Friday, September 30, 2016

Cars as a metaphor for understanding obesity

If we want to understand the accumulation of excess body fat, it's tempting to focus our attention on the location that defines the condition: adipose tissue.  Ultimately, the key question we want to answer is the following: why does fat enter adipose tissue faster than it exits?

It follows that if we want to understand why obesity occurs, we should seek to understand the dynamics of fat trafficking in adipose tissue, and the factors that influence it.  Right?

I don't think this is right, and here's a metaphor that explains why.

The speed of a car depends primarily on the force that its wheels exert on the asphalt below them.  If we want to understand why cars move quickly sometimes, and slowly at other times, we should seek to understand the dynamics of how force is transferred from the wheels to the asphalt, and the factors that influence it, right?

As you may have already surmised, that wouldn't be a very effective way of understanding car speed. To understand car speed, we have to move up the causal chain until we get to the system that actually regulates speed-- the person in the driver's seat.  Looking at the problem from the perspective of the wheels is not an effective way of understanding the person in the driver's seat.  Once we understand the driver, then we also understand why the wheels move how they do.

Similarly, in obesity, we have to move up the causal chain until we find the system that actually regulates body fatness.  The only known system in the human body that regulates body fatness is the brain.  Once we understand how the brain regulates body fatness, we'll understand why fat enters adipose tissue faster than it exits sometimes, eventually leading to obesity.

We already know a lot about how this process works, and that's why I focus my attention on the brain and behavior rather than the biochemical mechanics of adipose tissue.


Unknown said...

There are both micro and macro effects. Each individual may vary in which effect(s) affect their body fat levels.

What if the car is old, defective, and out of maintenance causing it to perform very poorly? What if there's a blizzard causing a decrease of speed? What if it's Sunny outside and Christmas Day and nobody's on the roads leading to fast and smooth speeds? What if there's a big accident blocking 3 of 4 lanes on the highway? What if you're driving a 18 wheeler causing you to drive more slowly? What if you're driving a German sports sedan and 90mph feels like 70mph causing you to drive quicker without knowing?

Jenx said...

I think this would be an effective analogy for most in the environment of a general readership but a surprising one on this blog where the readership is habituated to a more direct addressing of data. Less surprising but fun is unknown's attempt to tackle this development competitively while partially disabled by an intervening entity (even tho a mechanism on wheels)
Lesser point: a metaphor is where something is claimed to he something as in 'the moon's a balloon'. A simile is where something is claimed to be LIKE something as in 'The question hung in the air like a resisted chip at paleo barbecue.

Ellen said...

The driver is in a broken car. He/She can't slow it down easily and follow the speed limit properly because the speedometer doesn't work that well. That would be a more apt description IMO.

No matter what, they will get tickets and themselves in trouble because the car isn't working.

Some people can naturally regulate their weight and others cannot. I'm naturally lean - if you stop me off at Dunkin Donuts I'l be full on a 1/2 donut and a small coffee - I'm lucky this way. Working with overweight patients I have realized that they just don't seem to get the "fullness" signals they need from food.

I see what you're getting at but I think the metaphor is a bit off.

Stephan Guyenet said...

Hi Ellen,

Here is a bit of information that may help you see where I'm coming from: the "fullness" signal is perceived in the brain. It results from the brain integrating various signals of energy status that are coming from the periphery. This process is altered in obesity, not so much because the signals are broken, but because the brain hears them differently. Also, the genetics of obesity suggest that the genes that make some people (like you) inherently resistant to obesity, and others inherently susceptible to it, primarily act in the brain.

I can see how someone might read my post and think I'm saying that all of obesity is attributable to voluntary choices, but that's not what I mean. The brain does a lot of things that are beyond our conscious awareness/control and impact body fatness. The metaphor of the "driver" wasn't meant to imply that only voluntary choices matter, but rather that the brain is what regulates body fatness-- both through nonconscious and conscious processes.

thhq said...

Are you referring to involuntary or voluntary response Stephan? I was able to control obesity and diabetes entirely by voluntary mental effort. While I was doing this I observed involuntary responses which were probably mental. For instance, I still am just as hungry early in the morning after 9 years at a sustained weight lower weight. If I were to respond to the hunger signaling and eat to satiation I would be obese and diabetic again. In the sense of a car, my unconscious cruise control is defective and I have to drive with conscious effort. Wing's group has made similar observations on long term weight maintenance being a result of conscious behavior patterning. Eating breakfast daily and exercising may be automatic behavior for starving hunter gatherers but they are not automatic anymore.

Stephan Guyenet said...

Hi thhq,

Both. Either one could be dominant, depending on the person, but for most of us I believe the involuntary processes are dominant. Most people don't have the resolve to do what you do.

Also, if the involuntary processes weren't driving you to eat more, you wouldn't need to exert voluntary control over them.

thhq said...

I'd propose that modern life has overridden factors that formerly kept weight in check. Ubiquitous electronic media and the ready availability of cheap delicious salty greasy starchy snack foods, for a couple of instances. Obesity is an inevitable consequence. Metaphorically we're driving on the autobahn instead of the old scenic route. The hills and curves are gone, and we get to our destination a lot faster using less fuel.

Every weight loss strategy requires development of some kind of conscious discipline. Whether it's following dietary laws, or excluding particular macronutrients, or exercise, or counting calories, or fasting/meditation, etc etc they all have strictures that have to be followed or they don't work. Granted it would be desirable to find drugs or therapies that modify the unconscious signaling and render body weight steady under any external circumstances. But until then I believe we are still stuck arguing which diet is best....

Jim said...

As a computer programmer I am familiar with programs that follow a logical plan and can be debugged simply by analyzing a point of failure. However, there are master programs that respond to several asynchronous processes where it is impossible to predict all combinations of possible inputs from the several asynchronous processes that the master program attempts to harmonize. To the extent I can follow how my brain is responding to my body and environment, it seems more like the latter sort of program. Thus my brain does not seem to be a willful executive at the control panel, but rather a real-time tallier of an enormous number of votes. And what is voluntary or involuntary is never clear. It seems like a social construct that some of my actions are labeled "voluntary" because the voluntary actions can appear just as capriciously as some of the involuntary actions do, but I am held socially accountable for the former but not the latter. So yes, it is a wondrous system the body with its brain and adipose tissue, but who or what is in charge and held responsible for success or failure? The system of my body does not appear hierarchical to me.

thhq said...

Yesterday I received a copy of John Yudkin's popular diet book from 1958 "This Slimming Business". Yudkin is a seminal figure in the HFLC community. At the time he wrote this book he was a highly respected academic nutritionist. There are a few items that pertain directly to this thread, but I'll summarize some of the other interesting items as well.

-The average weight of a 5'8" man was 147 lbs, or 22.4 BMI. The average daily food consumption was 3000 kcal for a man.

-Yudkin is critical of the higher-than-historic consumption of sugar and starchy carbohydrates in the UK diet, and also of the idea that increasing exercise beyond a certain point is effective for weight loss. The diet that he developed is a counting scheme called the Unit Slimming Diet. It operates on a principle similar to the old ADA carb counting system for diabetics, is similarly organized in tables, and for all I know these may be the basis for ADA's tables of "carb exchanges". One CU is 5 grams of carbohydrates, with a target of 15 CU's a day. The entire day's count could be satisfied by a pint of ale, or 3 ounces of dry spaghetti, or 7 apples.

-Yudkin is a firm believer in calories in-calories out as the determiner of body weight, which is controlled by the brain through what he calls the "appestat". On p 57, he presents a graph of food consumption vs body weight for an unreferenced (a problem throughout the book) Indian study. Below a moderate level of activity, there is a steady rise in food consumption and body weight correlated with decreasing activity. However, above a moderate level of activity, increasing activity correlates with a steady weight and increasing food consumption. The graph strongly suggests that the body operates on a weight setpoint correctly if a person is active, and that the "appestat" fails if a person is sedentary.

-Like Keys 1960 popular diet book Eat Well and Stay Well, Yudkin's book is well written. He uses a light style, and had permission from from Ogden Nash to quote his little doggerel rhymes with cartoons. However he is thin on substantiation, and provides tables with no recipes and scant sample meal plans. In comparison, Keys writes in a more acerb style (similar to Sinclair Lewis), references and analyzes scientific work on nutrition, and provides many recipes and sample eating plans.

I'll continue reading and rereading this. It's easy to see why Keys was critical of Yudkin's lack of documentation for his assertions, though in the main points (sugar consumption is excessive and calories in-calories out) they're in agreement.

thhq said...

Reading this, and comparing with Keys approach, it appears that everything got muddled together in the 1980 dietary guidelines. Both Keys and Yudkin were highly respected academic nutritionists. Both believed in reduced eating and increased activity as being effective for weight loss, and in the basic truth of calories in - calories out. Both believed in the use of counting systems. For Keys this was his Scientific Reducing method of counting calories. For Yudkin it was counting of starch and sugar carbs in 5 gram counting units.

Keys method was rigorous on food intake and activity with general counsel to reduce saturated fat. Yudkin's method was rigorous on high glycemic carbohydrates with general counsel on not overeating (since eating more fat would supposedly self-regulate calories) and being more active.

The 1980 guidelines are an unhappy marriage of the two schools of thought. Keys emphasis on reducing fat and eating healthy grains is present, but the rigor of calorie counting is eliminated (thank you Dr. Yudkin). Yudkin's emphasis on eating less sugar and sweets is present, but the rigor of carb counting is eliminated (thank you Dr. Keys). The Food Pyramid doesn't do justice to either approach. In attempting to blend two effective dietary methods, the rigor needed for either method to work was lost.

The one thing that is completely lost in the 1980 guidelines is the importance of activity. Yudkin defends his low carb diet with this argument, saying that there is more benefit to cardiovascular health from being active and at normal weight than from restricting dietary fat. Maybe the 1980 guidelines included recommendations for activity, but all that is remembered and used is that Food Pyramid.

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