Wednesday, March 19, 2008

Thoughts on Obesity, Part I

From the US Centers for Disease Control website:

Since the mid-seventies, the prevalence of overweight and obesity has increased sharply for both adults and children. Data from two NHANES surveys show that among adults aged 20–74 years the prevalence of obesity increased from 15.0% (in the 1976–1980 survey) to 32.9% (in the 2003–2004 survey).
In hunter-gatherer and some semi-agricultural societies, obesity is rare. In most, it's nonexistent. Wild animals typically do not accumulate enough fat to interfere with vigorous exercise, and when they do, it's because they're about to hibernate or migrate. Wild animals also tend to have similar amounts of body fat between individuals (at a given age and sex), unlike industrialized humans. This makes me think that obesity is an unnatural effect of our current lifestyle. Whatever the cause, it's getting progressively more common.

According to certain nutrition experts, we know exactly what causes overweight. It's a character flaw known as overeating. Calories in, calories out. And the cure is to eat less. The problem is, this treatment has a poor record of efficacy.

Restricting calories is also fraught with problems. Each person's metabolism has a preference for a specific body composition within the context of a particular lifestyle. If total calories are restricted without changing diet composition, the body reacts vigorously to maintain homeostasis. Energy expenditure is reduced; muscle and organ mass diminish. The psychological effects are particularly bad, as anyone can tell you who has been on a low-calorie diet. In 1944, Ancel Keys undertook a calorie restriction trial in conscientious objector "volunteers" in Minnesota. They remained on a 1,570-calorie diet that was low in fat and protein and high in carbohydrate, for 24 weeks. Hardly a draconian calorie count. Here's a quote from the study:

As starvation progressed, fewer and fewer things could stimulate the men to overt action. They described their increasing weakness, loss of ambition, narrowing of interests, depression, irritability, and loss of libido as a pattern characteristic of "growing old".
Some of the men ended up suffering from neurosis and borderline psychosis before the end of the study, one culminating in self-mutilation. This is what we're being prescribed for weight loss?

There are some diet trends that have associated with rising obesity in the US. Per capita calorie consumption has increased. This increase is due to a higher consumption of carbohydrate. Total protein and fat consumption have been almost identical for the past 30 years. This period also saw increases in the consumption of unsaturated vegetable oils, hydrogenated vegetable oils and high-fructose corn syrup. It's hard to say from this association which of these factors (if any) has caused us to gain weight in the last 30 years, but it certainly isn't total fat or protein. Fortunately, we have other clues.


Ross said...

The psychological effects in the low-calorie study sound very much like what happens when you put someone on a tryptophan-free diet. Their body isn't able to make any serotonin, and depression-like effects begin within hours. Subsequent studies also found impairments in: memory, social cooperaction, and ability to recognize fear in facial expressions.

Do people have similar psychological effects from diets that are low in calories but normal in protein?

Stephan Guyenet said...

Interesting. They were on a low-protein diet, but not tryptophan-free. They were getting "token amounts" of meat and cheese. Do those findings apply to a low-protein diet in general?

According to the studies I've read, the perception of hunger has a lot to do with the amount of carbohydrate in the diet. If you feed someone a 1,570 calorie, low-carbohydrate diet, they have very little hunger.

Carbohydrate seems to stimulate the appetite, presumably by elevating insulin.

Unknown said...

The mention of animals in the first paragraph reminded me of how zookeepers are trying calorie restriction to deal with the problem of obese animals in captivity, according to this article I read the other day:
Someone ought to tell them about the psychological and metabolic problems that strategy might create.
Personally, I don't believe animals should be kept in zoos if they don't have the resources to provide proper natural diets and the amount of excercise and mental stimulation they need (same for people in prisons or schools).

Stephan Guyenet said...

Great, feed the bears molasses and granola bars until they get fat, then starve them.

I guess that's a pretty good analogy for what we're doing to ourselves!

Debs said...

Reid, I saw that article too and have been working on a rant about it. Sugar-free jello for polar bears is a solution??? Because that's really the kind of food they're adapted for, of course. What about feeding the animals foods they're naturally suited to eat? Oh wait, we don't do that for people, so it wouldn't make sense for animals, I suppose. Back to calorie counting it is, then.

No wonder that tiger in San Francisco wanted to eat someone.

Ross said...

I realized that my previous comment wasn't totally, so for the record here's some clarification. While perception of hunger is definitely a function of blood sugar, there were other psychological effects in the 1944 Ansel Keys low calorie study: depressed mood, irritability, anhedonia. These other effects might have been due to screwed up serotonin levels in the brain, caused by a shortage of the amino acid tryptophan. Tryptophan is the precursor to the neurotransmitter serotonin, which is involved in controlling mood. If you put people on a diet completely devoid of trypotphan they start showing symptoms of depression within 5 hours. Granted the people in this study were on low protein diets, not tryptophan-free. But on the other hand, they were on the diet for 24 weeks rather than a mere 5 hours... so if their intake of tryptophan was just slightly below the body's normal requirement, the problem would probably compound with time.

I tried to find information about the effects of low-protein diets in general. I found one paper about 50 years old in chickens, where they found that augmenting low-protein diets with tryptophan helped alleviate some problems. Hard to say how much that informs the human condition though. I'll keep my eyes peeled.

Ross said...

...So my big-picture point is that while some of the effects in the 1944 low-calorie study may have been due to caloric restriction itself per se, others may have been due to the lack of protein. Or rather, lack of one specific amino acid. Pure speculation at this point until I can find more info on low calorie/high protein studies or high calorie/low protein studies.

Stephan Guyenet said...

See I find that difficult to understand, because I do 24-hr fasts once a week. Obviously I'm not getting any tryptophan during that time, but I don't get any of the symptoms you mentioned.

I could see how the effect could be magnified over a period of weeks though. There's no doubt they weren't getting much protein, and it wouldn't surprise me to learn that was a big factor in the mood disturbances.

There are a number of other studies Taubes mentions in "Good Calories, Bad Calories" that involve calorie-restricted diets with enough protein and a fair amount of carb, that are difficult for people to follow as well.

It seems that a low-carb CR diet is easier to follow than a high-carb CR diet, from a hunger standpoint. Maybe it has to do with insulin's effects on hunger?

Ross said...

Tryptophan has to be transported across the blood brain barrier before it can made into serotonin. There are only 3 different amino acid transporters for the BBB, each of which will only transport certain amino acids. Each amino acid is only transported by one type of transporter. Tryptophan competes with most of the other neutrally charged amino acids at one of those transporters. And this transporter saturates with substrate after you've eaten protein. In the tph depletion studies the subjects were specifically given protein drinks that contained all other amino acids except tryptophan. Thus their BBB tranporters are saturated with other amino acids. While they would probably have a nominal amount of tryptophan still in their body from a previous meal, it is now outcompeted for transport by the vast amounts of other amino acids just dumped onboard. When you fast the transporters aren't saturated, so they can move across whatever little tph there may be in your blood.

As to the feelings of hunger in high carb vs low carb diets, insulin seems like a very likely culprit.

Stephan Guyenet said...

OK, I see. So it seems like that probably wouldn't have been a problem for the Keys subjects then, since it's more about the balance of aa than the absolute amount of tryptophan. Although I can definitely imagine that getting too little protein could contribute to mood disturbances.

Ross said...

It's more about balance only if you have enough absolute levels. Balance alone is not sufficient when the absolute amount of tryptophan intake is too low.

In an old study they took blood samples in people after 12hr fasting and measured levels of amino acids. Tryptophan was still 79% of normal, but only in people who were on diets with high levels of tryptophan (see table 8). In people who were on diets with low tph prior to fasting, their fasting levels were much lower. The point I'm trying to make here is that when you fast your body taps into reserves that you've built up. So if we're talking about tryptophan availability, 24hr of fasting is not the same as long-term malnutrition.

The crux of the matter with the Keys subjects is whether or not they were getting enough absolute amount of tryptophan in their diets. A quick & dirty google search ( told me that healthy adults need about 200 mg/day. This amount is found in 1/3 pound of chicken or 2/3 a cup of cottage cheese.

It seems quite possible that "token amounts" of meat and cheese would amount to less than the required amount for 200 mg tryptophan/day. And if the rest of the diet was high in carbs it was probably mostly bread, potatoes, and pasta which I'd imagine are very low in protein.

Stephan Guyenet said...

Ross, I'm on a rollercoaster here! First it's the Trp, then it's not, now it's the dad nab Trp again! Will you just tell me whether they went crazy because of the Trp or not?

Just teasing, haha.

Ross said...

it was the trp! although since they were conscientous objectors, they must have been crazy before the diet study even started

Patia said...

I'm in agreement with most of your thoughts on obesity in this post and in Part II. And I truly appreciate that you seem to refrain from vilifying fat people.

But I have to take some exception to your statement that "in hunter-gatherer and some semi-agricultural societies, obesity is rare. In most, it's nonexistent."

Rare, yes. Nonexistent, no.

Because how do you explain the numerous 25,000- and 30,000-year-old female figurines such as the Venus of Willendorf?

Anthropologists like to claim their big breasts and bellies signify pregnancy and that they are therefore fertility figurines. Maybe so, but these sculptures aren't just pregnant, they're FAT. I like to think they're ancient versions of a Barbie doll, but the truth is, no one really knows.

Stephan Guyenet said...


Yes those artist must have had a concept of overweight. There are some examples of obesity in non-industrialized societies, but my impression is they're pretty infrequent.

Neonomide said...

Stephan said...

"Interesting. They were on a low-protein diet, but not tryptophan-free. They were getting "token amounts" of meat and cheese. Do those findings apply to a low-protein diet in general?"

High-protein diets dimish tryptophan because several amino acid compete the same pathway. This has been noted even in 1-year study last year.