers Yamadera 2007 clinical evidence.
Core insight: glycine is one of the few amino acids that simultaneously serves structural (collagen), metabolic (GSH / creatine / heme), and signaling (neurotransmitter) roles. Its deficit isn't a single-pathway problem — it's systemic erosion.
1. Collagen synthesis (largest consumer)
The triple helix's Gly-X-Y repeat puts a Gly at every third residue — collagen is ~33% Gly. Adults synthesize 10-20 g of collagen per day, consuming 3-7 g of Gly. This is the chemical root behind the collagen-peptides/identity scene in the Atlas: 'why is collagen so Gly-rich?' is the mirror image of 'collagen synthesis drains the Gly pool'.
2. GSH (glutathione) synthesis
GSH = γ-Glu-Cys-Gly, with glycine as the third amino acid. The GSS enzyme (glutathione synthetase) joins γ-Glu-Cys + Gly → GSH (this is step 2 in the NAC L4 animation). Although Cys is the rate-limiting raw material in the NAC story, chronic low Gly can become a secondary bottleneck.
3. Creatine synthesis
Creatine is made in two steps:
AGAT (kidney): Gly + Arg → guanidinoacetate (GAA) + ornithineGAMT (liver): GAA + S-adenosylmethionine: The body's main methyl-group donor — it tags DNA, neurotransmitters, and more with methyl groups. → creatine + SAH
Glycine donates the carbon backbone for creatine, which is why vegans and vegetarians often have low baseline creatine (low Gly intake + no dietary meat creatine). Supplementing creatine bypasses this endogenous bottleneck.
4. Heme synthesis
The first step of porphyrin-ring synthesis (covered in the iron/heme-synthesis L4) is ALAS (mitochondrial), condensing Gly + succinyl-CoA → δ-aminolevulinic acid (ALA) + CO₂. Each porphyrin ring contains 4 glycines. The body makes ~2 million new red cells per second, continuously drawing Gly into the heme-production line.
5. Inhibitory neurotransmitter + NMDA co-agonist
In the spinal cord and brainstem, Gly is a classic inhibitory neurotransmitter (similar to GABA), binding the GlyR chloride channel and inhibiting motor neurons. Tetanus toxin works by blocking Gly release, producing muscle rigidity. In the cortex, Gly is simultaneously a mandatory co-agonist at NMDA receptors (both glutamate and Gly required to open the channel), participating in learning, memory, and neural plasticity. Gly receptor activation also contributes to sleep regulation in the spinal cord and brainstem — the next scene covers Yamadera 2007 clinical evidence.
Core insight: glycine is one of the few amino acids that simultaneously serves structural (collagen), metabolic (GSH / creatine / heme), and signaling (neurotransmitter) roles. Its deficit isn't a single-pathway problem — it's systemic erosion.
Why hub teaching matters
Nutrition textbooks split amino acids into essential / non-essential and discuss them one by one — this teaching style completely misses the metabolic topology between amino acids:Glycine is a hub: simultaneously feeds 5 pathways + 1 neural signalCys is a hub: GSH, taurine, Coenzyme A, structural disulfide bridgesGlu / Gln are hubs: neurotransmitters, purine synthesis, nitrogen balance, GSHMet is a hub: S-adenosylmethionine: The body's main methyl-group donor — it tags DNA, neurotransmitters, and more with methyl groups. as universal methyl donor, conversion to Cys, carnitine synthesisTrp is a hub: 5-HT neurotransmitter, niacin, melatonin
A chronic shortage of any of these hub amino acids simultaneously affects multiple systems, but textbooks at the 'nutrition' level usually just list them in tables without expanding the hub-spoke topology.
The Atlas wants to correct this: amino acids are not 20 independent entries — they form a metabolic topology map. Understanding the hub nodes matters far more than memorizing each amino acid's name.
This is one concrete instance of the Atlas's long-term goal: knowledge of the body should be organized as a system, not a dictionary.
五条通路各自的酶和反应式
胶原蛋白合成 (最大消耗)三股螺旋的 Gly-X-Y 重复, 每三个位置一个 Gly, 胶原蛋白 ~33% 是 Gly。成人每天合成 10-20 g 胶原, 消耗 3-7 g Gly。这是 atlas 在 collagen-peptides/identity 那一幕的化学根源: 为什么胶原蛋白富含 Gly从Gly 是限速辅料的反向角度理解就是胶原合成消耗 Gly 池。
GSH (谷胱甘肽) 合成
GSH = γ-Glu-Cys-Gly, Gly 是第三个氨基酸。GSS 酶 (谷胱甘肽合成酶) 把 γ-Glu-Cys + Gly → GSH (这是 NAC L4 第 2 步)。虽然 NAC 故事里 Cys 是限速原料, 但在 Gly 慢性不足的状态下, Gly 也可能成为次要瓶颈。
肌酸 (creatine) 合成
肌酸合成两步:
AGAT 酶 (肾脏): Gly + Arg → 胍乙酸 (GAA) + 鸟氨酸GAMT 酶 (肝脏): GAA + S-adenosylmethionine: The body's main methyl-group donor — it tags DNA, neurotransmitters, and more with methyl groups. → 肌酸 + SAH
甘氨酸是肌酸合成的碳骨架来源, 这是为什么 vegan / vegetarian 肌酸基线低 (Gly 摄入低加不吃肉类肌酸); 补肌酸主要是绕开内源合成的瓶颈。
血红素 (heme) 合成
卟啉环的合成第一步 (在 iron/heme-synthesis L4 那一幕讲过) 是 ALAS 酶 (线粒体) 把 Gly + succinyl-CoA → δ-氨基乙酰丙酸 (ALA) + CO₂。每个卟啉环含 8 个 Gly。红细胞每秒钟生成 ~200 万个新红细胞, 持续消耗 Gly 进入血红素生产线。
抑制性神经递质加 NMDA 共激动剂
在脊髓和脑干, Gly 是经典抑制性神经递质 (类似 GABA), 结合 GlyR 氯离子通道, 抑制运动神经元。破伤风毒素就是抑制 Gly 释放, 引起肌肉强直。在大脑皮层, Gly 同时是 NMDA 受体的强制共激动剂 (与 glutamate 一起需要才能开通道), 参与学习、记忆、神经可塑性。Gly 受体激动还在脊髓和脑干层面参与睡眠调节, 下一幕讲 Yamadera 2007 临床证据。
核心洞察: 甘氨酸是少数同时参与结构 (胶原)、代谢 (GSH / 肌酸、血红素)、信号 (神经递质) 三大维度的氨基酸, 它的缺口不是单一通路问题, 而是系统性弱化。
Chapter 3
Sleep at 3 g
Sleep at 3 g
Glycine's most heavily promoted supplemental use case is sleep improvement, and this signal is actually quite robust — better evidence than most 'sleep aid' supplements.
Key RCT evidence:
Yamadera 2007 Sleep Biol Rhythms (n=12 healthy adults + 19 adults with poor subjective sleep), 3 g glycine vs placebo 1 h pre-bed:
Subjective sleep quality scores improved significantly (Pittsburgh Sleep Quality Index / St. Mary's Hospital questionnaire)Objective polysomnography (PSG): sleep onset latency (SOL) shortenedSlow-wave sleep (SWS, deep sleep) duration didn't change significantly, but time-to-SWS arrived earlierREM sleep amount unchangedNext-day sleepiness reduced
Mechanism (Bannai 2012 J Pharmacol Sci): 3 g of Gly raises plasma glycine 2-3× for 2-3 hours, reaching the suprachiasmatic nucleus (suprachiasmatic nucleus: The brain's master clock — set by light, it runs the body's day–night rhythm.) region of the hypothalamus, where peripheral NMDA receptors are activated to lower core body temperature. Core-temperature drop is the key physiological signal for sleep onset — normally the body lowers temperature when preparing to sleep, and glycine accelerates this process. Simultaneously, glycine receptors in the spinal cord and brainstem reduce motor tone, helping the body relax.
This isn't a sedative, not GABA receptor agonism, not melatonin. It uses core thermoregulation — a completely different pathway — to assist sleep.
Clinical characteristics:
Doesn't produce daytime sleepiness — Yamadera 2007 + Inagawa 2006 both report improved daytime alertness (because nighttime sleep efficiency improves)No dependence, no tolerance, no receptor down-regulationMinimal side effects, dietary amino acid, excellent safetyDoesn't affect morning alertness, unlike melatonin or hypnotics
Evidence grade: B. Small samples but replicated; mechanism clear; clinical effect small to moderate.
Compared to other sleep-aid options:
Melatonin: strong for jet lag (A), weak for general insomnia (C)Glycine 3 g: subjective sleep quality + objective SOL (B)L-theanine: subjective relaxation (C-B), weak objective sleep dataMagnesium: weak signal in general population, strong in Mg-deficientCBT-I: A-level first-line for chronic insomnia
Glycine is one of the few sleep-aid supplements that is simultaneously cheap, safe, mechanistically clear, and RCT-supported.
Key RCT evidence:
Yamadera 2007 Sleep Biol Rhythms (n=12 healthy adults + 19 adults with poor subjective sleep), 3 g glycine vs placebo 1 h pre-bed:
Subjective sleep quality scores improved significantly (Pittsburgh Sleep Quality Index / St. Mary's Hospital questionnaire)Objective polysomnography (PSG): sleep onset latency (SOL) shortenedSlow-wave sleep (SWS, deep sleep) duration didn't change significantly, but time-to-SWS arrived earlierREM sleep amount unchangedNext-day sleepiness reduced
Mechanism (Bannai 2012 J Pharmacol Sci): 3 g of Gly raises plasma glycine 2-3× for 2-3 hours, reaching the suprachiasmatic nucleus (suprachiasmatic nucleus: The brain's master clock — set by light, it runs the body's day–night rhythm.) region of the hypothalamus, where peripheral NMDA receptors are activated to lower core body temperature. Core-temperature drop is the key physiological signal for sleep onset — normally the body lowers temperature when preparing to sleep, and glycine accelerates this process. Simultaneously, glycine receptors in the spinal cord and brainstem reduce motor tone, helping the body relax.
This isn't a sedative, not GABA receptor agonism, not melatonin. It uses core thermoregulation — a completely different pathway — to assist sleep.
Clinical characteristics:
Doesn't produce daytime sleepiness — Yamadera 2007 + Inagawa 2006 both report improved daytime alertness (because nighttime sleep efficiency improves)No dependence, no tolerance, no receptor down-regulationMinimal side effects, dietary amino acid, excellent safetyDoesn't affect morning alertness, unlike melatonin or hypnotics
Evidence grade: B. Small samples but replicated; mechanism clear; clinical effect small to moderate.
Compared to other sleep-aid options:
Melatonin: strong for jet lag (A), weak for general insomnia (C)Glycine 3 g: subjective sleep quality + objective SOL (B)L-theanine: subjective relaxation (C-B), weak objective sleep dataMagnesium: weak signal in general population, strong in Mg-deficientCBT-I: A-level first-line for chronic insomnia
Glycine is one of the few sleep-aid supplements that is simultaneously cheap, safe, mechanistically clear, and RCT-supported.
How to use, what not to expect
Recommended protocol (matching Yamadera 2007 + follow-ups):3 g glycine powder, 30-60 minutes pre-bedDissolve directly in water (glycine is water-soluble, slightly sweet, no flavoring needed)Or eat Gly-rich foods + a cup of bone broth (5-15 g gelatin ≈ 1.5-5 g Gly)Run continuously for 2-4 weeks and observe subjective + objective differences
What not to expect:
Not an 'instant knockout' — improves quality, not strong sedationWon't make you sleep 12 hours — sleep onset is faster, total duration unchangedDoesn't fix anxiety-driven insomnia, depression-driven insomnia, or chronic CBT-I-level insomnia — these need professional treatmentDoesn't replace lifestyle basics: dark before bed, no alcohol, cool bedroom (16-19°C is optimal), consistent sleep timing
Cautions:
Chronic kidney disease (CKD): high-protein + amino-acid loads need caution; physician guidanceOn clozapine-class antipsychotics: Gly is an NMDA co-agonist and may alter drug action (paradoxically there is positive evidence for adjunct use in schizophrenia, but still requires physician evaluation)Pregnancy / lactation: dedicated data is limited; food-source glycine is safe, but avoid supplement megadoses
Compared to other sleep-aid RCT protocols:
Melatonin 0.3-0.5 mg for jet lag: A gradeGlycine 3 g for general sleep quality: B gradeL-theanine 200 mg for subjective relaxation: C-B gradeMagnesium 200-400 mg in Mg-deficient: B grade (deficient population), C grade (general)CBT-I for chronic insomnia: A grade, first linePersistent severe insomnia: always seek professional evaluation
Practical principle: if you occasionally have trouble falling asleep (high stress / marginal jet lag / pre-training jitters), Gly 3 g is a low-risk high-ROI experiment. For chronic insomnia, don't rely on any supplement — do CBT-I or see a sleep physician.
试验具体测到了什么 · 降温这条路的细节
那项试验的完整结果:主观睡眠质量评分显著改善 (Pittsburgh 睡眠质量指数 / St. Mary's 医院问卷)客观多导睡眠图 (PSG): 入睡潜伏期 (SOL) 缩短慢波睡眠 (SWS, 深度睡眠) 时间没显著变化, 但到达 SWS 时间提前REM 睡眠总量没变第二天日间嗜睡感降低
降温这条路的分子细节 (Bannai 2012 J Pharmacol Sci): 3 g Gly 进血, 血浆 Gly 升高 ~2-3 倍, 持续 2-3 小时, 进入下丘脑视交叉上核 (suprachiasmatic nucleus: The brain's master clock — set by light, it runs the body's day–night rhythm.) 区域, 通过激活外周 NMDA 受体降低核心体温。核心体温下降是入睡的关键生理信号, 平时身体在准备睡觉时会自动降温, Gly 加速了这个过程。同时 Gly 受体在脊髓和脑干的抑制作用降低运动张力, 帮助身体放松。
临床特点:
不引起白天嗜睡, 反而 Yamadera 2007 加 Inagawa 2006 都报告日间清醒度改善 (因为夜间睡眠效率提高)不依赖, 不耐受, 没有受体下调机制副作用极少, 是膳食氨基酸, 安全性优秀不影响晨起警觉性, 不像褪黑素或安眠药
证据等级 B 级: 小样本但重复, 机制清楚, 临床效应小到中等。
对比其它助眠选项:
褪黑素: 时差强 (A), 一般失眠弱 (C)甘氨酸 3 g: 主观睡眠质量加客观入睡潜伏期 (B)L-Theanine: 主观放松 (C-B), 客观睡眠数据弱Magnesium: 一般人弱信号, 缺镁人群强CBT-I: 长期慢性失眠 A 级首选
甘氨酸是少数兼具便宜、安全、机制清楚、有 RCT 的助眠补剂。
Chapter 4
Collagen + GSH loops
Collagen + GSH loops
Glycine closes two direct metabolic loops, tying the Atlas's existing collagen and NAC/GSH stories together — this is the practical demonstration of 'one molecule, a hub'.
Loop 1: glycine ↔ collagen
Collagen synthesis consumes Gly (3-7 g/day)Collagen degradation releases Gly, Pro, Hyp back to the AA poolTraining, aging, and injury accelerate collagen turnover, raising Gly turnover demandClinical consequence: chronic athletes with joint pain, elderly with thinning skin, chronic injuries that heal slowly — these may partially reflect a Gly pool that's too small to support the needed repair rate (Meléndez-Hevia 2009's core hypothesis)
Practical meaning: if you're already doing the Shaw 2017 pre-training 5-15 g gelatin + 50 mg vitamin C protocol from the collagen-peptides scene, you're automatically getting a large dose of Gly (gelatin is 33% Gly = 1.5-5 g Gly). Glycine powder + vitamin C has almost identical cost-effectiveness to collagen peptide + vitamin C, because what's truly irreplaceable in collagen peptide is mostly Gly, Pro, Hyp. Collagen peptides do carry the additional Gly-Pro-Hyp tripeptide signaling hypothesis, so the two aren't fully equivalent, but glycine alone is a reasonable choice.
Loop 2: glycine ↔ GSH
GSH = γ-Glu-Cys-Gly, the third AA is GlyGSS enzyme joins γ-Glu-Cys + Gly → GSH (step 2 in the NAC L4)When Cys is replete and Gly is low, GSH synthesis rate is dragged down by Gly (though primary rate-limiting is Cys)Pérez-Torres 2017 review: in aging, diabetes, and chronic inflammation, reduced GSH synthesis is partially driven by an insufficient Gly pool
Practical meaning: if you're already supplementing NAC (to raise the Cys pool), adding Gly may further raise the GSH synthesis ceiling. This is a secondary bottleneck; in most cases NAC alone is enough. The NAC + Gly (GlyNAC) combo has shown oxidative-stress marker improvements in several small 2022-2023 elderly RCTs (Kumar 2023 Aging Cell etc.) — an emerging research direction.
Full hub topology:
```
dietary Gly
↓
endogenous SHMT synthesis (~3 g/day, insufficient)
↓
cellular Gly pool
╱ │ │ │ ╲
collagen GSH creatine heme neurotransmitter
```
All five fates compete for the same Gly pool. When any one is upregulated (heavy training raising collagen turnover, chronic inflammation raising GSH consumption), the others get indirectly squeezed.
This is why Meléndez-Hevia called it 'the weakest link in body metabolism': not because it's especially important, but because demand exceeds supply, there's no backup, and every pathway shares the same tight pool.
Loop 1: glycine ↔ collagen
Collagen synthesis consumes Gly (3-7 g/day)Collagen degradation releases Gly, Pro, Hyp back to the AA poolTraining, aging, and injury accelerate collagen turnover, raising Gly turnover demandClinical consequence: chronic athletes with joint pain, elderly with thinning skin, chronic injuries that heal slowly — these may partially reflect a Gly pool that's too small to support the needed repair rate (Meléndez-Hevia 2009's core hypothesis)
Practical meaning: if you're already doing the Shaw 2017 pre-training 5-15 g gelatin + 50 mg vitamin C protocol from the collagen-peptides scene, you're automatically getting a large dose of Gly (gelatin is 33% Gly = 1.5-5 g Gly). Glycine powder + vitamin C has almost identical cost-effectiveness to collagen peptide + vitamin C, because what's truly irreplaceable in collagen peptide is mostly Gly, Pro, Hyp. Collagen peptides do carry the additional Gly-Pro-Hyp tripeptide signaling hypothesis, so the two aren't fully equivalent, but glycine alone is a reasonable choice.
Loop 2: glycine ↔ GSH
GSH = γ-Glu-Cys-Gly, the third AA is GlyGSS enzyme joins γ-Glu-Cys + Gly → GSH (step 2 in the NAC L4)When Cys is replete and Gly is low, GSH synthesis rate is dragged down by Gly (though primary rate-limiting is Cys)Pérez-Torres 2017 review: in aging, diabetes, and chronic inflammation, reduced GSH synthesis is partially driven by an insufficient Gly pool
Practical meaning: if you're already supplementing NAC (to raise the Cys pool), adding Gly may further raise the GSH synthesis ceiling. This is a secondary bottleneck; in most cases NAC alone is enough. The NAC + Gly (GlyNAC) combo has shown oxidative-stress marker improvements in several small 2022-2023 elderly RCTs (Kumar 2023 Aging Cell etc.) — an emerging research direction.
Full hub topology:
```
dietary Gly
↓
endogenous SHMT synthesis (~3 g/day, insufficient)
↓
cellular Gly pool
╱ │ │ │ ╲
collagen GSH creatine heme neurotransmitter
```
All five fates compete for the same Gly pool. When any one is upregulated (heavy training raising collagen turnover, chronic inflammation raising GSH consumption), the others get indirectly squeezed.
This is why Meléndez-Hevia called it 'the weakest link in body metabolism': not because it's especially important, but because demand exceeds supply, there's no backup, and every pathway shares the same tight pool.
Creatine + heme loops
The full 'one molecule, five fates' teaching also needs the creatine and heme loops spelled out.Creatine synthesis loop
Creatine synthesis is two steps: AGAT in the kidney joins Gly + Arg → GAA (guanidinoacetate); GAMT in the liver joins GAA + S-adenosylmethionine: The body's main methyl-group donor — it tags DNA, neurotransmitters, and more with methyl groups. → creatine. This second step consumes substantial methyl groups, accounting for 40-70% of body SAM usage. Daily creatine synthesis is about 1.5-2 g, consuming ~0.5 g Gly, ~1 g Arg, and a large amount of methyl.
Vegans / vegetarians have low baseline creatine: no meat (which is the main creatine source), Gly intake is on the low side, and Arg comes mostly from plants (raising methylation demand) — both synthesis and intake are low. Supplementing creatine (3-5 g/day) bypasses the synthesis bottleneck and frees Gly for other pathways. This is why creatine supplementation effect sizes in vegans / vegetarians are typically larger than in omnivores (Solis 2023 / Forbes 2022 etc.).
Heme synthesis loop
ALAS in mitochondria joins Gly + succinyl-CoA → ALA (step 1 of the iron/heme-synthesis L4). Eight ALA molecules assemble the porphyrin ring; adding Fe²⁺ gives heme. Red cell lifespan is 120 days with 1% replaced daily, continuously drawing Gly into the production line. Blood loss, menstruation, and pregnancy raise Gly demand substantially.
Clinical meaning: menstruating women with low Gly intake may have heme synthesis lagging red-cell demand (even when iron is adequate). Meléndez-Hevia uses this as one of his empirical arguments for Gly being conditionally essential.
Neurotransmitter loops:
Inhibitory: GlyR chloride channels in the spinal cord and brainstem — this is why tetanus toxin blocking Gly release causes muscle rigidity (loss of inhibition → sustained excitation)Excitatory adjunct: mandatory NMDA co-agonist (both Gly and glutamate required), participating in learning, memory, and long-term potentiation (LTP)Sleep: the previous scene's body-temperature regulation + motor-neuron inhibition helps sleep onset
Summary: Gly is the most hub-like node connecting six Atlas stories — protein, iron, NAC, creatine, collagen, nervous — second only to Cys in connectivity. This is why the Atlas gives it its own island rather than burying it in 'amino acid miscellany'.
两条回路的酶、反应式和实操换算
回路 1: 甘氨酸 ↔ 胶原蛋白胶原合成消耗 Gly (3-7 g/天)胶原降解释放 Gly、Pro、Hyp 回 AA 池健身、老化、损伤让胶原 turnover 加速, Gly 周转需求上升
实操意义: 如果你做了 collagen-peptides 那条 Shaw 2017 训前 5-15 g 明胶加 50 mg 维 C, 你自动同时补了大量 Gly (明胶 33% Gly, 即 1.5-5 g Gly)。甘氨酸粉加维 C 在性价比上几乎等同于胶原肽加维 C, 因为胶原肽里真正不可替代的部分主要就是 Gly、Pro、Hyp。collagen-peptides 有 Gly-Pro-Hyp 三联肽假说的额外信号机制, 所以两者不完全等价, 但 Gly 单独也是合理选择。
回路 2: 甘氨酸 ↔ GSH
GSH = γ-Glu-Cys-Gly, 第三个 AA 是 GlyGSS 酶把 γ-Glu-Cys + Gly → GSH (NAC L4 第 2 步)在 Cys 充足、Gly 不足的状态下, GSH 合成速率被 Gly 拖住 (虽然主要限速是 Cys)Pérez-Torres 2017 综述: 在老化、糖尿病、慢性炎症人群, GSH 合成减低部分由 Gly 池不足驱动
实操意义: 如果你已经在补 NAC (抬 Cys 池), 额外加 Gly 可能进一步抬 GSH 合成上限。这是次要瓶颈, 大多数情况 NAC 单独就够。NAC 加 Gly (GlyNAC) 组合在 2022-2023 几项小型老年人 RCT 中显示氧化应激标志改善 (Kumar 2023 Aging Cell 等), 是新兴研究方向。
把两条回路并排看, 会发现它们抢的是同一笔钱: 一个人如果同时在大量训练 (胶原 turnover 高) 和处在慢性炎症里 (GSH 消耗高), 两条路会同时向池子伸手, 而池子并不会因此变大。
Chapter 5
Decision tree
Decision tree
Do you need to supplement glycine?
Glycine is one of the most underrated amino acids in the supplement aisle — excellent on cost-effectiveness, safety, mechanistic clarity, and clinical evidence, but with no marketing heat (because it's too cheap to support brand premiums).
Most meaningful candidates:
1. You eat only lean meat, chicken breast, whey: total protein is fine but Gly is short — 3-5 g/day glycine powder, more on training days
2. Your sleep quality is poor, sleep onset is slow: 3 g before bed (Yamadera 2007)
3. You're vegan / vegetarian: both Gly and creatine synthesis fall short — co-supplement Gly + creatine
4. Chronic athletes with joint pain, older adults with slow tissue repair: Gly 3-10 g/day, observe over 2-3 months
5. Chronic inflammation, diabetes, metabolic syndrome: the GlyNAC (Gly + NAC) combo is an emerging direction, B-C evidence
6. Women in menstruation / pregnancy / postpartum: Gly demand rises substantially — food sources plus modest supplementation is reasonable
Dosing protocols:
Sleep: 3 g before bedMaintenance / fill-the-gap: 5 g/day, any timeTraining and repair: 5-10 g/day, 2-3 g post-workout, 2-5 g spread across mealsClinical (GlyNAC, elderly antioxidant): 100 mg/kg/day (~7-10 g) + NAC 100 mg/kg/day (~7-10 g) (Kumar 2023 protocol, small RCTs only)
Cost:
Glycine powder: 1 kg ~$15-25, ~$0.015-0.025/g, 5 g/day = ~$0.10-0.15Collagen peptide: 1 kg ~$30-50, ~$0.03-0.05/g, 33% Gly, ~$0.10-0.15 per gram of GlyWhey protein: only 1.5-2% Gly, ~$1+ per gram of Gly
Glycine is one of the cheapest amino acids on the shelf — that itself is a fair-trade signal: no marketing premium, but also no 'miracle molecule' narrative to mislead you.
Correct forms:
Pure glycine powder (USP food-grade): best cost-effectivenessDon't buy magnesium glycinate as a way to supplement Gly — it's a magnesium product; some Gly content yes, but expensive and not the primary purposeDon't buy capsules — too little per pill, not economicalDon't buy 'complex amino acid blends' — opaque dosing, marketing premium
Safety:
Single doses up to 31 g have been safe in multiple studiesLong-term chronic 5-15 g/day RCTs show no significant side effectsSafer than the vast majority of supplements
Atlas verdict: in the supplement aisle, glycine is one of the few molecules with the clearest mechanism, the best cost-effectiveness, the fewest side effects, robust clinical evidence, and severe under-recognition. If you want to start a low-risk experiment in the supplement space, 3 g pre-bed or 5 g/day to fill the dietary gap is a very reasonable starting point.
Glycine is one of the most underrated amino acids in the supplement aisle — excellent on cost-effectiveness, safety, mechanistic clarity, and clinical evidence, but with no marketing heat (because it's too cheap to support brand premiums).
Most meaningful candidates:
1. You eat only lean meat, chicken breast, whey: total protein is fine but Gly is short — 3-5 g/day glycine powder, more on training days
2. Your sleep quality is poor, sleep onset is slow: 3 g before bed (Yamadera 2007)
3. You're vegan / vegetarian: both Gly and creatine synthesis fall short — co-supplement Gly + creatine
4. Chronic athletes with joint pain, older adults with slow tissue repair: Gly 3-10 g/day, observe over 2-3 months
5. Chronic inflammation, diabetes, metabolic syndrome: the GlyNAC (Gly + NAC) combo is an emerging direction, B-C evidence
6. Women in menstruation / pregnancy / postpartum: Gly demand rises substantially — food sources plus modest supplementation is reasonable
Dosing protocols:
Sleep: 3 g before bedMaintenance / fill-the-gap: 5 g/day, any timeTraining and repair: 5-10 g/day, 2-3 g post-workout, 2-5 g spread across mealsClinical (GlyNAC, elderly antioxidant): 100 mg/kg/day (~7-10 g) + NAC 100 mg/kg/day (~7-10 g) (Kumar 2023 protocol, small RCTs only)
Cost:
Glycine powder: 1 kg ~$15-25, ~$0.015-0.025/g, 5 g/day = ~$0.10-0.15Collagen peptide: 1 kg ~$30-50, ~$0.03-0.05/g, 33% Gly, ~$0.10-0.15 per gram of GlyWhey protein: only 1.5-2% Gly, ~$1+ per gram of Gly
Glycine is one of the cheapest amino acids on the shelf — that itself is a fair-trade signal: no marketing premium, but also no 'miracle molecule' narrative to mislead you.
Correct forms:
Pure glycine powder (USP food-grade): best cost-effectivenessDon't buy magnesium glycinate as a way to supplement Gly — it's a magnesium product; some Gly content yes, but expensive and not the primary purposeDon't buy capsules — too little per pill, not economicalDon't buy 'complex amino acid blends' — opaque dosing, marketing premium
Safety:
Single doses up to 31 g have been safe in multiple studiesLong-term chronic 5-15 g/day RCTs show no significant side effectsSafer than the vast majority of supplements
Atlas verdict: in the supplement aisle, glycine is one of the few molecules with the clearest mechanism, the best cost-effectiveness, the fewest side effects, robust clinical evidence, and severe under-recognition. If you want to start a low-risk experiment in the supplement space, 3 g pre-bed or 5 g/day to fill the dietary gap is a very reasonable starting point.
Stacking with other cheap AAs
The supplement aisle has a handful of cheap, under-known, genuinely useful amino acids that most consumers never hear about:Glycine (Gly): hub node — collagen, GSH, creatine, heme, sleep — entry-level high ROITaurine: an amino-acid-like molecule (-SO₃H not -COOH), cardiovascular, osmolality, bile-acid conjugation, retinal antioxidant — 1-3 g/day, moderate RCT signal across several indicationsLysine (Lys): essential AA, cofactor for collagen cross-link enzymes + a limiting AA (often short in grain/rice diets); solo supplementation is rare, mostly diet-drivenArginine (Arg): semi-essential, nitric oxide: A small signal molecule from the vessel lining that relaxes the vessel-wall muscle so the vessel widens. pathway precursor (but citrulline is more practical — covered in the citrulline scene), creatine + ornithine precursorMethionine (Met): essential, S-adenosylmethionine: The body's main methyl-group donor — it tags DNA, neurotransmitters, and more with methyl groups. methylation center, but excess Met raises Hcy — don't self-supplement carelesslyTryptophan (Trp): essential, 5-HT / niacin / melatonin precursor, but eating Trp-rich foods at night (turkey, milk) is safer; isolated Trp supplementation has 5-HT syndrome risk
Practical stacking:
Beginner: Gly 5 g/day + basics (protein, vegetables, training, sleep), watch for 4-6 weeks of differenceIntermediate: Gly 5 g + NAC 600 mg + creatine 5 g — three hub molecules in parallel, still under $30/monthSleep target: Gly 3 g pre-bedAntioxidant target: NAC + Gly (GlyNAC)Performance target: creatine + Gly + adequate total protein
These cheap amino acids have no marketing, no KOLs, no Instagram filter — which is precisely one reason they're trustworthy. When you see 'XX revolutionary new molecule, only $99/month', think of the Gly + NAC + creatine trio at $25/month, then decide.
买哪一种 · 一天多少钱 · 总评
甘氨酸是补剂区最被低估的氨基酸: 在性价比、安全性、机制清晰度、临床证据上都很优秀, 但没有营销热度 (因为它太便宜, 没有品牌溢价空间)。价格:
甘氨酸粉: 1 kg ~ $15-25, 每克 $0.015-0.025, 一天 5 g 仅 $0.10-0.15胶原肽: 1 kg ~ $30-50, 每克 $0.03-0.05, 含 Gly 33%, 每克 Gly $0.10-0.15乳清蛋白: 含 Gly 仅 1.5-2%, 每克 Gly $1+
甘氨酸是补剂区最便宜的氨基酸之一, 这本身是公平交易的信号: 它没有营销溢价, 但也没有神奇分子叙事来误导你。
该用的形态:
纯甘氨酸粉 (USP 食品级): 性价比最高不要买 magnesium glycinate 就为了补 Gly, 那是补镁的, Gly 含量虽有但贵且不主要不要买胶囊, 单粒太少, 不划算不要买 complex amino acid blend, 透明剂量低, 营销溢价
Atlas 总评: 在补剂区, 甘氨酸属于机制最清楚、性价比最高、副作用最少、临床证据稳健、被严重低估的少数几个分子之一。如果你想从补剂区开始一次低风险的实验, Gly 3 g 睡前或者 5 g/天补缺口都是非常合理的起点。
References · 8
- Meléndez-Hevia, E., De Paz-Lugo, P., Cornish-Bowden, A., & Cárdenas, M. L. (2009). A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Journal of Biosciences, 34(6), 853-872. 10.1007/s12038-009-0100-9
- Razak, M. A., Begum, P. S., Viswanath, B., & Rajagopal, S. (2017). Multifarious beneficial effect of nonessential amino acid, glycine: a review. Oxidative Medicine and Cellular Longevity, 2017, 1716701. 10.1155/2017/1716701
- Yamadera, W., Inagawa, K., Chiba, S., Bannai, M., Takahashi, M., & Nakayama, K. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms, 5(2), 126-131. 10.1111/j.1479-8425.2007.00262.x
- Bannai, M., & Kawai, N. (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. Journal of Pharmacological Sciences, 118(2), 145-148. 10.1254/jphs.11R04FM
- Pérez-Torres, I., Zúñiga-Muñoz, A. M., & Guarner-Lans, V. (2017). Beneficial effects of the amino acid glycine. Mini-Reviews in Medicinal Chemistry, 17(1), 15-32. 10.2174/1389557516666160609081602
- Shaw, G., Lee-Barthel, A., Ross, M. L. R., Wang, B., & Baar, K. (2017). Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. The American Journal of Clinical Nutrition, 105(1), 136-143. 10.3945/ajcn.116.138594
- Kumar, P., Liu, C., Suliburk, J., Hsu, J. W., Muthupillai, R., Jahoor, F., Minard, C. G., Taffet, G. E., & Sekhar, R. V. (2023). Supplementing glycine and N-acetylcysteine (GlyNAC) in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, physical function, and aging hallmarks: A randomized clinical trial. The Journals of Gerontology: Series A, 78(1), 75-89. 10.1093/gerona/glac135
- Forbes, S. C., Cordingley, D. M., Cornish, S. M., et al. (2022). Effects of creatine supplementation on brain function and health. Nutrients, 14(5), 921. 10.3390/nu14050921