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A Woman’s Body on Minimal Calories

Updated: Jan 30, 2020

I love social media, but it’s the worst when it comes to influencing how we perceive our bodies.

Before-and-after weight loss and body transformation photos, trending dietary “ways of life” (a.k.a., possible socially-acceptable restrictive diets), and toned women in skintight leggings and crop tops are among a few examples I scroll past on the daily.

Screenshots of #fitspo, #instafit, #fitnessgirl, and #healthy from Instagram.
Hashtags that play up health, but promote the singular theme of fit and toned/muscular.

Worse is when these influencers whom lack nutritional credentials venture into the realm of nutrition tips and coaching.

For instance, creating and selling a one-time meal plan PDF without regard for a woman’s health or their relationships with food and their body, possible history of weight cycling, training plan, medications, and menstrual history, among many other factors, is irresponsible and potentially damaging to a follower’s long-term health. In the athletic world, "helpful tips" may come from fellow athletes or influential coaches.

What many of these influencers or self-proclaimed, non-credentialed experts fail to understand is the HPG axis—or the hypothalamic-pituitary-gonadal axis*—and its sensitive connections to menstruation, reproduction, and bone health.

*Also referred to as the hypothalamic-pituitary-ovarian (HPO) axis.

Your Body is a Yacht, So Avoid Cutting Corners With its Upkeep

When a yacht is well taken care of, you have the best weekends on the water. That’s you feeding your body with enough calories to optimally run your brain, lungs, hormonal systems, and organs, plus providing enough fuel to promote exercise and activities of daily living (e.g., walking around work, to class, or up a set of stairs).

Now for the downside: When you begin to restrict how many calories you’re consuming and/or increase your exercise training load without adequately increasing your caloric intake, it’s like cutting corners on caring for your yacht. One day your yacht has a hole in it and begins to sink.

How do you initially adapt? Immediate survival: By throwing less important items overboard to keep the yacht relatively afloat.

The yacht’s hole is analogous to your starving body: Any time you chronically consume far too few calories than your body needs to optimally function, it begins to cut corners to keep itself afloat. The body then enters a chronic phase of low energy availability* (LEA) (read my blog post on that topic here) that negatively impacts the HPG axis.

The key word here is chronic. If one day when you don’t fuel enough, it’s not the end of the world. Your body can adapt and roll with the fluctuations.

*LEA is defined as chronically consuming fewer than 30 calories per kilogram of fat-free mass per day (kcal/kg FFM/day). Although Elliot-Sale et al. (2018) report that menstrual dysfunction was greater than 50% in participants consuming less than 30 kcal/kg FFM/day, the “severity of menstrual disturbances did not correlate with the magnitude of energy deficiency.”

Why Does Menstruation Stop?

The outcome of a chronically suppressed HPG axis is functional hypothalamic amenorrhea (FHA), or when a woman stops having her period for no other medically-diagnosable reason.

  • Weight loss*,

  • Excessive exercise,

  • Extreme stress, or any combination of these.

FHA develops after three sequential stages have occurred:

  1. The usual rhythmic release of gonadotropin-releasing hormone (GnRH) from the hypothalamus begins to pulsate erratically.

  2. GnRH’s dysregulation signals the anterior pituitary gland to reduce the pulse frequency of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The expected midcycle menstrual surge of LH becomes less pronounced or even absent.

  3. This pulsating mess results in a reduction of estrogen and progesterone production in the ovaries, thereby halting menstruation.

Fertility is not considered essential for immediate survival. If your body has limited resources, it’s not going to grow a baby, which is an energy-intensive process. Thus, menstruation stops when the brain chronically senses too few calories.

Granted, there are many reasons why impaired menstruation may occur, but here I’m only focusing on FHA due to its prevalence: It's the cause of 3% of primary and 20-35% of secondary amenorrhea cases** and female athletes are at even higher risks of FHA, with 50% of exercising women experiencing subtle disturbances and 30% experiencing amenorrhea.

*Typically rapid weight loss, dropping below one’s natural weight, and/or low body fat levels (the essential fat range for women is 12-15%, meaning the fat needed to support optimal hormonal functioning). **Primary amenorrhea refers to females who haven’t had their first period by age 16 years and secondary for those who have menstruated, but haven’t in three consecutive months.

Chronic LEA Outcome: Impaired Bone Health

Our skeleton provides us with a seemingly sturdy structure. However, just like the heart and lungs, bones are a living organ that are constantly changing and adapting to feedback from our body.

For females, peak bone mineral content (BMC) is gained between ages 11-14 years, with 92% of BMC gained by age 18. The estrogen hormone group is critical for proper bone metabolism by stimulating bone formation, reducing its breakdown, and increasing the release of vitamin D receptor sites (vitamin D is needed to absorb calcium from the gut).

The outcome of a female with chronic LEA during her early pre-teen and teen years is reduced bone mineral density (BMD) and the increased likelihood of fractures and early-onset osteoporosis. FHA during puberty leads to a frail skeleton.

As circulating estrogen levels decrease, BMD declines. The impact of this decline can worsen as the number of missed menstrual cycles accumulate, but not always.

The American College of Obstetricians and Gynecologists (2017) acknowledge that “in adulthood, a 10% decrease in BMD is associated with a 2-3-fold increase in risk of fracture” and “amenorrheic athletes have a 2-4-fold increased risk of stress fracture compared with eumenorrheic athletes”.

Unlike the return of menstruation seen with the reversal of FHA, chronic LEA can lead to irreversible reductions in BMD. A woman's skeleton will likely never fully recover.

Chronic LEA Outcome: Impaired Fertility

Since FHA results in menstrual cessation, spontaneous pregnancy is impossible for a FHA woman.

During puberty, FHA may result in the impaired development of sex characteristics essential for fertility. For adult women, uterine muscle loss occurs and, during pregnancy, increased risks include:

  • Inadequate maternal weight gain.

  • Impaired fetal growth and development.

  • Miscarriage.

  • Pre-term labor.

Other systems negatively affected by FHA include cardiovascular health, mental health, and sexual dysfunction. The article by Meczekalski et al. (2014) outline these in further detail.

Take-home Message: Steps Towards Improving LEA and Normalizing Menstruation

Impaired bone health and fertility are why it’s so crucial to prevent—versus treat—and diagnose LEA as quickly as possible.

If an athlete’s menstrual pattern is of concern, a medical doctor should be immediately involved to help with diagnosing the cause and monitoring ongoing care.

From the dietitian’s perspective, and in the presence of LEA, emphasizing the importance of matching calories consumed with calories burned is vital, plus calories required for weight gain, if appropriate.

Prior to counseling athletes on caloric goals, the dietitian should first evaluate the female athlete’s:

  • Detailed training logs.

  • Prior weight changes, both intentional and unintentional.

  • Social influences from friends and family.

  • Relationships with their body and food.

  • Usual dietary intake, including skipped meals and snacks, macronutrients, total calories, and bone-friendly micronutrients calcium and vitamin D.

  • Food avoidances, including intolerances, allergies, and restrictive diets (e.g., veganism, intermittent fasting).

  • Basic nutritional knowledge and possible food myths.

  • Excessive fluid intake, including caffeine.

  • High fiber intake, especially athletes who prioritize healthy eating and plant-based approaches.

  • Medications that impact appetite (e.g., antidepressants, stimulants).

  • Birth control use, type, and duration.

  • Age of menarche (i.e., first period ever) and menstrual history since.

Granted, this is a simplified list and other factors could be at play. In the presence of mental health concerns and eating disorders, the dietitian's approach and involvement of multidisciplinary team members will likely differ. Treatment becomes more complicated and slows the recovery process.

Further Reading

Organizes fluids and foods by group (e.g., cereals, bars) and provides tips per group on how to increase calories.

Reviews LEA, contributing causes, and how to calculate it (plus the difficulties of doing so).

Meczekalski, B., Katulski, K., Czyzyk, A., Podfigurna-Stopa, A., & Maciejewska-Jeske, M. (2014). J Endocrinol Invest,37(11):1049-1056.

Elliot-Sale, K.J., Tenforde, A.S., Parziale, A.L., Holtzman, B., & Ackerman, K.E. (2018). IJSNEM,28(4):335-349.

Ackerman, K.A., & Misra, M.

Beals, K.A., & Hill, A.K. (2006). IJSNEM,16(1):1-23.

Obstet Gynecol,129:e160-167.


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