Table 2.

Intervention studies on protein intake and testosterone. ^a

Study	Study type	Sample size	Duration of diet 1 (days)	Macronutrients, % of TEI (protein/fat/carbohydrate)		Protein intake (g/kg/day)		Change in total testosterone (diet 1 vs. 2) b
				Diet 1	Diet 2	Diet 1	Diet 2	nmol/L	%
Anderson et al., 1987	Crossover	7	10	44/21/35	10/20/70	3.9	0.9	−3.36	−20.7
Jaffe, 2013	Crossover	10	7	55/39/7	25/20/55	3.7	1.8	−14.46	−29.8
Langfort et al., 2001	Crossover	9	3	45/50/5	20/30/50	3.5	1.6	−3.44	−15.5
Michalczyk et al., 2019	Crossover	15	28	31/59/10	15/31/54	3.2	1.5	+ 3.32	+ 17.5
Toma, 2009	Parallel	17	49	30/39/31	14/25/58	2.6	1.1	−4.23	−19.4
Pourabbas et al., 2021 c	Parallel	30	42	25/30/45	17/32/50	2.3	1.4	+ 0.49	+ 1.6
Volek et al., 2002	Parallel	20	42	30/61/8	16/26/58	2.2	0.9	−0.2	−1
Tsai et al., 1993 d	Crossover	4	3	25/60/15	15/30/55	2.2	1.3	+ 3.2	+ 14.2
Hoffman et al., 2007 c	Parallel	21	84	25/30/46	15/29/56	2	1.2	−0.73	−2.6
Haun et al., 2018 c , e	Parallel	32	84	24/35/41	16/35/50	1.8	1.3	+ 5.48	+ 25.4

g/kg/day: g/kg of bodyweight/day; TEI: total energy intake.

^a Diets one and two were isocaloric, defined as within 10% of the total energy intake of each other, taking into account differences in energy intake requirements between groups. All samples were healthy, non-obese, young to middle-aged men.

^b Change from baseline scores used where possible, and in these studies, the percentage change in testosterone was calculated using the starting value for diet one (Haun et al., 2018; Hoffman et al., 2007; Jaffe, 2013; Pourabbas et al., 2021; Toma, 2009; Volek et al., 2002).

^c These studies used a protein vs carbohydrate supplement intervention, to increase protein intake. The unmarked studies used a higher protein diet; although often including protein supplements as well.

^d ‘F’ and ‘CHO’ diets were used.

^e ‘PLA’ and ‘WPC’ diets were used.