We know a good deal about how physiology can effect food choice, but what about psychological aspects? >> Well, I think it's actually quite difficult to separate psychology and biology when it comes to eating. How we think about food, and how we think about our appetite affects our experience of eating. Pleasure is really fundamental to eating. It's the anticipation of the pleasure of eating is what motivates us to prepare a meal, or order a meal at a restaurant, or get a take-away meal, from our local shop, and the pleasure of consuming that food is what keeps us consuming it. It rewards everything. So, it's fundamentally a part of the eating experience. Some people have argued that there's a homeostatic component of our eating, and there's a pleasure component. The idea is that eating really is about getting enough fuel, enough nutrients to fuel our bodily functions. That's the homeostatic part, but we're tempted to eat more than that by the hedonic aspects of eating. I didn't really buy that idea for a number of reasons, I don't think that is the experience we have from eating. All eating is pleasurable. We often have this idea that food taste less good. When we're full, or better when we're hungry. What we've found is actually the taste of food, how pleasant it tastes in the mouth, doesn't change much with eating. It's actually the pleasantness of eating, that is tasting the food and ingesting it, and when we're full, it's the pleasantness of eating, the pleasantness of ingesting the food that goes down. So, is that potentially one thing that could underlie overeating, that we eat even though we're full, even though we're satiated, because of the pleasure we're getting from taste, we just keep eating? >> Well yes, that would certainly be the case. By choosing highly pleasurable foods, foods that we really like, then we can overcome to an extent the lack of pleasure we get from the nerve, because we're full. I think it's interesting, fascinating, that they'll actually recover from that state point quickly. Just after a few hours, we're ready to eat again. And I think that reflects our biology. That's actually, we should be ready to eat. And it's not about balancing the energy that we've just used very recently, but it's about hedging against the possible availability of food in the future. I could give you an example of [INAUDIBLE] and the experience of eating. It's a very nice study by Rick Mattes, from Purdue University in the USA. What they did was, or part of what they did, was to show participants a novel drink they said they were developing. And on one occasion, participants were told. When you consume this drink, it has a special gelling substance in it. We're designing to help people, make people feel a bit fuller. And they demonstrated what would happen when it goes into the stomach, and they poured this drink into a beaker. And in the beaker was a chemical substance, so that when this drink was poured in, it appeared to gel, it became quite viscous. They also demonstrated what would happen to the drink without this special substance in, and that just remained liquid in the beaker. So when the participants actually consume, these drinks, actually, neither of them contained the gel. But if the participants believed they consumed the gel containing drink, they reported feeling much fuller. What's even perhaps more surprising is that those who thought it was a gel went on to eat less food later on. But also, this affected how fast their stomach empties as well, whether or not they believed that the drink had this gel in it. And even had some small, but reliable effects on gut hormone signals. >> So, what do we know about the affect of attentiveness on eating and food choice? Well, we do know that attention to eating is important. So, one of the basic demonstrations here is someone is distracted when they're eating, that they will eat more. Not only during the meal when they're distracted, but also interestingly, later on at the next meal. And the idea behind that is that our memory for what we've eaten recently has a big influence on our current food choices. So, we fed people soup at lunch, but this was clever soup bowl where we had a tube stuck in the bottom of the soup bowl, which the participants weren't aware about. But when we could pump in extra soup, or take out some soup from that bowl while they were eating, but effectively, what we could do was manipulate what people saw they'd eaten, how much they saw had been removed from the bowl, and separate that out from how much they actually ate. And the results showed that a person's fullness after the meal was strongly influenced by how they say they'd eaten, especially, actually, from about two hours after eating. So our interpretation of that is what you're left with is the memory of how much you've eaten, which was based on how much they perceived, they'd eaten. And that memory will be very important in making decisions about our next food choices. In order to form a good memory of what we've eaten, we must be attentive when we're consuming a particular meal, and distraction will disrupt that process. And new studies at the suggestion would be, of course I still overeat. What happens if you can't form memories of what you've eaten? So, there's been a few, I think very informative studies on amnesic patients, on patients who can't form good short term memories. And if they eat a meal. They then forget about the food, about that meal they've eaten. They have no recollection of that. If they're then offered a further meal, they will go ahead and eat that meal in its entirety. And in these studies. Some patients are being fed up to three reasonably sized meals, and showing no sign of actually stopping eating. For ethical reasons, the researchers stopped at that point, but what's really informative about these studies is that these individuals actually did complain of feeling uncomfortable, and so on. But didn't describe their experience as fullness, of having their appetite sated. So, without being able to remember having eaten, and associate that with physical sensations, they couldn't report fullness. And the pleasure of eating is that often, I think we interpret that as being indulgent, in relation to food. Actually, food is about feel, and healthiness and so on, and pleasure It has no place in that. That's not a helpful idea, nor do I think it matches biology. Actually, in terms of over eating, yes, pleasure is important. But food technology has made foods that are really very attractive. In a way, that's a good thing, we can enjoy those foods. But perhaps that does tempt us to eat more calories than we need. At the same time, it's not just about the patient. But it's the accessibility, but if I can just reach out and get it, then I will, and I will eat it. So, I can almost overcome that lack of motivation to eat, because food is so readily available. And to some extent, I think that is one of the big things that encourages over consumption. [MUSIC] I had a student once, who at the end of a lecture, he was sitting like he was having a think, and what would happen if you took two muffins, one was in a muffin shape, and the other one was shaped, and I had a feeling where it was going, I didn't have an answer for it, but- >> There's actually some great research by Paul that does that. So, he has a plastic dog turd that he puts next to food. And it becomes contaminated, he puts things in a jar that's labeled poison. And again, people become wary of that. Even though that's. This is a jar, it's just never been put in this jar, I promise you. His label, I'm serious. [INAUDIBLE] >> That's very powerful. >> Yeah, it's very powerful.