. 2020 Feb 18;52(3):329–360. doi: 10.1007/s00726-020-02823-6

Table 3.

Metabolic needs for glycine and its dietary provision in the 70-kg healthy adult human

Variable	Amount g/day
Dietary protein intake^a	52.5
Bioavailability of dietary glycine	1.42
Glycine intake from diet^a	1.58
Dietary glycine not digested (10%)	0.16
Digestible glycine intake from diet	1.42
Needs for glycine	10.1
Heme synthesis^b	0.25
Creatine synthesis^b	1.00
Purine synthesis^b	0.25
Glutathione synthesis^c	0.57
Net serine synthesis^a,d	1.36
Bile salt synthesis^c	0.06
Hippurate synthesis^c	0.54
Irreversible loss through oxidation to CO₂^a	5.03
Urinary glycine loss^c	0.11
Sweat and dermal glycine loss^c	0.08
Ileal endogenous glycine loss^e	0.66
Colonic endogenous glycine loss^e	0.15
Glycine synthesis (calculated)^f	8.16
From serine^c	2.54
From dietary choline^c	0.107
From threnoine^c	0.022
From endogenous sarcosine^c	0.142
From carnitine^c	0.006
From endogenous 4-hydroxyproline (Hyp)^g	5.34
Glycine synthesis (measured)^g	9.10
Dietary glycine intake meeting glycine needs	14%
Contribution of Hyp to whole-body glycine synthesis	59%

^aGibson et al. (2002). Adult humans consume 0.75 g protein/kg BW/day

^bYu et al. (1985). This value refers to the healthy adult consuming 1.5 g protein/day

^cMeléndez-Hevia et al. (2009)

^dThe value is estimated from the plasma flux of glycine (22.6 g/day in the 70-kg healthy adult; Ginson et al. 2002) and the net conversion of plasma glycine into serine (i.e., 6% of plasma glycine flux; Butterworth et al. 1958)

^eStarck et al. (2018)

^fThe average value of 10.1 g/day for the healthy adult consuming 0.75 g protein/day (Gibson et al. 2002) and 8.09 g/day for the healthy adult consuming 1.5 g protein/day (Yu et al. 1985)

^gThe value was calculated on the basis of the following: (1) the rate of degradation of mature collagens in the extracellular matrix is equal to the rate of net synthesis of collagen (i.e., the rate of collagen secreted from fibroblasts to the extracellular matrix; 96.5 g/day) in the healthy adult human (Meléndez-Hevia et al. 2009); (2) the content of 4-hydroxyproline in collagen is 10.73 g/100 g collagen; Wu et al. 2011); and (3) 90% of collagen-derived 4-hydroxyproline is catabolized to form glycine in the healthy adult human (Knight et al. 2006); namely, 96.5 × 10.73/100 × 0.90 × 75.07/131.13 = 5.34 g/day