Ever wondered why some people are more naturally lean and others more naturally overweight? You might notice a pattern from childhood through to adulthood – someone may have always been a slightly chubbier child, or perhaps were born to more overweight parents. Well, a lot of it may have to do with the number of fat cells you have.

Generally, as a child, the number of fat cells you have is a little more variable. The number can increase to accommodate more fat if it needs to. After your teens, your body tends to maintain the same amount of fat cells.

This may explain why chubbier children struggle more with their weight as they get older – they simply have more fat cells available to fill with fat compared to their thinner schoolmates.

Fat regulation is a bit like an orchestra conducted by various feedback mechanisms and hormones. One of these is Leptin. Leptin is produced by the fat cells themselves and signal to the brain when we have adequate fat stores. In response to leptin, the brain reduces hunger as it knows we have enough stored fuel. conversely, without leptin, hunger tends to remain high and we seek out more food. This comes from a prehistoric mechanism to ensure we kept an adequate amount of fat on us for fuel, in case of food suddenly becoming scarce.

Now think of an extreme version of two people, one with lots of fat cells, and another with just a few:

The same amount of fat in each person would look quite different. It would either fill up the few fat cells – i.e. you’d have fatter fat cells, or in the other person with lots of fat cells, the same amount of fat would only partially fill each cell:

Now, this would also affect the Leptin production differently. Fatter fat cells would produce a higher level of the ‘we’re full!’ leptin…whereas the half-empty fat cells wouldn’t. It takes a lot more fat to fill up the larger number of fat cells before they start sending that Leptin signal.

This could explain (among other complicating factors) why people who have been overweight, especially as a child, find it harder to keep the weight off – there are simply more fat cells crying out to be filled.

There is also a complicating factor called Leptin resistance. What this means is someone may have been overweight for some time and their fat cells have been shouting out that they’re full for a while, but the brain starts to become resistant to this ‘I’m full’ message and doesn’t respond by reducing the hunger levels – so we continue to eat and eat and overflow those fat cells with fat. Hello Obesity!

So – there’s a couple of things to be learnt from all this:

1) Keeping children healthy and not overweight could help reduce their battle with weight in adulthood

2) There may be cellular and genetic differences that determine how much fat we can store which explains natural differences between people

3) Leptin is an important signalling hormone, but we aren’t completely at its mercy. There are many interventions an overweight/leptin resistant individual can implement to improve the brain’s sensitivity to leptin and regulate appetite and fat storage. (more on this later!)

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