Link between heart-healthy diet and reduced miscarriage risk ‘not causal’

Following the diet recommended by the American Heart Association (AHA) before pregnancy decreases the chance of miscarriage by 13-15%, according to Spanish scientists writing in JAMA Network Open who compared the effects of different eating patterns on the gestational health of women undergoing infertility treatments.

However, experts urged caution against reading too much into the results, which they said only established an association, not causation.

“The reduction in the risk of miscarriage with the AHA diet could be entirely due to chance,” said Dr Bassel Wattar, consultant obstetrician and gynaecologist at Epsom and St Helier University Hospitals.

Infertility affects 17.5% of global adult population

Infertility is growing in prevalence: World Health Organization (WHO) figures released earlier this year indicate that 17.5% of the adult population worldwide experience infertility. Although lifestyle and environmental factors are thought to influence these rates, the role played by dietary patterns is for the most part unknown.

This study, led by researchers from the Universitat Rovira i Virgili in Tarragona, looked at a sample of 612 women aged 18 to 45 who underwent intra-uterine injection (IUI) and in vitro fertilisation (IVF).

The women’s diets as well as that of their partners were analysed to assess the extent to which they followed one of eight selected dietary patterns: the Trichopoulou Mediterranean diet; alternate Mediterranean diet; Panagiotakos Mediterranean diet; Healthy Eating Index; Alternate Healthy Eating Index; the AHA index; the Dietary Approaches to Stop Hypertension (DASH) index; and plant-based diets.

The researchers concluded that participants who most closely followed the pattern recommended by the AHA for cardiovascular prevention – characterised by a high consumption of fish, whole grains, omega-3 fatty acids and folic acid – were 13-15% less likely to experience pregnancy loss.

Findings ‘interesting’ but conclusions ‘too strong’

However, while experts agreed that there was “substantial evidence highlighting the importance of healthy eating and lifestyle intervention to optimise the outcome of assisted conception treatments among couples with subfertility”, they drew attention to limitations with this specific piece of research.

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“This study used routinely collected observational data on the dietary intake of patients undergoing assisted conception treatments (IVF, ICSI, and IUI). The quality of this type of data is often poor due to high recall bias when completing food frequency questionnaires,” explained Wattar.

“It is also important to consider the chance of performance and selection bias when analysing this type of data. While the findings are interesting, the conclusions made are a bit too strong considering the small size of the study (only 612 women which is relatively small compared to other dietary studies) and the high risk of bias.”

However, the study, which was carried out in collaboration with researchers from the University of Girona and Massachusetts General Hospital, may be useful for informing the design of future studies into the effects of nutritional interventions on fertility, he conceded.

“The study is helpful to highlight the potential benefits of different dietary regimes and lifestyle intervention,” Wattar said, adding: “At this stage, I would consider these findings only helpful to guide future research and too early to adopt them into clinical practice.”