How mood affects our taste for fat

Now I'm sure we've all found ourselves comfort eating ice cream directly from the tub at times of great stress, but a new study out this week suggests that people who are mildly depressed lose the ability to distinguish different levels of fat in foods.

We were joined by Paul Breslin from Rutgers University, and the Monnell Chemical Senses Lab in Philadelphia to talk about the work he condicted with Petra Platte and her team at the University of Wuerzberg in Germany.

Chris - First of all, how do we actually taste fat because you put something in your mouth and you say that tastes sweet or bitter, but what's the taste of fat?

Paul - Fat is largely experienced as a feeling on the skin inside the mouth. So, if you put a drop of oil on your fingertips and rub them together, you can tell that there's fat there because it's slippery. And we would feel it the same way in the mouth. It has to do with lubrication of the inside of the oral cavity and everything moving around in there. In addition to that, there's also receptors for fats on taste cells. We don't know exactly what they're doing yet, but they're probably participating in the perception of any kind of food fat that we would be perceiving.

Chris - So, when you began this study, what was the hypothesis that you were pursuing here?

Paul - So, the idea is that we know that we can manipulate our body's chemistry in particular, our brain chemistry either by taking drugs that manipulate the chemistry or through stress, anxiety, depression or mood. And that they all have an impact on this. It's been observed that certain drugs in certain states can impact taste, and what we wanted to be able to do is to look at the impact of mood manipulation, manipulating the emotions of people with video clips that we're happy or sad, on people who are very mildly subclinically either depressed or anxious and see what the impact would be on their ability to perceive a variety of different stimuli in the mouth and that would include things that taste bitter, sweet, salty, sour, as well as fats that were basically dairy creme. So, taking heavy cream and diluting it down with skim milk. So, you have a whole range of levels of fattiness and creaminess to perceive.

Chris - Sounds disappointing if you like the crème brulee. Why should a person find that their taste sensations are affected by mood?

Paul - The chemicals that are involved with how neurons in the brain talk to each other are also how the taste receptor cells and various cells in the mouth communicate with neurons that sends signals to the brain, letting you know what it's your mouth. So, the cells talk to each other with these molecules. And when you have a manipulation of mood or state, you can actually manipulate those chemicals. So, we know that there are certain classes of compounds involved with depression or anxiety. Chemicals like serotonin or noradrenaline, and that the same things that have to do with affecting how you feel when you're depressed or how you feel when you're anxious that have to do with neurons communicating with each other in the brain, also has to do with how the cells that are responsible for our tasting, what comes in the mouth, talk to these neurons. So, in principle, you should be able to manipulate someone's moods say, and alter the chemicals, not only that make them happy or sad from manipulating their brain chemistry, but simultaneously affect the chemicals in the mouth that affect how your taste receptor cells talk to those neurons.

Chris - What did you find when you did that?

Paul - So, there's an observation that other people have made, that people who tend to be anxious or people who are depressed clinically, when you ask them how they perceive various tastes in the mouth - bitter, sweet, sour, salt, they tend to rate them higher. In fact, people who are anxious have a tendency to rate most seemingly higher. Things seem brighter or louder when they're anxious and tastes also seem stronger. That also tends to be true for people who are depressed. It's also been shown that when you administer drugs, pharmaceuticals that manipulate these same systems that you can acutely and reversibly make these tastes seem stronger as well. So, we were experimentally taking people with very mild subclinical depression or anxiety. These weren't clinically depressed or anxious people, and we were manipulating their mood by showing them movie clips that were happy or very sad clips, or neutral boring ones. By doing that, we were trying to manipulate their chemistry and show that we could make these tastes stronger. We happen to also give them fats to evaluate and it was not really known what would happen under those circumstances. Fats it turns out, go the other way, when you manipulate mood by giving people these happy or sad video clips, if they're mildly subclinically depressed, they become worse at being able to distinguish between levels of fat in a cream.

Chris - Do you think that's significant in a sense that if someone is depressed, they're not going to care whether they watch their weight or eat a healthy diet.

Paul - Well, there are a couple of associations that have been known from studies of people in the past. One is that folks who are obese tend to have negative emotions and people with negative emotions have a tendency to overeat. We also know that people who are obese have a tendency to underestimate fat levels in food and their fat intake, and we also know that people who have a higher body mass tends to be low in their sensitivity to fat.

Those are all just observations. We were experimentally manipulating the system and really sort of showing that what those observations that had been made in the past were really making sense. And what it suggests is, that perhaps people who tends to be heavier, have a higher body mass, tend to be slightly more depressed or have more negative affect. This tends to affect their ability to perceive fats so that if they were eating something that was say high fat, they might not be able to know that it was high fat, relative to something that were like a skim milk that had very little fat in it. And if they did that and weren't paying attention to how much fat they're eating, it could in fact make their body mass go up, which would put them into sort of a positive spiral of being heavier and having more troubles as a consequence of that.

Chris - And equally, people who become depressed, yes, there may be some motivational factors but also, they could end up eating more than they think they are - fat intake that is, and that would translate into a weight gain which could then become self-fulfilling.

Paul - Yeah, the problem with this is that if you're not paying attention to what you're eating. You already have a predisposition to overeat and if you're not aware of how much fat you're eating then there's this cycle of obesity going up, negative emotions going up, overeating and inattentiveness, or inability to perceive fat level going up and on, and on, it would go.