The need to find fuel to generate energy is a profound drive within the biology of all living organisms: we all need food to survive. So it’s not surprising that our bodies have such a complex system to control food intake, driven by hormones.
Hormone levels also change when we lose weight. As much as we battle to trim down via diets and eating patterns, they’re also the reason most of us will regain the weight we lose – or more.
Quite close to these nerve cells is another set of nerves that powerfully inhibit hunger. They produce two different proteins that inhibit hunger: cocaine and amphetamine-regulated transcript (CART) and melanocyte-stimulating hormone (αMSH).
These two sets of nerve cells initiate and send hunger signals to other areas of the hypothalamus. So, whether you feel inclined to eat or not depends on the balance of the activity between these two sets of neurons.
But what determines which set of neurons dominates at any given time?
Hormones in the Blood
Let’s take a closer look at how each of these blood-circulating hormones work.Amylin, discovered in 1981, is made in the same cells that make insulin (the beta cells). It has been shown to inhibit food intake.
The exact role of pancreatic polypeptide is not yet known, but there is evidence that it inhibits hunger.
The hypothalamus also receives signals from pleasure pathways that use dopamine, endocannabinoids and serotonin as messengers, which influence eating behaviour.
Once full, the stomach reduces the desire to eat both by lowering ghrelin production and by sending a message to the hypothalamus. Ghrelin levels reach a low around 30 to 60 minutes after eating.
Levels of hormones that make us feel full – CCK, PYY, GLP-1, amylin and insulin – all increase following a meal to reach a peak about 30 to 60 minutes later.
How Weight Loss Affects Our Hormones
Several studies have found that diet-induced weight loss is associated with hormone changes that, together, promote weight regain.Following weight loss, leptin levels decrease profoundly. Other hormonal changes include increases in circulating ghrelin, GIP and pancreatic polypeptide and reductions in PYY and CCK. Almost all of these changes favour regaining lost weight, by increasing hunger, reducing satiety and improving the capacity to store fat. These hormonal changes seem to be present for at least one year after weight loss, leading to a persistent increase in hunger.
These findings suggest suppressing hunger after weight loss – preferably with a replacement of hormones – may help people maintain their new weight.
Several of these agents have recently been approved by different regulatory bodies in the United States, Europe or Canada, but only one – liraglutide – is a version of one of the naturally occurring appetite suppressants (GLP-1). The ideal medication to maintain weight loss would be a long-acting mixture of three or more of the blood-circulating hormones we examined above: leptin, amylin, GLP-1, PYY, CCK and oxyntomodulin.
But producing such a mixture is proving a considerable challenge, so researchers continue to investigate how this might be done.
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