Does standing up affect how food tastes?
Joining Katie Haylor to cast their eyes over this month's neuroscience news is Helen Keyes - perceptual psychologist from Anglia Ruskin University, and Duncan Astle - cognitive neuroscientist from Cambridge University. First up, Helen delved into a tasty paper about how your posture could have an impact on the tastiness of your dinner...
Helen - They wanted to build on a background of research that shows that all sorts of different sensory information can affect your taste perception. In particular, your visual and auditory senses affect how you perceive the taste of food. So the appearance of food and even something like a crisp sounds crispier, you experience the taste as more intense and flavourful. So, they wanted to see whether sitting down or standing up can also feed into that taste experience.
Katie - And how did they go about trying to look at this?
Helen - They theorised that standing up would put greater physical stress on your body. Your muscles will be working harder to keep you upright and also your heart will be pumping faster and harder to get the blood back up from your feet to your body. So they hypothesised that this physical stress would dull your sensitivity. We know that, in general, physical stress dulls your experience of pain, it responds to flashing lights and loud noises so they want to see whether it might also dull your taste perception, and there’s a theory that this is because stress hormones, perhaps caused by this physical stress, can slow neural connections in your brain. Most studies, when they want to induce stress do really nasty things to you like make you put your hand in a bucket of ice cold water or even inject you with cortisol which is a stress hormone.
Katie - Didn't we speak a while back about people being forcibly kept awake as well?
Helen - That's right, another really nice way to do it. But these authors were much kinder to their participants, and they induced physical stress simply by asking you to stand for 15 minutes, so it’s a nice kind study. And then they ran a number of experiments, they tested 350 participants and the participants very simply were either sitting down or standing up. And they were asked to rate a pitta chip on a deliciousness scale, so on a scale of 1 to 7. And they found that participants that were standing up rated their pitta chip as significantly less delicious than the participants that were sitting down. Now there's a huge amount of factors that could explain that finding so they ran some follow-up studies to see if it was this physical stress driving this effect. First of all they thought well, some people might associate eating whilst standing up with being in a rush.
Katie - Like me with my breakfast?
Helen - Exactly. So they measured if participants were eating more quickly when standing up, and they found that they weren't so that probably isn't what's driving the effect. They also wondered whether people when they're standing up they're in physical discomfort so they might be paying more attention to their body sensations and, therefore, be a bit more distracted from tasting the chip. And they found that that wasn’t the case either, people didn't rate themselves as paying any more attention to their body when there were standing up versus sitting down. So, it’s likely that with those explanations ruled out, it's probably the physical stress driving this effect.
They also ran a really neat follow-up study looking at whether this is just a negativity effect, so if you're standing up and if your body's under physical stress do you just rate food more negatively, and they found that that wasn't the case. When they asked their participants to eat unpleasant food; they made brownies, and some of those brownies had been made with a recipe involving half a cup of salt added into the brownies, they found that people standing up rated those quite favourably, they didn't notice the unpleasant flavour of salt. So, basically, it's not just standing up makes you rate all food more negatively, it's that standing up and that physical stress seems to dull your taste perception.
Katie - This is very interesting and it's something I'm going to take away for my own dietary habits, but what are the take-home points?
Helen - Well, a nice little side finding is that when people were standing up, probably because their taste sensation was dulled, they consumed less both of food and drink. So, one take-home might be if you really want to go on a diet perhaps, eat your food standing up and you might just eat less of it. But the real take-home message is that all of our mothers were correct, that we should definitely sit down to eat food if we want to enjoy that experience of food and appreciate the deliciousness factor of food.
Katie - Duncan?
Duncan - I was just wondering if we think we'd get the same thing if it was a different type of stress like emotional or psychological stress?
Helen - I think that's a really good question. And if we're talking about short-term stress, so any stress where a burst of cortisol is released, we would expect to find the same findings. If the effect is being driven by a cortisol flooding of the brain which is perhaps slowing your neural conduction, we might expect any sort of stress to produce the same effect of dulling your taste perception. However, we do know that longer term stress can have different effects on your body. The way your body stores fat and you can put weight on that way, and longer term low-level stress can also cause some people to overeat. So we probably would expect a short-term similar effect for any sort of stress but not a long-term effect.
Duncan Astle looked into a paper on autism, mice and... poop!
Duncan - Every few years in neuroscience there are these real crazes surrounding new topics or approaches, and one of the current crazes is around the gut-brain axis. The idea that the microorganisms that live inside your gut can release neuroactive substances which will influence brain activity and, thus, your behaviour. And people are undertaking studies on all sorts of disorders like irritable bowel syndrome, depression, anxiety, schizophrenia, and the basic approach is to take faecal samples from individuals who have those conditions and then transplant them into mice and see whether the mice display similar behaviours to the donors.
Katie - Okay. So talk us through what they did.
Duncan - In this study, they took samples from individuals with autism and they then transplanted those into a small number of mice. They then checked that the mice’s guts had been colonised with the bacteria in the sample, and they then observed the behaviour of those mice. And they observed that the mice who had transplants from individuals with autism spectrum disorder, or ASD, displayed more repetitive-like behaviours and differences in socialisation, relative to mice who had received transplants from donors who didn't have autism spectrum disorder.
Katie - Okay. So are autistic behaviours displayed in mice necessarily an accurate reflection of people’s autism?
Duncan - Well, this is the million dollar question really, with this paper. There are all sorts of methodological issues, so it's a handful of mice. It's a tiny, tiny sample size and it's very hard to imagine what the mechanism might be. But beyond those kinds of problems there's, I think, a deeper problem, which is that we can barely agree upon what constitutes autism in humans, let alone mice. So we already know, for example, that in some individuals the mutation of a single gene can result in autism-like behaviours, whereas in other cases autism can be highly overlapping with other conditions like attention deficit hyperactivity disorder, or language impairment, and we don't really know why that is. And the symptoms that a human who has autism can have can vary widely in scope and in severity, right from kids who might be entirely preverbal - so they can't use language- all the way to individuals who are extremely high functioning. We're just trying to grapple with the complexity of what autism means for a human being. So the idea that in this study they’ve managed to demonstrate that they can induce autism in these mice, it's kind of scarily simplistic.
Katie - Do we know how long-lived the effects were?
Duncan - They're short lived because later on they reversed the changes in the gut ecosystem that they had induced with the transplant and thus, according to the paper, they changed the behaviour of the mice back again.
Katie - Considering these challenges you pointed out, what do you think the value of this kind of approach is?
Duncan - I think there's some really careful work to be done here to start thinking about the mechanism by which what goes on in our digestive system could influence what's going on in our brain. But I think that we're an awful long way from starting to think about how that might influence really complex, kind of multisystem disorders like autism. I also think there's a real problem where we try and create animal models of a human condition. I think we've really reached the age where we should stop doing work on autism that doesn't take into account the perspectives of people who actually have autism.
Katie - Is there a precedent for doing this kind of experiment with slightly less complex conditions?
Duncan - There is. So something more like IBS, where there's more clearly defined aetiology and pathology, and we have a much clearer idea of the mechanisms at play in producing something like IBS than we do with something like autism.