Low Carb Diets II

The new Dietary Guidelines for Americans 2005 is specifically targeted towards preventing obesity. The previous food guide pyramid from 1992 emphasized a reduction in saturated fats to prevent heart disease. With an estimated 300 million worldwide expected to be afflicted with Type 2 diabetes in the near future, mostly due to obesity, we have a new priority. The guidelines recommend a diet that is high in fruits and vegetables, low in fat, and low in sugar. The latter recommendation was especially contentious with the food industry.

As expected, low carbohydrate diets like the Atkins diet were not held in high regard. However, there really isn’t overly strong evidence that they are unhealthy and in some cases they have been found to actually lower blood lipid levels! As a weight loss measure, low carb diets do seem to work although keeping that weight off is another matter as I discussed previously.

The Atkins idea is that carbohydrates make you fat. When you eat carbohydrates they get broken down to glucose (except fructose) which then triggers an insulin response. Insulin allows muscles to uptake and burn glucose (instead of fat). At the same time it suppresses the release of free fatty acids from adipocytes (fat cells). Thus when insulin levels are low, the muscles mostly burn fat (except during exercise). Glucose is thus spared for the brain which cannot burn fat. This much is true. However, Atkins also claims that when insulin levels drop after a meal, you get a strong hunger response. The data is not so clear on this point.

To make up for the lack of carbohydrates, you must eat more protein and a lot more fat. Thus low carb diets are high fat diets. The traditional Inuit diet is an Atkins diet. When you begin a low carb diet, the first thing that happens is that you get depleted of your glycogen (which is the body’s only store of carbohydrates). This is accompanied by a loss of water so you lose a lot of weight quickly. Your body then goes into a state of ketosis where the liver makes ketones. The brain only burns glucose or ketones. No one knows if maintaining ketosis for prolonged periods of time is detrimental. The fact that the Inuit did it for generations probably means it’s okay.

There may be other reasons for why the Atkins diet works. For one, the diet does limit calories. Secondly, there is some data that shows that restricting food choices can result in eating less. Thirdly, until recently, there were very few snacks that are low in carbs. Finally, the quick weight loss in glycogen and water may motivate people to stay on the diet.
However, people do eventually give up and the weight inevitably returns after two years.

I personally think, from a health point of view, that controlling the total amount of calories consumed is more important than the composition of the diet. If you are in energy balance, you will basically burn everything you eat so it doesn’t really matter if it is mostly fat or carbs. When you overeat, you are going to store that extra energy as fat. The data shows that losing just a little bit of weight can greatly reduce insulin resistance which is a precursor to Type 2 diabetes. Exercise also seems to confer benefits that go beyond the extra calories burned. So although eating lots of fruits and vegetables is probably good for you, if eating pork rinds helps you lose weight, then stick with that.

Advertisements

Oxygen

In the debate over global warming, little has been said about its affect on oxygen balance. Atmospheric oxygen serves two crucial purposes for sustaining life on earth. In the upper atmosphere it takes the form of ozone and blocks ultraviolet radiation. Without this layer, no life on the surface of the earth could exist. The second purpose is as an oxidant for respiring life forms. Most of the oxygen on earth is sequestered in rocks like silicon dioxide. Atmospheric oxygen comes exclusively as a waste product of photosynthesis of plants and prokaryotic organisms. The bulk of atmospheric oxygen comes from photosynthesizing bacteria near the surface of the oceans.

The air is comprised of 78% nitrogen, 21% O₂ and the rest as trace gases such as argon and carbon dioxide. The oceans also contain a large supply of dissolved carbon dioxide and oxygen. As water warms, it can hold a smaller amount of oxygen. Thus, as the oceans warm due to global warming, they are actually outgassing some oxygen (Keeling and Garcia, PNAS 99:7848-7853, 2002) . At the same time, oxygen in the atmosphere is also slightly decreasing due to combustion of fossil fuels.

Right now the decrease of oxygen in the ocean is 0.7 µmol per kg per decade. For comparison , the concentration of oxygen in the ocean is on the order of a few hundred µmol per kg. So the decrease is small but not insignificant. Given that one hypothesis for the extinction event 250 million years ago known as the Great Dying (see my previous entry) was due to a lack of oxygen in the oceans, I think that this is of some concern. We simply don’t know enough to predict the consequences of global warming. However, I really think we need to take it seriously. Affecting the carbon balance could have implications beyond the melting of glaciers and the increase of hurricanes. It could affect the oxygen that we breathe.

Gender Differences?

As the sides line up on the Larry Summers debate/debacle, more data is coming in. One of Summers suggestions was that women were less likely to want to make the sacrifice required for an intense academic job. An indication would be that the attrition rate for women would be higher throughout the training process. However, as reported in the New York Times today, after earning a bachelor’s degree in physics, American women are just as adept as men in climbing the academic ladder. A full report can be obtained from the AIP website. Currently women make up 22% of bachelor’s degrees and 18% of PhD degrees awarded in physics . In astronomy the numbers are much higher – in 2003, women earned 43% of bachelor’s degrees and 26% of PhDs. There also seems to be a huge surge in women in the last five years into both fields. Women comprise of 10% of physics faculty now and their numbers have been slowly increasing over the past few years.

The data shows that the main source of attrition of women from physics is between high school and college where half of the students in high school physics are females but fewer than a quarter of the degrees go to women. This supports Summers assertion that the problem may arise early. However, Summers then contended that this early gender disparity may be biological although he conceded that there is no evidence and challenged the audience to do the studies to test the hypothesis. As pointed out in the comments section of my previous post, Brad De Long shows data indicating that social factors may swamp out any biological effects.

My stance, which I’ve argued in Steve Hsu’s blog, is that even if there are biological differences, they are small and this knowledge is not useful and is potentially damaging. The data clearly shows that policies enacted over the past several years are having some effect. The percentage of women in science and engineering is increasing. We should continue to eliminate social barriers and wait another generation or two. If disparities still exist then perhaps we can start looking for other reasons.

Science Job Market

Steve Hsu has been arguing in his blog that young people should not be encouraged to pursue a career in science. He feels that they would find greater success if not satisfaction in a more lucrative field like finance, engineering, law or medicine. His argument is based on the premise that there are a plethora of well educated and well trained people from eastern europe, the far east and south asia that are willing to endure more hardship and take less pay for the same job. In the end, the top American students may waste 10 years pursuing an academic job that may never materialize. The various merits of this argument is debated in the comments to Steve’s posts. I do not deny that competition for academic jobs in science is fierce but why should it be less so in these other fields?

Law and especially medicine restrict the supply by limiting the number of students admitted to their respective professional schools and making it extremely difficult to practice in the US if one is trained in another country. Thus, in terms of these fields, our hypothetical top student interested in science would need to out compete other Americans to attain coveted slots in these schools. If they succeeded (and that is not guaranteed by any means) in getting admitted, employment as a physician or lawyer is reasonably certain if they went to a top rated school. From what I’ve seen, insurance companies have been declaring war on physician salaries for the past several years and law does not seem to be a guarantee of a high salary or job security.

Engineering and related discplines like computer science certainly have more options in industry than say physics or mathematics. However, it may not have many more opportunities than say chemistry or biology. Additionally, the same cohort of foreign students competing for jobs in science should also be competing for these fields. We have all heard about software outsourcing lately and I’m certain it will only get worse.

Finance is the area that Steve was really referring to in terms of missed opportunities for the top science student. Between ten and fifteen years ago, a wave of physicists entered finance. Many have done exceedingly well and have retired or could retire. However, I think that well is drying up as well. I don’t see why competition from foreigners won’t be any less fierce, if not fiercer here. The brightest students in other countries will probably follow the same advice Steve is giving. Correct me if I’m wrong but I bet that purely quantitative jobs are probably not as lucrative as they were in the hay days. The only way to really succeed in finance is to advance into a leadership position and being able to do that requires a skill set that is independent of those that are optimal for science.

So I think the bottom line is that if you are a truly spectacular student then you could probably be successful in medicine, law, engineering or finance. On the other hand you probably would be successful in science as well. Steve’s argument hinges on the fact that it takes a long time in science before you know if you have what it takes. Given that the average American will change careers five times in their life, I’m not sure if that is not true elsewhere as well. I think the bottom line is that we now live in a global economy and this will affect everyone. As they say, there is no free lunch.

Smallest multicellular organism

I’ve been searching for the smallest multicellular organism and there do not seem to be any adult creatures with fewer than a thousand cells. For some reason there seems to be no evolutionary advantage for being say an organism of two cells or three hundred cells. This seems to also hold true for colonies of cells like sponges or algae. No one seems to have an explanation for why this would be true.

The diversity among organisms on the order of a few thousand cells is immense. On the one hand we have the nematode worm C. elegans which has 959 somatic cells with a nervous system of about 300 neurons. It has muscles and a metabolic system that operates surprisingly like humans. It reproduces sexually with sperm and egg. It’s genome has 100 million base pairs encoding an estimated 17,800 genes.

On the other hand we have Trichoplax adhaerens which is a candidate for the simplest multicellular organism. It is the only species in the phylum placozoa. Trichoplax is comprised of a few thousand cells that differentiate into four types. It has no neural or muscular systems. It basically looks and acts like a large amoeba. It reproduces by binary fission or sometimes by budding although sexual reproduction may be involved like yeast. It has the smallest genome of any known animal at 50 million base pairs which is only a factor of two smaller than the nematode.

Both animals are about the same size – a few millimetres in length – and both have roughly the same number of cells but they have employed drastically different strategies for survival. So it seems that the constraint on minimum number of cells in an animal is not one of limited strategies. Perhaps is is a result of a constraint of molecular biology or cellular physiology.

Misuse of language

The way we misuse phrases and quotations may tell us something about how our brains work. I give three common examples. The first is “Now is the winter of our discontent”, which comes from Shakespeare’s play Richard III. The line refers to an ebb in discontent (for the house of York in Richard III’s case). Winter is meant to be a modifier of discontent. However, people almost universally use discontent as a modifier of winter as in there is an entire season of discontent and now we’re in the winter part of it. Even Steinbeck used it as the title of his book to indicate a state of disaffection. Some rephrase it to “Winter of Discontent” which could be thought of as a clever ironic pun of Shakespeare. However, if you think about it “Winter of our discontent” makes most sense when used as Shakespeare did.

Now why is it misused? I think part of it is laziness. Most people have never read Richard III. However, it may also be evidence that our memory for language is an attractor (Hopfield) neural network. In this idea, memories are attractors in a dynamical system each with a basin of attraction. “Winter of our discontent” is remembered as a complete phrase separate from its component words. If it was incorrectly associated with disenchantment the first time we encountered it, then it may be frozen as such. So the next time we wanted to express the sentiment (and who is more poetic and profound than Shakespeare) we would call up this quote without an examination of the true meaning.

The second misquote is “If music be the food of love, play on” from Shakespeare’s Twelfth Night. Most people use this quote as a positive statement about music. However, it actually is a negative statement about love. In the play, Orsino is heartbroken and wants to hear so much music that he will be come nauseated and no longer have any interest in love. In this case, I can see why it would be misused the way it has. Music is a surrogate for love so let’s have more of it.

The third oft misused phrase and one that irks me the most is “begging the question”. This term, which refers to a circular argument that presumes the truth of an assumption, is commonly used as a substitute for “raises the question”. I’ve heard many hyper-educated people misuse this phrase. People will say “The fact that X happens begs the question…”. I think in this case, people have heard this term in their youth but never understood what it really meant. However, it remained lodged in their memory and is now retrieved whenever a situation calls upon a particular question. In time I think this new and incorrect usage will eventually dominate and become accepted. This is too bad because now more than ever we really need to challenge those that “beg the question”.

Principle of Least Action

I’ve always been amazed at how much faith physicists have in the principle of least action, which says that all classical objects travel along a path that minimizes the action. In quantum mechanics, particles will take all possible paths but the amplitude is weighted by the classical action along the path (so the most likely path will be the one of least action). Steve Hsu discussed the path integral, which sums over the paths, in his blog recently.

From what I’ve seen as a spectator, “Theories of Everything” have fiddled with symmetries, spatial and temporal dimensions, been comprised of strings or branes or what have you but they’ve all been based on the premise that the quantum amplitude is giving by a sum over paths weighted by some action. I’ll be the first to admit that this approach does work amazingly well for all the energy scales that we have tested thus far. Quantum electrodynamics is the most accurate theory we have.

However, we should not forget that least action and it’s quantum cousin are assumptions. They were discovered empirically. Yes, in order to make any progress we must make assumptions but sometimes these assumptions are so internalized I don’t think people even realize they are making them. The greatest breakthroughs often involve questioning our basic assumptions. Relativity, quantum mechanics, plate tectonics, democracy, and so forth all arose as fundamental challenges to the prevailing status quo. So even if M theory turns out to be the right theory some day it still won’t tell us why we have the principle of least action.