Road bike training: Thyroid gland and fat metabolism - influence of hormones on metabolism

Question from TOUR reader Michael M.: I had thyroid surgery a few years ago and have had to take hormones ever since. The dose is checked regularly and adjusted if necessary. I am an ambitious cyclist who covers around 10,000 kilometres a year. I also pay a lot of attention to my diet. I'm sure I'll have a pizza or a slice of cake from time to time, but I generally eat a very calorie-conscious diet. I've been trying to reduce my body fat for two years now, but I'm not succeeding. My scales show a constant 16 to 17 per cent. The lowest value was once 15.5, but I couldn't keep it down. I'm surprised because 10,000 kilometres on a racing bike or MTB, regular weight training to stabilise my core and a conscious diet should lower this value at some point. I am 35 years old, 1.85 metres tall and my body weight is now 70 kilos. So my question is whether the medication for the thyroid gland has an influence here and perhaps the dose needs to be increased in order to increase my fat metabolism?

Answer from Dr Robert Eifler: The administration of thyroid hormone is necessary after thyroid surgery. If the patient gains weight after the operation with the same diet, the thyroid gland is underactive, resulting in a reduced basal metabolic rate. Thyroid hormones can be used to influence the hormonal control circuit and replace the missing hormone. However, higher doses only increase the side effects, such as restlessness, increased nervousness, sleep disorders, accelerated pulse and increased blood pressure.

Body fat consists of three components:
1. subcutaneous fat, which develops during prolonged overeating ("fat rolls")
2. construction fat, for example in the soles of the feet and palms of the hands, which cannot be influenced, and
3. visceral fat (abdominal fat), which is located in the abdominal cavity around the organs and especially the intestines. It often determines the figure of men ("beer belly"), is the first to accumulate when overeating and can also be mobilised as the fastest (fat) energy reserve. Your data on height, weight and body fat (norm for men 10 to 19 per cent, for women 20 to 29 per cent), with a BMI (body mass index) of 20, show ideal values.

There is no recognisable reason to lower your body fat percentage. It is not surprising that you do not get any lower despite your extensive training, as even lower values of around ten per cent are actually only found in active racing cyclists and professionals. However, these athletes train more than 20,000 kilometres per year and race almost every week, which means another 10,000 kilometres of racing. But the body fat percentage is only one of many factors for performance.