Jeopardy whiz Ken Jennings’ new book Because I Said So!: The Truth Behind the Myths, Tales, and Warnings Every Generation Passes Down to Its Kids dispels a lot of the parent myths we all heard when we were kids.
As early as 1961, pediatricians were doubting this old wives’ tale, but it’s hung on stubbornly. It is true that when we eat, our body diverts blood to the stomach to aid in digestion, but, as you may have noticed after every meal you ever ate in your life, that doesn’t immediately immobilize your arms and legs. Any kind of exercise after a big meal can be uncomfortable, so I wouldn’t recommend swimming the English Channel right after Thanksgiving dinner. But there’s nothing magically fatal about the combination of food and chlorinated water. If you’re swimming after lunch and start to feel a stitch, or bloated, or crampy, just hop out of the pool. Not one water death has ever been attributed to post-meal cramping, and the American Red Cross doesn’t include any food warnings in its lengthy swimming-safety guidelines. In fact, long-distance swimmers are routinely fed in the middle of long races, to make sure they stay nourished and hydrated.
So I don’t want to downplay the danger of nails: yes, puncture wounds can lead to tetanus, so kids should be vaccinated and adults should get their booster shot every ten years like they’re supposed to. But the famous rusty nail is a red herring. Rust, of course, is just harmless iron oxide and doesn’t cause infectious disease. Tetanus is spread by a hardy little bug called Clostridium tetani, which survives outside the body in the form of hardy little spores, much like anthrax. These spores are everywhere, so any kind of wound, from a deep scratch to an animal bite, can potentially transmit tetanus. There’s nothing magical about the rusty nail, except that rusty nails are often dirty, and dirt can be full of tetanus spores. Hyping the rusty nail is dangerous: it may give parents a false sense of security when their little darling gets poked with something rust-free that may nonetheless be contaminated with tetanus. The good news is that tetanus is now very rare (except in the developing world, where its neonatal form is still a serious problem). There are fewer than a hundred U.S. cases every year, mostly involving people who let their shots lapse, and only one in ten turns fatal. I’d guess that the Rusty Nail cocktail (Drambuie and Scotch!) probably kills more people every year than actual rusty nails do.
The army’s findings come from experiments it performed in the 1950s by sending soldiers out into subzero temps wearing arctic survival suits. . . . and no hats. Under those conditions, shockingly, lots of body heat was lost through the head! But, as a University of Louisville hypothermia expert named Daniel Sessler explained to The New York Times in 2004, you’d get the same results by leaving any body part uncovered. Our faces and necks are five times as sensitive to temperature changes as the rest of our bodies, so our heads may feel particularly vulnerable to cold on a winter’s day, but you’d lose just as much heat by putting on a hat but leaving, say, an arm or a leg uncovered. Dr. Sessler estimates that if the army were to retry their field test with their subjects wearing only swimsuits, only 10 percent of body heat would be lost through the head, and a 2006 University of Manitoba study found similar results. If your head is cold, sure, put on a hat, but it’s not a magical cure-all. If your hands are cold, wear gloves; if your feet are cold, try socks or slippers.
The most recent review of the relevant research was published by Eleni Mourtzoukou and Matthew Falagas of the Alfa Institute of Biomedical Sciences in Athens. They point to experimental evidence like that from Ronald Eccles at Cardiff University, who found that subjects given a chill by dipping their feet in cold water for twenty minutes were more than twice as likely to catch cold within the week compared to the control group. Several mechanisms have been proposed to explain the body’s potential vulnerability to colds when things get chilly, but there’s evidence in hypothermia cases that cold can both decrease and slow down the infection-fighting white blood cells circulating throughout your body. Cold can also cause vasoconstriction (narrowing of blood vessels) in your nose, where rhinovirus hangs out. This makes the hair-shaped cilia in your respiratory tract less effective at filtering out bugs.
The pioneer in this field was Jillian Clarke, a high school intern at the University of Illinois who spent part of 2003 dropping Gummi Bears and fudge-stripe cookies onto E. coli– treated floor tiles. Microbes contaminated the food immediately, not after some magical five-second window. (This is what you’d expect: landing on the germs is what does the trick, not sitting around waiting for more to drift by.) Clarke won an Ig Nobel Prize for her groundbreaking work, and a team that followed up at Clemson University found similar results. In one of their tests, a piece of bologna dropped on germy tile managed to gather 99 percent of the bacteria in the first five seconds!… Bottom line: most food can be retrieved from the floor after one second or one minute and you’d be just fine. But if there was something gross on the floor, the dropped food was equally gross before and after the five-second cutoff.
In 2011, anthropologists at North Carolina State published new evidence linking weight and bone size. By measuring 121 different femurs (yes, this is what might happen when you donate your body to science) they learned that overweight people do indeed have wider bones, because of differences in the amount of weight their skeletons have to carry as well as the different walking motions they tend to use. In other words, being big-boned doesn’t make you fat, but being fat might eventually make you big-boned.
…there’s a broad scientific consensus that there are specific and unique benefits to eating breakfast. Most studies on breakfast and weight gain, for example, have found that breakfast-skippers are, counterintuitively, fatter than breakfast-eaters, perhaps because skipping a morning meal leads to less appetite control and bad dietary choices later in the day. A 2011 University of Minnesota study found a possible mechanism for this: their breakfast-eating subjects had healthier glucose levels as long as five hours later, which would reduce their risk of obesity and diabetes. The health benefits of breakfast, particularly in children, aren’t limited to body mass index. The blood-sugar-regulating effects of breakfast have also been shown to reduce the risk of diabetes and heart disease. And multiple investigations of students all over the world, from Japanese medical students to American middle schoolers, have found an increase in daytime fatigue in the breakfast-skippers, leading to lower cognitive function. A 2002 study of underperforming kids in inner-city Boston public schools found that introducing a free school-breakfast program boosted math scores, behavior marks, and attendance.
A 2006 study at an Aberdeen, Scotland, hospital would go even farther than that. Doctors there took MRI images of healthy patients in three different sitting positions: hunched over, sitting up straight, and leaning back a full 45 degrees. The upright posture actually caused the most spinal disc movement, which leads to strain on the back… In a classroom setting, the best advice is probably for kids to sit at whatever angle of recline keeps the back feeling relaxed and supported, to take breaks for standing and walking as much as possible, and never to sit hunched forward.
This myth has been disproved by research as far back as 1923, when Mildred Trotter, at Washington University in Saint Louis, had three female subjects shave their body hair at different intervals for eight months. In 1928, Trotter repeated the experiment on the faces of four men, and both experiments had the same result: “Microscopic examination revealed that there was absolutely no increase in the diameter or color of the hairs before or after the shaving period.”
If your mouth microbes can turn any carbohydrate into acid, is there anything special about sugar? The answer is no. Bread, rice, many fruits and vegetables— all are starchy enough to keep the bacteria on your teeth drilling cavities for hours. You could eat a strict no-sugar diet, and if you didn’t brush and floss regularly, you’d still have the mouth of a Dickensian orphan. I suppose it’s plausible that sugars would be worse than other carbs because they’re stickier, but it turns out that’s not true either. In the 1990s, a New York University dental researcher named Harold Linke conducted a series of tests on the staying power of different kinds of dental plaque, and cooked starches were much worse than sugars. Your saliva is pretty good at washing away the remnants of a candy bar but not so hot when it comes to potato chips ground into molars.
In 2002, a Dartmouth physiology professor and kidney specialist named Heinz Valtin studied the myth for the American Journal of Physiology and concluded that the “rule” wasn’t just a lie, it was an accident. In 1945, the Food and Nutrition Board of the National Research Council recommended “one milliliter of water for each calorie of food” eaten. A nineteen-hundred-calorie diet would indeed work out to about sixty-four ounces of water a day. But, in typical American short-attention-span fashion, everyone appears to have forgotten the very next sentence: “Most of this quantity is contained in prepared foods.” That’s right, Mrs. Brown: most of our water gets to us in nonwater form. In fact, a National Institutes of Health doctor told the Los Angeles Times in 2000 that a healthy adult in a temperate climate could probably replace his body’s daily water loss on food alone, without a single glass of water! Dr. Valtin says that, unless you have kidney stones or a urinary tract infection or something, you should probably worry more about drinking too much water than not enough. …So what is the right amount of water to drink? Whatever your body tells you to, by this weird mechanism called “being thirsty.” You start to feel thirsty when the concentration of your blood goes up less than 2 percent, and that’s plenty of warning since dehydration doesn’t start until you hit 5 percent or so. Don’t count glasses, don’t fixate on urine color. Just go get a drink when you feel thirsty. And it doesn’t have to be water: a 2000 study by the Center for Human Nutrition found that even supposedly “diuretic” beverages like coffee, tea, and caffeinated soda provide almost all of the hydration that water does.
Dozens of recent studies, however, have soured doctors on the possible linkage. Sugar doesn’t really wind kids up, they now believe— it’s just that many of the occasions on which kids eat lots of sugar, like birthday parties and holidays, tend to be chaotic anyway. A revealing 1994 experiment by Daniel Hoover and Richard Milich put the blame for this myth squarely on the parents’ shoulders: they showed that moms and dads were much more likely to classify their kids’ behavior as hyper when told that the kids had just gotten buzzed on sugar. (In reality, all the kids in the study were drinking a sugar-free placebo.)
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