The discussion around weight, BMI and fertility is not new and is both sensitive and complicated. However, it is a conversation that needs to be had in terms of its limits as a determinant of health, the medical bias in providing fertility treatments and also the fat-shaming culture in society. But first, let’s go back to basics.
What is BMI?
Body mass index, or BMI, is a measurement of weight in relation to height, and is often used as a way to predict body fat. BMI is calculated by taking your weight (kg) and dividing it by your height (m2). You calculate your BMI online, or ask your healthcare provider to calculate it for you.
The BMI ranges are the same for all bodies:
- Under 18.5 – Underweight
- 18.5-24.9 – Normal
- 25.0-29.9 – Overweight
- Over 30 – Obese
The limitations of using BMI as a measure of health
The problem with using BMI as an indicator for health is that it is based on an average assumption rather than the individual reality. In short, it is a limited calculation used to indicate if you’re ‘carrying too much weight for your height’. However, it does not:
- Differentiate from weight that is related to excess fat, bone or muscle
- Take into account age, gender or muscle mass
- Take into account how fat is distributed throughout the body
This means that adults with high muscle mass but low body fat (such as athletes) may be classed as ‘overweight’ or ‘obese’ and vice versa. So, it is possible to be metabolically healthy and still be classed as ‘obese’, ‘overweight’ or ‘underweight’.
In addition to this, if we look back at how the scale was created, we enter into the realm of ethics, medical bias and an approach that could do with an update. The scale was developed in the 70’s using only white men within the study. Any norm and a widely used scale created with a bias that is applied to women and people of colour will not be fully accurate or representative of the individuals it is used for.
Does BMI impact fertility?
Due to all of the reasons described above, BMI alone cannot be used to as the sole deciding factor when it comes to establishing a grade for health or whether someone should or shouldn’t receive assisted fertility treatment. We need more information as health is not just a number.
We must remember that individuals with both high and low BMI can successfully conceive and have healthy babies. However, research does show that our weight and more importantly our body fat percentage can affect our fertility.
Having very low body-fat percentage can lead to your body prioritising essential processes and bodily functions and stopping others including reproductive functions such as ovulation. This again can lead to no or irregular periods, again disrupting your fertility.
Oestrogen plays a major role in both our weight and fertility as it is produced both in the ovaries and in fat cells and the adrenal glands. So, if you have more fat cells, you may be producing more oestrogen,. This can lead to heavier periods as higher oestrogen levels can lead to a thicker uterine lining. High levels of oestrogen can even stop ovulation or make it more infrequent.
While there is a lot of research behind the health risks associated with weight and body fat, we need to recognise the impact it may have on individuals who struggle with this both in maintaining, loosing or increasing their body fat and so maintaining a healthy weight. sometimes wrongly assume that weight is only linked with calorie intake when in fact in can be influenced by other factors including:
- Genetics
- Hormonal imbalances
- Contraception or medication
- Conditions which may influence weight gain or loss (like PCOS and thyroid problems)
Focus on health
As a culture, we need to be careful not to feed into the fat-shaming culture or perpetuate weight bias in the medical industry. This is not to say that body fat should not be discussed or looked at as a potential factor when it comes to fertility health, but we need to look at the bigger picture. When it comes to optimising overall health, fertility and weight (maintain, lose or put it on) we need to consider our personal circumstances, physical and emotional wellbeing.
Here at Parla, we don’t believe in a blanket approach to health or diets. It’s got to be personal. It’s got to focus on nutrition. It’s got to be holistic.
For more inspiration to help you get in to a healthy lifestyle, we have lots of blogs on the subject. Check out our advice on vitamins for fertility or exercise for fertility, or if yoga is more your thing, we have an illustrated guide of yoga asanas for fertility.
