As so often happens when one takes a closer look at references from one paper or another, one will find a paper far superior to the first. The glass half empty view is one of regret for wasting all that time on the inferior paper. The glass half full - hey, now I have more material for another post. Only I have a stack of about 20 papers in the queue, and these industrious researchers are coming out with more all the time, so material isn't really a problem, even after 170 blog entries.
Let's go for some peppy-ish music today. "What You Know" by Two Door Cinema Club. (right click in new tab)
The great thing about this superior paper is that it is free full text, and well worth taking a look for yourself. Avena et al, Sugar and Fat Bingeing Have Notable Differences in Addictive-like Behavior. It was published in a Journal of Nutrition Symposium, "Food Addiction: Fact or Fiction," and they wrote a convincing work. One caveat - this paper is primarily a review of rat studies. The brand new paper I blogged about last week where they stuck humans in the MRI is one of the first in humans showing neural correlates of addiction with the chocolate milkshakes. So there is definitely more work to be done before we stick a fork in it and declare that we have all the answers. That said, let's visit our rat studies.
People and rats tend to binge on "highly palatable energy-rich food." Binge episodes in research (and in my clinical experience) usually involve episodes of "bread or pasta, followed in frequency by sweets, fatty foods, or salty snacks" (the salty snacks are typically chips or popcorn, so for the most part grains + salt + vegetable oil). Those who prefer to binge on sweet food tend to binge more frequently.
By bingeing, I don't mean hanging out on the couch and eating half a bag of Doritos while watching old episodes of Top Chef. Binge eating in humans has a specific definition - a larger amount of food than normal within a 2 hour period, associated with at least three of the following: 1) eating until uncomfortably full, 2) eating large amounts of food when not hungry, 3) eating more rapidly than normal, 4) eating alone due to embarrassment about the amount of food consumed, 5) feeling disgusted, depressed, or guilty about the amount of food consumed, and 6) distress or anxiety regarding binge eating. Obviously rats don't fill out questionnaires about how they feel about eating, so I'm assuming the rat definition isn't quite so strict (and I would call this issue a problem with animal models of binge eating). I don't know if rats feel guilty about over-consuming.
The human definition is important to remember, because most obese people are not binge eaters. However, binge eaters are far more likely to be obese, and about 1/3 of people in medical treatment for obesity struggle with binge eating. Binge eating is an extreme of the overall issue with obesity in the West - somehow food consumption gets unhooked from the energy in and out regulatory cycles that kept us relatively lean for 10,000 generations - with emotional baggage and addiction to boot.
Back to rats! Many laboratories have done studies with sugar solutions, and they find (in general) that rats will binge on sugar if they are given intermittent access to it, or if they are given sugar after a period of fasting. Typically the sugar solutions are similar to the sugar concentration of soft drinks. Rats who have sugar and their regular diet available all the time tend to eat as much sugar as the restricted rats do, but they don't binge on it. And, importantly, the sugar bingeing rats and the sugar + regular food freely available rats don't tend to get fat. They eat sugar and compensate by eating less rat food.
Contrary to the notion that we don't "binge on fat alone," rats certainly do. Corwin et al. have demonstrated several times that rats who have ready access to their rat food will binge on shortening when it is available for only 2 hours each day. (I myself have never experienced an overwhelming urge to down a bucket of Crisco, come to think of it, and one of the papers notes "humans rarely if ever binge on pure fat.") Proving that at least some diet and obesity researchers have functioning brains and sticktoitiveness, Corwin more or less repeated the experiment with trans-fat free shortening 10 years later, and rats will binge on the new improved Crisco or the old, more deadly version. But, just like the sugar-eating rats, the rats tend to compensate for the extra Crisco binge, at least in these 6 week experiments, by eating less of their regular rat chow.
(Second song - Crystal Vases by The Last Royals)
Another group of rat researchers, leaving no stone unturned, compared intermittently available Crisco (in 2008 I don't know if this was trans-fat Crisco as Corwin's paper in 2007 noted they had trouble getting a hold of trans fat Crisco at the time for their comparison group) to rats given a high fat diet (I couldn't find the exact composition of their high fat diet, but every rat diet I could find at Dyets Inc., where the researchers obtained their rat food, uses soybean oil and corn oil for the fat) every third day for 8 weeks. Both groups would binge on the fat (for one group, pure crisco, for the other, high fat food mix), both groups gained fat (though didn't necessarily gain weight over all). Only the hydrogenated shortening exposed group had changes in leptin levels (their leptin levels increased, which is common with obesity) - this suggests that, at least in rats, hydrogenated vegetable oil has the potential to be more endocrine-disruptive than plain old vegetable oil, but both groups gained body fat, so who knows.
These same researchers also had groups of rats who got the high fat diet every day, a control diet every day, or Crisco every day, and none of the groups (intermittent, constant exposure, control, or not) had any differences in the amount of calories consumed. Only the intermittently exposed rats had bingeing behavior. All of the high fat or Crisco rats (intermittently exposed or not) gained body fat.
SO - in rats, at least, sugar alone causes binges when intermittently available. Vegetable fat and high-vegetabe fat diets will do the same (causing body fat increase without overall weight gain), and the sweet-fat mix (though finally using lard, it is in combination with soybean oil, and industrial lard undoubtedly has a higher omega 6 content than pasture pig lard, which I think is around 12% PUFA) causes bingeing AND weight gain.
A few more interesting things from the Avena paper: Rats given daily intermittent access to sugar will binge in the first hour of sugar access, and when the rats are given a high dose of naloxone (an injectable opiate blocker used in humans for overdoses - you end up with someone who is breathing again but in abrupt opiate withdrawal, so alive, but extremely unhappy and uncomfortable), they exhibit symptoms of opiate withdrawal. Similar signs of rat opiate withdrawal emerge spontaneously in sugar-bingeing rats who are put on a 24 hour fast, no naloxone necessary. And sugar-bingeing rats given a regular diet for 2 weeks will then eat 24% more sugar than ever before after the two weeks without. Sugar-addicted rats who have their fix taken away will also be more anxious, aggressive and will have lower body temperature (a sign of rat stress).
Similar findings (using naloxone again) were seen in rats fed an ad libitum "cafeteria-style" diet with a variety of foods such as cheese, cookies, and chocolate chips. And rats exposed to corn oil will show an increase in dopamine (the feel good chemical) release, and this release will also happen when exposed to just the taste of the oil. Avena's group tried to replicate these findings with a variety of sweet-fat or high fat combinations of rodent chow, but didn't observe the naloxone withdrawal effect, which is interesting.
And, another DING DING moment - Avena's group had found the withdrawal and unhappiness in sugar-bingeing rats after a 24 hour fast. They tried the same thing with rats fed a high fat diet (I'm sure the typical horrid industrial rodent chow), and observed that the rats were not anxious or have indications of distress after 24 hours without food. The researchers felt this was due to sugar stimulating opiate systems, and fat likely not doing so. I also wonder if high-fat rodents were more able to burn ketones so didn't experience uncomfortable fluctuations of energy as a high-carb (again, typically the industrial sugar, corn starch, casein, lactose, soybean oil blah blah blah combination) rat will tend to without eating.
The take-home message? Rats will binge on sugar and vegetable fat, but it is the sugar-fat combination that is the most detrimental to rat body-fat %. It seems that the sugar packs the most addictive punch, while the increase vegetable fat (particularly Crisco, whether trans-fat free or not) in combination with the rest of the industrial diet perhaps causes more metabolic harm.
Does this information apply to humans? Well, there are some differences (i.e. lack of human crisco-diving behavior) and many similarities. And gluten grains seem to be missing in these animal studies, while humans with binge-eating behaviors binge most commonly on bread and pasta.
You know what I think already. Eat real food, avoid the industrial stuff (particularly the vegetable oils), and to really play it safe, avoid the gluten grains too. I don't go too far out of my way to avoid too much sugar, personally - avoiding processed food in general does the trick. I eat fruit if I feel like it (usually bananas or berries, but grapes or apples or oranges are also typical), and usually it ends up being one serving a day. And when I cook recipes with sugar (which isn't all that often), I do cut sugar to 1/2 or 1/4 what the recipe calls for, and I tend to use raw honey or some other specialty ingredient - more because it is expensive and precious and more fun to eat, and easier to savor. I've had my current little bear of raw honey for 6 months. If you are worried about too much fructose, use rice syrup. I don't sweat a little ketchup or tomato paste or balsamic vinegar - it's never that much. Food should be an amazing celebration of nature, not a technological marvel (unless you are enjoying a high-end meal at a molecular gastronomy restaurant). Real food can be enjoyed and celebrated, and it is life-giving and nourishing, never the enemy.
I also have a new post on Psychology Today - Depression Crashed Your Party