Life isn't fair, and capitalism is making you fat
There's this blog that I've been reading for a long time (2 years or so?), and I've found it to be an excellent source of science-y information about food, nutrition, and biochemistry. The guy who writes it (Dr. Stephan Guyenet) has a PhD in neuroscience and currently studies the neurobiology of body fat regulation at the University of Washington. What attracted me to the blog in the first place was his ability to pick apart studies and look at what the results really said, as opposed to what was in the abstract or the study conclusion (surprisingly, not always the same thing). He's also really good at identifying assumption biases, particularly as they relate to study design.
Anyway. Dr. Guyenet is not actually a "paleo" eater but he's pretty paleo-friendly - I think he actually follows a more Weston A Price-type diet. Still, he has a lot of very interesting tidbits on his site and it's completely non-commercial (except for that one time where he was interested in the guy who ate nothing but potatoes for 2 months as a promotional stunt for the Washington Potato Growers Union).
His most recent series of posts is outlining his theory of why people carry more body fat than is necessary (beyond the meaningless "they eat too much" - if that were a useful explanation, obesity wouldn't be a problem - the question is WHY do they eat too much, unless you're Gary Taubes, in which case you just think they eat too much starch & sugar. Mr. Taubes still thinks "because they eat too much" is a crap explanation for obesity. It's a symptom, not a cause.)
Guyenet's theory, in a nutshell, says that people eat too much because modern food is too darned tasty, a lot of it tastes exactly the same every time you eat it, and it's available all the time. He postulates that the degree of "food reward" in a diet influences various mechanisms in the brain (leptin signalling among them) to raise the body's fat set-point (which is defined as the level of body fat that the body will defend by altering appetite) to take advantage of a recognized food surplus in order to store energy for later use. The key to this is that the brain uses "food reward" to determine food surplus - if there is a lot of tasty, satisfying food in the diet, the brain ramps up the appetite to take advantage of it. If the diet is bland and unrewarding, not so much - no matter how energy-dense the food is.
This worked very well in the past, when seasonal food variations meant that it was totally in your best interest to be able to override your normal appetite levels and stuff yourself silly for weeks on end when there were berries and fat little critters and easily accessible roots and whatnot, but that when you were down to the nasty bits of shredded dried meat and a few acorns in the back of the cave, it was a good idea to lose your appetite and live off your fat rather than eating the acorns too quickly, or burn yourself out trying to catch the last few skinny rabbits. Of course, back in the day, the stuff that hit the reward centres of the brain was the good, fresh, sweet & fatty stuff. Dried food (in the absence of things that make dried food delicious, like tamari sauce & maple syrup) is not so enjoyable to eat, requiring a lot of chewing for relatively little flavour, and stored nuts and tubers are just bland and filling. Fresh berries, or spring greens, or the livers and marrow of a freshly killed moose, on the other hand, are loaded with flavour, have interesting, easy-to-eat textures, and smell good. In other words, yum. This would even have worked for agrarian cultures, when fresh produce and newly-slaughtered animals would have produced a seasonal surplus that humans could use to bulk up, balanced by the late-winter fare of stored grains supplemented by whatever stored meat the technology could provide. Sugar and salt (both of which improve the taste of food and thus its reward value) have historically been precious commodities.
Humans aren't the only animals that store seasonal surpluses (or surpluses of any sort). Rats are opportunistic scavengers that also benefit from eating strategies that allow them to store fat against possible future scarcity. There are a lot of rat studies showing that you can make rats chubby by feeding them "supermarket food" (danishes, spam, oreos, etc.), whereas it's hard to make them fat on rat chow, even if the macronutrient ratios are the same. Yes, you read that right - the same percentages of fat, carbs & protein - but the rats will eat a lot more of it if it's tasty and has interesting textures. (Very little that resembles rat chow occurs in nature. Even the most disgusting-to-you potential rat food (bugs, human garbage) has objectively more flavour than rat chow.) You can produce a similar effect feeding two groups of rats the same stuff, only adding water to one group's food. The water makes the food taste better (to a rat) and they'll eat more of it and get fat. Humans are possibly a little more complex, and it's conceivable that other factors like sounds, ambient conditions, social aspects etc. have some influence on food reward. Also, humans rarely subsist on the human equivalent of rat chow - although one suspects that in the past, feeding prisoners gruel was a good call economy-wise not only because it was cheap, but because it actually worked to suppress prisoner appetites.
The other key to this theory is that the more similar a tasty food is to one that was eaten before, the more it tends to raise the set-point. This is because the brain learns to associate flavour (and probably texture & aural cues to some extent) with caloric intake, so tasty foods eaten repeatedly that taste the same each time are better at raising set-point than novel tasty foods. In other words, when you taste a new food, the brain says "better wait until we see what this does before we go nuts with it" but if it's one that's been eaten repeatedly with obvious caloric benefit, the brain goes all "dig in! eat as much as you can!" and loosens the reins on your appetite. (In other words, your brain knows damn well exactly how many calories are in that Big Mac and it's totally cool with that.) Non-tasty foods don't provide enough stimulation to trigger such a response, and completely flavourless foods seem to suppress appetite.
This whole theory makes some sense, and does explain why obesity rates have risen in the manner in which they have. Convenience foods - prepared foods you purchase, many of which are manufactured to be tasty rather than nutritious (ie, chips, cookies) - are a product of a market economy, and as such exist for only as long as consumers buy them. Industrial food manufacturers therefore engineer their food to provide as much "reward" as possible so they will be repurchased. (I heard on CBC's "Age of Persuasion" yesterday that Kellogs put a vast amount of money into concocting a unique "crunch" to outsell generic cornflakes.) Obesity rates closely mirror the availability and consumption of such foods. This also explains why the obesity rate in some traditional cultures skyrockets when people are exposed to western foods, even though the fat OR carb content remains the same or even decreases - because nearly all of the new foods (ie, shelf-stable & shippable to remoter locations) have been developed with palatability, not availability, in mind.
The obvious and unfortunate conclusion from this is that in order to obtain and maintain a desirable body fat percentage, far less delicious food is in your future - especially far less delicious "comfort food" that tastes the same every time - recipes with few ingredients in strictly controlled measure, packaged food (KD!) and fast food or even food from chain restaurants. Indeed, that's posited as the real reason that low-fat AND low-carb diets have some success, because initially, food reward is reduced on either, and eating processed food is typically reduced. These diets usually start to fail when dieters find ways to create the deliciousness to which they were previously accustomed within the boundaries of the diet (paleo brownies, yum! weight-watchers chocolate caramel pretzels!), which prompts their brains to go back to hungry-mode. (It should be noted, though, that a strict paleo diet limits fruits and sugars, even naturally occurring ones, on the grounds that these were not typically available year-round, and especially sugars (like honey) were hard to obtain and occasional, so a hard-core paleo diet would necessarily be lower in food reward values, so more likely to work long-term. Also more likely to result in some degree of social ostracization in the current food climate.)
This theory also suggests that stable and persistent fat loss, in a convenience-food environment, is going to be damned hard for individuals who are susceptible to excess food reward (in the same way that not everyone is susceptible to the pleasures of alcohol or crack cocaine). And, if you're one of those susceptible individuals (as I am) it's a sad thought that if you want to carry a healthy amount of fat, food is just not going to be as enjoyable or - importantly - such a reliable source of comfort. For the rest of your life. It's a good thing I never had any expectation of life being fair. On the other hand, it's probable that my extra flab is a good indicator that I've enjoyed food MORE than some other people up to now, so I guess it all evens out in the end, if this theory is correct.
There's actually a diet plan (more like a hack, but let's not quibble over terminology) that takes advantage of unflavoured food to reduce set-point easily. I'm experimenting with it now and I'll see how it goes. For the time being, the aforementioned blog post series is well worth reading.
Food Reward: A Dominant Factor In Obesity Part 1
Food Reward: A Dominant Factor In Obesity Part 2
Food Reward: A Dominant Factor In Obesity Part 3
Food Reward: A Dominant Factor In Obesity Part 4
There is also a podcast that is lengthy but worth listening to here.
Labels: food reward