Month: April 2007

Omega-3 and Arithmetic (evaluation)

Seth RobertsLeave a comment

When I read an empirical scientific paper I ask four main questions:

1. How clear is the effect or correlation? Generally measured by p values.

2. How clear is the cause of the effect?

3. How much can we generalize from this?

4. Assuming we can generalize, how much will this change what anyone does?

The overall value is something like the product of the answers. Most research gets a modest score on #1 (because a high score would be overkill and, anyway, the low-hanging fruit has been picked) and a low score on #4. Experiments get a high score on #2, surveys a low score.

Tim Lundeen’s little experiment that I described a few days ago, in which he found that a higher dose of DHA improved his arithmetic ability, gets a very high score:

1. The effect is very clear.

2. It’s an experiment. Because the variation was between two plausible doses of a food supplement, I doubt it’s a placebo effect.

3. The subject, the treatment, and the test are “ordinary” — e.g., Tim does not fall into a special group that might make him more likely to respond to the treatment.

4. Who wouldn’t want to improve how well their brain works?

From the point of view of a nutrition scientist, I’d guess, the effect is shockingly clear and direct. Experimental nutrition with humans almost always measures correlates of disease (e.g., correlates of heart disease) rather than disease. To me, an experimental psychologist, the results are shockingly useful. Practically all experimental psychology results (including mine) have little use to most people. The clarity of the effect does not quite shock me but I’m very impressed.

Omega-3 and Arithmetic (several analyses)

Seth Roberts4 Comments

In a recent post I described Tim Lundeen’s arithmetic data. He found that increasing his daily dose of DHA seemed to increase the speed at which he did simple arithmetic. Here is the graph:

Tim Lundeen's arithmetic data

I didn’t bother to do any statistical tests because I thought the DHA effect was obvious. However, someone in the comments said it wasn’t obvious to them. Fair enough.

If DHA has no effect, then the scores with more DHA should be the same as the just-preceding scores with less DHA. There are practice effects, of course, so I analyzed the data after practice stopped having an effect: After about Day 40. (And I left out days preceded by a gap in testing — e.g., a day preceded by a week off.) Thousands of learning experiments have found that practice makes a difference at first and then the effect goes away — additional practice doesn’t change behavior.

If I do a t-test comparing low-DHA days (after Day 40) with high-DHA days, I get a huge t value — about 9. If you’re familiar with real-life t values, I’m sure you’ll agree that’s a staggeringly high value for a non-trivial effect. The model corresponding to this test is indicated by the lines in this figure:

Tim Lundeen's data

The red (”more DHA”) points don’t fit the line very well, which suggests doing an analysis where the slopes can vary:

Tim Lundeen's arithmetic data

There is still a huge effect of DHA, now split between two terms in the model — a difference-in-level term (t = 4) and a difference-in-slope term (t = 3).

But this analysis can be improved because based on thousands of experiments I don’t believe that the less-DHA line could have a positive slope, as it does in the model. Or at least I believe that is very unlikely. So I will constrain the less-DHA line to have a slope of zero:

Tim Lundeen's arithmetic data

Now I get t = 8 for the difference in slopes and t = 4 for the difference in level. This is interesting because it implies that more DHA not only caused immediate improvement but also opened the door to more gradual improvement (indicated by the slope difference). DHA changed something that allowed practice to have more effect.

That’s a new way of thinking about the effects of omega-3 — actually, I have never seen any data with the feature that a treatment caused a practice effect to resume — so I have to thank the person who claimed the difference wasn’t obvious.

Birth of a Website

Seth Roberts2 Comments

Several months ago I got this email from someone at the Seed Media Group:

Thank you for your interest in being hosted by ScienceBlogs. In the last couple of months, we have received well over a hundred queries from bloggers representing an impressive breadth and depth of science
expertise. However, as we are trying to maintain a sense of community at ScienceBlogs, we are able to extend only a small number of invitations at a time. . . . In light of the very limited number of spaces we have to offer, we regret to inform you that we cannot extend you an invitation at this time.

This was sent to about 50 people. Their email addresses were visible. One of the recipients thought that we, the rejectees, could form our own umbrella website and wrote to us about this. I replied:

I love the idea of a form rejection letter leading to the founding of a competitive website — count me in!

Four months later I got an invitation to join the result, www.scientificblogging.com. It is now a well-functioning website with lots of interesting stuff.

New Way to Lose Weight?

Seth Roberts2 Comments

During the recent PBS special on obesity Fat: What No One is Telling You, a segment about surgery included this voiceover:

Until recently it was believed that the tiny stomach [that the surgery produces] is what forces the patient to eat less and lose weight. The surprise came when researchers learned that what makes surgery work so well is the cutting of some nerves in the bowel, which changes signals which flow between the gut and the brain.

I’m not surprised the researchers were surprised. The obvious function of nerves from gut to brain is to tell the brain food is present in the gut; and when enough food is present, to cause satiety. If this view of what the nerves do is correct, you would think that cutting those nerves reduces satiety signals and thus increases how much people eat at each meal — and thus causes weight gain. But the opposite is what happened.

The theory behind the Shangri-La Diet, however, easily explains the weight loss: Cutting the nerves reduced the calorie signal from food, thus reduced the strength of the flavor-calorie association. (After nerves are cut, your brain thinks that a 300-calorie food only has 150 calories. So the flavor-calorie association becomes weaker.) The weaker the flavor-calorie associations of your food, the lower your set point. The observation supports the theory so well that I will try to track it down to include in a revision of my paper.

The implication is that weight-loss surgery could consist of cutting some of those calorie-signalling nerves and nothing more. It would be relatively painless: Food would still taste good, especially in the beginning. (Because cutting the nerves does not change the memory stored in the brain.) Food would gradually taste less good as the flavor-calorie association become weaker. As flavor-calorie associations become weaker, your set point goes down. Causing weight loss without effort.

Omega-3 and Arithmetic (continued)

Seth Roberts14 Comments

Tim Lundeen, a Bay Area software developer, previously posted here about what happened when he increased his daily dose of DHA (an omega-3 fat in fish oil) from 400 mg/day to 800 mg/day: The next day, the speed with which he did simple arithmetic (e.g., 7 + 3) increased. At that point he had only four days from the high-DHA condition. Now he has two months. Here it is:

Tim Lundeen's arithmetic data

The y axis is the total time taken to do a set of 100 simple arithmetic problems.

Bottom line: The improvement continued, at roughly the same level. Very good evidence for an effect.

Tim had earlier found that doses of 200 and 400 mg/day of DHA had no apparent effect.

My main posts about omega-3.

Interview about Self-Experimentation (postscript)

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One of my favorite writers is Vladimir Nabokov. When he was alive, I not only read all his books but tried to read every word he wrote (in English). I have a folder full of photocopied interviews from newspapers and magazines. Late in his career, after my folder had become thick, Nabokov did something surprising: Came out with a book of interviews (Strong Opinions — here and here are excerpts), which put into book form most of what was in my folder. He wrote his answers to interview questions so this made some sense. Yes!, I thought, these interviews are just as interesting as I’ve always thought. I’d already read each of them about five times; I read them a few more times in book form.

I was such a big fan of Nabokov, and I liked his written interviews so much, that posting my answers to interview questions (here and here) was not an emotionally-neutral event. Partly it was a huge thrill — like being on your favorite TV show. Like being Nabokov For a Day. And partly it was humbling: My answers were way way worse than his.

Does the Type of Fat in Your Diet Affect Your Brain?

Seth Roberts8 Comments

Here’s how a Ph.D. student at UC San Francisco doing research on neural stem cells answered that question:

If dietary fat affected the brain in a significant way, we would know about it. It would have been discovered. Which isn’t to say it doesn’t affect it in a trivial way. Not just an acute action — like if you drink a small amount of alcohol or the effect of a sugar high. I mean the long-term functioning.

Why?

Because a lot of people would have tested it. Fat gets a lot of money. It’s a crowded area of research. People try to exploit it. It’s an area with a lot of public interest. It’s very popular to study anything related to fat. Also anything related to the brain. People are worried that they will lose their mind as they age. If there was something significant found it would have been a big story all over the New York Times.

She was very sure of this, it seemed to me.

My main posts about omega-3.

Interview about Self-Experimentation (part 2 of 2)

Seth Roberts2 Comments

8. How do you verify your results?

Repetition — first by me, later by others.

9. It seems your whole life is nothing but a self-experiment – how can your friends handle this?

Well, I spend a few hours in the morning differently than anyone else. I go to sleep earlier and wake up earlier than most people around me. And I eat less than most people. I like to think I make up for it by being in a better mood.

10. How do your colleagues react to your self-experiments?

Most of them think self-experimentation is a mistake, a waste of time. A few think it is creative and important.

11. Your most recent research is dealing with the effects of omega-3 on dental health. What is this research exactly about?

It’s not about dental health – that effect (omega-3 improved my gums) was an accident. It’s about the effects of omega-3 on my brain. I am varying the omega-3 in my diet in various ways and measuring how well my brain works in various ways. I began this research when I discovered that swallowing flaxseed oil capsules improved my balance. I was surprised but the effect makes sense: balance is controlled by the brain and the brain is more than half fat. Maybe you need the right fats in your diet if you want your brain to work as well as possible.

12. How did you get the idea of searching for the relation between omega-3 and dental health?

See answer to previous question.

13. How did you get the idea of taking oil to lose weight?

It was a three-step process. Step 1: I came up with a new theory of weight control. Step 2: I accidentally lost my appetite during a trip to Paris. I guessed that the cause was the unfamiliar sugar-sweetened soft drinks I’d been drinking because of the heat. This led me to discover that drinking small amounts of sugar water cause a lot of weight loss. Step 3: A friend pointed out that my theory predicted that flavorless oil should be just as effective as sugar water.

14. Are you going to search for a medical explanation for the effects of omega-3 fats?

No. Just convincing most people that there are effects is hard enough. It will also take a long time to learn how to maximize the effects. For example, what oils are best? How much oil is best? Other people are in a better position than me to try to explain the effects. But I don’t think it is terribly mysterious or surprising that dietary omega-3 should improve brain function: the brain is more than half fat. Surely the type of fat matters. My discovery is how big and fast the effect is. That’s not obvious.

15. When you consider your work as a whole, what is the most important result of your scientific research via self-experimentation?

Discovery of the effect of morning faces on mood. I believe depression is a deficiency disease, caused by too little exposure to morning faces. (See this paper for details.) No doubt that sounds very odd — even odder than the Shangri-La Diet — but consider this. In a wonderful book called The Good Women of China, the author, a Chinese radio host named Xinran Xue, wrote about her travels all over China to learn how different women lived. The last chapter is about visiting an extremely poor and backward community called Shouting Hill where an egg is a luxury and each women has multiple husbands because two or three girls are traded for a wife. She comes back to the radio station and tells her colleagues what she has seen. One of them asks, “Are they happy?” Another says, “Don’t be ridiculous, how could they be happy?” Because they were so poor — very poor even by Chinese standards. Xue answered:

I said to Mengxing that, out of the hundreds of Chinese women I had spoken to over nearly ten years of broadcasting and journalism, the women of Shouting Hill were the only ones to tell me they were happy.

It is pretty clear they saw plenty of faces in the morning.

Selenium, the Anti-Mercury

Seth RobertsLeave a comment

I’ve been worried about the mercury in tuna. I didn’t know that selenium protects against mercury damage. See this paper, for example — see Table 1. Moreover, the same fish that contain mercury contain protective amounts of selenium. “It appears that selenium levels in fish are high enough to give protection against mercury toxicity,” concluded a review article. These important facts were missing from all discussions of the dangers of mercury in fish that I had seen, such as this one.

I already take selenium supplements because selenium protects against cancer. An especially convincing bit of evidence for this effect is a map of United States county-by-county colorectal cancer rates. There is a sharp separation of high- and low-rate areas along the Ohio and Mississippi Rivers. Attempts to explain the difference eventually decided it was due to selenium in the soil of the low-rate areas.

Durian and SLD

Seth RobertsLeave a comment

The obvious connection between durian, the big smelly spiky Asian fruit, and the Shangri-La Diet is that both rely on flavor-calorie learning. We come to like the initially unpleasant smell and flavor of durian because we learn to associate it with the calories in the fruit. Here’s what happens:

“To anyone who doesn’t like durian it smells like a bunch of dead cats,” said Bob Halliday, a food writer in based Bangkok. “But as you get to appreciate durian, the smell is not offensive at all. It’s attractive.

From an article in today’s NY Times. The theory that led me to the SLD centers on flavor-calorie learning.

A less obvious connection is a principle that helped me discover that drinking sugar water causes weight loss. I was in Paris and lost my appetite — a rare event. The principle is that rare events are usually due to rare events. So I wondered what else unusual had happened. Well, there was something: I had been drinking several sugar-sweetened unfamiliar soft drinks per day. When I got back to Berkeley I started to test the possibility that sugar-sweetened water can cause weight loss and SLD was born.

For a fruit, durian has three rare properties:

    1. very strong, unpleasant smell
    2. very big
    3. hard to handle (because spiky)

Following the Rare-Causes-Rare principle, these should have a common explanation. Lightning does not strike thrice in one place for different reasons. According to Wikipedia,

The thorny armored covering of the fruit may have evolved because it discourages smaller animals, since larger animals are more likely to transport the seeds far from the parent tree.

That’s a good explanation of #3 and it explains the other two rare features (#1 and #2) as well. The reason for the strong smell (#1) is so that the signal will be broadcast a long distance: Large animals are less dense than small animals. We think of the smell of ripe durian as very unpleasant but perhaps almost all unfamiliar smells are unpleasant; so any random strong smell will seem very unpleasant. Big fruit (#2) means big tree and big tree means that seeds must be carried far away so as to be placed in soil where they will not compete with the mother tree. Coconuts are big and hard to eat. Pineapples are big and spiky.

The Rare-Causes-Rare principle also helped me discover the effect of morning faces on my mood and the effect of omega-3 on my balance.