Now We Have Food Reward In a Pill

Jonah Lehrer writes in the WSJ about a new pill approved by the FDA that is supposed to increase the good kind of food reward (FR), and decrease the bad kind of FR, hence help people eat less.

Last week, a U.S. Food and Drug Administration advisory committee voted overwhelmingly to recommend approval of Qnexa. If officially approved later this spring, it will be the first new prescription weight-loss medication to appear on the market since 1999.

The drug itself is a novel combination of two older drugs, an appetite suppressant with amphetaminelike properties and an anticonvulsant shown to reduce cravings for binge-eaters. In theory, Qnexa works by both increasing the pleasure of food and also reducing the desire to keep on eating, thus making it a bit easier to stick to our diets.

Why do I get the feeling this is all going to end in tears? The two components of food reward are "liking", hedonic impact or palatability and "wanting", incentive salience. Paleo-ish FR theory is that real food is high in palatability but low in incentive salience (stuff you don't want to eat when full), and crap-in-a-box is just the opposite. So Lehrer seems to be saying that Qnexa will temper the response to crap-in-a-box while increasing its palatability, so that food is (for obese people) more like what they'd experience when eating real food.

This pill seems to be going about things in the wrong manner.

Lehrer goes on to talk about a study that recently was published which is supposed to show that overeaters have lower FR by having lower dopamine response to "energy-dense" food.

This raises the larger question: What makes us consume that last slice of pizza or chocolate cake, even when we're no longer hungry? One common answer is that obesity is a byproduct of gluttony: People can't stop eating because they love eating too much. In a puritanical world, this leads many to view obesity as a kind of character flaw.

But this explanation turns out to be exactly backward. According to a new study from Kyle Burger and Eric Stice at the Oregon Research Institute, those who overeat may actually get less pleasure from food. So they're forced to consume larger quantities (and added calories) to achieve an equivalent reward.

The researchers began by asking 151 adolescents about eating habits and food cravings. Then, they stuck the teens in a brain scanner while showing them a picture of a milkshake followed by a few sips of the real thing. They were particularly interested in looking at the response of the dopamine reward pathway in the brain, a cortical network responsible for generating the pleasurable emotions triggered by pleasurable things.

By comparing the response of the reward pathway to the eating habits of the adolescents, the scientists were able to show that those who ate the most ice cream showed the least activation in their reward areas when consuming the milkshake. This suggests that they were eating more in desperate compensation, trying to make up for their indifferent dopamine neurons. People crave pleasure, and they don't stop until they get their fill, even if means consuming the entire pint of Häagen-Dazs.

Meh. The best thing I see there is that Lehrer correctly uses "this raises the question" rather than the oft misused "this begs the question". So fat people eat more ice cream because it has a lower marginal rate of pleasure? Or do we all have to reach a magical dopamine level, but fat people have a harder time reaching that level?

Okay let's look at the actual Oregon Research Institute study:

Background: Weight gain leads to reduced reward-region responsivity to energy-dense food receipt, and consumption of an energy-dense diet compared with an isocaloric, low-energy-density diet leads to reduced dopamine receptors. Furthermore, phasic dopamine signaling to palatable food receipt decreases after repeated intake of that food, which collectively suggests that frequent intake of an energy-dense food may reduce striatal response to receipt of that food. 

Hmm, my spidey sense is already tingling. What do they mean by energy dense food? The experiment is done with a milkshake, do they mean sugar in this case? As J Stanton pointed out it is indeed true that processed food has the highest energy density by weight, because they don't contain any water:

I’ll handicap the comparison by choosing an extra-fatty USDA Prime grade of prime rib, which contains 367 calories per 100 grams, or about 3.7 calories per gram. (Link.)

In contrast, rice cakes contain 392 calories per 100 grams, or almost 4 calories per gram. (Link.) That’s right: rice cakes are a denser source of calories than prime rib!
 
That’s because rice cakes, like all shelf-stable foods, have most of the water removed in order to preserve them and retard bacterial growth. As a rule, anything you’ll find in a box on the shelf will be dehydrated—and, in consequence, extremely calorie-dense.

I doubt that's what the authors of this study meant, though. Obviously it is the quality and content of the food that is important, not the energy density.

A milk shake has 112 calories per 100 grams. Something like a third as much as prime rib. And not even close to the energy density of a rice cake. Even ice cream only seems to average around 200 calories per gram, still much less energy dense than prime rib. Again from the study:

Results: Milkshake receipt robustly activated the striatal regions, yet frequent ice cream consumption was associated with a reduced response to milkshake receipt in these reward-related brain regions. Percentage body fat, total energy intake, percentage of energy from fat and sugar, and intake of other energy-dense foods were not related to the neural response to milkshake receipt. 

So the people who ate a lot of ice cream had an apparently reduced pleasure response. What this tells me is that sugar addicts have a higher tolerance to sugar, just as any other addict has to their drug of choice. What it does NOT tell me is that a pill that increases the reward of crap (and especially sugar) is going to magically cure obesity. Although it is possible that Qnexa could help sugar/wheat junkies break their addiction.