Table 1.
Dietary patterns and the risk of anovulation.
| First Author/Reference Number | Year | Study Design | Sample | Result |
|---|---|---|---|---|
| Dietary pattern | ||||
| Chavarro et al. [8] | 2007 | A prospective cohort study (NHS II) | 17,544 women, aged 25–42 years | Higher adherence to the FD was associated with a lower risk of anovulatory infertility compared to the lowest adherence (RR 0.34 (95% CI 0.23–0.48) vs. RR 0.68 (95% CI 0.52–0.89); p < 0.001). |
| Carbohydrates and low glycemic index diet | ||||
| Chavarro et al. [32] | 2009 | A prospective cohort study (NHS II) | 18,555 women, 25–42 years | An increase in cereal fiber intake by 10 g/day was associated with a 44% lower risk of anovulatory infertility among women older than 32 (RR 0.56 (95% CI 0.34–0.93); p = 0.02). The risk of anovulatory infertility was 78% higher in women from the highest quintile of total carbohydrate intake (60% of calories) compared to women from the lowest quintile (42% of calories) (RR 1.78 (95% CI 1.14–2.78); p = 0.005). A linear trend towards a higher risk of anovulatory infertility with increasing carbohydrate intake (p trend = 0.005). The risk of anovulatory infertility was 92% higher in women from the highest quintile of glycemic load compared to women from the lowest quintile (RR 1.92 (95% CI 1.26–2.92); p = 0.01). The risk of anovulatory infertility was 55% higher in nulliparous women from the highest quintile of glycemic index compared to women from the lowest quintile (RR 1.55 (95% CI 1.02–2.37); p = 0.05). Dietary glycemic index was positively associated with the risk of anovulatory infertility among nulliparous women (p interaction = 0.02). |
| Gaskin et al. [36] | 2009 | A prospective cohort study (The BioCycle Study) | 250 women, aged 18–44 years | Each 5 g/day increase in total fiber intake was associated with a 78% increased risk of an anovulatory cycle (RR 1.78 (95% CI 1.11–2.84); p < 0.05). Soluble fiber had a stronger, positive association with an increased risk of anovulation (OR 6.73 (95% CI 1.18–38.26) than insoluble fiber (OR 2.15 (95% CI 1.22–3.77) and fruit fiber (OR 3.05 (95% CI 1.07–8.71); p < 0.05). Dietary fiber consumption was positively associated with incidents of anovulation (p = 0.004), with an OR of 10.98 (95% CI: 1.5, 80.5) for women at or above the DRI (≥22 g/day) compared to the lowest DRI (≤10 g/day). |
| McGrice et al. [14] | 2017 | A Systematic Review of 7 intervention studies | Infertile women with obesity, aged > 18 years | The use of low-carbohydrate diet (less than 45% of total energy obtained from carbohydrates) was associated with a higher ovulation rate (p < 0.05) compared to the usual diet. |
| Palomba et al. [33] | 2010 | A randomized controlled trial | 96 PCOS women with obesity, aged 18–35 years with anovulatory infertility and known CC resistance | The intervention (structured exercise + 35% protein, 45% carbohydrate, 20% fat diet with calorie deficit + CC) was effective in increasing probability of ovulation under CC treatment. |
| Sordia-Hernández et al. [40] | 2015 | A randomized controlled clinical trial | 40 patients with the diagnosis of PCOS, infertility, and anovulation, mean age 26 years | 24.6% (14/57) of the cycles were ovulatory in women who consumed a low glycemic index diet. In those who consumed a normal glycemic index diet, only 7.4% (4/54) of the cycles were ovulatory (p = 0.014). |
| Plant and animal protein products | ||||
| Chavarro et al. [52] | 2007 | A prospective cohort study (NHS II) | 18,555 women, 25–42 years | The risk of anovulatory infertility was 27% lower in women from the highest quintile of intake of high-fat dairy products (≥1 servings/day) compared to women from the lowest quintile (≤1 servings/week) (RR 0.73 (95% CI 0.52–1.01); p < 0.05). Adding one daily serving of full-fat milk without increasing energy intake was associated with a reduction in the risk of anovulatory infertility by 63% (RR 0.37 (95% CI 0.19–0.70), p = 0.002). An inverse association between dairy fat intake and anovulatory infertility (p trend = 0.05). The risk of anovulatory infertility higher by 71% in women from the highest quintile of intake of low-fat dairy products (especially yoghurt and sherbet/frozen yoghurt) (one serving a day) compared to women from the lowest quintile (≤1 servings/week) (RR 1.71 (95% CI 1.24–2.77); p = 0.002). |
| Chavarro et al. [44] | 2008 | A prospective cohort study (NHS II) | 18,555 women, 25–42 years | Consuming 5% of energy from plant protein rather than from carbohydrates was associated with a 43% lower risk of anovulatory infertility (RR 0.57 (95% CI 0.32–1.00); p = 0.05). Consuming 5% of energy from vegetable protein rather than from animal protein was associated with a 52% lower risk of anovulatory infertility (RR 0.48 (95% CI 0.28–0.81); p = 0.007). The risk of anovulatory infertility was 41% higher in women from the highest quintile of total protein intake (23.1% of calories) compared to women from the lowest quintile (15.4% of calories) (RR 1.41 (95% CI 1.04–1.91); p = 0.02). The risk of anovulatory infertility was 39% higher in women from the highest quintile of animal protein intake (18.5% of calories) compared to women from the lowest quintile (10.2% of calories) (RR 1.39 (95% Cl 1.01–1.90); p = 0.03). Adding one serving of meat per day was associated with a 32% higher risk of anovulatory infertility (RR 1.32 (95% CI 1.08–1.62); p = 0.01). Adding one serving of chicken or turkey per day was associated with a 53% greater risk of anovulatory infertility (RR 1.53 (95% CI 1.12–2.09); p = 0.01). Consuming 5% of total energy intake as animal protein instead of from carbohydrates was associated with 19% greater risk of anovulatory infertility (RR 1.19 (95% CI 1.03–1.38); p = 0.02). |
| Kim et al. [49] | 2017 | A prospective cohort study (The BioCycle Study) | 259 healthy, regularly menstruating women, aged 18–35 years | Associations between intakes of >0 servings of yoghurt (RR 2.1 (95% CI 1.2–3.7) and cream (RR 1.8 (95% CI 1.0–3.2) and a higher risk of sporadic anovulation compared to no intake. |
| Zhang et al. [44] | 2020 | A prospective cohort study | 2217 infertile women with PCOS (with ovulation and without), aged > 18 years | PCOS women with anovulation had a higher rate of meat favorable diet than PCOS women with ovulation (54.60% vs. 41.30%, RR 1.69 (95%CI 1.28–2.23), p < 0.01). |
| Unsaturated and saturated fatty acids | ||||
| Chavarro et al. [53] | 2007 | A prospective cohort study (NHS II) | 18,555 women, 25–42 years | Each 2% increase in the intake of energy from trans unsaturated fats, rather than from carbohydrates was associated with a 73% higher risk of anovulatory infertility (RR 1.73 (95% CI 1.09–2.73); p = 0.02). Obtaining 2% of energy intake from trans fats rather than from n-6 polyunsaturated fats was associated with a 79% higher risk of anovulatory infertility (RR 1.79 (95% CI 1.11–2.89); p = 0.02). Obtaining 2% of energy from trans fats rather than from monounsaturated fats was associated with a more than doubled risk of anovulatory infertility (RR 2.31; (95% CI 1.09–4.87), p < 0.05). |
| Ghaffarzad et al. [60] | 2014 | A case-control study | 29 women with PCOS, aged 19–35 years | Higher concentrations of trans fatty acids (trans linoleate) in erythrocytes were associated with an increased incidence of ovulation disorders in this group of women (OR 1.218 (95% CI 1.016–1.46); p = 0.033). |
| Mumford et al. [54] | 2016 | A prospective cohort study (The BioCycle Study) | 259 regularly menstruating, healthy women, aged 18–44 years | The intake of PUFA docosapentaenoic acid (22:5 n–3) was associated with a reduced risk of anovulation (highest tertile compared with the lowest tertile: (RR: 0.42 (95% CI 0.18–0.95); p < 0.05). |
| Alcohol and caffeine | ||||
| Chavarro et al. [61] | 2009 | A prospective cohort study (NHS II) | 18,555 women, 25–42 years | Women consuming 2 or more caffeinated soft drinks per day were at a 47% greater risk of anovulatory infertility than women who consumed less than 1 caffeinated soft drink per week (RR 1.47 (95% CI 1.09–1.98); p = 0.01). Women consuming 10 g or more of alcohol per day (approximately > 1 drink/day) were at a 47% greater risk of anovulatory infertility than women who did not drink any alcohol (RR 1.47 (95% CI 1.02–2.10), p = 0.03). |
| Vitamins and minerals | ||||
| Chavarro et al. [76] | 2006 | A prospective cohort study (NHS II) | 17,544 women, aged 25–42 years | Women who consumed iron supplements were at a significantly lower risk of anovulatory infertility than women who did not use iron supplements (RR 0.60 (95% CI 0.39–0.92); p = 0.003). The risk of anovulatory infertility was 47% lower in women from the highest quintile of iron intake (77 mg/day) compared to women from the lowest quintile (11 mg/day) (RR 0.53 (95% CI 0.35–0.82); p = 0.003). The risk of anovulatory infertility was 40% lower in women from the highest quintile of nonheme iron intake (76 mg/d) compared to women from the lowest quintile (9.7 mg/d) (RR 0.60 (95% CI (0.39–0.92); p = 0.005). |
| Chavarro et al. [70] | 2008 | A prospective cohort study (NHS II) | 18,555 women, 25–42 years | The risk of anovulatory infertility was 41% lower in women who used multivitamins ≥ 6 times per week compared to women who did not use multivitamins (RR 0.59 (95% CI 0.46, 0.75); p < 0.001). The risk of anovulatory infertility was 39% lower in women from the highest quintile of intake of folic acid (1138 μg/day) compared to women from the lowest quintile (243 μg/day) (RR 0.61 (95% CI 0.37, 1.00); p = 0.04). |
| Gaskin et al. [71] | 2012 | A prospective cohort study (The BioCycle Study) | 259 women, aged 18–44 years | Women in the highest tertile of folate consumption (270.6 g/d) had a 64% lower chance of anovulation compared to women in the lowest tertile of folate consumption (100.9 g/d) (OR 0.36 (95% CI 0.14, 0.92); p = 0.03). |
| Kim et al. [77] | 1217 | A prospective cohort study (The BioCycle Study) | 259 regularly menstruating women, aged 18–44 years | Sodium intake < 1500 mg (RR 2.70 (95 % CI 1.00–7.31) and manganese intake < 1.8 mg (RR 2.00 (95% CI 1.02–3.94) were associated with an increased risk of anovulation, compared to higher intakes, p < 0.05. |
| Yahya et al. [75] | 2019 | A randomized- controlled, open-label study | 45 PCOS women, aged 18–40 years | Both dietary supplements (vitamin D3 or CO-enzyme Q10) in combination with CC, significantly improved ovulation rates in clomiphene citrate-resistant women with PCOS. |
| Rasheedy et al. [74] | 2019 | A double blind, randomized clinical trial | 186 women undergoing the induction of ovulation with CC, aged 25–35 years | Women with PCOS undergoing the induction of ovulation: vitamin D supplementation significantly improved the ovulation rate. More than 90% (92.5%) of women in the treatment group took CC (50 mg) twice daily and vitamin D3 (10,000 IU), and 78.5% in the control group (placebo) had successful ovulation (p = 0.007). |
Abbreviations: NHS II, Nurses’ Health Study II; RR, relative risk; Cl, confidence interval; FD, fertility diet; OR, odds ratio; PUFA, Polyunsaturated Fatty Acids; PCOS, polycystic ovary syndrome; DRI, dietary recommended intake; CC, clomiphene citrate, IU, international unit.