Food for thought
It’s got a cult-like following when it comes to weight loss, but can fasting harm your chances of conceiving?
More divisive than an adults-only wedding invite, fasting has attracted both fans and critics thanks to its role in everything from managing weight to improving focus. The latest topic dividing the science world? The link between fasting and fertility.
Call it intermittent fasting (IF) or time-restricted eating (TRE), the principle is the same – calorific restriction for a designated period (usually 16 to 48 hours) involving low-to-no food intake. As for the science, a 2018 systematic review* looking at the benefits of IF found it particularly effective not only for weight loss, but also for lowering important biomarkers such as blood pressure, blood sugar, insulin, cholesterol and inflammation.
So where does fertility fit in? Early research has sounded the alarm bell. A rodent study published last year showed that restricting water every other day for 12 weeks disrupted the production of reproductive hormones – including luteinising hormone, which triggers ovulation*. Then, in April, a study on zebrafish – which have a similar genetic structure to humans – linked food restriction with lower-quality eggs and sperm, even after the resumption of a normal diet*.
And yet, it may be a different story in humans. A study published last October in Obesity suggested that the effects of IF may not harm fertility at all. In this small-scale study, pre- and postmenopausal women participated in a TRE programme, which involved four or six hours of eating (without counting calories) followed by an 18- or 20-hour fasting window, during which they only consumed water and caffeine-free beverages.
Compared with the control group, the results showed that the TRE group lost 3% to 4% of their base weight. But more significantly, their levels of testosterone and sex hormone-binding globulin, a protein that carries reproductive hormones throughout the body, remained unchanged. Although levels of dehydroepiandrosterone – a hormone sometimes used by fertility clinics to improve ovarian function and egg quality – did drop, they were still found to be in the normal range
