What is leptin?
Leptin is a hormone produced by body fat.
Leptin acts on the brain to make you feel full.
The more fat a person has, the more leptin they produce.
In an ideal world, this should keep one’s body fat levels constant and within a narrow range.
So why are some people obese and others suffer from anorexia?
If I knew the full answer to this question, I wouldn’t be here…I would be dealing with the queue of people outside my door…
What I can tell you is that there is light at the end of the tunnel.
Why don’t our biological mechanisms to maintain a constant weight work well?
Mainly because our fat levels going outside a narrow range isn’t lethal.
These biological control mechanisms are also known as homeostasis.
(Homeostasis = biological mechanisms to maintain an equilibrium).
An example of homeostasis:
We have exquisite homeostatic mechanisms to keep our blood pH within a very narrow range of 7.35 to 7.45 – in this case homeostasis works extremely well; if your blood is a touch too acid or a teensy bit too alkaline the consequences could be fatal. Consequently, our elegant biochemical and physiological machinery is very finely tuned to make sure pH stays within this range.
A little, or even a lot, of extra fat clearly isn’t an immediate life or death situation, unlike blood pH.
What we do know about energy homeostasis
We still have a long way to go as far as fully elucidating energy homeostasis is concerned, but we do know that the ventromedial hypothalamus (VMH) in the brain plays a significant part.
What else is involved?
The ob/ob gene – mutations of the ob/ob gene in mice are associated with massive obesity.
How long have we known about all of this?
Not all that long.
To be precise, since 1994 – a seminal year for me – the discovery of leptin, the ob/ob gene and birth of my eldest son.
Leptin is part of the appetite signalling system – leptin converses between fat cells and the brain and informs the brain how much fat we have.
The brain then switches hunger on and off accordingly.
Why does energy homeostasis go awry?
We are clearly doing something to upset our energy homeostatic mechanisms – they function well in most other living organisms (domesticated animals being the main exception).
There’s evidently something about the human lifestyle that’s mucking with our own, and our pets, innate appetite signalling system.
What changes the fat-o-stat?
A study was conducted on rats that were made obese by feeding them ‘industrial’ type diets of refined ingredients – probably not dissimilar to junk and fast food diets in humans.
After making the rats obese, they were then fed exactly the same number of calories as lean rodents who were previously eating a normal diet.
A surprising outcome
Even though the obese and lean rats were fed exactly the same number of calories, the obese rats continued to gain fat, whereas the lean rats didn’t, regardless of the type of diet or even if the lean rats were given free access to food.
What’s going on?
The obese rats reduced their energy expenditure more than the lean rats did.
The most logical explanation for this behaviour is that the “set point” of the energy homeostasis system was amended. The industrial diet causes the rodents’ bodies to “want” to accumulate more fat, therefore they will accomplish that by any means necessary, whether it means eating more, or if that’s not possible, then by expending less energy.
This shows that poor diets can, in principle, dysregulate the systems that control energy homeostasis (in rodents at least).
Does this rat study have analogies in humans?
Probably yes, but one can’t know for sure.
One could hypothesise that ‘junk food’ and abnormal lifestyles lead to gradual fat gain by dysregulating the energy homeostasis system.
This system is not under our conscious control, and most likely has nothing to do with willpower.
I suspect that if one were to put a group of children on a junk food diet for many years, and then compare them to a group of children on a healthy diet with exactly the same number of calories, the junk food group would end up fatter as adults, even though calorie intake might be identical in the two groups (as in the rodent example).
Do calories matter?
It appears that the type of food one eats is as important as the quantity – so calories probably aren’t as important as previously thought.
One could speculate that when homeostasis is working fine and dandy our brain does all the calorie maths automatically, and energy balance requires no conscious effort.
Problems arise when our energy balance control mechanisms aren’t working well and we are constantly surrounded by cheap unhealthy food…all that’s left then is for our conscious will power to stop us from over eating.
And as I’m sure most of us know, it’s hard to resist that helping of chocolate cake even when we are feeling full.
Sufficient sleep makes a difference
Several studies have shown that insufficient sleep has detrimental effects on leptin.
Fish and omega 3 fatty acids
In cultures where fish is eaten daily, leptin resistance and leptin levels are low. Specifically it seems to be the omega-3 fatty acids in fish which help regulate leptin.
How to keep your energy control mechanisms functioning well
Easy to say, but not so easy to follow – get plenty of sleep, keep active, feast on vegetables and fruit, eat a little bit of fish, meat, eggs, and nuts and not much else…