Let it be known to the masses (all two of you, hi!) that Sci LOVES Diet Coke.
I mean, not as much as coffee or Pumpkin Spice Lattes, but it's a close second.
And I always heard what I'm sure everyone has heard, about how Diet Coke is HORRIBLE for you and the ASPARTAME!! The ASPARTAME will come and EAT YOUR CHILDREN. And then it will give you AUTISM because it's full of MERCURY. Or some such crap. I did worry slightly about aspartame, but as it's supposed to increase feelings of fullness, and not of hunger (though apparently women's health magazines would tell you otherwise), I'm not fretting overly much.
However, I do wonder. We can TASTE the difference between Diet Coke and regular, and maybe our gut doesn't know the difference. But what about our brains? Does your brain KNOW you are drinking Diet?
The question comes down to this: are the same areas of the brain activated when you drink sugary drinks as opposed to drinks sweetened with non-caloric sweetener? And does this VARY by the SIZE of the tasting you are doing?
Why size, you ask? Well it turns out that smaller sips of sweet things are more satisfying (to your brain) than huge glomphs. Small sips give you more taste exposure, and may end up increasing sensory satiety faster than large gulps. What they were interested in here was a DECREASE in sensory activation in the brain. Basically, after you drink a ton of something sweet, you should get decreases in sensory activation for that sweet thing. The question is whether or not your brain does this differently in response to non-caloric sweetener, and how much this varies by how big you're sipping.
To test both of these hypotheses, they took 10 dudes, and had them either eat normal breakfast or lunch, or fast for two hours. They put them in an MRI, and gave them sips of regular Orangeade or diet (this is pre-exposure). They then FED them either regular Orangeade, or diet, in a chunk. They fed them quite a bit of soda, almost half a liter (the actual volume was 450mL), served in either small sips of 5mL or big gulps of 20mL. Then, they plunked the guys BACK in the MRI (this is post-exposure), gave them tastes of regular soda or diet, and watched what happened. They also got rinses with water, really quite a bit of liquid.
They then scanned their brains, and also asked them about how full they felt, how hungry, how much Orangeade they wanted, etc. No notes on whether people completely hated Orangeade by the end of the study (or whether hatred of orangeade was in their screening).
We'll start with the behavioral data: obviously, after drinking ALL that soda, their fullness decreased, and so did their thirst. No ratings on how badly they had to pee. The largest change was in the desire to eat, which went down the MOST when the men had the full calorie soda. The participants also found the regular soda more tasty immediately, but didn't end up preferring either one.
Now, ONWARD to the BRAIN!
First off, they got no real effects of sip size, so that hypothesis goes out the window. But they DID get differences in brain activity in response to caloric vs non-caloric sweetener. In particular, they got three main brain areas affected; the orbitofrontal cortex, the amygdala, and the striatum.
The orbitofrontal cortex is an area of the brain located right behind your eyes, and it plays a lot of roles in decision making, reward, and emotion.
In this study, both types of drinks produced activation in the orbitofrontal cortex (reflective of either rewarding stimuli, or possible "hey...I wonder which one this one is..."), but the diet drink actually activated this area MORE than the regular drink.
In the amygdala was where they got some rather interesting stuff. The amygdala is an area (they say it's almond shaped but I don't see it) located right about two inches in or so, behind your ears. This area is mostly known for things like emotional memory, but it also plays a role in processing sensory cues (like taste) as they relate to reward (like sugar). When the participants were given regular or diet soda at pre-exposure in the MRI, the diet soda actually activated the amygdala MORE than the regular. Not only that, the REGULAR soda actually decreased activation! But after drinking that half liter of fluid I mentioned before, the activation went away (the post condition). This shows that the amygdala got used to the presence of the sensory cue of the soda when the soda was given over time, but doesn't really explain that deactivation of the amygdala they got with the regular, sugary drink.
Finally, we come to the striatum, where things turned out the total opposite of the amygdala. When the people were exposed to a single sip of soda (the pre condition), the striatum responded VERY strongly to the regular sugary drink, but didn't respond at all the to the diet drink.
After the exposure to the copious amounts of soda, the striatum apparently had nothing more to say on the matter.
So what does this all SAY!? Well, it does say pretty clearly that you brain can tell the difference between caloric and non-caloric drinks. Your brain, in a way, knows you are drinking Diet Coke, and not regular.
But what does that matter? Sci's not so sure, and she wishes they had addressed this a little in the discussion. In my opinion, a study like this, looking at brain activation, doesn't say as much as it can until it has an effect on behavior. The study participants may have had brains that knew they were drinking diet, but they sure didn't act like they knew or cared. So basically, this study seems like it's a little preliminary, and raises lots more interesting questions:
1) What are the effects on subsequent food intake? Do the participants eat more or less, and how do their brains respond? The authors looked at tomato juice and milk, and didn't get anything in terms of taste activation, but I wonder how they would respond to volume as well. Or solid foods for that matter.
2) What about the LADIES?! These were all men, and I want to see if women react differently, and how this could relate to changes in the menstrual cycle.
3) What do the activations in these areas really tell us about how these people are responding to regular or diet drinks? Does this mean your brain recognizes and imposter? Or does it just respond to "different"? Do the participants have preferences for a drink in a blinded taste test that would let you know?
And of course there are more questions. But it's a cool finding, that somehow, your brain knows your guilty secret. Your brain...KNOWS you're drinking Diet.
Smeets PA, Weijzen P, de Graaf C, & Viergever MA (2010). Consumption of caloric and non-caloric versions of a soft drink differentially affects brain activation during tasting. NeuroImage PMID: 20804848