By Brierley Wright, M.S., R.D., Nutrition Editor, EatingWell Magazine
More than 16,000 nutrition studies were published in peer-reviewed scientific journals in 2011. So it's no wonder our understanding of food and health is expanding and shifting. In fact, in the last 10 years, we've seen many new perspectives emerge (some former truths have now even become myths).
For EatingWell Magazine's July/August issue (our 10th anniversary!), we decided to look back some of the top nutrition revelations of the past decade, as reported by Karen Ansel, M.S., R.D.
1. True or False: A calorie is just a calorie.
False. You've heard it a million times: to stay weight-stable, calories in must equal calories out. (Find out how many calories you really should be eating here.) Now we're learning that may not always be the case. In a 2010 Food & Nutrition Research study, researchers asked volunteers to eat either a sandwich made from multigrain bread and Cheddar cheese or a white bread and processed cheese sandwich. When the researchers measured how much energy it took to digest and absorb each of the sandwiches, they found the volunteers used nearly twice as many calories to break down the multigrain sandwich. The reason: our bodies handle processed and unprocessed carbohydrates differently. "When you use a machine to strip away the bran, husk and fiber from carbohydrates, that machine is essentially expending energy that your body would normally use to break down those food components," says study co-author Jonathan Wright, Ph.D., a professor of biology at Pomona College.
2. True or False: Food is the only thing that influences weight gain.
False. Here's another reason to avoid the synthetic chemical bisphenol-A (BPA). Used in the linings of metal food cans and in hard-plastic containers and bottles since the 1960s, BPA is also found in everything from food-storage containers to recycled paper, the receipt the cashier hands you at the cash register--even dental fillings and sealants. And BPA will persist in our food supply: in March, the FDA rejected a petition from environmentalists to ban the chemical from food and drink packaging.
Science has linked BPA to early puberty, reproductive irregularities and cardiovascular and neurological damage. Now, a growing body of research suggests it may be making you heavier. In the late 1990s, studies revealed that BPA leads to developmental changes in the fat cells of unborn animals that cause those cells to multiply and soak up excess fat. Now experts say it's a problem for humans, too--a serious concern, since nearly 93 percent of us harbor BPA in our bodies. A 2008 Journal of the American Medical Association study found that people who were obese had 30 to 77 percent more BPA in their urine than normal-weight adults. Experts suspect that BPA promotes weight gain by stimulating the pancreas to rev up its production of insulin, leading to increased blood sugar levels and decreased insulin sensitivity.
"BPA doesn't just damage the development of one system: the more of it that's in your body the more prone you are to obesity, diabetes and heart disease," says Frederick Vom Saal, Ph.D., a professor of biological sciences at the University of Missouri. The good news is we don't store BPA in our bodies for long. Avoiding contact with it for just one week will flush it from your blood (it may still be stored in fat, and during pregnancy in the placenta or fetal tissue). While you may not be able to eliminate it entirely, try to buy fresh or frozen foods or foods in cans labeled BPA-free, store food in glass containers or plastic ones labeled BPA-free, and wash your hands after touching cash-register receipts and recycled paper.
3. True or False: Our bodies don't want us to lose weight for good.
True. If you've ever lost weight only to gain it back again, you'll be glad to know it might not necessarily be your willpower that's the problem. "Your body is constantly striving for equilibrium," says Manuel Villacorta, M.S., R.D., author of Eating Free (HCI Books, 2012). "When you do anything to disrupt that equilibrium, your body tries to tell you to eat more by altering production of hormones that control hunger."
Losing weight wreaks havoc on your hunger hormones in two ways: it triggers a decrease in hormones that suppress appetite, such as leptin and cholecystokinin, and boosts production of hormones that tell you to eat, namely ghrelin and neuropeptide Y. A 2011 New England Journal of Medicine study of 50 dieters found that, even a full year after losing weight, the volunteers' hunger hormones failed to return to pre-weight-loss levels.
The good news is you can eat to outsmart those hormones. "Skipping or delaying meals causes ghrelin, and your appetite, to increase," says Villacorta. "Eating every three to four hours will help control your appetite."
4. True or False: All fat is bad fat.
False. "Aim for about 30% of calories from fat," says Penny Kris-Etherton, Ph.D., R.D., F.A.H.A., a distinguished professor of nutrition at Pennsylvania State University. "Cutting too much fat out of your diet can raise triglycerides and decrease healthy HDL cholesterol, which are both risk factors for heart disease. When we replace fat with carbohydrates--refined carbohydrates in particular--our liver steps up its production of triglycerides."
Low-fat diets get a failing grade for weight loss too. "For many people, low fat really translates to high carb, which prompts a big glucose (and insulin) spike, causing blood sugar to then drop quickly, ultimately resulting in hunger," says Kris-Etherton.
The type of fat matters too. For optimal health, experts now recommend choosing mostly unsaturated fats (think: liquid vegetable oils, nuts, avocados) and limiting saturated fat because of its negative impact on cholesterol and heart health.
We're also learning that the villainization of saturated fats might not be so black and white. Emerging research suggests that some saturated fats may not be harmful. That's good news if you like dark chocolate, a food plentiful in stearic acid, which has little impact on cholesterol. Then there's lauric acid, the main fatty acid in coconut oil, which research suggests boosts beneficial HDL cholesterol (although it also raises unhealthful LDL). "Coconut oil is slightly less evil than other saturated-fat-rich foods like palm oil and shortening because of its impact on HDL," says Kris-Etherton. "But it still isn't good for you." Until more is known, stick with foods rich in heart-smart unsaturated fats, olive and canola oils, rather than scrutinizing the individual fatty acids in food.
5. True or False: Sugar is making us gain weight.
True. Today, the average American eats about 420 calories (28 teaspoons) a day--essentially a meal--from added sugars. That's a 12 percent increase from 25 teaspoons in 1970. All that sugar spells bad news for our waistlines. Although experts aren't sure of the exact mechanism, sugar has also been linked to an increased risk of diabetes, high blood pressure, metabolic syndrome and heart disease. No wonder leading health organizations, such as the American Heart Association (AHA), World Health Organization and USDA, have recently started urging us to slash the added sugar in our diets.
But if you think switching from white table sugar to a more natural sweetener, such as agave or honey, would be better for you, think again. Whether added sugars come in the form of white sugar, honey or high-fructose corn syrup, to our bodies they're exactly the same, supplying empty calories that provide little or no nutrition.
The big picture isn't the type of sugar we're eating, it's where we're getting it. "About 75 percent of all consumer packaged foods and beverages contain added sugars," says Barry Popkin, Ph.D., a distinguished professor of nutrition at the University of North Carolina. "But the major shift is the increase in sugar in beverages rather than foods." Over 35 percent of the added sugar in our diets comes from soda, sweetened drinks and sports drinks. The easiest way to trim your added-sugars intake is to banish all sweetened drinks.
6. True or False: You should avoid foods that are high in dietary cholesterol.
False. Years ago, if you had a cholesterol problem you were under strict orders to avoid cholesterol-rich foods like eggs and shrimp. Today, we know these foods are fine to eat in moderation. The truth is our bodies need some cholesterol to make hormones, vitamin D, bile acids (compounds that help us digest fat) and the membranes that line our cells.
While some of the cholesterol in your bloodstream comes from the food you eat, your liver manufactures anywhere from two-and-a-half to five times that amount every day. When your liver senses incoming cholesterol from food, it simply produces less. What really trips it up is saturated fat from foods like cheese, butter and fatty cuts of red meat. When bombarded with too much saturated fat, our bodies respond by clearing less "bad" LDL cholesterol from our bloodstreams (the same thing happens if you're genetically predisposed to high cholesterol). That means limiting saturated fat is far more important than axing all cholesterol from your diet. Keep your numbers in check by eating 7 percent or less of your calories from saturated fat (that's 16 grams for a 2,000-calorie diet). And the AHA recommends limiting cholesterol from foods to 300 milligrams a day (that's one and a half large eggs or, if you can believe it, 34 medium shrimp). If you have--or are at risk for--heart disease, cap cholesterol at 200 milligrams.
What food myth do you want to know the truth about?
By Brierley Wright, M.S., R.D.
Brierley's interest in nutrition and food come together in her position as nutrition editor at EatingWell. Brierley holds a master's degree in Nutrition Communication from the Friedman School of Nutrition Science and Policy at Tufts University. A Registered Dietitian, she completed her undergraduate degree at the University of Vermont.
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