Saturday, August 9, 2008

Hyperphagia

One of the things I didn't mention in the last post is that Americans are eating more calories than ever before. According to Centers for Disease Control NHANES data, in 2000, men ate about 160 more calories per day, and women ate about 340 more than in 1971. That's a change of 7% and 22%, respectively. The extra calories come almost exclusively from refined grains, with the largest single contribution coming from white wheat flour (correction: the largest single contribution comes from corn sweeteners, followed by white wheat flour).

Some people will see those data and decide the increase in calories is the explanation for the expanding American waistline. I don't think that's incorrect, but I do think it misses the point. The relevant question is "why are we eating more calories now than we were in 1971?"

We weren't exactly starving in 1971. And average energy expenditure, if anything, has actually increased. So why are we eating more? I believe that our increased food intake, or hyperphagia, is the result of metabolic disturbances, rather than the cause of them.

Humans, like all animals, have a sophisticated system of hormones and brain regions whose function is to maintain a proper energy balance. Part of the system's job is to keep fat mass at an appropriate level. With a properly functioning system, feedback loops inhibit hunger once fat mass has reached a certain level, and also increase resting metabolic rate to burn excess calories. If the system is working properly, it's very difficult to gain weight. There have been a number of overfeeding studies in which subjects have consumed huge amounts of excess calories. Some people gain weight, many don't.

The fact that fat mass is hormonally regulated can be easily seen in other mammals. When was the last time you saw a fat squirrel in the springtime? When was the last time you saw a thin squirrel in the fall? These events are regulated by hormones. A squirrel in captivity will put on weight in the fall, even if its daily food intake is not changed.

A key hormone in this process is leptin. Leptin levels are proportional to fat mass, and serve to inhibit hunger and eating behaviors. Under normal conditions, the more fat tissue a person has, the more leptin they will produce, and the less they will eat until the fat mass has reached the body's preferred 'set-point'. The problem is that overweight Westerners are almost invariably leptin-resistant, meaning their body doesn't respond to the signal to stop eating!

Leptin resistance leads to hyperphagia, overweight and the metabolic syndrome (a common cluster of symptoms that implies profound metabolic disturbance). It typically precedes insulin resistance during the downward slide towards metabolic syndrome.

I suspect that wheat, sugar and perhaps other processed foods cause hyperphagia. I believe hyperphagia is at least partially secondary to a disturbed metabolism. There's something about industrial foods that reached a critical mass in the mid-70s. The shift in diet sent us into a tailspin of excessive eating and unprecedented weight gain.

13 comments:

Charles R. said...

I think the leptin resistance issue is a key here. I was reading some comments to a post on another site in which someone who had lost a lot of weight via a low-carb diet still had significantly impaired leptin metabolism.

I bet this is much more common than is realized, but very few people (or their doctors) will go to that level of granularity in testing.

And this also ties into Gary Taubes's hypothesis that fat causes over-eating, not the other way around.

This is really good stuff, Stephan. Breaking down the actual numbers this way, and analyzing them leads to some interesting hypotheses. And what you've come up with seems to fit the data much more completely than what we've heard before.

Stephan said...

Charles,

Yes I was influenced by Taubes' idea that overeating is a result rather than a cause of a disturbed metabolism. It's a bit counterintuitive at first, but once you wrap your head around the biology it makes great sense.

I've always wondered about how well a person can reverse metabolic damage. That's an interesting anecdote about the person who lost weight but still has impaired leptin metabolism. What does that mean exactly, did he still have high fasting leptin? I wonder what it would take to correct that.

There's still a lot to be learned about leptin and why it gets out of whack so often in cultures with modern food habits. I'm going to try to keep my finger on the pulse of leptin research.

Dennis Mangan said...

The fact that these changes started in the 70s points to a possible explanation: culture. Do your own thing, who cares what anyone else thinks, and so on. When I was a kid, obese people were stared and laughed at, but there is no longer any stigma, because almost everyone is fat. Have you ever noticed that fat people eat, like, all the time?

As for dietary changes, magnesium might be a better explanation for metabolic syndrome.
http://ncp.sagepub.com/cgi/content/abstract/23/2/142 (for example).

AA said...

We can probably add 'poor diet advice' to the list of atrocities inflicted on indigenous peoples. More devastating than influenza.

Stephan said...

AA,

I agree 100%. How you could give diet advice to a strikingly healthy culture boggles my mind. It's incredibly arrogant.

Tony Kenck said...

I am a regular reader of your blog. Good stuff. I wonder how much our exercise has increased in terms of kcal/day.

That could be a partial explanation for the additional calories consumed as well as the metabolic disturbance hypothesis. Likely there is a combination of these and other factors.

If people are exercising, but their cells are still hungry, exercise won't help them lose weight in the long run.

Not disagreeing with you in any way. It seems like so many contradictions. I suspect that the chronic underfueling (hungry cells due to hormonal perturbations) has led to reduced metabolisms, but this is partly offset by exercise.

There is some writing along these lines on the Emotions for Engineers blog at http://www.emotionsforengineers.com

Cheers,
Tony

Charles R. said...

"When I was a kid, obese people were stared and laughed at, but there is no longer any stigma, because almost everyone is fat. Have you ever noticed that fat people eat, like, all the time?"

dennis, you've actually completely missed the point here (and aren't paying any attention to the science). You're falling back on the tired, old "obesity is caused by gluttony or sloth" line.

Fat people eat all the time because they are hungry all the time, not because they don't get shamed enough to stop eating.

And they are hungry all the time because (as this post and the next one points out) the SAD (Standard American Diet) interferes with the built-in hormonal mechanisms that tell us when to stop eating.

And also because as you develop insulin resistance, it's developed unevenly, and muscle cells develop it prior to fat cells. That means that as soon as you eat, and over-produce insulin, the glucose you should have available for energy is shunted to fat storage, and your blood sugar drops. When your blood sugar drops, you get hungry.

And because you have so much circulating insulin, you don't release the stored fat for burning. So you have to eat again, or faint from low blood sugar.

It's not about will power, or gluttony, or lack of self-control or lack of being ostracized. It's about biology and hormones.

Dennis Mangan said...

"It's not about will power, or gluttony, or lack of self-control or lack of being ostracized. It's about biology and hormones."

No, it's not ALL about willpower, but it's a factor, and those who blame it solely on the composition of the diet are missing something. So, people are so hungry that as soon as they arrive at the mall they need to head for the food court and scarf something greasy? Right. Just remember that guy who ate every meal at McDonalds for a month and didn't gain weight.

Charles R. said...

No, it's not ALL about willpower, but it's a factor, and those who blame it solely on the composition of the diet are missing something. --Dennis

Please read the next post, then you can continue your argument about will power, only you will need to relate it to the psychology of rats, not humans. Because as that experiment shows, feed rats the SAD, and they overeat. Feed them a more nutritionally sane diet, optimized for their biochemistry, and they don't overeat.

If you want to argue that it's possible to stop eating even when your body is telling you to do so, then of course, you're right. It's possible.

But that's not what we're discussing here. We're discussing where the initial impulse to overeat comes from, and how we can turn that off, and all the body's inborn hormonal mechanisms work to maintain healthy weight.

See the point is that the body is very good at maintaining weight, when the mechanisms to do so are working properly. And our SAD interferes with that, according to the research that Stephan is bringing up.

Maybe you, personally, can push yourself back from the table now and then. But I can pretty much guarantee you that if you had a biochemistry that was vulnerable to metabolic syndrome, and ate the SAD, and were hungry all the time--and not just hungry but often ravenous--will power wouldn't be enough.

And even a little overeating, over time, can put on a lot of weight. And as the fat builds up, the hormonal signals to eat get stronger and stronger, and the signals to stop get weaker and more obscured.

Dennis Mangan said...

How many morbidly obese people make more than, say, $200K a year? I don't have the data, but my guess would be: not very many. SES is correlated to obesity; hence, willpower, sometimes known as future time preference, is a factor in obesity.

One thing I find interesting is the sense of certainty of those who advocate high-fat diets. Someone loses some weight on Atkins, and all of a sudden they've see The Truth. You can lose weight on amphetamines too.

Stephan said...

Hi Tony,

According to the data I've read, energy expenditure has only increased slightly on average. Probably not enough to offset the increase in calories.

Although I will say that the energy expenditure data have their problems. One of them is from the NHANES survey, and is self-reported. Since our concept of exercise has changed in the past 37 years, it's hard to say what it means that twice as many survey respondents considered themselves inactive in 1971 than in 2006.

The other data point is from a study that measured energy expenditure directly, but it wasn't a large enough cross-section of the population to be 100% confident.

Nevertheless, it would be hard to argue that energy expenditure has declined from these data, which many people do anyway.

Anyway, that was a bit of a tangent, but basically I agree with your thoughts on exercise (and the basic ideas on the blog you linked to). If your metabolism is screaming for calories, exercise isn't going to cut it unless you are ready for a truly heroic workout routine.

Sue said...

Yes, you can lose weight on amphetamines but its not a healthy way to do it. Much better to do it via a high fat diet whilst repairing your metabolism.

robrob said...

wow, obese people were laughed at and shamed? no wonder they got fatter, they felt so shamed they dieted to lose weight and ended up fatter in the long run. thanks for helping the obese people to get more obese. your a saint.

if you see a depressed person deride them too so they will use their willpower (since they are so lazy everyone knows that)to shake it off.

let's shame everyone who doesn't meet out expectations or who does't live up to our standards of perfection. that would make everyone so happy!!!

and obese eat all the time is a myth. I am and certainly don't eat all the time. I go for 6-8 hours or more between meals because I am not hungry. sure I eat so do the thin people. in fact my thin friends are always hungry, piling food into their mouths while I sit there eating nothing.

I don't eat fast foods, I don't eat ice cream or anything like that, not anymore don't drink a pop everyday anymore, still obese however. by the way stephan you might be on to lowering ones carbs especailly simple processed because when I stopped eating bread, cereals (except the highest whole grain with very high fiber natural cereals occassionally)

I stopped using shelfed oils and use mostly extra virgin olive oil.
increased my protein, increased fiber supplementation, etc my desire for junk foods has gradually been diminishing and desire to move around more increased too, plus chromium, vita b really has made a difference as far as craving junkier foods goes.

I am sleeping better too. still having problems but they have shown dramatic improvements.

by the way one thing that causes overeating and weight gain for sure, undereating.I think they call that dieting for weight loss.

RRR