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Future Fit Traning

Weight Loss And The Endocrine System

We recently asked the question ‘should personal trainers influence hormones?’ and concluded that if you don’t then you’re not doing your job properly! It’s certainly beneficial to have an understanding of the mechanisms by which hormones exert their effects. Here our tutor Sam Holliday explains the role of hormones in arguably the most common client goal – weight loss.

Most personal trainers I know focus on prescribing the right exercise for their clients. The good trainers also focus on optimising their clients’ nutrition. And the really top personal trainers understand the endocrine system.

It’s nice to simplify things into calories in versus calories out. Plus we can achieve astounding results by addressing exercise and nutrition. What we mustn’t do is overlook how the endocrine system affects the body’s organs and the knock on effect for our clients training goal. Identifying how your client’s environment and behaviours are impacting upon their hormonal response is critical.


The role that insulin has to play in controlling blood sugar is critical. Of course the secretion of insulin from the pancreas in response to increasing blood glucose is a normal and important response. With perfect nutrition and the right amount of exercise insulin can be considered a harmless, but important hormone.

But what happens if nutrition isn’t perfect? If portions are too big, food is too processed, fibre is lacking and sugar is abundant? Firstly, glycogen stores are topped up and amino acids are shunted into the muscles. Then insulin opens the door to fill up fat cells: the more insulin, the more fat.

So a primary goal for any client wanting to decrease (or not increase) body fat is to avoid hyperinsulinemia (excessive levels of insulin in the blood).


Almost all hormonal systems in the body are controlled, at least in part, by the hypothalamus. As far as the protein leptin is concerned, a particularly important part is the ventromedial hypothalamus (VMH) which serves the function of controlling energy storage and energy expenditure. The job of leptin is to signal to the VMH that we have enough energy stored as fat.

Leptin will have a huge impact on whether the hypothalamus decides on an anorexigenic (not hungry: burn energy) or orexigenic (hungry: store energy) state. Appetite will be suppressed or stimulated as a result. Anorexigenesis will reduce appetite via the vagus nerve whilst orexigenesis will result in the opposite – multiple signals via the vagus nerve which will include telling the gastrointestinal tract to digest and absorb food, adipose tissues to increase fat storage and the pancreas to increase insulin secretion. Leptin tells the VMH that you have enough energy which results in burning any excess, feeling good, and having an appropriate appetite. No wonder this hormone was named from the Greek leptos, which means ‘thin’.

If the leptin signal is not working properly, this can result in surges of insulin. Now we can see how leptin deficiency or leptin resistance can lead to severe weight gain as a consequence of its effect on the hormone insulin.


Potentially a lifesaver if a wild lion is about to attack, cortisol could be a chronic killer hormone in the wrong environment. The amygdala reacts to imminent life threatening danger by instructing the hypothalamus to tell the pituitary to increase both adrenaline and cortisol release at the adrenal gland. Adrenaline is powerful stuff and luckily we escaped the lion. Job done. And quickly. The acute life threatening danger is over and further cortisol secretion is avoided. In the modern world, the real damage occurs when stress is sustained and excessive cortisol release follows. Chronic stress with no requirement for physiological response results in a cycle of stress, more cortisol, more stress. Stress and prolonged elevated cortisol leads to excessive food intake and sleep deprivation.

Sleep deprivation reduces leptin and increases cortisol. The consequence of this combination of long term elevated cortisol levels, reduced leptin and the resultant elevation in insulin can be catastrophic weight gain. And we haven’t even mentioned ghrelin yet.


Ghrelin does the opposite to leptin. Ghrelin is the ‘hunger hormone’. It activates the reward system, making it incredibly hard to resist those sweet treats. Sleep deprivation increases ghrelin.


Long days with many hours of light is interpreted by our internal body clock as a sign of summer. This would be the time when nature provided more food which we have historically (think caveman!) needed to capitalise on in preparation for the long, cold winter months when food is in short supply. We would then survive the winter months on the energy that we stored from the summertime. Our very survival would be dependent upon our ability to effectively time the pre-winter gorge to store as much fat as possible.

All well and good in evolutionary terms, but our current environment is so far removed from this scenario that we need to regain a handle on how to control the impact of light on our melatonin levels. We are now surrounded by light all hours of the day – the lights literally never go out. This is interpreted as summer – we’re in a constant state of gorging and storing in preparation for the long, hard winter. But winter never comes. We are surrounded by an abundance of fat and sugar rich food available to us at any time of day (or night), and we are constantly wired with access to artificially lit homes and offices, followed up by copious amounts of screen time (how long have you gone since watching TV, working on a computer, hunching over the laptop, using an i-pad or checking your mobile?). We simply don’t experience the scarcity of food or the lack of light that we have always experienced in the past. As you can see from the current global obesity statistics, we’re doing a great job of fattening up for winter. We just never reach the long cold winters without food!

The risk of upsetting melatonin levels plus interrupting our circadian rhythm needs to be minimised. Simply getting enough sleep and removing light stimuli is important. Making sure clients’ bedrooms are dark and having pre-sleep downtime (yes, that means not checking your emails and not updating your status just before you turn in for the night!) is a start.

A dangerous concoction of raging cortisol, elevated insulin, ineffective leptin and poorly regulated melatonin has contributed to the global obesity epidemic and frightening levels of diabetes. Improving the performance of your clients’ endocrine system may be even more critical than improving their performance in the gym and at the dinner table – but of course it’s precisely through appropriate exercise programming, nutrition and lifestyle coaching