The new Temper Trap song is just lovely: Trembling Hands (right click to open in new tab)
All that business doesn't mean I'm not still neck-deep in interesting scientific papers. There's a big problem, actually, in that my psychiatry practice is bursting full and the articles keep coming…if I've ignored your email, there are 10 more pressing emails in front of yours. Sorry!
Papers that have been on the back burner for a while but deserve some attention:
Obesity is associated with high serotonin 4 receptor availabiity in the brain reward circuitry
Reward, dopamine and the control of food intake: implications for obesity (free full text)
I work a lot with addiction. Alcohol, pot, nicotine, opiates, cocaine. Not a lot of meth around here, but otherwise we have a fairly full spectrum. And no one thinks cocaine addiction lives in the liver. It's the brain. You like something to excess, even if it stinks (nicotine, pot), makes you puke (opiates, alcohol), or makes you crazy (cocaine). You take more and more, even if it isn't enjoyable, just to chase the anticipatory feeling of eating it. What better describes eating a whole sleeve of Pringles? "I was hungry." or "That was disgusting but I could eat another sleeve."
I don't think calories in and calories out is the whole story. Otherwise we could all have just enough nicotine, or just enough cocaine. But some of us can't, just like food. Some of us face a world of twizzlers and Taco Bell and go "meh." Others need a $20,000 gastric bypass to sever the hormonal feedback loops.
But I'm biased. Some folks think the whole reward/brain/calorie thing is garbage*. That's cool. Everyone is entitled to an opinion. Obese people and mice keep lighting up the reward circuitry PET scanners, with the endocannabinoids, dopamine, serotonin, opiates, GABA, cholecystokinin, neuropeptide y, and norepinephrine all playing a role, and serotonin drugs keep getting FDA approved to treat obesity. So I suppose I am just used to thinking this way. Leptin, insulin, orexin, ghrelin, neuropeptide y, and certain key areas of the brain (hypothalamus, hippocampus, amygdala) and regulation of endocrine systems (thyroid) and muscle systems regulating metabolism, calorie burn, fidgeting, the whole shebang. And what I see, over and over, is neurochemistry lit up like firecrackers by highly rewarding foods. See the definition of palatable if you are confused.
The most interesting thing about the Kitavans is that they don't exercise more than the average active American, and they have food to spare. Piles are left for the dogs. They are skinny, but they have easy calories available in excess. So should we, if our brain neuroendocrine system worked properly, as it should with natural available foods and not the hyperengineered frankenfoods of the 20th and 21st centuries. That's my opinion.
Back to the papers. In the first, a long history of rodent papers are cited, but in this paper, actual humans were examined for the amount and receptivity of serotonin 4 receptors (5HT-4) they had in certain key reward areas of the brain. Turns out the higher your BMI, the more active 5-HT4 receptors women had in the reward areas of the brain. Happy and inactive 5-HT4 receptors are associated with the "fed state" and satiety. In the reward areas, 5-HT4 transmission controls opiate and dopamine transmission. The "neocortex" or the place of human "free conscious will" as it were is fairly light in 5-HT4 neurons. It's the deeper areas of the brain, places of urges and impulse, that light up in PET scans of the obese.
The free full text review paper is also useful in describing the hypothalamus and how food intake is regulated (via amino acids, fats, and other signals).
(I've linked this song before, but it deserves a new listen: Kasabian, Reason is Treason)
Based on findings from imaging studies, a model of obesity was recently proposed in which overeating reflects and imbalance between circuits that motivate behavior (because of their involvement in reward and conditioning) and circuits that control and inhibit pre-potent responses. This model identifies four main circuits: (i) reward--saliency (ii) motivation--drive (iii) learning--conditioning and (iv) inhibitory control--emotional regulation--executive functioning.
In folks with addictions, the consumption of high quantities of "palatable" substances (or food) will result in an enhanced reinforcing value of the food and weakening of the control circuits.
The definition of a "palatable" food is anything you could eat when you are stuffed. Like Pringles. Or pie. Or kraft macaroni and cheese. Or ramen. Anything you can eat when you are stuffed should rarely be eaten. That may be the cardinal paleo rule.
But it's only the brain. It has little to do with macronutrients (except super low fat, super low carb, or low protein foods are likely to be highly "palatable" in our definition). You won't get fat on garlic, or plain baked potato, butter, or even (gasp) a banana.
My opinion. I welcome you to read others!
*The main argument here being that the nutritional transition occured with poor and crappy foods… white flour, beer, white sugar. Have the folks arguing against this theory never tasted ramen noodles or kraft macaroni and cheese?