. 2021 Sep 25;13(10):3375. doi: 10.3390/nu13103375

Table 1.

Effect of low energy availability and energy deficits on circulating testosterone concentrations.

Source	Participants	Duration	Intervention	Key Findings
[78]	n = 14 men Elite bodybuilders	11 weeks	Energy-restricted group (n = 7): decrease calories and increase energy expenditure through exercise Control group (n = 7): energy intake and training volume were maintained.	Significant decrease in TT in the energy-restricted group compared to the control group ES energy-restricted group = 0.49 ES control group = 0.07.
[76]	n = 34 Healthy adults (men and women)	31 days	40% energy deficit for all protein intake groups Group 1 (n = 11; 10 males, 1 female)—0.8 g∙kg⁻¹∙day⁻¹ Group 2 (n = 12; 10 males, 2 females)—1.6 g∙kg⁻¹∙day⁻¹ Group 3 (n = 10; 8 males, 2 females)—2.4 g∙kg⁻¹∙day⁻¹	Significant reduction in TT compared to the weight maintenance period in all groups ES group 1 = 3.38 ES group 2 = 0.39 ES group 3 = 0.36.
[79]	n = `2`4 males Elite distance runners	7 days	Low energy available group (n = 6): (<30 kcal·kg FFM·day⁻¹) Moderate energy available group (n = 18): (30–45 kcal·kg FFM·day⁻¹)	Significant reduction in TT in the low energy available group compared to the moderate energy available group ES = 1.3.

Source

Participants

Duration

Intervention

Key Findings

[78]

n = 14 men

Elite bodybuilders

11 weeks

Energy-restricted group (n = 7): decrease calories and increase energy expenditure through exercise
Control group (n = 7): energy intake and training volume were maintained.

Significant decrease in TT in the energy-restricted group compared to the control group
ES energy-restricted group = 0.49
ES control group = 0.07.

[76]

n = 34 Healthy adults (men and women)

31 days

40% energy deficit for all protein intake groups
Group 1 (n = 11; 10 males, 1 female)—0.8 g∙kg⁻¹∙day⁻¹
Group 2 (n = 12; 10 males, 2 females)—1.6 g∙kg⁻¹∙day⁻¹
Group 3 (n = 10; 8 males, 2 females)—2.4 g∙kg⁻¹∙day⁻¹

Significant reduction in TT compared to the weight maintenance period in all groups
ES group 1 = 3.38
ES group 2 = 0.39
ES group 3 = 0.36.

[79]

n = 24 males

Elite distance runners

7 days

Low energy available group (n = 6): (<30 kcal·kg FFM·day⁻¹)
Moderate energy available group (n = 18): (30–45 kcal·kg FFM·day⁻¹)

Significant reduction in TT in the low energy available group compared to the moderate energy available group ES = 1.3.

FFM = Fat free mass; TT = Total testosterone concentrations; ES = effect size. Effect size was estimated as (mean 2 − mean 1)/pooled standard deviation.