/dev/mull

i've been meaning to post about scientific stuff i've read recently, but i've been a tad busy. the long weekend gives me some time to clear my "fun" to-do list.


i usually don't cite science news, since it's a popular magazine. while the authors (usually) try hard to get the science right, they're not perfect, and in any case, their desire to popularize science sometimes leads them to simplify complex information to the point of being wrong. however, science news recently ran an article on psychology and its problems which has direct quotes from researchers trying to solve the field's problems. that makes it a primary source worth talking about.

( they're just a little confused about how to cure what ails them )

a recent JAMA paper on how the brain responds to fructose and glucose has made something of a splash in the popular press, frequently leading to claims along the lines of "proof that high-fructose sweeteners make you fat!" or some such rot. the paper doesn't actually prove that. i'm not entirely sure what it does prove -- i think it's mostly interesting to specialists in the field -- but i thought i'd try to clear the air a bit.

a little background: both glucose and fructose are simple sugars (monosaccharides) that the body can run on directly. there are some important differences between them:

* the body can run on glucose directly, but fructose is first metabolized by the liver into other compounds which the body runs on.

* the brain runs only on glucose, and takes it directly out of the bloodstream.

* ...and as a consequence, if we don't get enough glucose in our diets, the body makes some to keep the brain going.

* other tissues also run on glucose, but their ability to take it up is controlled by insulin.

from these alone, i would have expected that the body responds differently to glucose and fructose. in fact, the obvious result -- which silly reporters seem to have gotten all excited about -- is that if you take in a lot of glucose all at once, you'll get a much larger insulin spike than if you take in the same amount of energy in fructose.

the paper provides a bunch of details on the differences. most of the paper is about different brain responses, which i can't say much about. that's beyond my training (i'm a biochemist, dammit, not a doctor!). however, it does make perfect sense to me: since the brain needs glucose specifically, i'd expect it to react different to getting some than not. i'm actually curious now how the brain reacts to getting the same amount of energy as fats and proteins (vs the two different sugars)... i did say i'm a biochemist. :)

the researchers also looked at other responses, including both objective and subjective measures of how satiated the sugars make people feel. the former were made by looking a bunch of peptides that regulate hunger and satiety:

Baseline levels of plasma glucose, fructose, insulin, GLP-1, PYY, leptin, ghrelin, and lactate were not different between the glucose and fructose conditions (TABLE2). Glucose ingestion caused significantly greater elevations in plasma glucose..., insulin..., (Figure 1B and C), and GLP-1... concentrations compared with fructose ingestion, whereas plasma fructose, lactate, and PYY levels were greater after fructose ingestion compared with glucose ingestion (Table 2). Levels of leptin and ghrelin were not significantly different following ingestion of fructose compared with ingestion of glucose.

(statistical details elided)
so, the things we'd expect to respond directly to the two different sugars did the expected things, which is a good positive control. of the others, only peptide YY -- which is involved in the regulation of appetite -- responded differently. if the peptide YY results were taken in complete isolation, they'd say that fructose is better at suppressing appetite than glucose. (but i wouldn't do that, especially given the lack of difference in leptin and ghrelin concentrations.)

subjective effects were made by ye olde tenn pointe scale survey, a method the researchers provide citations for being valid. i didn't check the cited papers because:

There was no significant difference between glucose vs fructose ingestion on predrink-postdrink changes in hunger..., fullness..., or satiety[.] Glucose ingestion resulted in a significant difference in predrink-postdrink changes in fullness... and satiety..., whereas fructose ingestion did not have a significant effecton predrink-postdrink changes in fullness... or satiety[.]

(statistical details elided; my emphasis)
so there's not much to see in terms of how "filling" the two sugars are. i can't quite explain the differences in their pre- vs post- effects in isolation, except to say that the sample population was pretty small (20 people), so it may just be a fluke. more research is clearly required; send more sweet drinks. ;)

so, given the absence of real differences here (unless you're a peptide YY fan), why did the press get all excited? i'd say it was because the authors shot their collective mouths off in their first sentence in an attempt to seem "relevant":

Importance Increases in fructose consumption have paralleled the increasing prevalence of obesity, and high-fructose diets are thought to promote weight gain and insulin resistance. [...]

Of course, they might just as well have said that increases in fructose consumption have paralleled increasing standards of living worldwide, increasing global temperatures, increasing number of exoplanets known, or any number of other silly things which are the reason sensible people say that correlation doesn't prove causation. bad researchers, no credibility.

i'm generally suspicious of simple explanations for large problems. my bias specifically in this case is for falling exercise and increasing food availability as people have gotten wealthier. i don't see that this paper has done much to say one way or the other.

purple crab!



if these were vertebrates, i wouldn't hesitate to call them microfauna, since they're between 2cm and 4cm wide -- that's, um... ¾" to 1½" wide or so -- but that's plenty big when compared to an ant or gnat.

described in: Hendrik Freitag; Revision of the genus Insulamon Ng & Takeda, 1992 (Crustacea: Decapoda: Potamidae) with description of four new species; Raffles Bulletin of Zoology 60, 1, 37-55. (PDF)

there's an unfortunate emphasis on reducing carbon dioxide concentrations as the way of slowing/preventing global warming. while i have a certain interest in wholesale conversion of the power industry to methods that generate no carbon dioxide, there's simply not the money available to do it. so, we're fortunate that there are other ways of reducing warming, and they have valuable secondary effects besides.

a new paper in science proposes a short list of methods for reducing greenhouse warming and simultaneously improving human health. the trick for doing that is to reduce methane (which reacts to increase surface ozone) and black carbon (soot, which screws up our lungs all by itself).

the authors apply some apparently-standard methods to identify 14 specific measures which will reduce 90+% of the global greenhouse warming attributed to methane and soot, improve human health, and are cheap enough to implement. most of the ones for reducing methane try to trap it at the source (coal mines, pipeline leaks, and biodegradable waste). OTOH, most of the solutions for soot simply prevent it, by getting rid of the worst cars and trucks and requiring the rest to have better filters, and in the developing world, replacing wood- and dung- fired stoves with ones burning gas.

because the model is globally-optimized, most of the effects are in india and china, simply because they have lots of people and lots of pollution. i was going to throw the paper on the "interesting but not immediately useful pile", but stopped when i looked more closely at the global warming maps.

( big maps )

pretty picture shamelessly nicked from the beeb, since it's a derivative of a picture from the frog's discoverers.

A frog species that appears to be the world's smallest has been discovered in Papua New Guinea by a US-based team.

At 7mm (0.27 inches) long, Paedophryne amauensis may be the world's smallest vertebrate - the group that includes mammals, fish, birds and amphibians.

The researchers also found a slightly larger relative, Paedophryne swiftorum.

...

from the beeb

original paper in PLoS: Ecological Guild Evolution and the Discovery of the World's Smallest Vertebrate by rittmeyer et al.