Posts Tagged ‘rats’

Rats binge on pure fat, but escape with sanity in tact

Since there’s very little human data out there, I’ve been doing a bit of digging on differences in bingeing behavior between carbohydrate- and fat- fed rats.  What I’ve managed to unearth is fairly striking.  Rats appear eager to binge on any kind of diet, but this frightening fact is offset by the fact that only high carbohydrate diets induce addiction-like symptoms.

Rats are made binge eaters by offering them highly palatable foods for only short periods of time (approximately two hours) throughout the day.  Regular lab chow is available for consumption the rest of the time.   What we find is that rats binge on three kinds of foods: high sugar chow, high fat (vegetable oil) chow, or a combination of both sugar and fat in the chow.  Rats that binge solely on sugar or solely on fat manage to maintain average body composition.  Here, rats self-restrict and normalize after their bingeing periods, simply by eating less of the normal chow. However, rats with daily access to a sweet-fat mixture gain weight.  This is what we witness with human beings.  It lines up with our knowledge of insulin release and fat storage.  Combining sugar and fat is the most insidious obesity-inducer of all.


High sugar rats:

Rats are made sugar addicts by being provided with laboratory chow 100 percent of the time, but for a short period of time, approximately 2-4 hours, provided access to sucrose solutions.  When that sucrose window is removed from the rats’ daily routine, they demonstrate symptoms of opiate withdrawal.  These include horrific behaviors such as paw tremor and violent head shaking.   What worse, their symptoms and their frantic lever-pressing increases the longer they’ve gone without sugar.   They also, when forced to abstain from sugar, demonstrate a 9 percent increase in alcohol intake, demonstrating cross-links in substance abuse.  Sugar addiction can induce alcoholism.  Fascinating and scary, huh?

High fat rats:

Some literature suggests, moreover, that similar patterns emerge with high fat binges.  Teegarden and Bale demonstrated in one study that rats on both high fat, high carbohydrate, and mixed binge diets for 4 weeks, when removed from the diets, demonstrate severe anxiety and endure aversive environments to reach their preferred foods.   They conclude that dietary withdraw and changed habits induces the rats’ stress state, which in turn induces “dietary relapse.”  This data indicates that a stark change in eating habits, rather than the macronutrient ratios of the diet, is responsible for the extreme stress the rats display.   Neurochemically, this makes sense as well.  Both fat and sugar have strong effects on dopamine release, such that withdraw from a conditioned, pleasurable diet negatively effects the rats.

What we ultimately find, however, is that rats love fat, and do in fact binge on fat, but never experience symptoms of addiction or withdraw on a high fat diet. This lines up with my own experiences bingeing, and with those with whom I’ve conversed about fat binges.  It is in fact totally possible, and totally satisfying, but not quite as demonic as sugar.  The rats in this study were fed high fat diets, removed from the opportunity to binge, and then observed for addict-like behavior.  None emerged.  (!)  They also showed no sign of opiate dependency.   Moreover, most remarkable part, in my opinion, is that rats fed both a 100 percent fat diet and a 45 percent fat diet demonstrated no signs of addiction or withdraw. What we learn here is that fat has a neurochemical stabilizing effect on the brain.  While definitely pleasurable to binge on fat, it is not what induces addiction symptoms.  In rats.  In humans, too, I’d bet.  Loads.

Why do signs of opiate-like withdrawal emerge with sugar but not fat bingeing?
The relative lack of opiate-like withdrawal behavior after fat bingeing demonstrates the importance of opioid systems in differenetiating sugars and fats and their subsequent effects on behavior.  Both sugar and fat effect dopamine signalling in similar ways, but opioids are another question entirely.  You can read more about it here, but in brief: based on some recent data and neurochemical processes, it seems as though the lack of opiate-like withdrawal signs in fate-bingeing rats may be caused by fat-induced peptide activation, which can inhibit opioid transmission.  In essence, fat likely interferes with opioid processes and effects in the brain.

The authors of this study conclude with the same caveat that I do.  “Although we have not noted signs of opiate-like withdrawal in fat-bingeing rats, that does not mean that excessive fat intake cannot produce addictive-like behaviors.  Withdrawal is not a necessary criterion for drug craving, just as food deprivation is not necessary for food craving.”

Sugar is the big demon here, but fat is not well understood, and it can still be a part of an unhealthy diet or disordered eating style.  I have personally binged on just fat before (ever had 1000 plus calories of coconut?  Pork Rinds? Macademia nuts?  Bad. News. Bears.)   I do know, and I do feel, the satiating effects of fat.  I think about food far, far less when there is fat in my diet, and honestly, the types of cravings I feel now are orders of magnitude less than the cravings I felt on my 100 percent carbohydrate diet (can you believe I did that?  Oh my god.)   What’s more, keeping the carbs away, even ones as innocuous as vegetables, helps, too.  Recall that the rats experienced the same phenomenon.  Mixing sugar and fat was the worst combination for them, inducing both weight gain and symptoms of withdrawal.

It’s really nice to have this rat model, and to see our physiological responses validated.  As complicated as our decisions and our lives are, we have comrades in mere rats, and we are all victims here.  Cheer up, compadre!  Eat some avocado and fuck the lollipops and we’re on the road!   We’re not all the way there, to this destination of perfect mental and physical health, but we’re certainly walking and enjoying the stroll, which is all we could possibly ask for. 



03 2011

Food addiction: Harder to kick than cocaine?

I’ve heard people debate it before.  I’ve felt it, before.  And I’ve heard Robb Wolf discuss it before.  And the general consensus is that food is an addictive substance.  Eating can be a positively reinforced habit that our brains constantly crave.  The worse part, however, is that we can never go “cold turkey” off of food.   With each meal we are forced to recondition the habit.   “Relapse” constantly threatens us.  This makes food, science is beginning to show, more difficult to kick than hard drugs.  Yikes.

Research shows that all drugs—alcohol, nicotine, cocaine, heroin, and foods, particularly sweet foods—are habit forming in like ways.  They overstimulate the brain’s reward system, which creates a vicious cycle of dopamine supply and demand.

This “reward system” consists of a circuit of neurons that run through the ventral tegmental area, the nucleus accumbens and the prefrontal cortex in the brain.  It is normally activated when an animal does things–such as eating or sex–that help it to survive. This activity increases levels of pleasure-related hormones such as dopamine and serotonin.  This is natural, and this is awesome.   What is not awesome is when drugs overactivate the circuit, and dopamine levels soar.  Dopamine receptors get blown out, such that we are now forced to conduct our lives with a malfunctioning dopamine system (this is the same thing ecstasy does to our serotonin receptors).  We learn to mitigate this “deficiency” with whatever drug caused it in the first place.  One whole banana cream pie, please.

This also means that addictions worsen over time.  What may start out as an innocent habit, such as always going to the fridge when you get home from work, some day may not feel like enough.  So instead of having a salad at that time, now you crave fruit.  Or cheese.  Or fruit cheesecake (mmm).  And in a year you’re coming home and used to downing a big gulp and a whole bag of chips.  These things happen to us, and they happen so slowly that we never notice until we try to stop and realize that we can’t.

Because, as I mentioned above, food is a constant in our lives.  It isn’t going away.  We need to de-condition the pleasure response, and we need to kick certain foods to the curb for good, but it’s very tricky business, staying alive and healthy and doing so at the same time.  After someone dependent on a substance stops using it, it often takes time for depleted dopamine receptors to return to baseline levels.  I find that my need to eat decreases with how often I eat, and I suspect that this is because my brain has adjusted to more normal dopamine levels during that time period.  I also find that my need to eat decreases drastically when I don’t eat carbohydrates, something I’ve discussed before, and is definitely worth keeping in mind.

To quit an addictive cycle, low dopamine levels must be tolerated, but only for a given period of time.  For mice addicted to cocaine, it can take two days to regain normalized levels.  For rats in one study on food addiction, it took two weeks.


To gauge just how much the quantity of dopamine receptors had affected these rats’ eating behavior, Kenny and Johnson of the Scripps Research Institute of Florida inserted a virus into the brains of a test group of the animals to knock out some dopamine receptors. The researchers found that– rather than gradually increasing reward thresholds and accompanying overeating behavior— the dopamine deficient rats took to overeating immediately when given access to a high-fat, high carbohydrate diet.

So the researchers designed an experiment to try to draw a human parallel with the rats, training them to expect an electric shock when they saw a certain light cue. Unlike their plain old chow-fed counterparts (a mix of sprouts and vegetable oils and other crap), obese rats accustomed to food rewards would keep right on gorging even when they knew a shock was coming.

But these are rats!, you protest.  Does the same apply to humans?

You bet your sweet ass it does.

Gene-Jack Wang and Nora Volkow of the Brookhaven National Laboratory discovered that obese people share that dopamine deficiency with many cocaine and alcohol abusers. Their study injected 20 volunteers–10 obese subjects and 10 control subjects– with a radioactive chemical tag designed to bind to dopamine receptors in the brain. Then they scanned these individuals using positron emission tomography and counted the numbers of receptors they saw. The obese subjects not only had fewer dopamine receptors than did the normal-weight subjects, but the number of receptors was lower for patients who were heavier.  With increasing weight, and presumably increasingly “unhealthy” diets, dopamine levels decreased.  People who are conditioned to get dopamine from foods need more and more as their addictions worsen.


There is a lot of discussion in the scientific community about genetics, and how it plays a role in chemical addiction.  While true that some people are more susceptible than others, I don’t really fucking care.  Two rats in the whole study above abstained from bingeing.  Two. Fuck those two.  We’re all susceptible.  The lesson here isn’t that science is going to find some miracle to cure addiction (though of course we’ve all got our fingers crossed) or even that it’s going to be able to tell us who is most susceptible to the addiction demon, but rather that we’ve all got to be careful.

And we have just got to forgive ourselves if we find that we have food addictions or habits.   Food can never (and should never) be eliminated from our lives, so we are forced to confront disordered behaviors while continually interacting with our demons.  It’s hard as shit, and if you hate yourself for struggling I will come right to your house and shake you.  Depression and feelings of self-loathing decrease dopamine levels, so every time you have negative feelings about yourself you are only helping the monster.


Addiction is nasty, but it’s not unconquerable.  Long roads and enduring positivity are the names of the game.  Breathe.  Love.  Breathe.  Love.



03 2011