By Karen Ansel, M.S., R.D., "What We’ve Learned,"July/August 2012
The first widely read nutrition study was published in 1872 in the British Medical Journal. Back then, researchers produced nutrition studies slowly, publishing fewer than five (and sometimes just one) a year. Today it’s a completely different story. In 2011, more than 16,000 nutrition studies were released in peer-reviewed scientific journals. It’s no wonder our understanding of nutrition is always expanding and shifting. In the last 10 years, we’ve seen new perspectives emerge regarding everything from fat to food sensitivities. That’s why as EatingWell celebrates its 10th anniversary, we’re taking a moment to look back at the top 10 revelations of the past decade.
1. Our genes and diet are related
The completion of the Human Genome Project in 2003 provided a blueprint of our DNA and helped give rise to nutrigenomics, the science of how the nutrients we consume impact our genes. “We now know that certain cancers, cardiovascular disease and other chronic diseases that accompany aging can be prevented or delayed by matching our diets to our individual genomes,” says Patrick J. Stover, Ph.D., professor and director of the Division of Nutritional Sciences at Cornell. For instance, roughly 58 percent of people with high blood pressure are genetically salt-sensitive, so simply limiting the amount of salt they eat can lower their blood pressure. But before you go running to your doctor or dietitian for a genetically prescribed diet, know that “there are still many challenges in classifying people by their genotype and designing a food system that can provide an individualized prescriptive diet,” says Stover.
2. Not all fat is bad fat
At the end of the 20th century, “low fat” seemed to be the ubiquitous mantra of health professionals, government organizations and countless food products, but today, research suggests that trimming fat to less than 25 percent of our calories isn’t a great idea. “Cutting too much fat out of your diet can raise triglycerides and decrease healthy HDL cholesterol, which are both risk factors for heart disease,” says Penny Kris-Etherton, Ph.D., R.D., F.A.H.A., a distinguished professor of nutrition at Pennsylvania State University. “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. “Instead, aim for about 30 percent of calories from fat.”
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. What we call saturated fat is actually a mosaic of building blocks called saturated fatty acids, such as lauric, myristic, stearic and palmitic acids. Emerging research suggests that some of these 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.
3. A calorie isn’t just a calorie
You’ve heard it a million times: to stay weight-stable, calories in must equal calories out. 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.
4. Food sensitivities aren’t all in our head
Twenty years ago, if you told your doctor that eating foods like bread made you feel sick, he or she would likely have told you it was all in your head. Today we know roughly 1 percent of us suffer from celiac disease, an autoimmune reaction triggered by gluten in grains like wheat, barley and rye. And experts estimate that approximately 20 million Americans (6 percent) suffer from gluten sensitivity.
“We’re in the same place now with gluten sensitivity that we were with celiac disease 20 years ago,” says Alessio Fasano, M.D., director of the Center for Celiac Research at the University of Maryland School of Medicine. “Many of the symptoms of gluten sensitivity, such as abdominal bloating, difficulty concentrating and fatigue, are present in celiac disease. But by listening to patients, we’ve learned that many people who test negative for celiac disease still see their symptoms improve on a gluten-free diet. This led us to believe there was another condition, which we now call gluten sensitivity.”
5. We need more vitamin D than we thought
Thanks to our obsession with sunscreen, a short list of vitamin D-rich foods and hours spent indoors, three out of four Americans don’t get enough vitamin D. While we once thought vitamin D deficiency was only a problem for people living in northern latitudes, a 2010 Pediatrics study found that 56 percent of teens living in the sunny South were vitamin D-insufficient, meaning they didn’t soak up enough rays to produce the amount of D required for optimal health.
No wonder the Institute of Medicine (IOM) recently tripled its recommendation for the “sunshine vitamin” to 600 IU daily (800 if you’re over 71). The new quota is critical for strong bones, but many experts say you may need even more to lower risk of heart disease, type 2 diabetes, multiple sclerosis and many kinds of cancer (the upper limit is 4,000 IU). Moreover, it’s nearly impossible to get enough D from foods, especially when “vitamin D-fortified foods, such as milk and some orange juices, usually only have about 100 IU per serving,” says Michael F. Holick, Ph.D., M.D., director of the vitamin D, skin and bone laboratory at Boston University School of Medicine. The amount of vitamin D you make from sun exposure depends on several factors, such as the color of your skin, where you live and even how old you are. Because of that Holick recommends a three-pronged approach for everyone: eat D-rich foods (namely wild-caught salmon, which delivers more D than farmed salmon, UV-exposed mushrooms and fortified dairy and orange juice), get 10 to 15 minutes of sun on your arms and legs (and abdomen and back when possible) sans sunscreen three times a week during spring, summer and fall (when you can get enough UV rays to produce sufficient vitamin D) and take a supplement of 1,500 to 2,000 IU of vitamin D3 each day.
6. There’s one more reason to avoid BPA
The synthetic chemical bisphenol-A (BPA) has been used in the linings of metal food cans and in hard-plastic containers and bottles since the 1960s. It’s also found in everything from foodstorage 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.
7. How we get our nutrients matters
Even though more than half of all U.S. adults pop at least one dietary supplement a day, recent research reveals pills can’t match the disease-preventing power of food. “In their natural form, nutrients in food—like vitamins, minerals and phytochemicals—are present in specific, balanced concentrations and work together in a highly synergistic way,” says Manuel Villacorta, M.S., R.D., author of Eating Free (HCI Books, 2012). Consider avocados: they’re rich in heart-healthy fats as well as vitamin E, a nutrient that requires fat for absorption. While you could get vitamin E from a pill, you can’t absorb it without the fat that nature conveniently packaged in the avocado.
What’s more, some supplements taken in excess can be harmful. In the mid-1990s, a small body of research suggested that people whose diets were rich in vitamin E were less likely to develop heart disease. But a 2005 Journal of the American Medical Association study found that people who had vascular disease or diabetes and took 400 IU of supplemental vitamin E daily were 21 percent more likely to be hospitalized for heart failure. Similarly, studies show that smokers who take supplemental beta carotene are more likely to develop and die from lung cancer even though people who eat lots of beta-carotene-containing foods (carrots, watermelon) have a lower risk of cancer. The evidence is so strong that the IOM advises against beta-carotene supplements.
8. Dietary cholesterol isn’t so evil
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 American Heart Association (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.
9. We’re eating too much sugar
In the past 40 years, the amount of added sugars in our diets has skyrocketed. 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 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.
10. Our bodies don’t want us to lose weight for good
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 Villacorta. “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 <3m>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.” At least that’s news we like to hear.
Karen Ansel, M.S., R.D., is a spokesperson for the Academy of Nutrition and Dietetics and a regular contributor to EatingWell. Her third book, The Calendar Diet (Wagging Tail Press), came out in March.