Consumption of Vegetable Protein Linked to Anovulation

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Low levels of vegetable protein linked to anovulation

SUMMARY: FOOD THAT BOOSTS OVULATION

In this study, healthy women with regular periods who consumed 21.0 ±4.7 grams of vegetable protein per day, specifically legumes (dried beans, mature lima beans, refried beans and beans in sauce), had 22.3% higher progesterone levels and a 47% lower risk of anovulation.

doi.org/10.1210/clinem/dgab179

Background

Plant based sources of dietary protein has gained in popularity in recent times, due to the increased risk of various diseases, and potential environmental contaminants, from animal sources of protein.

This includes reproductive disorders such as endometriosis and irregular periods leading to ovulatory infertility.

However, despite these 2 original studies the relationship between dietary protein intake and female reproductive hormones is poorly understood.

Past studies have primarily investigated the effects of vegetarian diets, limiting the ability of health professionals to make specific dietary recommendations.

Aim

To evaluate the relationship between consumption of animal and vegetable proteins, as well as specific food sources, on female reproductive hormone levels and sporadic anovulation.

Methodology

A total of 259 women enrolled in the BioCycle study, with regular menstruation (between 21–35 days), meeting the inclusion exclusion criteria participated in this study. 

For reference women using contraceptives, taking supplements, on a restricted / high phytoestrogen diet, with BMI less than 18 or greater than 35, chronic conditions (e.g. diabetes mellitus), menstrual disorder, uterine abnormality, pregnant or breastfeeding in the past 6 months, were excluded from this study to reduce potential bias.

During each menstrual cycle (fasting) blood samples were collected from each woman up to 8 times per cycle, for 2 cycles in total. Specifically samples were collected on day 2 of menstruation (one visit), mid-follicular phase (one-visit), peri-ovulatory phase (3 visits), and early-mid-late luteal phase (3 visits) during each cycle. The precise timing of each visit was adjusted according to the woman’s reported cycle history and confirmed using fertility monitors.

From these blood samples, the following hormones were measured; estradiol, follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, testosterone and sex hormone-binding globulin (SHBG).

Anovulation was defined as no serum LH peak in the mid or late luteal phase and progesterone ≤ 5ng/mL.

Dietary assessment was carried out, up to 4 times per cycle (menstruation, mid-follicular phase, expected ovulation, mid-luteal phase) by an interview-assisted 24-hour dietary recall of dietary intake the day before blood collection. Overall intake of total protein, animal and vegetable protein was estimated along with the specific protein foods consumed.

Covariate assessment was carried out to allow for adjustment of confounding factors including demographics (age, weight, height, race, education, marital status), lifestyle factors (physical activity, cigarette smoking, alcohol, heavy metals) and reproductive history (parity, past oral contraceptive use etc).

Results

Initial baseline characteristics showed that participants were young (mean age 27.3), of normal BMI (mean 24.1 kg/m2), physically active (85%) and predominantly nonsmokers (96%).

Overall distribution of caloric intake was 15.7% protein, 33.9% fat and 50.8% carbohydrates, whilst 84% of women met the RDA of total protein for women of reproductive age. Of the 509 cycles in total monitored, 42 were classified as anovulatory.

Next statistical analysis of total and animal protein intake found no significant link to hormone levels. On the other hand vegetable protein intake, specifically among the lowest tertile, was associated with lower luteal phase progesterone (-18%) and higher FSH (3.8%) compared to women in the mid tertile for vegetable protein intake. 

Interestingly substitution model analysis, whereby increasing protein intakes and reducing carbohydrates or fat intake, did not significantly change these findings.

After adjustment for potential confounders, total or animal protein intake was also not associated with anovulation, however the lowest tertile of vegetable protein intake women was linked to an increased risk of anovulation (relative risk = 2.53). These results remained true after substitution model analysis.

Analysing individual food consumption, further statistical analysis found that egg intake (vs no egg intake) was linked to higher FSH (4.6%), while intake of legumes showed higher progesterone levels (22.3%) and consumption of nuts / seeds lowered FSH (-4.0%).

Overall the intake of legumes (dried beans, mature lima beans, refried beans and beans in sauce) lowered the risk of anovulation by 47% (relative risk 0.53), where as the intake of nuts or seeds increased the risk of anovulation (relative risk = 2.12).

Limitations

  1. Short-term study (2 cycles)

Funding

No external funding was declared for this study.

Glossary

Confounders
A distortion that modifies the estimated measure of an association.

Follicular phase
First half of the menstrual cycle, from the start of menstruation to ovulation.

Luteal phase
Second half of the menstrual cycle, from ovulation to the start of menstruation.

Parity
Equal pay.

Peri-ovulatory phase
Follicular phase.

Phytoestrogen
Plant compounds which are structurally and/or functionally similar to mammalian estrogens.

Relative risk
The risk that a certain event will occur. (Relative risk = 1.5 means the event is 1.5 times more likely to occur)

Tertile
Any two points that divide an ordered distribution into three parts.

Similar studies

Chavarro J E, et al. (2008). Protein intake and ovulatory infertility. https://doi.org/10.1016/j.ajog.2007.06.057

Barr S I, et al. (1994). Vegetarian vs nonvegetarian diets, dietary restraint, and subclinical ovulatory disturbances: prospective 6-mo study. https://doi.org/10.1093/ajcn/60.6.887

Pirke K M, et al. (1986). Dieting influences the menstrual cycle: vegetarian versus nonvegetarian diet. https://doi.org/10.1016/S0015-0282(16)49884-5


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