Danger of Low Carb Diets:
Wurtman, director of the Program in Women's Health at the MIT Clinical Research Center, and colleagues have found that when you stop eating carbohydrates, your brain stops regulating serotonin, a chemical that elevates mood and suppresses appetite. And only carbohydrate consumption naturally stimulates production of serotonin.
"When serotonin is made and becomes active in your brain, its effect on your appetite is to make you feel full before your stomach is stuffed and stretched," said Wurtman. "Serotonin is crucial not only to control your appetite and stop you from overeating; it's essential to keep your moods regulated."
Antidepressant medications are designed to make serotonin more active in the brain and extend that activity for longer periods of time to assist in regulating moods. Carbohydrates raise serotonin levels naturally and act like a natural tranquilizer.
Wurtman's husband, Richard Wurtman, the Cecil H. Green Distinguished Professor at MIT and the director of the Clinical Research Center, along with former graduate student John Fernstrom, discovered that the brain makes serotonin only after a person consumes sweet or starchy carbohydrates. But the kicker is that these carbohydrates must be eaten in combination with very little or no protein, the Wurtmans' combined research determined.
So a meal like pasta or a snack of graham crackers will allow the brain to make serotonin, but eating chicken and potatoes or snacking on beef jerky will actually prevent serotonin from being made. This can explain why people may still feel hungry even after they have eaten a 20-ounce steak. Their stomachs are full but their brains may not be making enough serotonin to shut off their appetites.
And what do protein dieters (especially women) miss most after the second week? Carbohydrates. Women have much less serotonin in their brains than men, so a serotonin-depleting diet will make women feel irritable.
"There are people we call carbohydrate cravers who need to eat a certain amount of carbohydrates to keep their moods steady," said, Wurtman, co-founder of Adara, a weight-management company whose programs are based on her research. "Carbohydrate cravers experience a change in their mood, usually in the late afternoon or mid-evening. And with this mood change comes a yearning to eat something sweet or starchy."
Thus, it's not just a matter of will power or mind over matter; the brain is in control and sends out signals to eat carbohydrates. According to Wurtman's clinical studies, if the carbohydrate craver eats protein instead, he or she will become grumpy, irritable or restless. Furthermore, filling up on fatty foods like bacon or cheese makes you tired, lethargic and apathetic. Eating a lot of fat, she said, will make you an emotional zombie.
"When you take away the carbohydrates, it's like taking away water from someone hiking in the desert," Wurtman said. "If fat is the only alternative for a no- or low-carb dieter to consume to satiate the cravings, it's like giving a beer to the parched hiker to relieve the thirst -- temporary relief, but ultimately not effective."
By GINA KOLATA May 6, 2003
Every athlete, every fitness enthusiast has heard the advice to drink plenty of water. Drink as much as you can. Don't wait until you are thirsty. By then it may be too late. You may be seriously dehydrated, risking dizziness, collapse, even death. "Stay ahead of your thirst," athletes and would-be athletes are told.
But now USA Track & Field, the national governing body for track and field, long-distance running and race walking, says that advice is wrong. In what it calls a major revision of its guidelines, the organization says endurance athletes, who may be consuming huge amounts of water over the course of a long event, may risk seizures, respiratory failure and even death from drinking too much.
Instead of drinking as much as they can, the new guidelines say, runners should drink when they are thirsty. People in long races like marathons may want to weigh themselves before and after long practice runs to see how much they lose from sweating and drink that amount when they race, and no more.
Dr. David E. Martin, an exercise physiologist at Georgia State University in Atlanta, called the change revolutionary and overdue. He is a co-author of a new advisory statement on fluid replacement in marathons written for the International Marathon Medical Directors Association. It was a supporting statement for the track and field advisory.
Dr. Martin said the old advice was leading to water gorging, with people stopping at every water stop, downing water cups and so diluting their blood that their sodium levels plummeted, a condition known as hyponatremia.
The problem occurs in any endurance event that gives people the time to drink and drink and drink. It emerges among people who hike the Grand Canyon, in those who compete in Ironman Triathlons and, most notably, in marathons.
Hyponatremia is not a problem for elite marathon runners, Dr. Martin said, because they go too fast to drink too much. "Running at a five-minutes-per-mile pace," he said, "there's no way you can drink enough to get hyponatremia."
Those runners, he added, have their own water stations, the elite water stops, where they have their own sports drinks that they have chosen in advance.
Instead, Dr. Martin said, the problem is with slower runners, who may take as long as nine hours to run a race. They may be running with groups of friends, raising money for a favorite charity. Or they may be tourist runners, people who plan vacations around marathons.
"We're worried about this increasingly large group of people, taking courses in how to run a marathon, going to shoe shops to learn how to run," Dr. Martin said. "What has been told to them is the party line. Make sure you drink. You can't drink too much. Carry water with you or you will get dehydrated. Don't worry about heat, just drink more. That's wrong. It's wrong, wrong, wrong."
What about the risks of dehydration, leading to heatstroke as the body temperature soars? Grossly exaggerated, medical experts say. Most athletes who collapse at the finish line suffer from postural hypotension, a drop in blood pressure when blood pools in the legs, and not from heatstroke.
Examining information on illnesses in marathons since 1985, Dr. Martin and Dr. Tim Noakes of the University in Cape Town in South Afri ca, write in the advisory statement, "It has been difficult to find any studies in which dehydration has been identified as the sole important causative factor in even a single case of exercise-related heatstroke."
But they reported that they found 70 cases of severe hyponatremia.
Many start the race overhydrated, having fallen for what Dr. Heinz Valtin, a physiologist at Dartmouth Medical College, deems a medical myth: that dehydration is always lurking and must be fended off with more or less constant sipping of water.
In a paper published in November in The American Journal of Physiology, he said he could find no scientific support for the common advice for healthy adults to drink at least eight glasses of water a day and that the benefits that have been claimed - weight loss, relief of constipation, less fatigue, increased alertness and so on - have no foundation in rigorous studies. "In my opinion, the vast majority of healthy people do not need that much water," he said.
Dr. Martin agreed, saying: "People have been carrying bottles of water with them. Some people actually get water intoxication syndrome. They feel lethargic from drinking too much. I worry about the sanity of those people."
By Lennard Zinn
This report filed December 24, 2002
Dear Lennard Zinn;
Here is why I ask: I always thought that if you were riding by yourself, then you had to work harder than if somebody was drafting behind you because as you move through the air, it flows past your bike and body and creates turbulence as it swirls around in the void of space behind you. This almost creates a suction behind you pulling you back against your forward progress (if my logic is correct). However, if somebody pulls in behind you to draft, they fill this void of space behind you, the movement of air flows past you and then continues to flow past the second person, resulting in less turbulence and swirling air behind you. Thus, if this is right, like for some reason I've always believed it to be, then you can t stays the same? Would the answer change if you were going up an incline at 20mph? What if there was a 5mph headwind?
Thanks for your time. I hope you find this to be an interesting and challenging question and I look forward to seeing your answer. I think this is a particularly good question for triathletes. At a recent sprint distance race, I heard a friend claim, "some guy drafted off me for almost the entire 10 mile bike."
Based on your answer, this either benefited my friend and boosted his
average speed, or it made him work harder and left him more tired for
the run. Thanks again.
Answer from aerodynamics professor and Project 96 and 1984 U.S. Olympic
Team bike designer, Dr. Chester Kyle:
The next in line needs about 71 percent of the lead rider's power, and
the third and fourth riders about 65 percent. See "Racing cyclist
power requirements in the 4000-m individual and team pursuits", Medicine
and Science in Sports and Exercise, v31, no.11, pp 1677-1685, 1999. J.P.
Broker, C.R. Kyle and E.R. Burke.
Answer from aerodynamics guru and advisor to the U.S. Postal team, John