As F-words go, fat and fertility both wield the power to make even the most opinionated loudmouth clam up. As evidence grows that striving to cut too much of the former can screw with how your body naturally takes care of the latter, it’s time we opened up a little.

While unceasing muscle-bound, sweat-drenched Instagram stories and discussions over brunch tables collapsing under generous portions of hearty protein-packed dishes seem to confirm that the strong-not-skinny message is alive, well and motivating health choices across Australia, outside the wellness bubble, the statistics show a different story. In the most recent WH Global Naked Survey, a staggering 90 per cent of readers surveyed said they wanted to reduce their levels of body fat, while Roy Morgan Research shows 72 per cent of Aussie women aged 18-24 want to lose weight even though only 36 per cent have a BMI in the overweight category. It points to a desire to get really lean. But as this body goal remains hugely popular, what isn’t immediately clear is the damage super-low-fat goals will make to your future gains – and it’s all down to a simple yet little-known concept called energy availability.


We’re talking about fertility specifically, and that monthly reminder that everything in the ovary arena is in working order. “Anyone who exercises is automatically lauded as healthy, even when they’re not,” says Francesca Baker, 30. She took up running at university to counterbalance boozy nights and burgers, but wound up hooked on daily gym sessions and restrictive diets. “I stopped taking the contraceptive pill around the same time, so I told myself that the abrupt stop in my periods was down to that, instead of what was quickly becoming an out-of-control desire to be ‘healthy’.”

It wasn’t healthy. Francesca was suffering from relative energy deficiency in sports (RED-S, pronounced ‘reds’). “RED-S is a disparity between food intake (the energy and micronutrients you’re consuming) and the nutrition required to cover the energy demands of basic housekeeping tasks in the body and exercise,” explains sports endocrinologist Dr Nicky Keay. Like a smartphone on 9 per cent battery, fail to top up its juice and it reverts to an energy-saving mode where automatic functions – in women’s case, periods – switch off.

Unsurprisingly, humans aren’t quite as homogeneous as iPhone models, so the level at which these processes slow or halt is different for every woman. A regimen or body fat percentage that one can maintain without saying goodbye to regular periods could affect the reproductive cycle of another.

“When you’re focused on significantly lowering body fat, whether through following an extreme exercise regimen and/or restricting kilojoules, the body perceives you to be in a stressed state and decides this is not the time to reproduce,” says Dr Meggie Smith, reproductive endocrinology and infertility expert at the University of Southern California. “Signals from the brain to the ovaries, known as the hypothalamic-pituitary-ovarian axis, shut down. The luteinising hormone [which triggers ovulation] isn’t produced and the ovary neither releases an egg nor makes oestrogen and progesterone.”

While being overweight or obese disrupts your reproductive system by producing too much oestrogen, veer towards the other extreme and “you essentially enter a post-menopausal state”, warns Smith.


Given that RED-S could severely disrupt your fertility, it’s fair to wonder why this hasn’t been grabbing headlines. Until recently, the phenomenon was known as the female athlete triad – or simply ‘the triad’ (we can’t imagine why the acronym FAT didn’t take off). The triad linked energy deficiency to menstrual disturbances and loss of bone mineral density to explain once-puzzling period loss data, such as why 69 per cent of female university-aged dancers* and 65 per cent of female long-distance runners* didn’t have regular cycles. But in 2014, the International Olympic Committee renamed it, realising that the triad wasn’t actually a threesome after all.

Energy deficiency was also found to slow metabolic rate, impair immunity, increase fatigue and affect cardiovascular and even gut health. Today, it’s broadening further: in July last year, the British Journal Of Sports Medicine published University of Virginia research that explored RED-S in undernourished male athletes, while Keay believes the pressing issue for women is decoding its effect on non-athletes – you know, the rest of us.

“Elite athletes have the expertise of a coach or team doctor. A dedicated amateur with no such support is therefore more at risk of RED-S if they’re taking measures to significantly decrease body fat through exercise and dieting,” she explains. “I see this in dancers: aspiring students are often at risk until they join a company, where there is a support network.”

Keay’s interest isn’t just professional, though. A fanatical gymnast as a child, she would train four times a week, alongside ballet classes that together left her incredibly lean. As a result, it wasn’t until after her second son was born – conceived with the help of an ovulation-inducing tablet and injection – that she got her first period. She was 32. “I was fortunate to work in a hospital where I could seek conception advice. If I hadn’t had this medical knowledge, who knows what would have happened. That’s why it’s important women are aware of RED-S.”


“In my experience, those most susceptible to falling into difficulty are women in their twenties for whom motherhood feels a long way off,” says registered dietitian and sports nutritionist Laura Clark. “They hit the gym six or seven times a week – sometimes twice a day. Intense training is one thing, but if the nutrition isn’t there to support that energy expenditure and body function, body fat drops significantly and you will run into real difficulties.”

To the dilemma of too much exercise versus too little food, Smith says that kilojoule restriction is far more dangerous than high-intensity exercise. The study ‘Neuroendocrinology of Nutritional Infertility’ (not one to try to say while spinning) found that just one month of a significant drop in energy intake could mess with menstrual function.

But as long as the body composition scales show a BMI in the healthy range, you’re golden, right? Well, the experts can’t seem to agree on how useful traditional measurements are. The late biologist Rose Frisch found that evaluating weight alone could be misleading – as muscles are heavy (80 per cent water compared to 5-10 per cent water in fatty tissue), many athletes appeared in the ‘normal’ weight range despite having no periods. Even with body composition scales, Clark points out that you’ll get different results depending on where you are during your menstrual cycle, as that affects how much water your cells hold.

Frisch was the first to link low body fat to infertility and suggested that women needed at least 17 per cent body fat to fall pregnant – nicknaming it “sex fat”, as it provides the energy for reproduction. This is in line with numbers released by the Royal College of Nursing in 2015, stating that the healthy body fat percentage for a women aged 20 to 40 is between 15 per cent and 31 per cent.

It’s why energy availability – the numerical difference between energy intake and expenditure from exercise – is the new buzzword. “The energy requirement is 45 calories per kilogram of lean body mass for endocrine function,” says Keay. “However, it’s also about the quality of your diet. I had a dancer who got to that level by eating biscuits and sweets, but she still had no periods as she wasn’t covering the major food groups.”


Spotting whether you’re at risk of RED-S is best done via the process of elimination. “Even if your weight is steady, if your periods have stopped or become irregular and you’re not on a contraceptive method, don’t ignore it,” urges Keay. “Your doctor will exclude other causes first, like polycystic ovary syndrome and thyroid disorder, then look at your nutrition in line with your training load.”

Health and training experts also highlight other signs that your quest to become lean is going too far, even before your periods show any changes. Personal trainer Luke Worthington recommends being alert to physiological changes like hair loss (a sign of inadequate nutrition), increased body hair (where the body develops a layer of soft downy hair as insulation) and a pot belly caused by intestinal gas. Psychological warning signs are just as important to be mindful of. “If you find yourself obsessing over a missed workout, scheduling your entire life around exercise or meal prep and losing interest in sex, take them as cues that you may be too focused on your goal of getting leaner in an unhealthy way,” he adds.

As to any long-term impact, loss of periods through too little body fat is reversible. Your fertility is informed by a whole host of factors, from your age to how much you drink and how stressed you are. Consultant sports gynaecologist Michael Dooley says that if you’re not underweight and not losing weight via restriction, then you’re likely to conceive unless other medical conditions are at play. His research looks into the possibility that unreleased eggs aren’t lost for good due to RED-S, but are stored, freezer-like, inside your body.

Getting normal menstrual function back is, in fact, more food science than rocket science. The International Olympic Committee’s report on RED-S found that the only strategy that has received scientific scrutiny – and worked – was to add an energy-rich supplement (in the study, it was a daily liquid meal product of around 1255-2510 kilojoules) and a weekly rest day. The general advice when you’re exercising hard is to think about what you can add to your diet, rather than what you can take away.

This article originally appeared in the June issue of Women’s Health.

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