Why does food make me happy?

Chris Smith asked neuroscientist Giles Yeo, from Cambridge University, to cook up an answer and Rob in London. 

Giles - I think, first of all, we feel happy when food arrives because the anticipation of food and when the taste of food will tickle a set of neurons in the brain that releases dopamines that makes you feel happy. Now why would this be the case?

You eat, I think, primarily to fulfill a metabolic need, so that is I’ve burned a thousand calories I need to eat a thousand calories. The problem is that you need to eat more than a thousand calories - say 50,000 years ago in the Serengeti - because you’re not guaranteed your next meal. So what happens if you have to eat more than you need to buffer against the time when you actually don’t have enough food. In order to make your body fight the ‘I’m slightly full’ feeling to eat more of the chocolate cake when it arrives, for example, it makes the chocolate cake taste so good.

It’s the so-called dessert tummy. Dessert tummy is actually in your brain. The dessert tummy are actually the dopamine neurons in your brain making the chocolate cake taste good so that you’ll continue to eat it even though you’re stuffed with 2,000 calories of venison.

Chris - That’s the making room even though you’re full feeling? That circuit in process when you say to the kids eat your greens and they say, “No, I’m full”, and then you say “would you like some chocolate cake for afters?”. And they suddenly have room for it. That’s that system?

Giles - It’s that system and the key thing there as well is caloric density. For example, when you’re actually thinking about eating your greens, and because they're packed full of fibre the number of calories for every given gram of celery - as we talked about is not that high. Whereas chocolate, which is high in fat and sugar, then for every given gram you get a lot of calories which means that you can stuff them in all the little areas of your full stomach to make sure that you eat as much as possible. But the problem is there came a time when there was feast and famine. The problem is this has become toxic in our feast environment and part of the problem with obesity today.

Chris - And just finishing the show where we began Giles, you began and I took you to task about Monster Munch and things - I was just kidding. But how is the vegan diet working out for someone who normally eat a normal western diet and you’ve put yourself on this vegan diet regime? How’s it working out?

Giles - It’s very interesting. I can’t eat enough and so I’ve dropped half a stone in three weeks.

Chris - I was going to say you do look like you’ve lost a bit of weight. Are you saying you cannot physically eat enough to feel full?

Giles - Ah, no. So what happens is I get full when I’m eating, but the food I’m getting full on is calorically less dense, so lentils and celery or something. I’m just eating the stuff where I’m mechanically full, but because I’m getting less calories out of it, then I get hungry quicker. I don’t tend to be a grazer; I don’t tend to snack a lot and so I’m getting into caloric deficiency.

My wife’s very excited about this that I’m losing weight, it has to be said. So it is very interesting for me I have to say and so I have lost the weight even whilst not cutting down on my food. I’ve been eating: I’m going to go home tonight and I’m going to have a great big bean burger, but I’m going to feel hungry later in the evening because I can’t eat pudding. I can’t have apple pie; I can’t have anything with eggs or butter in it, and I’m not going to be able to have pudding to get my dessert tummy to tickle my dopamine neuron.

Chris - How have you coped with it? Because a lot of people say when they change their diet quite radically all of a sudden they find that they do not feel right for a while. Probably because their microbiome is a bit upset and they’ve tuned their microbiome to eating what they normally eat, and then they suddenly make a diet switch and they say it takes a while to settle down. Are you coping okay with the total diet switch?

Giles - I’m coping okay. I have to say that the first week, week and a half, I realised I’m only a few weeks in and I got a bit ‘windy’ shall we say, but the windiness has gone away. So no, there was definitely an adaptation of my gut microbiome to this drastic change in my diet.

Chris - Do you think you’ll carry on doing this afterwards or are you going to be so glad to get back to a bacon sandwich?

Giles - There are a lot of people out there who are getting all ready to be offended by me doing this, but the reality is I think I’ll probably stick to vegan two or three times a week. I think it’s been good. I do think I eat too much meat - I do. And now that I’ve actually spent nearly a month learning vegan recipes, I’m excited and I’m not as scared to cook the food. I think two to three times a week vegan is something that I probably will stick to.