Archive for November, 2010

Hard work makes food taste better

November 7th, 2010
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This is a quirky study, published this week in Proceedings of the Royal Society B by researchers at Johns Hopkins. The basic message is: if you have to work harder to get a certain type of food, you end up finding it tastier than food that you didn’t have to work as hard for. As the press release explains:

[M]ice were trained to respond to two levers. If the mice pressed one lever once, they were rewarded with a sugary treat. Another lever had to be pressed 15 times to deliver a similar snack. Later, when given free access to both tidbits, the rodents clearly preferred “the food that they worked harder for,” [researcher Alexander] Johnson said.

The results held up even when the hard-to-get food was a low-calorie version of the treat. This means, Johnson suggests, that “down the road, obese individuals might be able to alter their eating habits so as to prefer healthier, low calorie food by manipulating the amount of work required to obtain the food.”

That’s a heck of a public health message. Yes, our problem is that healthy food is too easily available, and junk food is too hard to get. To solve the obesity crisis, we need to make potato chips freely available on every corner, while making possession of a carrot a felony offense — that’ll train people to love the taste of carrots!

Okay, okay. It’s a neat (and amusing) study, and it confirms something most of us already knew: food tastes better when you’ve worked up an appetite. Let’s leave it at that, and not pretend we’re going to use this idea to train our taste buds.

Sports drinks hydrate you but water doesn’t?

November 4th, 2010

There’s an interesting abstract in the November issue of the British Journal of Sports Medicine on how well various drinks hydrate you. We’re talking purely hydration here: how fluid is absorbed and how much blood volume expands, not about whether you get extra energy and so on.

Very simple experiment: have the volunteers drink 500 mL of either water, 3% carb drink, or 6% carb drink (the “standard” sports drinks on the the market are about 6% carb). Use a radioactive stable isotope tracer (deuterium oxide) to follow where the ingested fluid goes, and take blood samples before (two samples) and after (eight samples over the following hour). The results: there was no difference in the carb drinks — both of them increased blood and plasma volume. In contrast, plain water DIDN’T increase blood or plasma volume. The explanation:

This is likely to be due to the sodium and carbohydrate content of these drinks.

Okay, I have to admit I’m a little confused. We know that too much carb (>6% or so) or sodium in a drink will slow the rate at which water empties from the stomach. Now this result is saying that too little will also slow it. This seems plausible, given that osmosis dictates the rate of gastric emptying — though it’s then strange that there was no difference between the two carb drinks. I have a couple of other questions:

1) If they’d kept taking blood samples for longer than an hour, would the blood volume of the water drinkers eventually have increased? Or is there some other route for the water to exit? (I find it hard to believe that they’re going to get diarrhea from drinking pure water.)

2) How did the plasma osmolality of the subjects change? That’s what some researchers believe is the key marker of hydration, as opposed to simply blood volume.

Part of the reason I don’t have the answer to these questions is that I’ve only seen the abstract to this paper. It’s in the “electronic pages” of the current BJSM issue, and I can’t for life of me figure out if there’s a full paper, and if so how I get it. Anyone who knows the answer (to the questions above, or simply to how to get the paper!), please let me know.

UPDATE 11/04:

Okay, some helpful comments below… but I’m still confused. The reason this result jumped out at me, I think, is that I’ve been looking through some of the old literature on hydration for a forthcoming article. So, for instance, I was reading Costill and Saltin’s 1974 article in the Journal of Applied Physiology, “Factors limiting gastric emptying during rest and exercise,” which says right in the abstract “At rest the addition of even small amounts of glucose (> 139 mM) induced a marked reduction in the rate of gastric emptying… These data demonstrate the importance of minimizing the glucose content of solutions ingested in order to obtain an optimal rate of fluid replacement. In combination with high-intensity exercise even small amounts of carbohydrate can block gastric emptying.” There are a whole bunch of studies with similar findings; here’s one from 1988 that found that plain water emptied faster than a variety of glucose concentrations while cycling.

On the other hand, I’ve certainly heard lots about how isotonic solutions are most quickly absorbed. How do I reconcile these two sets of data? Is it in the difference between gastric emptying and plasma volume expansion? Where else does the water go?

The magic carbo-loading calculator

November 3rd, 2010
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Okay, I’m a bit late to the party on this one. A couple of weeks ago, the newswires were buzzing with the news of MIT/Harvard MD-PhD student Benjamin Rapoport’s new calculator that allows you to determine exactly how much carbohydrate you need to load up on before running a marathon. Putting aside my initial skepticism (surely how much carb you need to load up on is well known by now?!), I finally had a chance to check out both the calculator and the PLoS Computational Biology paper it’s based on (the full text is freely available at the link).

The quick summary: the calculator is just a toy, and should not guide your fuelling decisions; the paper, on the other hand, I found surprisingly interesting — though I still wouldn’t use it to plan my fuelling strategy. Read more…

Biomechanics for performance and injuries

November 1st, 2010

My Jockology column in today’s Globe and Mail takes a look at the growing use of biomechanics technology by elite and recreational athletes, both to enhance performance and address injury problems. The two guys I spoke to were Dana Way, the Winnipeg-based biomechanics expert who travels with the Canadian track team, and Reed Ferber, who runs the University of Calgary’s Running Injury Clinic and has been rolling out a 3-D gait analysis system at clinics in western Canada.

[…] In typical laboratory “motion-capture” systems, small reflective markers are affixed to the athlete’s body at key points such as joints and extremities. Video cameras connected to a computer record the motion of these markers, and use the data to draw a stick-figure that duplicates the essential features of the athlete’s motion.

While traditional systems used a single camera to capture motion in two dimensions, the latest systems use multiple cameras to create a three-dimensional model. Major League Baseball’s Boston Red Sox, for example, are using a 20-camera system to analyze the throwing motion of their pitchers.

At the University of Calgary’s Running Injury Clinic, biomechanist Reed Ferber has been using an eight-camera system with 20 reflective markers to analyze the running gait of his patients and research subjects. But he’s found that for the 3-D gait analysis systems he’s started installing at sports clinics across the country, three specially designed cameras are sufficient. [READ THE WHOLE ARTICLE…]

The accompanying graphic, by the Globe‘s Trish McAlaster, does a nice job of showing how the 3-D gait analysis works: