By examining these relationships with and without suppression of estrogen synthesis, we found that lean mass, muscle size, and strength are regulated by androgens; **fat accumulation is primarily a consequence of estrogen deficiency**; and sexual function is regulated by both androgens and estrogens.[4] In the groups that received testosterone, inhibition of estrogen synthesis (cohort 2), as compared with intact estrogen synthesis (cohort 1), was associated with **significant increases in the percentage of body fat**, subcutaneous-fat area, and intraabdominal-fat area and with significant decreases in sexual desire and erectile function.[4]

In the state of chronic starvation, the hypothalamic gonadotropin-releasing hormone (GnRH) is regulated down. Subsequently, lower LH pulsatility, as well as reduced levels of oestradiol and testosterone, can be observed in females.[12] Thus, underweight and energy deficit lead to **low estrogen as a consequence of being underweight/starving**, via hypothalamic–pituitary–gonadal axis suppression; the paper discusses endocrine changes as manifestations of underweight, not estrogen deficiency as a cause of low body weight.

Dysfunction of the hypothalamic-pituitary axis includes hypogonadotrophic hypogonadism with relative oestrogen and androgen deficiency, growth hormone resistance, hypercortisolaemia, non-thyroidal illness syndrome, hyponatraemia, and hypooxytocinaemia. Hypothalamic amenorrhea results in low androgen levels, in addition to low oestrogen levels, in women with anorexia nervosa. Here, **relative estrogen deficiency is described as an endocrine manifestation of anorexia nervosa (a severe underweight/eating-disorder state)**; the article does not state that estrogen deficiency causes underweight, but rather that underweight/eating disorder leads to low estrogen.

Estrogens deficiency enhances metabolic dysfunction predisposing to type 2 diabetes, the metabolic syndrome, and cardiovascular diseases.[31, 32] ... The decrease in estrogen levels in menopausal women is associated with the loss of subcutaneous fat and an increase in abdominal fat.[42]

Women transitioning through the menopause experience a decrease in fat-free mass (FFM), including bone and skeletal muscle, and an increase in fat mass (FM), which is predominantly in the abdominal region.(1) Studies of both animals(2, 3) and humans(4, 5) suggest that this is related to the loss of ovarian function and, specifically, the loss of estrogens. ... Our working model is that the loss of estrogen leads to decreased energy expenditure (EE), thereby disrupting energy balance and contributing to fat gain. ... In summary, preclinical and clinical studies have provided evidence that the loss of estrogens leads to unfavorable alterations in body composition (increase in central FM, decrease in FFM) and decreases in total energy expenditure (TEE), resting energy expenditure (REE), and physical activity.

This link between reproductive function and body weight control is largely mediated by the female sex steroid hormones, particularly estradiol and progesterone. In general, estradiol regulates homeostatic nutrition in women by decreasing food intake and increasing energy expenditure. Female reductions in food intake during the peri-ovulatory period are a consequence of the anorectic action of estradiol. Overall, this evidence suggests that abnormally high or low levels of estradiol can both lead increased insulin resistance in the brain and peripheral tissues. This review describes **physiologic estradiol as anorexigenic (reducing intake, increasing expenditure)**; it associates extremes of estradiol with metabolic dysfunction rather than stating that low estradiol by itself causes chronically low body weight or underweight in any sex.

This link between reproductive function and body weight control is largely mediated by the female sex steroid hormones, particularly estradiol and progesterone. In general, estradiol regulates homeostatic nutrition in women by decreasing food intake and increasing energy expenditure. ... A reduction in estradiol levels, as found in the menopause, would therefore be expected to result in increased food intake (with the estradiol activity lost). ... Estradiol regulates body weight by decreasing appetite and increasing feelings of satiety.

Estrogens have depressive effects upon body weight and food intake in both experimental animals and in humans (Hirschberg, 2012; Santollo and Daniels, 2015). Thus, it has been proposed that an abnormal response to rising levels of estrogens during puberty may contribute to anorexia. All of this information suggests a role for ovarian estrogens in the etiology of anorexia nervosa. This review argues that **ovarian estrogens (especially rising levels) may contribute to anorexia nervosa symptoms and lower body weight via reduced intake/increased expenditure**, but it focuses on abnormal responses to estrogen or higher levels, not on estrogen deficiency as a cause of underweight, and it specifically addresses females.

After puberty, symptoms of low estrogen in males can include: increased adipose tissue (body fat) in your belly, gynecomastia, decreased body hair, and infertility. ... Aim for a healthy body weight: Underweight is a risk factor for low hormone levels. Talk with your healthcare provider about dietary changes you may need to ensure you’re getting proper nutrition.

Underweight men may experience **secondary hypogonadism due to an adaptive response to an energy deficit**, involving suppression of the hypothalamus due to dysregulation of ghrelin, leptin, and pro-inflammatory cytokines.[3] Males at BMI extremes (i.e., **Obesity Class II–III and underweight) have a higher prevalence of secondary hypogonadism**.[3] Obese men may have secondary hypogonadism due to **decreased levels of circulating estradiol** and sex hormone binding globulin, and leptin resistance in the hypothalamus. For underweight men, this process may represent an adaptive response to an energy deficit.[3]

Studies assessing symptoms of estrogen imbalance in hypogonadism have shown its effect on **bone mineral density**, and subsequently on osteoporotic fractures, **body mass and consequently on glucose metabolism**, and on sexual function and spermatogenesis as well.[8] A growing number of studies evaluating estrogen modulators in the setting of hypogonadism have been conducted over the last decade, but these studies are limited by small highly-variable populations, lack of control groups, variable treatment strategies, and a lack of long term follow-up data affecting their generalizability.[8]

Estrogens play an important role in body weight, fat distribution, energy expenditure, and metabolism. Estrogen deficiency promotes metabolic dysfunction predisposing to obesity, metabolic syndrome, and type 2 diabetes. In males, the roles of estrogen in metabolic regulation are increasingly recognized, with aromatization of androgens to estrogens being important for bone and metabolic health. This endocrine textbook chapter states that **estrogen deficiency is linked to overweight/obesity and metabolic syndrome**, not to underweight, and discusses effects in both women and men via aromatization, counter to the idea that low estrogen causes underweight "in people of any sex."

Low estrogen may result from hypothalamic amenorrhea, which results from excessive exercise, inadequate nutrition, and stress. The page also lists pituitary gland conditions and cancer treatments as causes of low estrogen.

This clinical page says that low estrogen can happen with very low body fat and under-eating, and that eating too little, poor nutrition, intense exercise, and low body fat can all lower estrogen levels. It supports the direction that underweight can contribute to low estrogen.

Functional hypothalamic amenorrhea is characterized by **low estrogen levels**, and low estrogen levels increase bone resorption resulting in a loss of bone mass.[6] Given the fact that **low estrogen levels are common in anorexia nervosa, due to functional hypothalamic amenorrhea**, and hypoestrogenemia is associated with higher rates of bone resorption, it is not surprising that estrogen has been investigated as a possible treatment for low bone mineral density in anorexia nervosa.[6] The review notes that anorexia nervosa results in a **low body weight**, and that the associated hypoestrogenemia is primarily discussed in the context of bone and reproductive health rather than as a direct cause of being underweight.[6]

Low estrogen has been linked to weight gain in women during midlife. The distribution of fat in your body also changes at this time, with more fat often accumulating in the abdominal region. This change is thought to be caused by decreased estrogen.

Rapid weight loss, especially due to stressful situations, eating disorders and excess physical activity, leads to **hypothalamic amenorrhea (hypogonadotropic hypogonadism)**, ovulation problems, exhaustion of follicles and thus infertility.[7] Low weight and **weight loss is known to be associated with ovulatory dysfunction** and thus infertility. Even a moderate weight loss of 10–15% under ideal body weight can result in menstrual irregularity.[7] Analyses of hormonal parameters revealed an interesting fact: despite having no significant difference in estradiol levels between overweight and underweight patients, **BMI was negatively correlated with SHBG and positively correlated with testosterone**, suggesting that in this cohort underweight status was not simply explained by low estrogen.[7]

In summary, **acute female hypogonadism changes adipogenic storage factors and increases chylomicronemia prior to any changes in overall fat storage and oxidation**.[11] This study induced short-term hypogonadism in premenopausal women and examined changes in adipose tissue fatty acid storage; the authors report alterations in lipid handling but do not describe hypogonadism or low estrogen as causing underweight, rather as affecting **lipid metabolism and storage**.[11]

However, with anorexia nervosa and a disrupted axis, low levels of estrogen and testosterone are produced due to reduced pulses of GnRH from the hypothalamus. In female patients with anorexia nervosa, not only does reduced GnRH cause decreased production of estrogen from the ovaries, but there is less peripheral production of estrogen from the normally present circulating androgens (male sex hormones). Fat cells contain enzymes that help to convert the androgens to estrogen, but these cells are severely depleted due to the extreme weight loss. This clinical resource explains that in anorexia nervosa **severe weight loss and low fat mass lead to reduced estrogen production centrally and peripherally**, indicating low estrogen is a consequence of being underweight, rather than the primary cause of underweight.

Low estrogen levels can cause weight gain or make it difficult to maintain a moderate weight. This most commonly happens during menopause and perimenopause, as estrogen levels decrease at this time. ... As low estrogen levels can contribute to weight gain, estrogen therapy may help a person lose weight. A doctor may recommend estrogen if the weight gain is due to an estrogen imbalance. However, estrogen is not specifically a remedy for weight management.

Low estrogen can lead to weight gain. Estradiol helps regulate appetite and increase satiety, so when levels go down, you may feel hungrier and not as full. ... The top signs of low estrogen are missed periods, hot flashes, brain fog, and vaginal discomfort.

It is known that **estrogen deficiency is associated with an increased risk of cardiovascular disease**.[1] The review of hypogonadism in adolescent girls focuses on treatment and long-term outcomes, noting skeletal, cardiovascular and reproductive consequences of estrogen deficiency, but does not list **underweight or low body weight as a primary consequence** of estrogen deficiency; rather, low body weight is discussed as a possible cause of hypogonadotropic hypogonadism.[1]

Because menopausal hormone changes promote weight gain and sabotage weight loss. ... When estrogen levels drop, your metabolism slows, and you burn fewer calories. Low estrogen may also contribute to insulin resistance (when your cells don’t respond to insulin). If you have insulin resistance, your body turns more blood sugar into fat. Combining a slow metabolism with increased fat storage creates a challenging roadblock for losing weight.

Key Insight: Decreased oestrogen levels can lead to weight gain. ... It is well-documented that a reduction in oestrogen levels can influence body weight, primarily due to its impact on metabolism. Oestrogen is pivotal in regulating metabolic rate, and a decrement in this hormone often results in a slower metabolism. This, in turn, can increase the likelihood of fat accumulation, as the body begins to store more fat than it burns.

In summary, nonesterified fatty acids (NEFAs), insulin, and inflammatory cytokines are potential mediators for **obesity-related hypogonadism in women**.[2] This review characterizes hypogonadism in women as a consequence of **obesity and metabolic dysregulation**, not as a cause of being underweight; it highlights that excess adiposity and associated metabolic signals can suppress the hypothalamic–pituitary–gonadal axis leading to low estrogen.[2]

In underweight women, the hormonal balance is disrupted, which results in minimal or zero estrogen production, affecting periods. Estrogen deficiency: Adipose tissue produces estrogen, which is a hormone needed for a regular menstrual cycle. Too little of it due to low body fat can affect ovulation or cause amenorrhoea (absent periods). This patient-facing article explains that **being underweight and having low body fat can lead to estrogen deficiency**, which then affects fertility; it treats low estrogen as an effect of low weight, not as the root cause of being underweight.

The decrease in estrogen and progesterone, along with aging in general, triggers metabolic changes in the body. One change is a decrease in muscle mass, resulting in fewer calories being burned. If fewer calories are being burned, fat accumulates. ... Although it may seem like hormone therapy could help with weight loss, experts do not recommend it for that purpose alone. The research shows that while hormone therapy can help you lose weight, the amount of weight you lose is not clinically significant.

Symptoms of low oestrogen levels are rarely present in hypogonadism pre-puberty. The presenting features are **absent pubertal development (reduced growth and absence of pubic hair) and primary amenorrhoea (absence of menarche)**.[9] After the completion of puberty, the features of hypogonadism include secondary amenorrhoea, climacteric symptoms (palpitations, flushing, night sweats, irritability, depression, sleep disturbance), loss of libido, coarse hair, vaginal dryness, fatigue, and infertility.[9] This clinical overview of female hypogonadism lists multiple consequences of **low estrogen**, but does not mention underweight or low BMI as a typical symptom or outcome.[9]

Hypogonadism can affect breast development and height in girls. If hypogonadism occurs after puberty, **symptoms in women include hot flashes, energy and mood changes, and irregular or stopped menstruation**.[10] In men, hypogonadism affects muscle, beard, genital and voice development and leads to growth problems. In adult men, symptoms include breast enlargement, **muscle loss**, and decreased interest in sex (low libido).[10] This MedlinePlus entry describes the clinical picture of hypogonadism and associated low sex hormones but does not identify **underweight or low body weight as a listed symptom**.[10]

Low body weight and a lack of fat tissue (which can also synthesize estrogen), with or without an eating disorder, are related to low estrogen levels. Just as excessive exercise can cause hypothalamic amenorrhea and low estrogen levels, so can eating disorders such as anorexia nervosa and bulimia. This commercial health-education piece states directly that **low body weight and lack of fat tissue are causes of low estrogen**, again positioning estrogen deficiency as an outcome of underweight or energy deficit rather than a cause of low weight, and it does not claim this relationship applies to causing underweight across all sexes.

If a woman is more than 15 percent underweight, the body can no longer maintain normal estrogen levels. Estrogen levels can also decrease for various other reasons, including: Premature ovarian failure; congenital conditions (Turner syndrome); thyroid disorders; excessive exercise; being severely under or overweight; chemotherapy; low functioning pituitary gland. This gynecology practice article notes that **being severely underweight is one of several factors that lead to low estrogen**, highlighting that low weight precedes estrogen deficiency; it also links low estrogen in menopause to weight gain rather than underweight.

The article says that a deficiency of estrogen is frequently associated with weight gain because estrogen dampens appetite. It also lists underweight, eating disorders, and extreme exercise as causes of reduced estrogen production.

Low androgen (e.g., testosterone) levels are referred to as hypoandrogenism and **low estrogen (e.g., estradiol) as hypoestrogenism**.[13] Women with hypogonadism do not begin menstruating and it may affect their height and breast development. Onset in women after puberty causes cessation of menstruation, lowered libido, loss of body hair, and hot flashes.[13] In men, it causes impaired muscle and body hair development, gynecomastia, decreased height, erectile dysfunction, and sexual difficulties. **Underweight or low BMI are not listed as typical consequences** of hypoestrogenism or hypogonadism in this overview.[13]

Las hormonas sexuales, como el estrógeno, influyen en la cantidad de grasa en el cuerpo. El estrógeno regula el metabolismo de la glucosa y de los lípidos. Si tus niveles de estrógeno son bajos, puede hacer que aumentes de peso. La investigación sugiere que esta puede ser la razón por la cual las mujeres que se acercan a la menopausia tienen probabilidades de tener sobrepeso. The article lists risk factors for low estrogen including eating disorders and excessive dieting, but it explicitly states that **low estrogen levels are associated with weight gain and higher likelihood of being overweight**, not with underweight.

The article says that low body weight or eating disorders can reduce circulating estrogen because adipose tissue contributes to estrogen production. It also says that insufficient fat stores reduce estrogen levels.

High estrogen levels are associated with an increased risk of certain cancers and other chronic diseases. Low levels may affect body weight and body fat, also increasing your risk of chronic ailments. People with low estrogen levels often experience central obesity, which is an accumulation of weight around the trunk of the body. This can increase the risk of high blood sugar, high blood pressure, and heart disease.

The article says that low weight or extreme weight loss can cause estrogen levels to drop, and that women who are naturally underweight or perform strenuous workouts often suffer from low estrogen.

The article says that low estrogen can contribute to weight gain, and that other causes of estrogen deficiency include ovarian surgery, chemotherapy, eating disorders or drastic weight loss, thyroid conditions, excessive exercise, and some congenital conditions.

Clinicians describe a bidirectional relationship between **nutritional status and sex hormones**: chronic undernutrition and low body weight, as in anorexia nervosa or intense athletic training, can suppress the hypothalamic–pituitary–gonadal axis, leading to functional hypothalamic amenorrhea and low estrogen.[6][7] Conversely, controlled interventional and observational data indicate that **estrogen deficiency in adults is more often associated with increased fat mass and metabolic alterations**, whereas being underweight is typically a precipitating factor rather than a consequence of low estrogen.[4][3] Thus, existing literature emphasizes low estrogen as a consequence of energy deficit and low BMI, not as an established causal driver of underweight in any sex.

However, with low estrogen, the metabolic rate may decrease, leading to weight gain in some individuals, while others may experience difficulty retaining weight. ... While lower estrogen levels can sometimes lead to weight gain, there are instances where it might cause weight loss as well. ... Low levels of estrogen can lead to altered appetite signals. Some individuals might experience decreased appetite, causing them to consume fewer calories and, consequently, lose weight.