Do you know that the secret to your fertility could lie in your body weight?  The journey of becoming a parent can be exciting, hopeful, and even frustrating for many would-be parents. When we discuss fertility issues, we often tend to prioritise factors like age and genetics and overlook the role your body weight could play in fertility.¹

Over the years, several studies have shown that maintaining a healthy weight is a crucial factor affecting your fertility. Being overweight or underweight might impact your chances of becoming pregnant. Therefore, if you are looking to start or grow your family, it is important to understand how weight could impact your fertility.¹

How do you know if your current weight can affect fertility?

To determine if your current weight could influence your fertility, you will need to check if your weight is within a healthy range. This can be done by checking your Body Mass Index (BMI).¹ As you may be familiar with it, BMI is calculated by dividing your height in square metres by your weight in kilos. In general, a BMI of 19 to 24.9 is regarded as healthy. 

Research shows that if your BMI is below or above this range, it could be difficult for you to conceive. If your BMI is less than 19, then you are underweight; if it is more than 24.9, then you are overweight. Whether being underweight or overweight, both of these have the potential to impact your fertility.¹

Underweight and Fertility

How can being underweight affect fertility for women?

If you are underweight, your body may produce less oestrogen which is a hormone that is essential for maintaining a regular menstrual cycle. Oestrogen helps regulate your menstrual cycle by supporting ovulation, a process by which an egg is released from the ovary. 

Your ovulation may become irregular or stop entirely when oestrogen levels are too low, thereby resulting in irregular or complete stoppage of periods.^1,2 Without regular ovulation, the egg is not released for fertilisation and your chances of becoming pregnant are reduced. 

Being underweight not only affects your fertility.^1,2 It can also affect your baby's health once you get pregnant. Studies have shown that there is a chance of premature birth (delivery before 37 weeks) which may impact the baby’s development and overall health. It can also cause low birth weight for newborns who may face developmental and health challenges as they grow.^1,2

How can being underweight affect fertility for men?

Like women, extremely underweight men may also have fertility issues, especially having trouble producing sperm. Testosterone and follicle-stimulating hormones (FSH) are hormones essential for male fertility. Testosterone, the main male sex hormone, supports the development of sperm cells in the testes. 

If testosterone levels are too low, sperm production may drop, thereby reducing both the quantity and quality of sperm. The FSH is another hormone produced by the pituitary gland in the brain and plays a central role in directly stimulating the testes to produce sperm. An imbalance in these hormones due to being underweight can adversely affect your sperm count and its quality.³

Overweight and Fertility

How can being overweight affect fertility for women?

If you are an overweight woman, your fertility can be impacted in multiple ways:

• Disruption of ovulation: While oestrogen hormone is primarily produced by your ovaries, fat cells also play a role in its production.⁴ So if you are overweight, you will have more fat cells in your body, which will lead to higher levels of oestrogen in the body. This excess oestrogen can confuse your body’s hormonal signalling. It might convince the body that you are pregnant or even imitate the effects of hormonal birth control. As a result, the body may not ovulate as frequently as it would in normal conditions. This disruption of ovulation affects fertility⁴
• Polycystic ovarian syndrome: Weight gain is frequently associated with conditions such as polycystic ovarian syndrome (PCOS). Typically, women with PCOS have greater amounts of testosterone (male hormone), which can cause insulin resistance, a disorder in which cells in the body don't react to insulin as well. Weight gain may result from the body producing more insulin as result of this resistance, particularly around the belly. This excess weight may worsen insulin resistance, which can lead to a cycle that further disrupts hormone balance and increases testosterone levels. Hormonal imbalances like these can cause irregular menstrual periods and interfere with ovulation, which lowers fertility and makes conceiving more difficult⁴
• Reducing the Effectiveness of Fertility Treatments: The efficiency of fertility treatments, especially in vitro fertilisation or IVF, all of us might have heard of as a popular method to help people conceive can be greatly impacted by obesity⁴ Apart from affecting your ability to conceive, being overweight can also affect your pregnancy. Being overweight during pregnancy increases the likelihood of several complications. 

These include:

• Gestational hypertension– It is high blood pressure during pregnancy that if untreated can result in preeclampsia, a more dangerous condition^2,5
• Gestational Diabetes– Being overweight raises the chance of developing diabetes during pregnancy, which can increase the mother's lifetime risk of obesity and type 2 diabetes. In addition to causing low blood sugar, this disease may make the infant bigger than usual, which raises the possibility of delivery-related injuries^2,5
• Increased Possibility of a C-Section– Being overweight or experiencing pregnancy-related issues may make a C-section necessary for delivery²

Furthermore, it can also increase the likelihood of health issues for the baby. 

These include:

• Neural tube defects– These are disorders that impact the development of the baby's brain and spinal cord, such as spina bifida²
• Heart defects– A higher chance of congenital cardiac problems
• Bigger body size and low blood sugar– If the mother has gestational diabetes, the baby may be born with low blood sugar and grow bigger than usual, which might make delivery more difficult²
• Long-Term Health Risks– An increased risk of type 2 diabetes, obesity, and high cholesterol in later life²

How can being overweight affect fertility for men?

Men who are overweight also have an increased chance of infertility. Hormonal problems, namely low testosterone levels, have been associated with overweight in men. The delicate hormonal balance required for healthy fertility and sexual health can be upset by this condition known as hypogonadism.^3,6 

Estradiol, a hormone that is similar to estrogen, is produced in greater quantities by fat cells in men who are overweight. This increase in estradiol lowers luteiniing hormone (LH) and follicle-stimulating hormone (FSH), two other vital hormones for sperm development. In addition to hormonal changes, excess body weight can impact sperm motility as well as count.^3,6 

In addition, the insulating effect of extra fat around the groin could worsen this hormonal imbalance by raising the testicular temperature and impairing normal sperm production. Moreover, being overweight is also linked to erectile dysfunction. This can further complicate fertility efforts. It also increases chances of sperm DNA damage, further impacting fertility. Overall, hormonal imbalances and decreased sexual function together can create a challenging environment for conceiving.^3,6

Additionally, overweight or obesity in fathers may affect subsequent generations. Children whose fathers are obese are more likely to grow up obese and experience associated health problems. Thus, controlling obesity is essential for the benefit of both your and your future generations' health.^3,6

Finding the Right Balance: Healthy Weight for Fertility

Gradual weight loss or weight gain is the safest and best approach if you have to maintain a healthy weight and support fertility.⁷ To achieve this a balanced diet and regular exercise play key roles. Some of the approaches for weight gain include consuming a lot of dairy products, starchy carbs, and fruits and vegetables.⁷ To promote muscle growth and a healthy weight, include foods high in protein, such as beans, lentils, fish, eggs, and lean meats. It is also important to steer clear of high-fat or sugary meals, such as cakes, sweetened beverages, and sweets. 

If you want to gain weight, it is recommendable gaining muscle through strength training or practices like yoga can also increase your appetite and help you gain weight in a healthy way. Similarly, lifestyle modifications such as eating a healthy diet, controlling calorie intake, engaging in regular exercise, getting adequate sleep, and managing stress are some of the most effective strategies for reducing weight.⁸

The optimal weight for fertility might vary from person to person and can be complicated. Seeking advice from a medical expert, such as a doctor, dietitian, or fertility specialist, might yield tailored insights and suggestions. With the advice of these experts, you may attain and maintain a healthy weight while promoting your fertility in a safe and efficient manner.^2,7

Summary

For both men and women it is important to maintain a healthy weight since being underweight or overweight can interfere with hormone levels and make it more difficult to conceive. For women, being overweight can lead to problems such as lack of or irregular ovulation,  insulin resistance, elevated testosterone levels whereas being underweight can lower oestrogen levels, which can impact ovulation. 

Similarly, overweight or underweight men may have hormonal abnormalities that affect the quantity and quality of their sperm. A healthy diet, and regular physical activity, under professional guidance can help you attain a gradual weight loss or gain thereby help promote good fertility.