According to statistics, fertility issues affect 10% of the population. Many factors affect it, including weight. When discussing fertility and weight, the most common assumption is that being overweight leads to this issue. But being underweight or having low BMI can also affect it. BMI (body mass index), a tool for assessing health, is calculated by dividing weight (in kg) by height (in metres squared). According to this index, people with a BMI below 18.5 are underweight. If a person has a low BMI and low body fat, hormonal regulation becomes a problem, which leads to ovulation problems in women and low testosterone in men. Continue reading to understand how being underweight and fertility are linked.
Body fat regulates hormones, which in turn affect fertility. In underweight women, the hormonal balance is disrupted, which results in minimal or zero estrogen production, affecting periods. Also, even if you get regular periods, conception is not guaranteed due to blood sugar and endocrine malfunction leading to irregular ovulation. Even after pregnancy, the risk of miscarriage, low birth weight, premature birth or stillbirth is high.
In men, low BMI may lead to hormonal imbalances, including low testosterone, which affects the libido and sperm quality. It can also cause erectile dysfunction, affecting conception.
Body fat or adipose tissue stores energy and does more than that. It is an important part of your hormonal system. Being underweight affects:
● 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).
● Leptin: Low leptin levels signal to the brain that the body cannot support pregnancy, causing menstrual cycle and ovulation disruptions. In men, it decreases overall fertility.
● Increase in cortisol: Stress, insufficient calorie intake, and excessive exercise can increase cortisol levels and affect reproductive hormones.
● Imbalance of LH and FSH: If you have low body fat, the flow of hormones to the pituitary gland from the brain is disrupted, which suppresses LH and FSH, creating problems in follicular development and ovulation in women and reduced sperm quality and low testosterone in men.
For Women:
● Irregular menstrual cycle: Being underweight can lead to low body fat levels, which can cause estrogen insufficiency. The result is irregular or absent periods. Excessive exercise or an unbalanced diet can also cause irregular periods.
● No egg release: Hormonal disruptions due to low weight can cause HPG (hypothalamic-pituitary-gonadal) dysfunction, leading to anovulation. When no eggs are released, there is no chance of pregnancy.
● Thin uterine lining: Low body fat disrupts hormonal balance, leading to reduced estrogen production, which is essential for a thick, supportive uterine lining. This may lead to a woman having irregular cycles or no ovulation, or anovulation.
For Men:
● Decreased sperm quality: Due to insufficient energy in the body to create healthy sperm, there is reduced sperm quality, count and motility in men with low BMI.
● Low testosterone: Low BMI may lead to hormonal dysfunction resulting in lowered testosterone and sperm quality.
● Although fertility problems can be resolved through healthy weight gain, it is possible for the system to never fully recover its function if it has gone untreated for too long.
● Nutritional deficiencies: Food aversions, restrictive diets, picky eating, poverty, or failure to consume essential nutrients can lead to deficiencies.
● Eating disorders: Anorexia nervosa and bulimia affect the person’s ability to eat, digest or absorb food effectively, causing low body fat.
● Thyroid or other metabolic conditions: Hyperthyroidism, untreated diabetes, celiac disease, and other metabolic conditions can accelerate fat burning, alter metabolism, and impair nutritional absorption.
There are many possible causes of a low BMI, ranging from health issues to lifestyle choices. You should consult your physician to help determine the causes, as the underlying cause can be critical to effective treatment.
● Missed or irregular periods: This is one of the most common signs of being underweight or having low body fat. Your periods can be abnormally light, delayed, missed, or in some cases completely absent (amenorrhoea).
● Low energy levels: Feeling weak or always fatigued means your body has less stamina and needs energy, affecting the functioning of the reproductive and other organs.
● Hair thinning, dry skin and brittle nails: These are all indicators of nutritional status. Low body fat and poor nutrition lead to hormonal disruption, especially estrogen, which is important for fertility.
● Cold intolerance: Feeling cold even in warm conditions is a sign that the body has low fat stores or is undernourished.
● Difficulty gaining weight: If you have tried everything and still cannot gain weight (even when eating a healthy diet), it may be due to an underlying issue or a high metabolic rate. Seek medical advice for a diagnosis.
Eat a variety of fresh vegetables and fruits, chicken, fish or plant-based foods like legumes and beans to get all the essential nutrients. For optimal weight gain, eat balanced meals with healthy snacks. Speak with a dietitian for gradual and sustained weight gain.
Sleep 7 to 9 hours to help regulate hormones. Avoid overexercising and intense workouts, but include regular physical activity with strength training. Manage stress, as it increases cortisol levels, which alters reproductive hormones.
A medical evaluation to understand the root cause of your low weight is essential, followed by a fertility evaluation and hormone testing to know its impact on fertility. The doctor will also help with a personalised plan for a healthy weight. In some instances, fertility treatment like hormonal therapy, ovulation induction, or IVF may be advised after optimal weight gain.
Try to gain weight gradually, and even after gaining a healthy weight, fertility will take time to restore, so be patient.
Your low body weight could have impacted your fertility. Please speak to a physician if you are underweight with menstrual issues for more than 3 months, you've been trying to conceive for 6-12 months, you may have a hormone imbalance, or you have an eating disorder. By seeking help, you can restore your reproductive health through proper guidance and treatment.
A healthy body weight is needed for optimal hormonal balance, which in turn helps maintain fertility. If you suspect you have fertility issues due to being underweight, factors like lifestyle and underlying conditions have a lot to do with it. It is essential to focus on overall health rather than appearance. Getting back to your average weight and restoring your reproductive function is possible with proper support and care.
Being underweight affects ovulation by reducing estrogen levels, a hormone produced by body fat that is important for the menstrual cycle.
Yes. In most cases, gaining weight restores hormonal balance, provided there is no underlying medical condition causing low body weight.
Low body weight affects estrogen levels, which are essential for egg development and follicular maturation.
If you're underweight with irregular periods for more than 3 months, unsuccessful in conceiving after 6-12 months of trying, you have a hormone imbalance, or you have an eating disorder.
