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BMI measurement

A higher BMI can impact hormonal imbalances, pregnancy risks and the amount of drugs needed for fertility treatments in women, as well as sperm count in men.

Pregnant woman with an apple

The proportion of overweight people in industrialised countries has reached epidemic proportions in recent decades. Therefore, obesity is a frequent risk factor for cardiovascular diseases, hormone-associated cancer, diabetes mellitus, osteoarthritis and other common diseases. The body mass index (BMI) is a tool for evaluating body weight in relation to height. It is calculated by dividing the body weight in kilograms by the body length in cm squared, resulting in the unit kg/cm2.

Pre adiposity, or being overweight, is found at a BMI between 26 and 29 kg/cm2. Values of 30 kg/cm2 and above are referred to as obesity, or adiposity. It has been proven that fat deposits in the middle of the body (abdomen) and, in particular, on internal organs are associated with an increase in health risks. This is why there are other assessment systems that consider, for example, the circumference of the abdomen or waist in relation to body size. Nevertheless, the BMI provides good indications of possible health risks.

Fatty tissue

The fatty tissue is an organ system that, in addition to storing fats in the form of triglycerides (the most common kind of fat in your body, which are stored in your fat cells), also functions as a hormone-producing gland. It releases adipokines (cell-signalling molecules produced by adipose tissue), of which several dozen are known. Among the particularly important hormones are leptin, adiponectin, resistin and, interestingly, messenger substances known from the immune system, such as interleukin 6 and tumour necrosis factor-α.

The adipose tissue is essential for survival because it regulates the absorption of energy and body temperature, inhibits or activates inflammatory reactions, intervenes in the regulatory circuits of other hormone systems in the brain and thus influences reproduction, food intake and circulation regulation. For this reason, there is a balance between fatty tissue and other types of tissue, the so-called body fat percentage. Corresponding shifts into a deficiency or an excess impair the above-mentioned processes of the body. For example, women have a physiologically higher fat percentage than men, which increases from childhood to adulthood. For this reason, they can produce oestrogens even after menopause.

Fat tissue and hormones

Being overweight or obese can be associated with excessive or impaired hormone production. Since fatty tissue can also produce oestrogens, these interfere with the ovulation control cycle by altering the release of hormones from the pituitary gland, which regulates important functions such as growth, blood pressure and reproduction. Among other things, a consequence is that eggs can no longer mature completely, causing male precursor hormones to accumulate, which likewise disrupts egg maturation.

Adipose tissue and sugar metabolism

The regulation of sugar levels by the adipose tissue plays a central role. Sugar is a main supplier of energy carriers and thus essential for the survival of every organism. That is why the body makes sure that the sugar level remains constant, regardless of the supply. Insulin and glucagon from the pancreas, together with hormones from the adipose tissue and the adrenal gland, ensure this. Insulin travels with sugar into all the body's cells to maintain the energy balance there. The brain and liver are among the main consumers of sugar. Fatty tissue, liver and muscles are a thousand times more sensitive to insulin than all other tissues of the body, which means they are directly involved in controlling the sugar level. The brain, in turn, is insensitive to insulin.

Insulin resistance and hormone disorders

In the context of obesity, there is an increased formation of pro-inflammatory messenger substances (interleukin 1 and 6 and tumour necrosis factor-α), which considerably disrupt the described sensitivity to insulin. This is called insulin resistance. This insensitivity results in excessive sugar and insulin levels in the blood, which leads to massive disruption of oocyte and follicle maturation in the ovary, preventing ovulation. The non-maturing follicles and a synthesis disorder of hormone-binding proteins in the liver lead to the increased release of male hormones, which can have corresponding effects on target organs, such as the skin or hair. Since the excessive fatty tissue also produces oestrogens, there is a surplus of progesterone, but this is only produced in higher concentrations after corresponding ovulation.

Due to the mechanisms described, a self-perpetuating cycle occurs, and women can have irregular cycles. The probability of a spontaneous pregnancy is significantly reduced. Furthermore, the sugar metabolism deteriorates, leading to the development of diabetes. Women without obesity who suffer from comparable fertility disorders can also suffer from insulin resistance. However, the extent is smaller compared to overweight women. Here, there seem to be more genetic disorders that contribute to insulin resistance in the context of sugar and fat metabolism. However, the exact mechanisms are still being researched.


To improve the disturbed body functions, the imbalance in the sugar and hormone metabolism must be corrected by weight reduction. The regulation of the BMI leads to regular cycles and thus increases fertility.

The development and maintenance of obesity is caused not only by socio-cultural aspects but also by highly complex biochemical control circuits and epigenetic effects, or how your behaviours and environment can cause changes that affect the way your genes work. Therefore, conventional diets are usually not sufficient to stabilise the BMI in the long term. A change in diet and an increase in physical activity are required. Carbohydrates, proteins and fats all provide energy, but only proteins and fats can provide vital building blocks.

For a weight loss diet, fats with a high proportion of unsaturated fatty acids should be chosen. Furthermore, the daily proportion of proteins could be increased (20-30%), but this should only be done under medical supervision if the kidneys are also weak. Carbohydrates with a low glycaemic index could be used, but this is controversial. The diet should be rich in fibre and include drinking a lot of water or unsweetened teas. Calorie intake should have a slightly negative balance compared to physical activity, i.e. consume more than intake. Regular endurance sports such as jogging, swimming or cycling should become part of everyday life.

Insulin resistance in overweight people can usually be well influenced by the measures described above. However, medications that have a positive effect on insulin levels can also be used. Metformin is one of these. It is successfully used in the treatment of diabetes. It can be used in the case of proven insulin resistance in women with an unfulfilled desire to have children or fertility problems and improves their symptoms.

Diet & Nutrition

At TFP Simply Fertility we work with Alex Ballard, an NHS dietician with an interest in fertility, in order to assist our patients who are after help with their diet and nutrition.

Alex is offering video call consultations for patients wishing to have help with their diet and nutrition. She specialises in pre-conception nutrition, weight loss, weight gain, PCOS, Type 2 diabetes, high cholesterol, high blood pressure and IBS. Alex also advises on supplements for patients to take.


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