Comparison 1. Cyst(e)ine vs. placebo in added to cysteine‐free PN.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Weight gain during the study (g/kg/day)	1	36	Mean Difference (IV, Fixed, 95% CI)	‐4.1 [‐9.72, 1.52]
2 Increase in length (cm/ 6 days)	1	36	Mean Difference (IV, Fixed, 95% CI)	0.0 [‐0.41, 0.41]
3 Increase in head circumference (cm/ 6 days)	1	36	Mean Difference (IV, Fixed, 95% CI)	0.30 [‐0.11, 0.71]
4 Nitrogen retention (mg/kg/day)	4		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
4.1 All studies	4	95	Mean Difference (IV, Fixed, 95% CI)	31.81 [8.18, 55.43]
4.2 RCTs only	2	39	Mean Difference (IV, Fixed, 95% CI)	51.97 [18.21, 85.73]
4.3 Documented low nitrogen intake	1	10	Mean Difference (IV, Fixed, 95% CI)	36.20 [‐20.90, 93.30]
4.4 Documented lack of tyrosine intake	2	56	Mean Difference (IV, Fixed, 95% CI)	24.54 [‐1.56, 50.65]
4.5 No documented low intake of other nutrients	2	39	Mean Difference (IV, Fixed, 95% CI)	64.64 [9.12, 120.16]
4.6 Preterm only	4	73	Mean Difference (IV, Fixed, 95% CI)	40.53 [13.52, 67.55]
4.7 Full‐term only	1	16	Mean Difference (IV, Fixed, 95% CI)	‐14.0 [‐79.24, 51.24]
5 Plasma level of free cyst(e)ine (micromoles/100 ml)	4		WMD (Fixed, 95% CI)	Subtotals only
5.1 All studies	4	112	WMD (Fixed, 95% CI)	2.48 [1.44, 3.53]
5.2 RCTs only	2	56	WMD (Fixed, 95% CI)	2.21 [0.86, 3.57]
5.3 Document low nitrogen intake	1	10	WMD (Fixed, 95% CI)	6.88 [1.58, 12.18]
5.4 Documented lack of tyrosine intake	2	56	WMD (Fixed, 95% CI)	3.19 [1.50, 4.88]
5.5 No documented low intake of other nutrients	2	56	WMD (Fixed, 95% CI)	2.05 [0.72, 3.38]
5.6 Preterm only	4	90	WMD (Fixed, 95% CI)	2.46 [1.28, 3.64]
5.7 Full‐term only	1	16	WMD (Fixed, 95% CI)	1.79 [‐1.76, 5.34]
6 Total plasma cyst(e)ine level (micromoles/ 100 ml)	1	20	Mean Difference (IV, Fixed, 95% CI)	9.40 [5.13, 13.67]