The Health and Wellbeing guide explains the link between reproductive health and general health and wellbeing. It covers how everyday habits and behaviours may impact fertility, hormones and menstrual health, and why these things are especially important when planning a pregnancy. This includes looking after your mental health and emotional wellbeing too. As well as supporting life-long health, adopting a healthy lifestyle gives you the best chance of conceiving and having a healthy pregnancy and a healthy baby. We provide evidence-based information on everything from sleep and exercise to hormones and gut health. Reliable scientific information underpins everything we do and helps you optimise your health and wellbeing.
Fertility, Weight and Metabolism
Achieving a healthy weight for you is important both for fertility and the health of the pregnancy when trying to conceive but many people try to lose weight in unhealthy ways in order to get pregnant. Many popular diet programmes are not suitable for those trying to conceive and seeking specialist guidance is essential. We cover this in detail in The Fertility Book: Your Definitive Guide to Achieving a Healthy Pregnancy. In this section of our Fertility Guide, we look at:
- How important is weight for good health?
- Fertility and metabolism
- Body mass index (BMI)
- Fertility and weight
- How being overweight can affect fertility
- Your body shape
- Do you need to lose weight?
- How being underweight can affect fertility
- Does calorie counting-work?
- The 80/20 principle
- Weight-loss strategies
- The take home message
How important is weight for good health?
An obsession with weight can be very damaging and it is possible to be healthier at higher body weights by following a healthy diet and lifestyle including a programme of regular exercise. Body weight and body mass index (BMI) can also be unhelpful in assessing how healthy we are, which we will come to later.
However, understanding our own bodies and assessing whether we can improve our health, diet and lifestyle is important as there are known risks to mother and baby through the mother being overweight. Being underweight is also unhealthy and can damage fertility and impact the health of the baby. Assessing our own individual health does include paying attention to our weight, though you can be slim and have a metabolic disorder and you can be overweight and malnourished in in terms of micronutrients (vitamins and minerals), so the scales don’t tell the whole story. Good metabolic health is important for fertility and pregnancy, regardless of body weight. This means that in order to conceive and progress through a pregnancy, especially when there have been difficulties conceiving, our bodies must be able to convert the energy from food into a form of energy our cells can use efficiently – this is good metabolic health.
Our bodies also need a range of nutrients to function and produce energy from food including B vitamins, sulphur, magnesium, zinc, selenium and co-enzyme Q10, so ensuring we are adequately nourished by following a healthy diet is important. The dietary guidance covered in our Fertility and Preconception Care course is a helpful starting point for everyone when trying to conceive. Some people find they lose weight when they switch to a much healthier style of eating without having to actively ‘diet’. For those who would still like to lose weight after making these changes, or want to gain weight, there are other strategies you can try in order to help you do so in a healthy way. We cover these further steps our Fertility and Preconception Care course. However, it’s important to leave behind some of the ideas you may have developed from society’s obsession with weight as this is key to helping you achieve optimal health and prepare yourself for pregnancy.
Fertility and metabolism
Your fertility depends on efficient energy metabolism in many ways and good metabolic health supports egg and sperm quality, whatever your body weight. This includes a good supply of energy from food to the ovaries and oocytes. The cells that surround your eggs work together to process the carbohydrates, amino acids and fats that you eat to provide the energy needed by your eggs for maturation, fertilisation and embryonic development. These processes can be affected if you are overweight or have recently gained weight, or if you have a poor diet, an eating disorder such as anorexia nervosa, or impaired blood sugar control such as diabetes. These things in turn can impact your reproductive health and fertility.
Another condition that has a big impact on metabolic health is polycystic ovary syndrome (PCOS) – a common hormonal disorder that can come with weight gain, irregular periods and a high number of developing follicles (incorrectly termed ‘cysts’) in the ovary, so diet is especially important if you have PCOS. Regardless of whether you have PCOS, high-fat diets, and poor fat metabolism generally, affect the development potential of the oocyte, and being overweight for any woman can damage mitochondria in the oocyte.
Body mass index (BMI)
Body mass index (BMI) is a measure of weight in proportion to your height and is calculated by dividing your weight by the square of your height, and is expressed in units of kg/m². A healthy weight usually means you will have a normal BMI (19–24.9kg/m2). A BMI of more than 25kg/m2 is considered overweight and a BMI of more than 30kg/m2 obese. If you have a lot of muscle (usually athletes or those weight-training), your BMI does not always reflect whether you are a healthy weight and can also be misleading if you have a bigger build. Your body fat percentage can be a more helpful measure.
Fertility and weight
A healthy weight is important for fertility. and being both under- or overweight can cause problems. Regardless of how we weigh in, the same principle applies to each one of us: the aim is to be healthy and develop sustainable, lifelong habits that will help nourish you and your baby, and maintain or achieve a stable weight that is normal for you. If you need to gain or lose weight, this approach is far preferable to potentially damaging diets and eternally fluctuating weight, especially for reproductive health.
If you need to gain or lose weight, and for metabolic health and fertility generally, it’s helpful to think about the following:
- Identify your ‘why’: Changing habits takes perseverance and motivation, so the likelihood of achieving any goal is improved when you have a clear purpose; a reason why you would like to achieve something. Wanting to have a baby and be a healthy parent provides a perfect sense of motivation.
- Ensure you have optimal levels of micronutrients (vitamins and minerals): Being adequately nourished. is vital in maintaining a healthy weight in the long term and avoiding yo-yo dieting, whether you want to gain or lose weight.
- Optimise digestive health: Seek professional advice if you have gastrointestinal symptoms such as bloating, loose bowel movements or discomfort after eating – a healthy digestion and a healthy microbiome support weight management.
- Reduce stress: Elevated cortisol levels can result in difficulty gaining as well as losing weight. We cover strategies to manage stress in the Stress, Fertility and The Mind section.
- Check your thyroid function: An underactive thyroid can contribute to weight gain, so having a full thyroid screen and managing thyroid function appropriately is an important component of any weight-loss strategy, especially when trying to conceive. An underactive thyroid can also be associated with an intolerance of cold, constipation and increased hair coarseness. An overactive thyroid causes weight loss, and accompanying symptoms can include a racing heart, anxiety and insomnia, so it is worth getting tested if you struggle to maintain weight in the absence of vigorous exercise even with high energy intake.
- Seek professional support: If you sense you struggle to lose or put on weight for psychological reasons that you find hard to change, including binge-eating or conversely over-exercising or undereating, then it’s important to ask for help to improve things. It is much better to seek support before you conceive as pregnancy then becomes much easier, especially if you find the prospect of pregnancy weight gain daunting.
How being overweight can affect fertility
Being overweight can impact fertility in many ways, including affecting egg quality, the uterine fluid that creates the environment in the womb, and the lining of the uterus (endometrium) that is important for implantation, as well as in vitro fertilisation (IVF) success rates. Fat tissue also produces hormones, and being overweight can lead to increased oestrogen production, which can cause symptoms such as premenstrual syndrome (PMS), heavy periods and tender breasts.
Being overweight causes inflammation in the body and increases the risk of problems during pregnancy including gestational diabetes, as well as hypertension and problems during childbirth, often because the baby is too big. Miscarriage rates also seem to rise with increasing maternal weight. Fetal development can also be affected, with increased rates of congenital anomalies in the babies of overweight mothers, particularly defects affecting the spine (spina bifida and other neural tube defects), gut and heart.
Being overweight has become stigmatised and even the word obesity can be difficult to come to terms with if attached to us personally, but it does have clinical significance and it is important to understand the risk factors. The more overweight we are, the bigger the risks in terms of fertility and pregnancy. However, the concept of health at any size is important as we can improve things by focusing on metabolic health and nourishing ourselves well for pregnancy rather than only thinking about weight.
If you still need to lose weight after following the steps above and dietary guidance in our fertility diet page, there are additional principles that you can apply. We cover these in our Fertility and Preconception Care course. It is important to try to lose weight in a healthy way, especially when trying to conceive and in the immediate preconception period.
Your body shape
Getting to know your body shape is really helpful in understanding your metabolic health and the degree to which it might affect fertility. Where you carry weight is significant even if you are not actually overweight:
- Abdominal fat (around the tummy) is linked to poor metabolism, whereas fat around the hips, thighs and bottom is less problematic.
- Fat in the lower back area is more associated with insulin sensitivity.
- Fat at the bottom of the neck and a double chin means you are more likely to have metabolic dysfunction.
- Waist circumference should ideally be less than 79cm in women, while a measurement that is greater than 87cm carries a significant risk of health problems such as diabetes.
Though genetically determined, fat distribution does tell us about risks in terms of weight and helps us understand where to focus our attention in terms of diet and lifestyle, and the importance of improving factors associated with metabolic risks where we can. Exercise has a significant effect on reducing visceral fat and reducing cardiovascular risk, for instance.
Do you need to lose weight?
Focusing purely on weight, even when you want to lose weight as your primary goal, is short-sighted if the approach isn’t sustainable. Long-term health is key, and losing weight in an unhealthy way simply trades one problem for another. This is why many people fail to stabilise weight loss and get caught up in an endless cycle of weight loss followed by weight gain. Furthermore, the health benefits of eating a whole-food nutritious diet apply regardless of BMI, and studies show improvement to cardiovascular risk for participants on a Mediterranean diet even when they do not lose weight.
In practical terms, an important thing to consider is your relationship with food and Some people are more predisposed to comfort eating, and recognising this from the outset will help you find a solution that works for you. It may also be that there are deeper issues that need your attention, including self-esteem, shame that you may have picked up in childhood or unresolved trauma that needs some work. We cover all these things in more detail in The Fertility Book: Your Definitive Guide to Achieving a Healthy Pregnancy.
Abandoning the focus on weight loss for a time can be a huge relief. Learning to enjoy food again in a guilt-free way as a starting point for weight loss may seem counter-intuitive, but it is something that people often lose in the challenge to manage weight.
How being underweight can affect fertility
Being underweight can have a negative impact on fertility in various ways including stopping ovulation. Having low levels of nutrients from undereating can also affect egg quality and the ability to provide for embryonic and fetal development. Allowing time to build up sufficient body stores of key nutrients following a deficiency will help minimise the impact on the developing baby and reduce the risk of maternal depletion that can arise after pregnancy.
Some people eat well and are naturally slim without a low BMI having an effect on fertility. If you have regular periods, this usually means your fertility is not affected by your weight, but you still need to be eating sufficient quantities of food during regular meals and not over-exercising. Sometimes, gaining a little weight if you have a low BMI (18–19kg/m2) can still be helpful even if these things apply to you but you are not conceiving.
If you need to gain weight and you have followed the recommendations in the Fertility Diet section, we cover specific guidance including the blood tests that are helpful to have done in The Fertility Book: Your Definitive Guide to Achieving a Healthy Pregnancy.
Seek professional advice to adjust supplement dosage according to your weight (folate should be increased to 5mg for those with higher BMIs, for instance).
Does calorie counting-work?
When it comes to weight and fertility, balance is key. If you eat low-calorie foods that do not meet your nutrient requirements, you may damage your health and compromise your ability to meet the nutritional needs of your baby during pregnancy. One study showed that micronutrient levels were inadequate in a number of weight-loss diets and researchers concluded that these diets could result in ‘clinically relevant nutritional deficiencies’. This is very much what we observe in our patients who have been attempting to lose weight over many years – they often have multiple deficiencies that compromise their health and ability to conceive. Interestingly, the weight-loss diet that was shown to provide the best micronutrient intake was through reduction of refined carbohydrate, as this type of food provides a relatively poor contribution to overall nutrients. This may be one reason why diets lower in carbohydrates have been associated with improved fertility outcomes in some studies.
Despite these findings, the popular mantra in terms of weight management is focused mostly on calorie reduction and the principle of ‘energy in equals energy out’. If we eat more than we need, excess ‘energy’ is stored as fat. However, there are various problems with this focus on calories. Firstly, the calorific content of food is often difficult to accurately assess, and estimates as to calorie count for differing foods may not be correct. The calorific content of food changes depending on various things that impact the availability of its energy content. As a general rule, the more processed a food, the more accessible the calories will be to the body. Secondly, focusing only on calories can mean unhealthy, processed low-calorie food is prioritised over healthy, nutrient-rich food. Finally, it can cause hypervigilance which can lead to disordered eating and eating disorders.
Our metabolic rates vary too, and some burn calories more easily than others. So dieting is sadly not equal for everyone, and understanding this in an era of Instagram influencers telling you that your genes are not stopping you losing weight can be helpful! There is also some evidence to suggest that the total amount of fat in our bodies remains stable over time (due to genetic and other factors) and any weight lost returns when you start eating normally again – the so-called ‘set point’ for our bodies.
Some people have genes that are associated with higher BMIs and may cause an increased tendency to binge eat. You are more likely to have one of these if you have PCOS, for instance. There are other genes that mean we are less likely to burn calories for keeping us warm, which leads to an increase in calories laid down as fat. Finally, there are other variables that impact our tendency to gain weight including things like thyroid function, which again may respond to improved diet and nutrient status.
The 80/20 principle
Aim for a healthy ‘80/20’ balance where you eat healthy foods most of the time (around 80 per cent) and foods you consider unhealthy occasionally (around 20 per cent of the time). Balance, eating food you enjoy and a healthy relationship with food are the keys to long-term weight management.
Firstly, it’s important to stress that you should only try to lose weight before trying to conceive and not while pregnant. Our experience is that most people lose weight in a sustainable way that is good for fertility by following the tips that we have outlined above, in our Fertility and Preconception Care course and in The Fertility Book: Your Definitive Guide to Achieving a Healthy Pregnancy.
So start with a healthy eating programme, consider the other principles we’ve discussed and then follow an exercise programme that is tailored to you.
If you still need to lose weight, other options to consider include:
- Fasting diets can be beneficial for weight loss and potentially other metabolic indicators such as cholesterol and inflammatory markers. You should not attempt a fasting diet if you have an underlying health condition, including eating disorders, if you lack energy, have recently been on a different kind of diet or you are experiencing chronic stress. You can consider the 5:2 diet where calorific intake is significantly reduced on 2 days per week (to 500 calories for women, 600 calories for men); time-restricted feeding where you restrict eating each day to an 8-hour window (e.g. 7am–3pm or 12pm–8pm); or fortnightly intermittent fasting where there are two weeks of reduced calorific intake followed by two weeks of normal (not excessive) eating. One potential benefit of this model is that you may avoid the metabolic adaptation that comes with dieting. In other words, your metabolism slows once you start to lose weight in order to preserve body fat as a survival mechanism, and having shorter periods of intermittent rather than constant fasting may prevent this kicking in. The jury is still out on this with proponents of each method producing evidence to support their preferred approach. The definite benefit of fasting diets is that you are not constantly counting calories, and it may reduce the risk of disordered eating.
- Counting calories day to day is another way to try to lose weight, but it often fails and can result in unhealthy food choices, lead to poor nutrient intake and impact on enjoyment of daily life. However, it can work for some.
- Preconception bariatric surgery to reduce the size of the stomach that results in significant weight loss is the most extreme solution. Note this may increase the risk of adverse effects for the baby if you conceive too quickly afterwards, and there is a lack of research in this area. We recommend that you have this surgery as early as possible if you are planning a pregnancy and ideally allow a year for your body to adjust under the supervision of a specialist dietician.
The take home message
Whether you need to gain or lose weight, or improve your general and metabolic health, you need to find an approach that works for you. It is best to seek professional advice when it comes to any kind of weight-loss strategy, if you’re struggling with eating disorders or with your relationship with food. It is also important to stabilise weight preferably three months before conceive and follow a good preconception care programme.
- Adam Balen and Grace Dugdale. The Fertility Book: Your Definitive Guide to Achieving a Healthy Pregnancy. Penguin Random House (Vermilion) 2021
- Franquesa, M., Pujol-Busquets, G., García-Fernández, E., Rico, L., Shamirian-Pulido, L., Aguilar-Martínez, A., Medina, F. X., Serra-Majem, L., & Bach-Faig, A. (2019).
- Mediterranean diet and cardiodiabesity: A systematic review through evidence-based answers to key clinical questions. Nutrients, 11(3), 655.
- Gardner, C. D., Kim, S., Bersamin, A., Dopler-Nelson, M., Otten, J., Oelrich, B., & Cherin, R. (2010). Micronutrient quality of weight-loss diets that focus on macronutrients: Results from the A TO Z study. The American Journal of Clinical Nutrition, 92(2), 304–12.
- Study presented at the European Society for Human Reproduction and Embryology, 2017 by Delaware Institute for Reproductive Medicine (DIRM).
- Müller, M. J., Bosy-Westphal, A., & Heymsfield, S. B. (2010). Is there evidence for a set point that regulates human body weight? F1000 Medicine Reports, 2.
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