Archive

Posts Tagged ‘nutrition’

Worms, booze and life extension

February 7th, 2012

An odd little study from researchers at UCLA, just published in PLoS ONE (full text here; press release here) looks at how alcohol extends lifespan in worms. In fact, these particular worms double their lifespan when you given them a little booze. But “little” is the operative word here: they used ethanol diluted by a factor of 20,000:

“The concentrations correspond to a tablespoon of ethanol in a bathtub full of water or the alcohol in one beer diluted into a hundred gallons of water,” Clarke said.

And more wasn’t better: a little more doesn’t provide any additional lifespan benefits; a lot more produces “harmful neurological effects” and kills them. So the optimal dose is a tiny amount.

What does this mean for humans? Very little, at this point. Still, it’s hard not to compare the results to all the human studies that have found longevity benefits for very moderate amounts of alcohol consumption (i.e. a glass a day), but not for larger amounts. It’s still not clear whether the apparent benefits relate to the ethanol itself, or to all the antioxidants and fancy compounds found in wine (and possibly beer). Could humans be affected by a mechanism similar to what’s going on in these worms?

“While the mechanism of action is still not clearly understood, our evidence indicates that these 1 millimeter–long roundworms could be utilizing ethanol directly as a precursor for biosynthesis of high-energy metabolic intermediates or indirectly as a signal to extend life span. These findings could potentially aid researchers in determining how human physiology is altered to induce cardio-protective and other beneficial effects in response to low alcohol consumption.”

Time to go pour a tablespoon of ethanol in my bathtub, I guess!

How many carbs do you need to max out your muscle stores?

January 23rd, 2012

My column in today’s Globe and Mail takes a look at some recent field research on carbo-loading the day before a marathon:

[...] To find out whether this revised advice works in practice, researchers in Britain followed 257 London Marathon participants for five weeks prior to the race, collecting data about their training and eating patterns. The runners had an average age of 39 and an average finishing time of 4 1/2 hours. The results were published in the International Journal of Sports Medicine.

Sure enough, day-before carbohydrate consumption mattered. Runners who ate more than seven grams of carbohydrate for every kilogram of body weight (g/kg) ran 13.4 per cent faster than a comparable group of runners who ate fewer carbohydrates but were otherwise identical in terms of age, body mass index, training and marathon experience. Surprisingly, the amount of carbohydrate consumed during the marathon didn’t matter as much. [READ THE WHOLE ARTICLE HERE]

Most people don’t realize what an enormous amount of carbohydrate you have to take in to maximize your glycogen stores — which is why only 12% of the runners in the study hit the 7 g/kg threshold. Trish McAlaster did a nice job with an accompanying graphic showing just how much you’d need to eat and drink to hit 5 g/kg (the average in the study), 7 g/kg, or 10 g/kg (which is the amount suggested for elite athletes). Note that I’m not suggesting you should actually eat four plates of plain pasta for dinner — this is just to put the amounts in context!

[CORRECTION: Reader Mike LaChapelle just pointed out that the math doesn't add up in the graphic. The "threshold" lunch should include 500 ml of sports drink. That being said, I should clarify that I'm not recommending these menus as exactly what you should eat; it's aimed at giving a sense of the quantities involved. In real life, I'd go for more variety, and include things like fruit and vegetables!]

,

The more you eat, the faster you go (in ultraendurance)

January 10th, 2012

A few months ago, I blogged about a study that observed correlation between in-race carb intake and race time in Ironman triathletes. What was significant about that paper is that it looked at a topic that has been studied to death in the lab, and took it out into the real world. There are a lot of “problems” with the real world that make it hard to nail down causes and effects — but ultimately, the whole point of this type of research is to understand what’s happening in the real world. So these observational studies, despite their challenges, are very important.

That’s by way of intro for another small study, just published in the International Journal of Sport Nutrition and Exercise Metabolism, from researchers in New Zealand. They looked at the nutritional intake of participants in a brutal cycling race, the K4, which covers 384K and includes 4,600 metres of climbing. The average finishing time of the 18 study participants was 16 hours and 21 minutes! The key points:

  • The estimated calorie burn for the race was about 6,000 calories; the average intake was just 4,500 calories, so there was a big caloric deficit.
  • There was a significant inverse relationship (p=0.023) between number of calories consumed and finishing time. The more calories you managed to cram down your gullet, the faster you finished!

Is this a surprise? Given that the race was so long, it makes sense that taking in enough energy was a significant challenge. Obviously the same thing doesn’t apply during, say, a 100-metre sprint. The question is: where’s the breakpoint, beyond which energy intake becomes a significant independent predictor of performance? I think the general assumption is that it’s probably a bit below marathon distance — so it would be really interesting to see a study like this, with a very large number of participants, at a marathon.

Des Davila, and learning to increase your carb intake

December 31st, 2011

Great in-depth profile of Desiree Davila in the current Runner’s World, leading up to the U.S Olympic Marathon Trials later this month. One passage that caught my eye, referring back to the 2008 Trials:

Davila ran her plan, clocking 5:48 mile splits. At mile 21, she was eight seconds behind eventual third-place finisher, Blake Russell. “And then I just completely fell apart,” Davila says.

It was a fueling issue. As a track runner, competing in the 1500, the 5000, and the 10,000, Davila never had to take fluids. More to the point, she couldn’t. When she tried, everything came up. “I thought, Well, I don’t want to lose breakfast, too, so I’ll just stop drinking fluids on the course.”

That doesn’t work over 26.2 miles. Or at least not for her. She struggled to cross in 2:37:50, for 13th place.

The fueling issue would be addressed—directly. During long workouts, Davila would force herself to drink. Her system, well, rejected it. “It was actually kind of disgusting,” she says. But week after week, her body eventually adapted. “Gross,” she says, “but necessary.”

Every time I write about carbohydrate intake during long endurance races (e.g. here), I get comments from people who say “Well, that may be true for the subjects in that study, but unfortunately that doesn’t work for me. My stomach can’t handle that.” Good thing Davila didn’t just accept that as an unchangeable fact of life.

Pre-race carbs influence marathon pace

December 23rd, 2011

Cool field study on carbohydrate loading that I missed when it came out in the International Journal of Sports Performance over the summer, but just noticed on Amby Burfoot’s Twitter feed. Researchers enrolled 257 runners preparing for the 2009 London Marathon in a five-week online study where they entered all sorts of details about their training and diet leading up to the race. The subjects had an average age of 39, and an average finishing time of 4:34.

Needless to say, there were many factors that predicted running time: gender, BMI and training being the most obvious! The most interesting was nutrition:

In addition, although individual differences in race day diet did not strongly influence the marathon performances of recreational athletes, the amount of carbohydrate ingested during the day before race-day was identified as a significant and independent predictor of running speed. Furthermore, those runners who ingested more than 7 g carbohydrate per kg body mass during the day before the event ran faster in general and also maintained their running speed to a greater extent than those participants who consumed lower quantities of carbohydrate.

This may remind you of a study I blogged about a few months ago, showing correlations between in-race carbohydrate intake and Ironman finishing time. In this case, the better predictor is day-before carb intake, not in-race carb intake — perhaps not surprising, since a marathon is much shorter than an Ironman triathlon. Here’s the most interesting data:

The most obvious question here is: Is this correlation or causation? It’s certainly plausible — in fact, it’s probable — that the most serious runners who’ve trained best are also those who realize they should eat a lot of carbs. To address this, the researchers did a matched-pair analysis. There were 30 runners who consumed more than 7 g/kg of carbs. From the rest of the subjects, the researchers extracted another 30 runners pair-matched to the carb eaters so that there was no statistical difference in age, BMI, training data, and marathon experience between those two groups of 30.

In the graph above, the open squares are the carb eaters, and the open circles are the matched group that ate fewer carbs. The finding remains the same: the runners who ate fewer carbs ran slower — and perhaps more importantly, their speed declined more sharply during the race, particularly between 35 and 40K.

Non-randomized observational studies like this need to be treated with caution, needless to say. This isn’t “proof” that eating carbohydrates the day before the race makes you faster. But it certainly fits with our current understanding of endurance physiology, and it offers a tangible target for midpack marathoners: 7 grams of carbohydrate per kilogram of bodyweight (a number that conveniently agrees with studies that have found that a single day at 10 g/kg is enough to fully max out your glycogen stores).

Salt intake, and why taste is like a dog whistle

December 21st, 2011

I was reading a profile of British historian Lucy Worsley in the New Yorker last night, in which the writer (Lauren Collins) takes part in the authentic re-enactment of the meal eaten by King George on February 6, 1789:

THEIR MAJESTIES DINNER

Soupe barley

4 chickens roasted

3 pullets minced and broiled

7 3/4 mutton collop pyes

6 perch boiled

2 breasts of lamb a la pluck

2 salmic of ducks

13 loin veal smort

(And a partridge in a pear tree, presumably.) The article is both fascinating and funny, but the culinary payoff after an enormous amount of work ends up being a bit anticlimactic:

If every age has its sounds and smells, it also has its flavors. The taste of 1789 can be a dog whistle to modern palates… “You’ve had your tongue burnt off by a Mexican chili, and you’ve been eating sugar cookies since you’ve been able to stand [says Marc Meltonville, co-head of the Historic Kitchens team;] if something’s subtle, sweetened with rose petals, how are you going to be able to taste it?”

This made me think of the long-running and bitter debate about the “right” amount of salt consumption, and how tastes are formed. Just this morning, the New York Times reported on a neat new study suggesting that the amount of salt you’re fed as an infant determines your taste for it in later life. But taste for salt is also somewhat plastic. When my wife and I started eating together, her taste for salt was dramatically higher than mine. Now, a few years later, our tastes have sort of met in the middle. She no longer adds as much salt to food as she used to; but when I visit my parents, I find that I now need to add salt to dishes that I loved for many years with no added salt.

And I still struggle to reconcile all this with the widespread message that we’re eating wayyy more salt now than we used to (and thus salt is responsible for the current epidemic of hypertension). As I wrote last year about a study by Harvard’s Walter Willett:

He and a colleague reviewed studies between 1957 and 2003 that measured sodium excretion in urine — a very accurate way of determining salt intake that gets around the difficulties in figuring out exactly how much salt is in your food. They found two main things: (a) sodium intake averaged about 3,700 mg per person per day, which is way higher than the upper recommended limit of 2,300; and (b) it essentially hasn’t changed in the half-century studied.

Interestingly, these results agree almost exactly with similar reviews of studies from 33 different countries: salt intake is high, and it hasn’t changed in recent memory.

And Henry VIII, according to Worsley in the New Yorker piece, ate 20 grams of salt each day!

Why the brain matters in obesity

November 25th, 2011

Those of you interested in nutrition may already be following the online debate between Gary Taubes and Stephan Guyenet — back in August, Guyenet critiqued Taubes’s carbohydrate-insulin hypothesis, and now Taubes is returning the favour by critiquing Guyenet’s food-reward hypothesis. I’m not going to get into the nitty-gritty of the debate here, except to say that I think it’s a mistake to frame this debate as an “either-or.” Despite Taubes’s insistence to the contrary, the two ideas can coexist — and even if they do, I suspect they still don’t add up to the “whole truth” about obesity. Here’s one reason why.

In one of his recent posts, Taubes makes the distinction between body-centred and brain-centred theories of obesity (or you can think of it as physiology vs. psychology, one of his commenters points out). Taubes believes obesity originates in the body:

In this paradigm, specific foods are fattening because they induce metabolic and hormonal responses in the body — in the periphery, as its known in the lingo — that in turn induce fat cells to accumulate fat. The brain has little say in the matter.

Leaving aside the precise mechanism, I largely agree with the idea that regulation of calories in and calories out isn’t under the conscious control of the brain. And I’m pretty sure Guyenet would agree too. But I’m not quite ready to conclude that the brain plays no role.

This is a figure from a study published in the Archives of Pediatrics & Adolescent Medicine in 2009, from researchers at Penn State (no wisecracks please). The text is freely available here. The study followed 1,061 children, who were tested at the age of 3 for self-control (the length of time they were able to refrain from playing with a fun toy after being asked not to) and then again at the age of 5 for delayed gratification (the classic Marshmallow Test, which I’ve written about before, except using M&Ms, animal crackers or pretzels: they could have a small amount anytime, or a larger amount if they waited 3.5 minutes). Then their BMI was tracked until their turned 12.

The results are pretty clear: doing well on either or both of the impulse-control tests predicts less weight gain nine years later. So the question is: how can a test that involves (not) playing with a toy when you’re 3 years old predict future weight gain, if the brain has no say in weight gain?

Let me be absolutely clear: I don’t think “better impulse control” will play any useful role in weight loss for the vast majority of people. Once you’re overweight, I suspect physiology totally swamps psychology in most cases. But if you’re looking for an overall understanding of the mechanisms of weight gain and loss — and if, like Taubes, you insist that the correctness of your theory means that all alternate ideas must be 100% incorrect — then I believe you can’t ignore the brain (and its interactions with the modern food/physical activity environment) completely.

The brain senses macronutrient RATIOs, not just amounts

November 24th, 2011

The classic syllogism of “nutritionism” goes something like this:

  1. Eating food A makes people healthy.
  2. Food A contains nutrient X.
  3. Therefore we should isolate nutrient X, manufacture it in powder form, and ingest it large quantities to become healthy.

This seems pretty logical, and I certainly wouldn’t have questioned this basic mode of thinking a decade ago. And of course the approach has had many successes — taking vitamin C really does ward off scurvy if, for whatever reason, you’re subsisting on a diet devoid of vitamin C. But when we shift from “correcting deficiencies” to “enhancing health,” the approach seems to sputter, as people like Michael Pollan have argued.

The question, from my perspective, is: Why? Why do so many studies find that taking an isolated nutrient fails to reproduce the benefits observed from ingesting that nutrient in the context of a whole food (or, perhaps even more importantly, a whole meal or whole dietary pattern)? There are obviously many factors, such as the rate at which the nutrients are absorbed, and synergies between different nutrients in the food (a possible explanation for why nitrites are “good” when they from spinach and beets but “evil” in the context of fatty hot dogs).

A new study published last week in Neuron (press release here, abstract here) offers another clue. The study looked at the activation of “orexin/hypocretin” neurons in the hypothalamus, which “regulate energy balance, wakefulness, and reward.” It has long been known that glucose levels in the brain reduce the activation of these neurons. Researchers at the University of Cambridge tested how they responded to protein and fat, and found that certain amino acids increase the activation of the neurons, while fatty acids have no effect.

Okay, so the brain responds to macronutrient levels in the body. Cool. Carbs turn this particular neural signal up, and protein turns it down. And if you eat both protein and carbs at the same time, you’d expect that the net result will be the sum of the two signals. But that’s not what the researchers found. The combined protein-and-carb signal was a nonlinear combination of the two individual signals — meaning that these neurons were, in effect, responding to the protein-to-carb ratio rather than amounts. As the researchers put it:

In summary, our data show that the activity in the orx/hcrt system is regulated by macronutrient balance, rather than simply by the caloric content of the diet.

The bottom line: if you try to understand how this particular aspect of human physiology works by breaking food down into its constituent nutrients and testing them one by one, you’re doomed to failure because its response to individual nutrients is different from its response to combinations of nutrients. Which leads to a corollary: if you try to create a healthy diet by assembling a collection of pills and powders, you’re almost certainly sacrificing some of the synergies present in real foods.

Asker Jeukendrup on Gatorade and Geb

November 10th, 2011

While I was in New York earlier this week, I had a chance to chat with Asker Jeukendrup, the new “global senior director” of the Gatorade Sports Science Institute. After Amby Burfoot’s wide-ranging interview with him in September, I was curious about what that would mean both for his research and for Gatorade — which, as I wrote about in a Globe article back in 2009, had seemed to be moving away from evidence-based science and toward marketing gimmicks like adding theanine to “improve focus.”

So, after our conversation, I’m now at liberty to reveal… well, nothing. Asker promises that the Gatorade formulas will change, possibly in the short term but certainly in the medium term as new research directions yield results. What those research directions are he wouldn’t reveal, but he emphasized a shift from hydration to the full spectrum of performance nutrition. Two key focuses: energy delivery and recovery. What does this mean? His previous work on “multiple transportable carbs” (which he made famous for PowerBar) showed that the bottleneck for athletes trying to get carbs to their muscles is getting the carbs across the intestinal wall. My totally uninformed guess is that he’s looking at novel ways (different types of carbs? different molecular structures? different ratios?) of getting carbs across that barrier more quickly.

One other interesting nugget. A few months ago, I blogged about a study that included an unverified claim that Haile Gebrselassie lost 10% of his body mass due to dehydration during his world record marathon run. Jeukendrup has worked extensively with Geb — and though that data is confidential, I pressed him a bit about this claim. He confirmed that the 10% figure was reasonable. Geb’s a very small guy who’s capable of working at an inhumanly high work rate for an extended period of time. The result: he generates a huge amount of heat, and thus sweats a lot, likely more than two litres an hour. It’s not practically possible to drink anywhere near this much at world-record marathon pace, so Geb loses a ton of weight.

So the obvious question is: does this rather severe level of fluid loss hurt Geb’s performance? Jeukendrup’s guess: no. The primary mechanism through which dehydration might hurt performance is through reduced blood volume forcing the heart to work harder. But you can compensate for reduced blood volume to some degree: for example, your veins (which return the oxygen-depleted blood to the heart) contract, effectively shortening the circulatory loop. Geb’s example doesn’t prove anything either way — obviously it’s possible that he’d be a 2:02 guy if he drank more. But it’s hard to argue with a world record, unless we have some compelling reason to think that dehydration held him back (and I can’t think of one).

,

Higher carb intake = faster Ironman finish

October 26th, 2011

Here’s a graph, from a recent paper on nutrition during long (marathon and longer) endurance competitions, that’s worth a close look:

What do you see? A bunch of dots scattered randomly? Look a bit more closely. The data shows total carb intake (in grams per hour) by racers in Ironman Hawaii (top) and Ironman Germany (bottom), plotted against finishing time. It comes from a Medicine & Science in Sports & Exercise paper by Asker Jeukendrup’s group (with several collaborators, including Canadian Sport Centre physiologist Trent Stellingwerff) that looked at “in the field” nutritional intake and gastrointestinal problems in marathons, Ironman and half-Ironman triathlons, and long cycling races. The basic conclusion:

High CHO [carbohydrate] intake during exercise was related to increased scores for nausea and flatulence, but also to better performance during IM races.

So basically, taking lots of carbs may upset your stomach, but helps you perform better. It’s important to remember that gastrointestinal tolerance is trainable, so it’s worth putting up with some discomfort to gradually raise the threshold of what you’re able to tolerate.

Anyway, back to that graph: while it may look pretty random, statistical analysis shows a crystal-clear link between higher carb intake rates and faster race times, albeit with significant individual variation. Obviously there are some important caveats — it may be, for example, that faster athletes tend to be more knowledgeable about the benefits of carbs, and thus take more. Still, it’s real world data that tells us the people at the front of the race tend to have a higher carb intake rate.

One other point worth noting. The traditional thinking was that humans generally couldn’t process more than 60 grams of carb per hour. Over the last few years, thanks to multiple-carb blends, that threshold has been pushed up to 90 grams of carb per hour. In this data set, about 50% of the triathletes were taking 90 g/hr or more.

[UPDATE 10/26: Given all the comments below about the variability in the data, I think it's worth emphasizing what should be a fairly obvious point. The only way this data would come out as a nice straight line is if Ironman finishing time depended ONLY on carb intake, and was totally independent of training, experience, talent, gender, body size, and innumerable other factors. This is obviously not the case, so we should expect the data to be very broadly scattered. What the statistical analysis shows is that, with p<0.001, faster finishers tended to have consumed carbs at a higher rate. There are many ways to interpret this data; one possibility is that, if your carb consumption is below average, you might wish to try a higher rate of consumption (e.g. 90 g/hr) to see if it helps.]

,