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Leptin, fasting and female fertility

Health Science

Leptin is a protein produced by fat cells as well as cells lining the stomach wall. Leptin's job is to tell your body how much fuel you have in storage and when you are full. It also mediates in the regulation of metabolism by entering the central nervous system where it acts on receptors in the brain that control energy expenditure.

The protein Leptin is decreased by fasting, chronic caloric restriction, regular exercise, lack of sleep and psychological stress. But what does it mean? If I am low in Leptin, will I be ravenous all the time? The answer is no. Hunger is not regulated by Leptin alone. If this was the case, pharmaceutical companies would be selling Leptin injections like no other and obesity would no longer exist. Well, sadly for our overweight divas, this is not the case. Thousands of environmental and endogenous factors play a role on hunger regulation.


Leptin sensitivity is a term used for hunger signalling. Leptin sensitivity means that your hunger receptors will respond to Leptin. Conversely, if we lose the ability to sense Leptin, appetite control is lost. Being Leptin resistant means that your hunger receptors won't register its satiety signalling.
As Leptin levels rise with increased human adiposity, brain receptors are less sensitive to the satiation signalling of Leptin. In other words, the fatter you become, the hungrier you get! This explains why overweight and obese people with high body fat are likely to be Leptin resistant. Paradoxically, Leptin resistance is considered "an evolutionary advantage" that kept us around as a species for thousands of years… But today we see it as “a modern world disadvantage" and a big contributor to the obesity epidemic.


The effects of either Leptin resistance (high body fat) and a fall in Leptin (low calorie dieting, fasting, exercise) are similar in evolutionary terms. The former indicating "gorge before the next famine" and the latter "move and find food to survive".

Endocrinologist Rexford S. Ahima, explained this beautifully:
It is possible that leptin’s role as a starvation signal
conferred survival advantage during famine by limiting
thyroid-mediated thermogenesis and the high energy cost
of reproduction and promoting feeding and energy storage [ … ]
An increase in energy efficiency mediated
by low leptin prolongs longevity.
When food is scarce for a long period of time, Leptin levels decrease. You get hungrier. That hunger motivates you to look for food. Whilst you are busy at that, Leptin also mediates to decrease your energy cost, as your body doesn't know when it will get food again. Energy efficiency mediated by Leptin promotes the following reactions: your metabolism slows down, your cells live longer and your female reproductive capacity subdues. 

Caloric restriction, chronic exercise and fasting are known to promote longevity through Leptin mediation. However, these are known to lower Leptin and estrogen levels, which may suppress female reproductive capacity. Scientists believe that this is part of an early human adaption mechanism around food scarcity and hardship. Such adaptation means increased strength and cell durability – but at the expense of reproductivity. Scarcity and hardship did not seem to be biologically suitable times for pregnancy or child bearing.

Chronic dieting, fasting and regular intensive exercise trigger very similar physiological and biochemical reactions.  There is indeed a trade-off between benefits and side effects. So the question goes back to you. This is your decision. What’s more important to you at this point in time..?


So... what do you think? Should women fast?? VOTE NOW by clicking HERE. Share your views with us in our Health Divas Fasting Forum.

To learn more about the effects of fasting in women, read Should Women Fast?


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