Comparison 1. Protein supplementation versus no supplementation.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Growth: weight	6		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
1.1.1 Weight gain (g/kg/day)	5	101	Mean Difference (IV, Fixed, 95% CI)	3.82 [2.94, 4.70]
1.1.2 Weight at term‐equivalent age (grams)	1	76	Mean Difference (IV, Fixed, 95% CI)	61.00 [‐160.23, 282.23]
1.1.3 Weight at end of study (grams)	1	14	Mean Difference (IV, Fixed, 95% CI)	250.00 [‐41.56, 541.56]
1.2 Growth: length	5		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
1.2.1 Length gain (cm/week)	4	68	Mean Difference (IV, Fixed, 95% CI)	0.12 [0.07, 0.17]
1.2.2 Length at term‐equivalent age (cm)	1	76	Mean Difference (IV, Fixed, 95% CI)	‐0.50 [‐1.65, 0.65]
1.3 Growth: head circumference	5		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
1.3.1 Head growth (cm/week)	4	68	Mean Difference (IV, Fixed, 95% CI)	0.06 [0.01, 0.12]
1.3.2 Head circumference at term‐equivalent age (cm)	1	76	Mean Difference (IV, Fixed, 95% CI)	0.30 [‐0.24, 0.84]
1.4 Growth: skin fold thickness	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
1.4.1 Skinfold thickness (mm/week): triceps	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
1.4.2 Skinfold thickness (mm/week): subscapular	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
1.5 Duration of hospital stay (days)	1		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
1.6 Feeding intolerance	1		Risk Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.7 Necrotising enterocolitis	1		Risk Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.8 Blood urea (mmol/L)	4	81	Mean Difference (IV, Fixed, 95% CI)	0.95 [0.81, 1.09]
1.9 Serum albumin (g/L)	1		Mean Difference (IV, Fixed, 95% CI)	Subtotals only