>"The catabolic effects of long-duration cardio may require more protein even than strength training, ironically."
That's not what the data suggests.
Elite Kenyan marathoner's diets are approximately 10% protein (or 75g per day), 75% carbohydrates and 15% fat. Corn is the primary energy source. Non-Kenyan runners who have adopted a similar diet have done so with excellent results.
It's not that protein is a primary fuel source for muscle, but that excessive long-duration cardio actively breaks down muscle tissue. I'm familiar mostly with empirical evidence: long-duration ocean rowers (60-180+ days of 8+ hours/day rowing) typically lose 30-40# of body mass, much of that lean tissue.
Elite Kenyan marathoners aren't particularly known for being heavily muscled. Elite sprinters, on the other hand, typically are.
I could dig for some more rigorous research, no time presently.
My original (and still current) point is that protein is an essential macronutrient and that in the interest of general fitness, people should consume it fairly constantly throughout the day, at roughly 0.5 - 1.25 g/lb body mass.
A champion Kenyan marathoner, say, Geoffrey Mutai, weighs roughly 53 kg (123 lb) at 182 cm (6 ft). If he's representative of the Kenyans consuming 75g of protein per day, he actually illustrates my points fairly well:
1. He's consuming 0.6g protein per pound body mass. Which is in the range I'd suggested for general health.
2. I'd suggested that athletes engaged in long-duration cardio should eat more protein, or suffer catabolic effects. Mr. Mutai exhibits the second part of that statement. While it's an absolutely horrid measure of anything resembling health, BMI gives us at least a scale to compare relative body mass to height ratios. Mutai's clocks in at 16.6, where "normal" is generally given as 18.5-25, and a bodybuilder, at 3-6% bodyfat, may clock in at 30-40. The argument here isn't fitness or appropriateness to task, it's to point out that our Kenyan here is at the very low end of the body mass-to-height scale, as a consequence of having both exceptionally low bodyfat, and very little muscle.
3. The unanswered question and unstated assertion is how this affects longevity and quality of live, and that we're discussing snacking habits, nutrition, and exercise in the context of general fitness in a general population that's not, as a rule, prone to trotting off for 26.21875 mile jaunts on a daily basis, though some may partake occasionally. Longevity of athletes is a mixed bag: American football players pretty notoriously die young (55 or so median). Finnish Olympians, according to one study, showed a few added years of longevity. The Stanford Runners Study (long-term longitudinal research) shows very consistent benefits of regular exercise, though I believe this is generally not inclusive of daily marathon-distance bouts. I'm not aware of the specifics of Mutai's training, but suspect much of it takes place at sub-marathon distances as well.
There's also the matter that extreme devotion to a single mode of exercise can lead to other problems. Long-distance cyclists, it turns out, suffer from both muscular and skeletal weaknesses due to the specifics of muscle stimulus, bone loading (or lack), and biochemical changes induced by hours spent on a bike. They're now encourage to strength train to make up for this, though it's another sport that rewards a light, wiry frame.
And finally, yes, if your goal is to be very, very good at winning marathons, you want to be tall, light, slow-twitch, very efficient at metabolizing glycogen, and very good at metabolizing fats (former for higher output, latter as lipid metabolism is generally rate-limited). In a fitness-for-goals perspective, Mr. Mutai is precisely where he needs to be.
For the average Joe or Jane, perhaps not so much.
These, and the sharp bit at the end, are my points.
That's not what the data suggests.
Elite Kenyan marathoner's diets are approximately 10% protein (or 75g per day), 75% carbohydrates and 15% fat. Corn is the primary energy source. Non-Kenyan runners who have adopted a similar diet have done so with excellent results.
http://jonathaninthedistance.blogspot.com/2008/06/nutrition-... http://www.letsrun.com/forum/flat_read.php?thread=1452065 http://dailyrunningtips.com/kenyan-runners/kenyan-runners-an... http://www.runaddicts.net/health-nutrition/secrets-from-the-...