Last week a journalist asked me why the 5% improvement in arithmetic speed produced by butter was important. In an earlier post I said I’d given a poor answer. A few days later I figured out what I should have said. The article was delayed, it turned out, so there was time to use my new strategy. I answered the question like this:

I was excited by this discovery because it was so big and unexpected. Someone once found a correlation between IQ and reaction time. The higher your IQ, the faster your reaction time. I don’t know what the exact function was but a decrease of 30 milliseconds might correspond to 10 more IQ points. I felt a little bit smarter. It was so unexpected because hardly anyone was going around saying butter is good for you — and thousands of people were saying it is bad for you. The only ones saying butter is good for you were the followers of Weston Price, and they had almost no evidence for what they were saying. Compared to their evidence, my evidence was crystal clear. Among mainstream nutritionists, butter is universally scorned. Yet my data suggested exactly the opposite — that it had a large amount of an important nutrient I wasn’t getting enough of. If mainstream nutrition advice could be so wrong, it would have big implications for what we eat. Maybe other things we are constantly told about what to eat are also wrong.

I discovered this big effect of butter by substituting butter for pork fat. So the reason butter was so helpful wasn’t anything as simple as animal fat is food for us. I ate plenty of animal fat before I started eating lots of butter. The reason was something more specific.

Eating a half-stick of butter (60 g) every day apparently improved how fast I can do simple arithmetic problems (e.g., 7-5, 3+1). I improved about 5% — from 630 to 600 msec per problem. My scores had been at 630 msec for months. They suddenly dropped.

A reporter said to me that a 5% improvement isn’t much. You couldn’t notice it. Why did this matter?

I did not reply “ what good is a newborn baby?” I said it mattered for three reasons:

1. You cannot easily produce such an improvement. I was already doing very well. For example, I had already lowered my scores a lot via omega-3. Imagine the world record for the 100 meter dash suddenly dropping 5% due to eating something you can find in a supermarket.

2. A 5% improvement is just the beginning. There is room for optimization — better dosage, better timing of taking the butter, and so on.

3. The brain is a mirror of the rest of the body. Learning the best diet for the brain, at least in terms of fat, will help us learn the best diet for the rest of the body, just as learning what house current is best for one electrical appliance is a guide to what other electrical appliances are designed for. They’re all designed to work with the same house current.

Alas, this is not just a poor answer, it’s what I actually said. I give myself a C+. Reason 1 is almost gibberish. Reason 2 is technocratic. A good answer is more emotional. Reason 3 is okay, if not very clear.

At Berkeley I knew a student who had transferred from a junior college. He is/was black. He had probably gotten into Berkeley because Berkeley administrators wanted to admit more black students. He complained one day that he got C’s on his essays even though “all the words were spelled correctly.” It was frustrating, he said. I am in a similar situation here. My answer is poor but I cannot easily do better.

Since I discovered that butter makes my brain work better, I have been eating half a stick (60 g) per day. Usually half in the morning and half in the evening. It is hard to eat by itself but easy to eat with other foods. I’ve tried a dozen ways of doing this. My top three additions:

1. Pu’er tea. The most convenient. As convenient as drinking tea. Put the butter in hot tea, wait till it melts. I can eat at least 20 g of butter in one cup of tea. Butter tea is common in Tibet. Thanks again to Robin Barooah.

2. Cherry tomatoes. The healthiest and fastest. Slice the tomatoes in half lengthwise, eat each half with a similar-sized piece of butter. It is like that classic Italian combination, mozzarella and tomatoes.

3. Thin-sliced roast beef. The most delicious. Wrap a piece of butter with the roast beef. However, I already eat plenty of meat, it is hard to get thin-sliced roast beef in Beijing, and it is so delicious I end up buying a lot of thin-sliced roast beef.

None of these additions affects brain function (measured by arithmetic score), as far as I can tell, although I suppose the tea wakes me up.

My recent heart scan score was about 50% less than you’d expect from an earlier score. Why the improvement?

During the year between the two tests, I’d made one big change: eat much more animal fat. That’s the obvious explanation. Three things support it:

1. Mozaffarian et al., as I blogged, found a similar result.

2. The animal fat (pork fat and butter) had both produced large immediate improvements when I began to eat them. The pork fat had improved my sleep; the butter, my arithmetic scores. This sort of large immediate effect we associate with the supply of a missing necessary nutrient — giving Vitamin C to someone with scurvy, for example. My brain, at least, needed much more animal fat than I’d been eating. Different parts of the body need different nutrients, sure, but they all must work well with the same set of nutrients. If Nutrient X helps one part of the body, it is more likely to help another part.

3. My initial score put me at the 50th percentile for my age. I’d had an unusual diet for a long time. I stopped eating bread, potatoes, rice, pasta, and dessert 13 years ago. I’d started consuming lots of omega-3 and fermented foods a few years earlier. It was possible that those other changes produced improvement but if so it was a strange coincidence that, as my score got better and better over the years, I happened to measure it for the first time just when it crossed the 50th percentile.

This explanation makes a prediction: If you greatly increase your animal-fat intake, your heart scan score should improve. A commenter said what he’d read on paleo-diet forums supported this prediction: “If you hang out in the paleo/low carb forums, you see this kind of thing a lot.”

I posted yesterday that a recent heart scan found my arteries about 50% less calcified than a previous scan predicted. Apparently the improvement was due to eating much more animal fat (pork fat and butter).

In 2004, an American Journal of Clinical Nutrition article found something similar: heart disease progressed less in women who ate more saturated fat. “In postmenopausal women with relatively low total fat intake, a greater saturated fat intake is associated with less progression of coronary atherosclerosis,” the authors wrote. Here’s how they saw this finding:

The inverse association between saturated fat intake and atherosclerotic progression was unexpected. However, this finding should perhaps be less surprising. Ecologic and animal experimental studies showed positive relations between saturated fat intake and CHD risk (8). However, cohort studies and clinical trials in humans have been far less consistent (9 —12). Furthermore, most studies of dietary fat and CHD risk have been performed in men (15, 16). The relations in women—particularly postmenopausal women—are much less well-established, and evidence from dietary intervention trials suggests that diets low in saturated fat may have different effects on CHD risk factors in women (15, 17—22).

In their study, women with the highest intake of saturated fat did not get worse during the study period, whereas women with lower intakes did get worse.

An editorial about this study described some of the evidence that supports the “article of faith” that “saturated fat . . . accelerates coronary artery disease”:

One of the earliest and most convincing studies of the better efficacy of unsaturated than of saturated fat in reducing cholesterol and heart disease is the Finnish Mental Hospital Study conducted in the 12 y between 1959 and 1971. In this study, the usual high-saturated-fat institutional diet was compared with an equally high-fat diet in which the saturated fat in dairy products was replaced with soybean oil and soft margarine and polyunsaturated fats were used in cooking. Each diet was provided for 6 y and then the alternate diet was provided for the next 6 y. After a comparison of the effects of the 2 diets in both men and women, the incidence of coronary artery disease was lower by 50% and 65% after the consumption of polyunsaturated fat in the 2 hospitals.

My results make the results of that earlier study exceedingly puzzling. I found a large change in one direction; the Finnish study found a large effect in the opposite direction. Given the huge effect (50% or 65% reduction) observed in the Finnish study, it is hard to understand why “cohort studies and clinical trials in humans have been far less consistent”.