A recent study published in the European Journal of Clinical Nutrition evaluated the effects of time-restricted eating (TRE) and caloric restriction (CR) on sex hormones.

Study: Effect of time restricted eating versus daily calorie restriction on sex hormones in males and females with obesity. Image Credit: goffkein.pro/Shutterstock.com

Background

TRE is a weight loss intervention, with a reduced eating window (4–10 hours) and fasting for the remaining time with energy-free beverages.

Despite the health benefits of TRE, there have been concerns about its impact on sex hormones. That is, some research claims that TRE may negatively affect estrogen levels, which might lead to irregularities in the menstrual cycle and fertility issues.

Similarly, some research on males claims TRE might reduce testosterone, muscle mass, and libido. However, the impact of TRE on sex hormones is largely unknown due to a scarcity of literature.

Moreover, trials have been small, lacked controls, and were shorter in duration, with no study assessing the effects beyond two months.

About the study

In the present study, researchers evaluated the effects of TRE on reproductive hormones in males and pre- and post-menopausal females compared to CR, and no intervention was performed over 12 months.

This was a secondary analysis of a published trial comparing CR and TRE effects on metabolic risk factors and body weight. Individuals aged 18–65, with a body mass index between 30 kg/m² and 50 kg/m² were included.

Individuals were excluded if they were smokers, pregnant, diabetic, shift workers, perimenopausal, using an intrauterine device, on hormone replacement therapy, or had unstable weight within the past three months. Subjects were randomized to CR, TRE, or control groups. The trial involved weight loss and maintenance phases for six months each.

TRE subjects ate ad libitum between 12 and 8 pm and fasted subsequently with energy-free beverages until noon the next day for the initial six months. During the maintenance phase, the TRE window was extended (10 am to 8 pm).

On the other hand, the CR group reduced the energy intake by 25% daily for the first six months and consumed their calculated energy needs in the next six months.

Controls were asked to maintain regular exercise, eating habits, and weight. Fasting blood samples were collected; circulating levels of total testosterone, dehydroepiandrosterone (DHEA), progesterone, estrone, estradiol, and sex hormone-binding globulin (SHBG) were measured.

A two-way analysis of covariance compared changes between groups. The relationship between sex hormones and body weight was evaluated using Spearman or Pearson correlation coefficients.

Findings

126 participants were screened; 30 individuals were randomized to study groups. Of these, 77 participants completed the 12-month study; analyses were limited to 73 completers with sufficient blood for hormone measurements.

Of these, 10, 44, and 19 were males and pre- and post-menopausal females, averaging 42, 39, and 56, respectively. A significant reduction in body weight was observed in the TRE and CR groups relative to controls by month 12.

However, there were no differences between CR and TRE groups. SHBG, DHEA, and total testosterone levels in females and males were unchanged over time and between groups.

Progesterone, estradiol, and estrone were measured in postmenopausal females only; their levels were unchanged in intervention groups. Further, weight loss was unrelated to changes in sex steroids in both males and females.

Conclusions

In sum, TRE induces significant weight loss but does not affect sex hormones in males or females with obesity over 12 months compared to CR and controls.

Changes in sex hormones might have occurred during the initial months of the intervention, which gradually returned to baseline levels as body weight stabilized over time. Nevertheless, more research is needed to corroborate these results.