Hormone Series: Part 1 Leptin

In this series we are going to break down some of the key hormones that the body produces and explain what they do, how they do it and what we can do (if anything) to influence theses hormones to help us reach or physique or performance goals.


One of the new kids on the block in terms of hormones is leptin. Discovered in the mid 1990’s leptin was found to be released from adipose cells, historically adipose tissue (body fat) was seen as a relatively inactive tissue with its only function being the storage of excess energy. However more recent research is starting to find complex interactions between fat cells and other tissues in the body. Fat cells interact with the body through both local (surrounding tissues) and global (in other regions of the body) mechanisms including the release of specialised signallers that have a number of different and wide reaching metabolic effects in the body. Leptin is one of these ‘signals’ that has implication for both fat loss and weight gain.


Leptin is a 167 amino acid peptide hormone and when released from adipose tissue has impacts on overall body metabolism. It achieves some of these effects by entering the brain and affecting our control centres, giving information to those parts of the brain that are responsible for regulating our metabolic rate. When we have an excess of energy intake and/or our fat cells energy levels are high then leptin is released at a higher rate thus signalling to the brain that we have an excess of energy and we need to step up or efforts to keep our metabolic rate high in order to use this extra energy. It does this in a number of different local and global ways but one global mechanism is through influencing the release of thyroid stimulating hormone (TSH) which then travels to the thyroid gland, a butterfly shaped gland surrounding the windpipe, and signals the body to produce thyroid hormones. Thyroid hormones (which will get its own part in this series) are direct modulators of metabolic rate and energy expenditure.



Unfortunately for us we can’t just keep producing more and more thyroid hormones to account for our excess energy intake as that really wouldn’t be great for our cells. We also try and increase the amount of heat we release form the body, but yet again there’s only so much heat we can generate to dissipate the extra energy before this would mess up our internal environment… so that’s why, despite our bodies best efforts to adapt, we will put on body fat if we have sustained periods of excess calories. Luckily though, our bodies do pretty well at adapting to relatively short term fluctuations in energy intake.


In overweight and obese people it was suspected that they might have low leptin levels and this meant they gained weight rapidly and lowered their metabolic rate. In reality what researchers found was that overweight people had high leptin levels, however their sensitivity to leptin was poor. It appeared that long term exposure to high leptin levels in effects ‘fried’ the receptors in the brain, meaning that their metabolic adaptation to changes to calorie intake is poor.


As leptin is in effect the ‘fuel gauge’ of the body, when we lose body fat our leptin levels also lower and our body responds in the opposite way by reducing metabolic rate to conserve energy. This can make fat loss challenging and is one of the reasons why fat loss is not typically linear when on a consistent calorie deficit.. the leaner you become the lower leptin is, the lower your metabolic rate and the harder it becomes to push the body to lower levels of body fat. This is great from a strictly survival perspective, not so much for trying to get abs for the summer! Unfortunately for those who are overweight, weight loss will still reduce metabolic rate even when body fat levels are still high. Lower leptin levels are also triggers of other pathways that tell us to eat which again makes us feel hungry and dieting that bit harder still.


So what can we do to improve leptin, or at least maintain leptin levels when trying to lose body fat? Well the use of higher calorie periods during dieting may have some positive impact on leptin, although the impact on ‘boosting’ metabolism is likely to be small unless periods of refeeding are extended longer than a few days. It has been suggested higher fat diets are associated with more sustained leptin levels, however carbohydrates are associated with improved leptin sensitivity, so it is likely that a more balanced approach to nutrition containing both of these macro-nutrients is most beneficial in terms of maintaining overall metabolic rate, providing a more sustainable diet and On a final note, whatever nutritional strategy we apply for fat loss it is still highly likely to reduce your metabolic rate, so we need to consider adjusted nutrient intakes after we have completed our fat loss phase in order to prevent rapid and excessive weight gain that is the common rebound suffered by some people when they have lost weight, especially if this weight has come off rapidly with severe calorie restriction.


Thanks for reading..


Dr P.


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