So Suzanne, can you tell us a little bit about the influences the brain has on eating behavior? >> Yes, so to help us understand how the brain is engaged in eating behavior, we can perhaps dissect it into its different components. So we know that the brain is engaged in how much we eat, but it's also involved in what we eat, or the decisions that we make from day-to-day about whether we choose healthy foods or unhealthy foods, for example. It's also involved in helping us to decide when we eat. If we organize our food intake into meals or if we, for example, snack between meals. And it's also engaged in decisions about why we eat, and of course then we think of hunger as being a primary drive for why we eat. Even hunger avoidance can be an important reason for why we eat. But of course food is pleasurable. We like to eat. It's a natural reward and so of course we eat, because parts of the brain that are involved in pleasure or reward processing are engaged. >> So it's natural perhaps to assume that many of the decisions that we make are conscious decisions in terms of eating. Is that true? >> Well, eating behavior, of course to some extent, must be involving conscious decisions. If I was to offer you a box of chocolates, you would look through that box deciding which ones and how many. Or if you're me, you might eat the whole box. But decisions like that are conscious decisions. But a great deal of our eating behavior actually is not made by conscious decisions. Now, we know that's the case, because people that go on a diet find it very hard to stick to their new regime. I mean, if willpower was really important then they would be able to just use their conscious brain to have a successful diet. But food restriction unfortunately causes changes in our behavior, such that all our best intentions are thrown out of the window because we start to crave food. We become obsessed with food and this is nature's way of encouraging us to sustain enough foods. Our ancestors, for example, didn't always have food. They had to go out into their environment to find it. And when they found it, it wasn't sufficient to just stop when they felt satiated. They had to eat beyond satiation and they had to eat a variety of foods. In order to preserve themselves for a future famine. >> So those brain systems that our ancestors had in the past, they still exist in us. What impact does that have on how we eat in our modern environment? >> Well of course, for our ancestors, it was all about survival. To find food rewarding helped them to find diverse foods. To find foods and to find a variety of different nutrients, and also an adequate food supply. Unfortunately, in our modern environment, to find food rewarding, that's no longer our friend. It acts against survival because of course we overeat, and we indulge and people are eating way beyond their metabolic need, much of it driven by the reward value of the foods around us. >> So these brain pathways that are involved in, potentially involved in overeating, are they related to any other behaviors? >> So the brain's natural reward system is one which is designed for many aspects of survival. We think of sustaining enough food. But also, in fact, we need to repopulate. It's involved in reward from sex, for example. Unfortunately, also the brain's reward system has been hijacked by addictive drugs. So alcohol, cocaine, these sorts of drugs. They target the same system that was really designed as a survival system. So processes, we can learn very much about processes involved in eating behavior by studying the impact of addictive drugs on this rewards system and vice versa. >> The brain, presumably, gets information from the rest of the body about hunger levels and about energy stores. What processes are involved in that? >> The body can communicate information to the brain through a number of different roots of course. For example, there are fairly short term signals that arise from the gut. So the gut can communicate information to the brain about the amount of food we've eaten, or about its composition even. And this signalling most likely involves, for example, nervous reflexes, you feel hunger pangs if you haven't eaten. But of course, we often feel hungry, even although we don't have hunger pangs. And that suggests that other systems are communicating between the gut and the brain. And so then we have the possibility of course, that hormones serve that role, and there are a number of different hormones that are involved. So we have a hormone, for example, called ghrelin, and it's a hormone produced by the empty stomach. So when we are hungry the stomach produces a lot of this ghrelin, and it's released into the blood. It signals to the brain important information that helps us to find food. It targets the rewards system, in other words, the craving system in the brain. And it also targets brain areas involved in energy balance. And these are areas that help us just to get an adequate food supply if we've been exercising, or if we haven't eaten, for example. So it's an acute signal helping us to replenish our stores, if you like, to signal it's time to eat. In addition to these acute signals, we also have more long term signals to the brain. Our brain needs to know about our body weight and then we think of this hormone called leptin. Which is produced by your white adipose tissue. It's an important signal from fat to brain, telling us simply how much fat we have. Or especially if the amount of fat we have changes. So if we go up in body weight, we have more fat. There will be more leptin, and the brain gets to learn this. Likewise, if we drop in our bodyweight then this drop in leptin will signal go eat. And so the brain pathways, especially involved in energy balance, are an important target for this hormone, leptin. But it also signals to brain areas involved in reward and cognition. We often feel the sensation of hunger even when our tummy is not rumbling, so there must be other mechanisms also. It could be, for example, that after we've absorbed nutrients that these are sending information to the brain. So it would be the absence of nutrients in some way that would signal hunger information, but we truly don't know much about how that would be signaled yet. What's much more likely, I think, is that hormones are involved and that they are signaling. They are the mediators of information between the gut and the brain. Communicating information about, for example, how much food we've eaten or the content of the food even. And we're only beginning to understand some of the mechanisms that might be involved there. >> Given what we've learned about hormones and the parts of the brain that they target, is any of that translated into a medical therapy for obesity? Unfortunately, not. The pharmaceutical industry, and even academic sectors, have invested decades and a lot of money into trying to exploit the hormonal system as a target for obesity. To use hormones to suppress appetite, or in some way change our dietary choice. But it hasn't really come to anything yet. I think we really need to know much more about the basic mechanisms involved and the brain target pathways that are engaged by these hormones if we're to actually make progress in drug development. There's a lot of work still to be done. [MUSIC]
