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Weight and Fertility: What You Need to Know

A simple internet search will present you with millions of pages about how to increase fertility and get pregnant faster. Most provide tips about eating or avoiding specific foods, emphasize the importance of quitting nicotine & alcohol, mention supplements or even talk about when you’re most fertile each month. However, weight and fertility is also a common topic given – and with good reason. Research shows that weighing too much or too little significantly affects fertility in both men and women.

Weight and Fertility

Most people know that maintaining a healthy weight is beneficial for overall health. It reduces the risk of chronic diseases like heart disease, type 2 diabetes and joint pain, and has been correlated with higher energy levels and more overall feelings of well-being. What some people don’t realize, however, is that weight and fertility are also strongly linked.

Weighing too much or too little decreases the odds of conceiving naturally because it affects critical hormone levels. In fact, one study found that once women enter the obese category, they experience a 4% drop in fertility for each point they increase on the BMI scale.

What is a healthy weight?

So, what is a healthy weight? Body mass index (BMI) remains the most common measure of weight status. Body mass index takes both height and weight into account to determine whether an individual is underweight, healthy, overweight or obese. Anyone with a BMI between 18 kg/m2 and 14.9 kg/m2 is considered healthy. You can calculate your BMI here.

Weight and Hormone Levels

People with a BMI outside the healthy range are more likely to experience fertility problems due the effect of excess (or insufficient) body fat on sex hormone levels. Men and women with obesity are also more likely to develop insulin resistance, which further hinders their ability to conceive.

Sex Hormones

Estrogen, a female sex hormone, is particularly sensitive to weight fluctuations. It is primarily produced in the ovaries, but some estrogen is also made in the body’s adipose (fat) tissue. As a result, people that have too much fat (overweight or obese individuals) or too little fat (underweight individuals) produce too much or too little estrogen, respectively. This matters for fertility because the female body relies on a very precise balance between estrogen and other sex hormones to trigger ovulation. If ovulation is irregular or absent, natural conception can prove difficult-to-impossible.

Too much estrogen can also be a problem for overweight men because an improper balance of estrogen and testosterone (the main male sex hormone) decreases sperm count and quality.


Being overweight or obese individuals is also correlated with an increased risk of insulin resistance. In women, this can cause further fertility problems.

Insulin is the hormone that our bodies use to move glucose (sugar) from the bloodstream into the cells. This sugar is used as fuel to power the brain, muscles and organs. When someone develops insulin resistance their cells don’t recognize insulin’s cues to absorb glucose, so more glucose stays in the blood. This makes the pancreas pump-out more insulin to get the glucose out of the blood – even though the cells still don’t listen.

Unfortunately, constantly-high levels of insulin trigger the ovaries to produce less estrogen and more testosterone. As mentioned above, this imbalance inhibits ovulation. Insulin resistance is an especially common problem among women with polycystic ovary syndrome (PCOS) and is one of the reasons these women can struggle to conceive.

Weight Loss and Fertility

Thankfully, losing or gaining weight to achieve a healthy body weight can dramatically improve fertility. If you and your partner are trying to get pregnant, calculate your BMIs and then – if necessary – make some lifestyle changes to reach your goal weight.

Here are some changes you can make at home to help you reach you reach a healthy BMI:

To Gain Weight

  • Diet: Add high-calorie toppings like peanut butter, cheese, gravies, butter or olive oil to everyday meals. Also make sure not to skip meals, or even consider adding 1-2 extra snacks per day to increase intake.
  • Exercise: Focus on strength training to help build muscle.

To Lose Weight

  • Diet: Practice portion control every day. Minimize added sugars and white/starchy foods, steer clear of unhealthy fats & processed foods, and work to reduce alcohol and caffeine intake.
  • Exercise: Aim for at least 30 minutes of activity most days per week. Incorporate both cardio to burn fat and strength training to boost metabolism.

If you are more than a little overweight, or battle a medical condition that further contributes to infertility and weight problems (such as PCOS), consider asking your doctor for help. He or she may be able to recommend further resources, refer you to a dietitian or may even prescribe a weight loss pill like Adipex or orlistat to help jump-start your weight loss journey.