I don't know about you guys, but in times of stress, I eat my feelings. And I mean, why wouldn't I? My feelings are delicious! The taste like popcorn and peanut butter M&Ms and fudge and pepperoni pizza.
But then, when the stressful times are over, well, I've got to go back to eating salads and kale and cabbage and maybe not eating a whole bag of chocolate EVERY night of the week.
And you know what? It's HARD. It's really hard to go back to eating normally after a few weeks of delicious salt and fat and sugar bingeing. When I get home at the end of the day...I don't want a salad any more! I want my peanut butter M&Ms! I don't want my wholesome steel cut oats, my brain starts telling me that chocolate is the breakfast of champions!
Often I can't do it, especially if my life continues to be stressful (which, let's be honest, it always is). And of course, we all know why this is so hard, after all, those delicious fatty foods taste way better than my own homemade energy bars and kale chips (sorry). But some studies are showing it's more than just missing the taste. It may be a matter of withdrawal and relapse.
Side note: This paper, and many others like it, reference high fat diets and sugar as "addictive" and talk about "withdrawal" and "relapse" in terms that we usually associate with addiction. There are some objections to this terminology, or rather, to the immediate use of it when discussing highly tasty food. I'm inclined to agree with some of the issues. I think there IS food addiction, but I'm not too pleased with the connotations you get when you use words like "withdrawal" and "relapse", when the thing you are speaking of is a natural reward that we NEED for survival. I have more thoughts on this and perhaps I will put them in a later post. But for now, allons-y!.
Sharma et al. "Adaptation in brain reward circuitry underlie palatable food cravings and anxiety induced by high-fat diet withdrawal". International Journal of Obesity, 2012.
I've written before about food intake, stress, and reward. There is a great deal of evidence to show that things like high fat and high sugar diets make you feel good, and are very rewarding indeed. They can reduce markers of stress and increase the neurotransmitter dopamine in areas of the brain that are related to feelings of reward, like the nucleus accumbens.
Of course, it's important for food to be "rewarding". If we didn't like it, after all, we might not eat it, and certainly wouldn't prioritize it high enough. The body does what it needs to do. But after reward, especially after long periods, the brain doesn't tends to just come back down to normal baseline. Instead, we talk about periods of "withdrawal", especially when we talk about things like drugs. Withdrawal is a very negative state of affairs. Often you feel physically sick, but you also can feel psychological distress, irritability, anxiety. And with drugs, this will often cause you to crave the drug more, just to relieve your distress. These feelings and cravings are accompanied by changes in your brain, particularly changes in the reward-related dopamine system, and in things like brain-derived neurotrophic factor, which plays a large role in signaling to remodel connections with in the brain.
And food may not be all that different. In this study, the authors took groups of mice and exposed them either to either to a high fat or a low fat diet for six weeks. On the high fat diet, mice gained weight, of course. After the six weeks were up, some of the mice in the high fat and low fat diet groups were each put on normal diets, in "withdrawal" from their accustomed food. They then conducted a battery of tests to see how the animal's behavior was altered following exposure to that high fat diet and the withdrawal.
What you can see above is a self-administration paradigm for sucrose, or for high fat food. In self-administration, you give a mouse a lever. When he hits the lever, he gets a sucrose pellet, or a high fat pellet, depending on the day. What you are looking at here specifically is something called a progressive ratio. This is supposed to measure how motivated an animal is to get something rewarding, by measuring how HARD the animal is willing to work. So at first he presses the lever once, gets a pellet. Win. He presses the lever again, but this time he has to press 2 times. Then 4. Then 8. Then 16. And so on. The "breakpoint", is the point at which the animal just gives up and decides it's not worth the work. This is a paradigm used a lot in studies of drug reward, and it works for tasty food as well.
What you can see is that the mice that were in withdrawal from a high fat diet worked a HECK of a lot harder for sugar AND for high fat (even though they had not seen sugar before), than mice on a low fat diet. They were willing to keep going long after the low fat diet mice gave up. This may mean that the mice "wanted" the high fat or high sugar MORE, due to their previous exposure to a high fat diet.
So that first measure is one way to look at "craving", which is one aspect of withdrawal. But what about other things like anxiety? To look at that in a rodent you need the elevated plus maze. This is a large plus shaped maze that is elevated off the floor (so the mouse can't just, you know, hop off). Two of the arms are closed in with walls, and two are open. Mice and rats are generally not fond of wide open spaces (you wouldn't be keen either if you were a prey animal), and spend a lot less time in the open arms of the maze. And this is exacerbated when your mouse is anxious. The more anxious the mouse, the less time they spend in the open.
And you can see above that animals who are in withdrawal from a high fat diet (right bar) spend a lot less time in the open, and enter the open arms a lot less than animals either on a low fat diet, or not in withdrawal. So the withdrawal from the high fat diet makes them behave more anxiously.
But anxiety behavior is one thing and measures of stress are another. Animals that behave in an anxious way may well be stressed, and you can tell that by measuring the amount of corticosterone in the blood. Corticosterone (cortisol in humans) is one of the most important stress hormones. And if you look at the graph above, you will see that high fat diet withdrawal is a stressful experience! Animals in withdrawal from a high fat diet show more corticosterone in the blood than all other groups.
All of these changes went along with changes in brain-derived neurotrophic factor in the nucleus accumbens, something which has been implicated before in things like drug addiction and withdrawal.
So it looks like there is a "withdrawal" from a high fat diet. I've seen many previous studies showing altered receptors following high fat diets, like D2 receptors, for example, so we know that some aspects of the reward system are altered, but this is a nice example of how the alterations can affect behavior after the high fat is gone. And changes like this, if they persist in humans (and they may very well), could help to determine while so many diets fail, and why it is so incredibly hard to give up that chocolate habit. It doesn't just taste so good, you also really do miss it when it's gone, and this might drive you to things like craving and feelings of stress. It's not a cure for over -eating, or the end of obesity, but it's a start to explain why we eat the way we do, and why we have a hard time giving it up.
Sharma, S., Fernandes, M., & Fulton, S. (2012). Adaptations in brain reward circuitry underlie palatable food cravings and anxiety induced by high-fat diet withdrawal International Journal of Obesity DOI: 10.1038/ijo.2012.197
Full disclosure: I wrote this post after pepperoni pizza and peanut butter M&Ms. Yeah, a little stressed around here.