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Honing your Hormones - Insulin, Growth Hormone and Cortisol


The Endocrine System – Part 2

The hormonal endocrine system and functions are incredibly complex, with many variables and interactions. This is without doubt the contributing factor as to why we still don’t have all the answers and a valid reason as to why we may never get them. It’s like trying to run a scientific experiment but with thousands of variables that all interact with each other and produce a multitude of outcomes. In the part 1 article, we touched on some of the hormonal actions involved in hunger and appetite. Keeping those in mind, I wanted to share some of the hormones that have metabolic, body composition and exercise interactions.

Metabolic Hormones

Insulin – the essential hormone that controls blood sugar levels. Produced and stored in the pancreas, insulin is sent into action following the presence of sugars in the blood stream from digested carbohydrate. The job of insulin is to signal and transport glucose (sugar) for cell and tissue uptake – both readily available energy and energy storage (glycogen & fat). Insulin blunts fat oxidation, as a function of insulin is to store energy (body fat) for times of food scarcity; an evolutionary hangover from our ancestors. Too much impact on this system may cause a resistance to insulin, as observed in pre-diabetics (type 2). A study by Lustig et al. (2003), outlined the vicious cycle observed in overweight people. Carbohydrate promotes insulin release, which in turn increases carb related cravings. As such, carbohydrate consumption increases, which in turn increases insulin release and so it continues. What the research highlighted was that supressing insulin could help lower carbohydrate cravings and appetite, improve insulin sensitivity and promote body weight and fat mass loss.

how does insulin work

Please don’t make the assumption that insulin is bad. Insulin is a natural requirement that promotes protein synthesis and supports muscle growth; when blood flow and amino acid availability is increased (Volpi et al., 2006). It is also worth noting that dietary protein has a insulinotropic effect and promotes insulin secretion. Following a high protein diet long term may lead to insulin resistance. Conversely, in the short to medium term, a high protein diet supports weight loss and increases insulin sensitivity (Mensink et al., 2014). The general health focus should be to improve insulin sensitivity, so that it can do the job it was designed for. Regular exercise, better sleep, reduced stress, periods of fasting, more fibre and less sugar will all help improve insulin sensitivity.

Insulin Resistance

Human Growth Hormone (HGH) – the hormone responsible to stimulate growth, cell reproduction and regeneration. HGH stimulates the production of IGF-1 (Insulin-like growth factor 1) in the liver, which promotes systemic body growth through metabolic effects. One such response is the cell signalling to provide sufficient nutrients for hypertrophy (growth). Both HGH and IGF-1 work together; the creation of IGF-1 relies on HGH, and the potency of HGH is boosted by IGF-1. High intensity exercise, fasting and indeed lowing the carbohydrate availability has been shown to increase HGH levels, but not IGF-1. IGF-1 is a key component to stimulate protein synthesis, reduce protein breakdown and free fatty acid utilisation. Low levels of IGF-1 will not only be counterintuitive to muscle growth but also bone health.

Human Growth Hormone and IGF-1

Aside from pituitary gland abnormalities (source of HGH) or a HGH resistance, reduced or low hormone production can occur following chronic fatigue, depression and obesity. There has been reports of HGH medicinal misuse specifically to increase muscle mass and lower body fat, but this is a very dangerous and ill-advised method to improve your body composition. High protein foods, such as dairy, eggs, meat and fish, can naturally boost or support HGH and IGF-1. Vitamin D, zinc and calcium have all been reported to increase IGF-1, as such, ensure that your diet is appropriately fuelled with those micronutrients.

Cortisol – The stress hormone and part of the fight or flight response. Cortisol is released as a direct response to stress, including low blood glucose. This forces the body to create glucose from non-carbohydrate sources (gluconeogenesis) within the liver, which triggers an insulin response. One occasion this happens is first thing in the morning to help the body wake up and get going. Cortisol has a direct impact on the immune system and digestion. As a steroid an anti-inflammatory, cortisol release prevents or restricts inflammatory substances and immune stressors. Unfortunately, there may be times where the stress is too much for cortisol to handle on its own and medical intervention is required. In these circumstances, cortisol is actually inflammatory as the system is overloaded. It was once thought that high levels of cortisol were attributed to weight gain. Perhaps under certain conditions that may be true, but in many situations, such as intermittent fasting. A rise in cortisol levels occur due to the stress, but this does not cause weight gain.

The role of cortisol

The key is effective cortisol management; allowing your body to work as it should. A healthy balanced diet, regular exercise, optimal sleep and weight management would all help regulate a healthy cortisol response. After all, we need cortisol, it’s our internal superhero with a mission to protect us. When cortisol is set into action, such as during and following exercise, appropriate rest and recovery is essential to help cortisol levels return to the pre-exercising amount. A little bit of inflammation is required to instigate a positive response, but too much of a good thing leads to bad effects.

Take Aways

As with the hunger hormones discussed in our previous article, insulin, HGH and cortisol may well be discussed and understood in isolation, but the interaction, partnership and involvement with the human body, should be discussed as a collective, based on individual circumstances and variables. Trying to therefore create a set of rules or laws to live by, end up being the standard repetitive answers that have been heard many times. In reality, you are what you are; the crucial part for health, is to make your body and its system operate at an optimal level. This should and would clearly change depending on life-stage, fitness, health, ethical, cultural and many more personalised specific reasons. It would probably take more than a lifetime to try and understand it. As a starting point try to do the fundamentals well:

  • Regular exercise – 150 minutes per week or 30 minutes per day (5 times per week).
  • Eat a healthy macronutrient balanced diet – the occasional treat won’t hurt but it’s about what dominates your diet, think include rather than exclude.
  • Don’t smoke, drink minimal alcohol.
  • Get outdoors more.
  • Small body and mind stressors are good for you, such as exercise.
  • Find time to relax - mindfulness, meditation and self-space.
  • Create healthy sleep habits to help you get 8 hours a night.
  • Be happy and have fun!

Written by our resident Nutritionist, Gareth Nicholas


  1. Velasquez-Mieyer PA, Cowan PA, Arheart KL, Buffington CK, Spencer KA, Connelly BE, Cowan GW, Lustig RH. Suppression of insulin secretion is associated with weight loss and altered macronutrient intake and preference in a subset of obese adults. Int J Obes Relat Metab Disord. 2003 Feb;27(2):219-26. doi: 10.1038/sj.ijo.802227.
  2. Fujita S, Rasmussen BB, Cadenas JG, Grady JJ, Volpi E. Effect of insulin on human skeletal muscle protein synthesis is modulated by insulin-induced changes in muscle blood flow and amino acid availability. Am J Physiol Endocrinol Metab. 2006 Oct;291(4):E745-54. doi: 10.1152/ajpendo.00271.2005. Epub 2006 May 16. 
  3. Rietman A, Schwarz J, Tomé D, Kok FJ, Mensink M. High dietary protein intake, reducing or eliciting insulin resistance? Eur J Clin Nutr. 2014 Sep;68(9):973-9. doi: 10.1038/ejcn.2014.123.