Nobody heard anything about leptin twenty years ago, but nowadays it's hard to imagine trying to understand the mechanisms of energy economy without including the unique properties of this hormone. Acknowledging the essence of the effectiveness of leptin is the key to knowing the nature of metabolism. What's more important, however, knowing more about that issue may be a milestone towards increasing the efficiency of improving body composition. For leptin is the key to slim shape.
In this article I will try to clarify the matters connected with the specified effectiveness of this hormone, including the aspect of using this knowledge in practice.
Leptin – what is it and what role does it play in regulating metabolism?
Leptin is a peptide hormone which is produced and released to blood mainly through the adipocytes (i.e. it's so-called adipokine, as this term describes biologically active substances released by adipocites). Its biological role is very wide and connected with the regulation of energy economy of the body. Most of all, leptin informs the brain about the energy resources in the body. The release of this hormone to the blood mostly depends on the level of body fat, although, the quality and quantity of food also matters. Leptin affects the body by special receptors found within different tissues and organs, among others, in the hypothalamus in the area of hunger and satiety.
The increase of the level of leptin is a signal for hypothalamus that the energy reserves are full and the consumption may be ended – as a result, the appetite is weaker. Additionally, high level of leptin may also strengthen the release of energy (it speeds up metabolism). In case of the fall of the level of this hormone, the effect is opposite. You can notice the feeling of hunger, and the energy expenditure is lower (metabolism slows down).
Leptin – the hormone with multiple use
Participating in regulation of collecting and spending energy is not all. The truth is, leptin influences functioning of many organs and systems in the body, and the receptors specialised in reading signals sent by leptin, are present in almost every cell of it. Research show that functioning of the immune system also depends on the level of leptin. Too low amount of this hormone leads to lower immunity towards infections. That's one of the reasons why undernourished people get sick more often than others. Leptin also influences functioning of reproductive system. Low status of this adipokine leads to decrease and lower release of sex hormones, and in extreme cases – it can lead to hypogonadism and infertility.
This hormone also arouses the activity of thyroid (among other functions, this is how it speeds up metabolism, although it also influences body fat via the sympathetic nervous system), it influences pancreas and the production of insulin, it arouses releasing pro-inflammation cytokines (which can be a problem with too high level of leptin). Basically, there are more and more revelations from the scientific world concerning further properties of this hormone and its influence on the human body. I will definitely come back to the topic of extended features of leptin in other articles, however, in this one, I would like to focus only on its influence on the mechanisms responsible for the functioning of energy economy.
The leptin paradox
When two decades ago a group of scientists with Dr Friedman as a leader discovered the presence of leptin, the enthusiasts claimed “the end of the era of obesity”. As it was believed, increased activity of this hormone causes lower appetite and stronger energy expenditure, there just needs to be supplied its proper amount to people with excess body weight. It was revealed quite fast that the situation is not that simple. It was observed that the level of leptin among overweight people is... high. I would rather say, too high. The result of these observations occurred to be quite intriguing. Because a hormone which was supposed to speed up metabolism and lower satiety “didn't work” like it should be in case of large body mass. How did the scientists explain that paradox?
The situation when the level of leptin is high and there are no effects of its action, is called leptin resistance, which is a state when the cells “don't see” the signals sent by this hormone. As a result, the situation is similar to that when there isn't enough leptin in the body, i.e. stronger appetite together with lower energy expenditure. So, the body works in mode supporting the problem of further gathering of body fat. It can be noticed among people who already suffer from large overweight. They have slower metabolism and the mechanisms controlling food intake – disturbed. It leads to the consequent increase of body mass, what leads to higher level of leptin and fosters lowering leptin resistance.
The mechanisms of developing leptin resistance are not quite known yet. At present, there are many studies done in order to establish whether the key factor of developing this abnormality is the disturbance of transporting leptin through the blood-brain barrier, or pathology of receptors. However, it is known that leptin resistance can be reduced efficiently by decreasing the level of body fat and the change of diet.
How to improve leptin sensitivity?
The nutrition factors which influence significantly the reduction of the mentioned disorder:
essential decrease of consuming energy in total,
essential decrease of consuming carbs,
there are also preliminary studies pointing that some food ingredients can improve leptin sensitivity, just like curcumin – a compound found in curcuma, popular spice. However, such revelations should be treated carefully.
Therefore, low-calorific diet (in justified cases also very low-calorific diet) and low amount of carbs at the same time, may be an efficient way of improving leptin sensitivity fast (thanks to such actions it's possible to bring back the state when cells read the signals sent by this hormone efficiently). Such food strategies may occur justified for people with high level of body fat and excess amount of leptin, as well as leptin sensitivity. However, it does not mean that these strategies are good for everybody. It may sometimes happen that the factor which makes it harder to get rid of excess amount of fat is not only hyperleptinemia and disturbed leptin sensitivity, but also too low level of leptin. When can such situation take place?
Perhaps “leptin deficiency” is too far-reaching simplification, but it presents the situation which may take place among people who want to decrease the amount of body fat and already have not so big amount of it. As I mentioned before, the level of leptin depends mainly on spare fat resources (as well as the diet composition). Excess amount of leptin, together with leptin sensitivity, occur mainly in case of obesity (rarely overweight). With lack of pathological excess of adipocites, the level of this hormone is rather even.
Introducing more serious calorific restrictions together with significant decrease of consuming carbs may lead to a situation when the level of leptin gets too low. It's easy to figure out what the consequences will be: slower metabolism and increased appetite. These are not good conditions for reduction. That's why people who aim at improving shape rather than fighting overweight, should use different strategies, including:
introducing slight calorific deficit,
being careful when lowering the consumption of carbs,
considering rotation in consuming carbs during training and non-training days,
introducing “reset” - breaks in reduction every 6 – 10 weeks with temporary increased calorific content of diet (introducing diet with neutral energy balance),
when using low-carb diets – including temporary charging and solutions like “refeed day” (it's a topic for another article).
The problem is complicated because there isn't much research which would verify the efficiency of the procedures mentioned above. However, there are reasons to think that such actions are effective. In fact, it is confirmed during an experiment that the increased consumption of carbs helps increase the level of leptin. It is often used during reduction with success. However, you should remember, that all kinds of precise protocols concerning “leptin management” are speculations and they shouldn't be treated as golden rule. You should know that they may not work in some cases.
Leptin is an important hormone which takes part in e.g. the regulation of functioning of metabolism. It's important that, in some part, we can influence the activity of this hormone and use its properties as a tool when working on the body composition. The information found in this article obviously do not give the whole picture of the action of leptin, or the matter of manipulating its level. These topics will be developed in further articles.