Christian Leichsenring asked:
Dear Naked Scientists,
Right now, I'm reeeeally hungry, feeling shaky because of my low blood sugar and all. I'm wondering though why my stupid body doesn't realise that there are plenty of nutrients around my waist so I would neither have to feel bad nor to run for a cheese sandwich. I've heard that burning fat is a slow process but from experience I can tell that this feeling only gets worse. So I'd be glad if you could answer this question in one of your upcoming shows: why do I feel so abhorrently hungry when there's enough to digest without actually involving my digestive tract?
Thanks and keep up the great show -- I'm going to get myself some bread and cheese now. Cheers,
Christian Leichsenring from Bielefeld, Germany
We put this question to Professor Stephen O'Rahilly from the Institute of Metabolic Science at Addenbrookes Hospital and Dr. Giles Yeo from Cambridge University...
Stephen - My name is Stephen O'Rahilly and I work in the on the Addenbrooke’s campus. The signals to eat and the signals to be hungry seem to be generated from within the brain. Two of the key signals that allow the brain to access information about the state of nutrition are the hormones leptin and ghrelin. Leptin comes from fat tissue and probably its most important function is that when we become too thin and the leptin level drops in the blood below a certain threshold, then we become ravenously hungry. However, when we have accumulated too much fat, our brain tends to become effectively deaf to the signals coming from adipose tissue. Ghrelin has a rather opposite effect. It’s a hormone produced by the stomach and it’s an anticipator of meals. It rises before we expect to have a meal and it seems to have a critical role in promoting food intake and promoting our ability to lay down food as fat.
Giles - Given the importance that eating has on keeping us alive, our brain has evolved mechanisms to make sure that it also feels good or rewarding to eat, the “Ooh factor.” Certain foods such as energy dense, sweet and sticky desserts trigger the “Ooh factor” better than others, giving us the motivation, making sure we store all the extra energy we can. Remember, we have evolved over tens of thousands of years to stay alive through multiple famines and any increase in motivation to continue to search for food was an evolutionary advantage. Our problem is that after years of natural selection, ensuring that we eat as much as possible to stay alive, we now have to try and adapt to an environment of too much food.
Hannah - So, the hunger hormone grehlin spikes before mealtimes giving us learned hunger pangs even if love handles and pot bellies are already kindly storing energy for us around our waists since we have evolved to be motivated by food and seek it out.