As most of you know from my posts on twitter, I attended an incredibly informative seminar regarding menstrual dysfunction in female athletes. The presentation was “Recovery of Menstrual Dysfunction Induced by Low Energy Availability,” presented by Dr. Mary Jane De Souza, who is a brilliant professor and researcher in the Kinesiology and Physiology Departments at Penn State. This seminar was both valuable to me as a female athlete as well as a future nutrition professional, and I received a lot of requests to summarize the information that was presented.
First, an overview of energy availability is necessary in order to understand our body’s physiological adaptations. Our body’s energy expenditure is made up of three things: the basal metabolic rate (BMR), thermic effect of food (TEF), and thermic effect of exercise (TEE). The basal metabolic rate uses the greatest portion of our energy. BMR is basically the amount of energy needed to sustain proper bodily functions – energy needed for respiration, reproduction, cardiac capacity, ATP production, etc. The thermic effect of food and thermic effect of exercise make up a much smaller portion of energy used. TEF is the energy needed to digest specific macronutrients, and TEE is exactly what it sounds like: energy needed for functional movement, including exclusive exercise as well as simply moving and existing in the real world. When low energy availability exists – primarily energy availability that is lower than what is needed to maintain proper bodily functions – *hormonal changes occur. The hypothalamus is suppressed, which causes these changes. Leptin decreases, along with insulin, Insulin-like Growth Factor (IGF-1), and thyroid function. In addition, ghrelin, Peptide YY (PYY), cortisol, and growth hormone (GH) increase. All of these hormonal changes cause further suppression of Gonadotropin Releasing Hormone (GnRH), Luteinizing Hormone (LH), and Follicle Stimulating Hormone (FSH). Lack of LH causes complete suppression of estrogen and progesterone production, leading to amenorrhea. Specifically, LH drops when we have around 30 calories per kg of FFM per day. The pattern that LH and FSH levels fall into mirror the pattern of prepubertal levels of these hormones. *A review of these hormones' specific functions is summarized at the bottom of this page. When we eat, we use energy for reproduction, growth, thermoregulation, cell maintenance, movement, etc. When energy availability is low, energy is shunted away from growth and reproduction. These just become low priority, so the body does not make the hormones important for these processes. This is primarily why we see issues with both menstrual function and bone health impairment. Actually, when we see low energy availability in female athletes, our primary concern is the impact on bone. Estrogen plays a vital role in controlling osteoblast/osteoclast activity. Specifically, osteoclasts are suppressed by estrogen activity, leading to less bone breakdown (resorption). When estrogen is not produced endogenously, excess bone resorption can occur. This is especially an issue when female athletes are consuming low calorie and low calcium/Vitamin D3 diets. Estrogen’s role in bone health is specifically why professionals are more concerned with female bone density, female menses, elderly females, etc rather than males. In fact, young female athletes are at an especially high risk due to the development of bone mass. Bone mass is accrued mostly during adolescence – more than 90% is accrued before the age of 20. Achieving an individual's peak bone mass is vitally important to diminish the risk of osteoporosis later in life. If calories, Calcium, and Vitamin D are restricted during the time period when bone mass is being accrued (aka adolescence), the individual will be at a higher risk of osteoporosis because they will achieve a lower bone density. So – female athletes typically lose their menstrual cycles due to these hormone decreases caused by overexercising, undereating, or a combination of these two. The common mistake, however, is in assuming that hormone levels have been restored upon the resumption of menstruation. The optimal menstrual cycle has an estrogen peak, followed by a LH peak, leading to the release of a follicle. Thereafter, a corpus luteum forms from the follicle and produces progesterone. This cycle is not really necessary to understand, but the order of hormonal levels released is what is important. There are different types of cycles that can occur with menstruation: anovulatory, luteal phase defect, and optimal. An anovulatory cycle means that ovulation is not occurring. This means that there are not enough hormones to stimulate ovulation (not enough estrogen). A luteal phase defect cycle occurs when there is not enough progesterone. Both of these issues mean that reproductivity is impaired and bone health is still at risk, but these are undetectable without testing for the hormones specifically. A menstrual cycle does not signal that these hormonal levels are okay. Basically, Dr. De Souza performed a refuel study with female athletes to evaluate the amount of calories necessary to induce menstrual function as well as the resulting hormone responses. The study increased the athletes' calories 20-30% above baseline. The average body fat of the athletes was 22%, and the majority recovered menstrual function (with this caloric increase) within the first 3 months. However, half of women did not resume menses, and most resumed cycles were anovulatory (meaning hormone levels were still inadequate.) The study found that for each increase in BMI by 1kg/m2, recovery probability increased about 25%. The average increase in bodyweight to recover menses was about 10%. Hormone Functions Leptin - signals satiation Insulin - stimulates glucose uptake into cells IGF1 - acts similar to insulin Thyroid hormone (T3/T4) - regulates growth hormone creation and regulates metabolic rate Ghrelin - signals hunger PYY - suppresses digestive activities, signals satiation Cortisol - regulates the body's responses to stress, acts on blood glucose levels and carb/fat/protein metabolism, immune responses GH - stimulates growth of all tissues GnRH - stimulates secretion of LH and FSH, large surge of GnRH right before ovulation, stimulates follicular growth FSH - stimulates the growth of the follicle and increases estrogen production LH - triggers ovulation and corpus luteum development Estrogen - peaks at the middle of the cycle to trigger LH release (to signal ovulation), prepares uterus for pregnancy; functions in bone health to suppress osteoclast activity (osteoclasts break down bone) Progesterone - prepares uterus for pregnancy
0 Comments
Leave a Reply. |
Archives
August 2020
Categories |