Thursday, May 26, 2016
Busting the Top 10 Carb Myths
Busting the Top 10 Carb Myths
By Carrie Dennett, MPH, RDN, CD
Today's Dietitian speaks with nutrition professionals to distinguish truth from error.
There was a time when fat was the most-maligned macronutrient. Now, carbohydrates seem to be nutrition public enemy No. 1. From the Atkins diet and the South Beach Diet to Grain Brain and Wheat Belly, carbs are getting a bad rap. And while some carbs, such as fruits and vegetables, get a thumbs up from Paleo proponents, grains, dairy, and legumes are considered a no-no. Is this fear of carbs really warranted? According to nutrition research, the answer is a qualified no—the devil is in the details.
As dietitians know from Nutrition 101, carbohydrates come from plants, and many plant foods are rich in the vitamins, minerals, phytochemicals, and fiber that are vital to good health. Research shows that Mediterranean-style and other plant-based diets with high fiber content and low glycemic load have a beneficial effect on glucose metabolism, whereas dietary patterns high in meat are associated with an increased risk of type 2 diabetes.1
Although grains may be the most controversial carb, results of several studies suggest whole grains, but not refined grains, are protective against type 2 diabetes.2 The intact nutrients and fiber in whole grains, together with their lower glycemic index and glycemic load, may improve insulin sensitivity and glucose metabolism, while refined grains are lower in fiber and nutrients and have a higher glycemic index or glycemic load.2 This supports recommendations in the 2015–2020 Dietary Guidelines for Americans that at least one-half of all grain intake should come from whole grains.2,3 Glycemic index is a measure of how the carbohydrate in a specific food raises blood sugar; glycemic load is based on how much of that food's carbohydrate is eaten.
David Jenkins, MD, PhD, DSc, Canada research chair of nutrition and metabolism in the University of Toronto's department of nutritional sciences, and developer of the glycemic index,4 says that bread and pasta can be healthful carbohydrate sources if the pasta is cooked al dente and the bread is very dense, unsweetened, and packed with intact grains.
Cereal, or grain, fiber is associated with a reduced risk of type 2 diabetes and cardiovascular disease (CVD).2,5 Analysis of data from the Nurses' Health Study and the Health Professionals Follow-Up Study found that higher whole grain intake was associated with reduced mortality, especially deaths due to CVD.6 These results were independent of other demographic and lifestyle predictors of mortality, including overall dietary quality. Similarly, results from the prospective NIH-AARP Diet and Health Study, which followed 367,442 individuals for 14 years, found that intake of whole grains was associated with a lower risk of death from all causes.7 Furthermore, whole grains contribute to intestinal health and a healthy weight.
In spite of this research, carb-phobia, especially grain-phobia and fruit-phobia, persists. That's unfortunate, because fruits, whole grains, and many other carbohydrate-rich foods, including legumes and starchy vegetables, offer good nutrition as well as pleasure. Following are the top 10 myths that get in the way of many people consuming carbohydrates.
Myth 1: Only Breads and Grains Contain Carbs
One irony about carb-phobia is many people can't accurately define what it is they're afraid of. Mandy Unanski Enright, MS, RDN, RYT, owner of Nutrition Nuptials in Red Bank, New Jersey, says that when she asks clients what type of foods contain carbs, they always respond with bread, pasta, and rice. "So this takes some educating that most plant-based foods contain carbs to some extent, along with milk products. And all are important for a healthful diet."
"I don't think most people realize that fruits and vegetables are carbs," says Lainey Younkin, MS, RD, LDN, owner of Lainey Younkin Nutrition in Boston. "I always find it interesting and funny when someone wants to cut out carbs but wants to eat healthfully. I'm like, 'Do you know that fruits and vegetables are carbs?' When they think carbs, they're thinking about bread, pasta, and rice. So I always clarify between healthful carbs—ones that are high in fiber and low in sugar—and not-so-healthful carbs."
Myth 2: Carbs Are Fattening
Several studies have found that whole grain intake is associated with a reduced risk of weight gain,2,8,9 and similar associations have been observed between fruit intake and weight,8,10,11 provided that calorie needs aren't exceeded.12 But that's not what sells diet books.
"I have many clients who tell me that they don't eat carbs because they are 'fattening,'" says Lindsey Pine, MS, RDN, CSSD, CLT, Los Angeles-based owner of TastyBalanceNutrition.com. "However, when we discuss their food logs, there are carbs all over the place—bananas and other fruit, oatmeal, protein bars, etc. They think they aren't eating carbs when in fact they don't know what a carb is in the first place."
While many studies have found low-carb diets to be more effective for weight loss than low-fat diets in the short term, in longer-term follow-up both approaches produce modest weight loss at best.13,14 Kathy McManus, MS, RD, LDN, director of nutrition at Brigham and Women's Hospital in Boston and one of the investigators for the Preventing Overweight Using Novel Dietary Strategies (POUNDS LOST) study, says that calories matter more than macronutrient ratios. The POUNDS LOST study examined the effects of four heart-healthy diets varying in fat, protein, and carbohydrate composition on weight loss and long-term maintenance.15
"The POUNDS LOST trial showed that reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrient they emphasize," she says. "This means that we can individualize healthful meal patterns based on cultural and personal preferences to support weight loss. Individualized plans can help with sustaining long-term adherence."
David Ludwig, MD, PhD, a professor in the department of nutrition at Harvard T.H. Chan School of Public Health, director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital, and author of Always Hungry? Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently, says that while a low-fat diet high in processed carbohydrates can program the body for excessive weight gain, a diet with moderate amounts of minimally processed carbohydrates, along with healthful fats, does not.
Myth 3: All White Foods Are Unhealthful
"The most common comment I get is 'All white food is bad,' or 'My doctor told me to stay away from anything white,' or even better: 'Those white foods will kill you,'
I hear a lot from clients that they avoid 'white foods.' The one that always gets a bad rap is the poor potato, which is a great source of potassium, vitamin C, and some fiber if the skin is eaten."
One obvious flaw with the "no white foods" concept is that while white rice and white flour are refined and missing the fiber and nutrients found in their whole grain counterparts, many white foods are high in nutrients, including cauliflower, mushrooms, and the allium family (eg, garlic, onions, and leeks). As for potatoes, that depends. Ludwig says that the classic white, starchy russet potato has a glycemic load similar to that of white bread, so both can cause unhealthful elevations in blood sugar; other potatoes, including yellow-, red- and purple-skinned varieties, are "in a different category" because they have a moderate glycemic load.
Myth 4: Low-Carb Diets Are Healthier
Low-carb diets have been shown to improve some metabolic markers, including blood lipids and insulin sensitivity,16 but a 2013 meta-analysis suggests that they don't reduce the risk of CVD and overall mortality. In fact, carbohydrate restriction was linked with a 30% increased risk of mortality from all causes, and a slightly increased risk of cardiovascular events.17 Carbohydrate intake of only 15% below recommendations has been associated with reduced vascular health, independent of major CVD risk confounders, likely due to decreased intake of fiber, fruit, or root vegetables, and/or increased consumption of protein-dense products such as meat and dairy.18
Kelly Jones, MS, RD, CSSD, LDN, is an assistant professor of nutrition and exercise science at Bucks County Community College in Newtown, Pennsylvania, owner of EatRealLiveWell.com, and director of nutrition at Newtown Athletic Club, where she teaches a class called "The Truth About Carbs." "It is amazing how many people hear and think they should consume high-protein snacks/foods to fuel a workout," she says.
Ludwig agrees with the evidence suggesting that low-carb diets can produce favorable metabolic shifts in the short term,19 but feels that sticking to a low-carb diet for longer periods isn't necessary. "For most people, we can accomplish most of the benefits by targeting the highly processed carbohydrates and still enjoying the taste and diversity of natural carbohydrates."
Myth 5: Carbs Cause Inflammation
Some dietitians say the top reason clients avoid carbs is because they believe they are "bad for you," Enright says. "This of course leads to more probing of what exactly they mean by 'bad.' Usually it winds up referring to weight gain, but sometimes you hear claims about inflammation, or that they can cause diabetes."
Chronic inflammation is a concern because it may be an intermediary between obesity and cancer, CVD, and other chronic diseases.20 One reason that whole grains may reduce the risk of type 2 diabetes is by reducing inflammation.21,22 High intake of whole grains has been shown to reduce concentrations of inflammatory markers, including C-reactive protein and increase blood concentrations of adiponectin, a cytokine released by adipocytes (fat cells) that increases insulin sensitivity and reduces inflammation.2
In addition, laboratory research and human feeding trials both have found that whole grains and other whole plant foods, as well as their constituent parts, such as insoluble fiber, magnesium, and phytochemicals, consistently have beneficial effects on glucose metabolism, blood lipids, endothelial function, antioxidant activity, and inflammation.6
Myth 6: Avoid Fruit Due to High Sugar Content
Chere Bork, MS, RDN, owner of Savor Your Life Today (www.cherebork.com), says she sees many clients who are confused about fruit. "Many are just starting to realize that fruits are carbs, and they want to eliminate them now. I see some clients eating the produce aisle in their blender and others moderate because they're afraid to put more in."
Enright says she sees similar issues. "I have to educate that the sugars found in fruit are natural sources and are different from the sugars that are added to foods and beverages."
While it's true that the main source of calories in whole fruit is sugar, predominantly fructose, Ludwig says that those sugars are sequestered, surrounded by fiber, in the fruit's cellular structure. "You'd never get a surge of fructose that would take a hit on the liver or a surge of glucose that would cause a surge in insulin," he says. "It's the added sugars that cause a problem."
Gabriele Riccardi, MD, FAHA, a professor of endocrinology and metabolic diseases at Federico II University in Naples, Italy, says research has shown that increased consumption of fruit and berries is associated with a lower risk of type 2 diabetes. "This is particularly true for fruit that's fiber rich like apples, pears, kiwi, and strawberries," he says.
Jenkins also says a healthful, lower glycemic index diet can include temperate climate fruit like apples and oranges and all sorts of berries.
Myth 7: Sugar-Free = Carb-Free
Beth Lutton, RD, LDN, a dietitian at Mainline Medical Associates in Altoona, Pennsylvania, says she has patients who don't eat fruit or yogurt because they have a lot of sugar in them, yet they will eat pretzels or rice cakes in unlimited amounts.
Ludwig says that one of the big misconceptions about carbs, fostered in part by the old Food Guide Pyramid, is that all sugars are bad and all starches are good, because even highly processed starches were placed at the base of the pyramid, while sugars were at the top. "White bread raises insulin and glucose more than table sugar," he says. This misconception further highlights the fact that many clients don't fully understand what a carb is or how it behaves in the body.
Myth 8: All Carbs Are the Same No Matter Where They Come From
Clients also may not understand that quality counts. Jones says she often hears that people with diabetes, especially those with type 1, perceive all carbs as created equal, whether they come from soda, sugary cereal, or quinoa.
"I am often discussing with clients and families the differences between refined grains and whole grains," says Suzanne Farrell, MS, RD, owner of CherryCreekNutrition.com in Denver. "I also occasionally have clients unsure about various fruits and whether some are too high in sugar. There's also confusion about the potato and if it can be included or not in their plan."
not all carbs behave the same way in the body," and that many traditional carbohydrate-rich foods provide health benefits because they have a low glycemic index or low glycemic load and are rich in fiber and nutrients.
"Both quantity and quality of carbohydrate foods must be considered, but the latter is more important, adding that healthful carbohydrate foods including whole grains, legumes, most vegetables, fiber-rich fruits, pasta, and low-fat dairy can be consumed without major concerns, provided individuals stay within their calorie requirements.23 "Conversely, refined carbohydrate foods with a high glycemic index should be consumed in limited amounts since they're rapidly digested and induce a sharper postprandial rise in blood glucose; this is relevant for appetite regulation and the risk of developing type 2 diabetes,
Myth 9: All Simple Carbs Are Bad; All Complex Carbs Are Good
On the flip side, "All simple carbs are 'bad' and all complex are 'good,' while lactose and bananas are simple and white bread is actually a complex starch."
Just as a simple carb (sugar) may come packaged in an apple, a glass of milk, or a can of soda, complex carbohydrates (starch and fiber) also come in both whole and processed forms, and Ludwig points out that whole grain bread can be highly processed. "Whole kernel grains like buckwheat, quinoa, and wheat berries have much more nutrition and they digest more slowly."
Myth 10: The Glycemic Index Is All That Matters
The glycemic index has led many clients and patients to believe that it's better to eat a chocolate candy bar than a carrot or a slice of watermelon because the candy bar has a lower glycemic index value. However, experts say a food's glycemic index value shouldn't be used in isolation, but should be considered alongside the food's other qualities, such as calories, nutrients, and fiber, when considering the impact of diet on health. The glycemic load of the food—and the overall meal—may be more critical for supporting healthful blood sugar levels.24
Diets with a high glycemic load rapidly increase blood glucose and insulin levels, while diets with a low glycemic load moderate these responses, and evidence suggests that diets with a low glycemic load may be associated with lower levels of inflammation.24 While the glycemic load of the diet can be reduced by decreasing total carbohydrate intake, evidence suggests that restricting total carbohydrates may have adverse effects on health.18 Altering the quality of carbohydrate foods may be the smarter, more healthful move.25
One 2012 intervention study of 82 adults found that in diets with equal macronutrient compositions (including 55% from carbs), a diet with a low glycemic load resulted in lowered C-reactive protein and increased adiponectin in overweight and obese participants.26
Bearers of Truth
As nutrition experts, it falls to dietitians to be the voices of reason heard above the din. "Well-educated people are teaching their children to eat high protein and low carb because they truly think that it is a healthy diet," says Julie Satterfeal, MS, RDN, LD, owner of Triple Braided Nutrition and Wellness (www.triplebraided.com) in Huntsville, Alabama. "Fad diet proponents/promoters are doing a better job getting their false message out than we are as the nutrition professionals. I sure hope that we can turn this around."
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1. Alhazmi A, Stojanovski E, McEvoy M, Garg ML. The association between dietary patterns and type 2 diabetes: a systematic review and meta-analysis of cohort studies. J Hum Nutr Diet. 2013;27(3):251-260.
2. Aune D, Norat T, Romundstad P, Vatten LJ. Whole grain and refined grain consumption and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. Eur J Epidemiol. 2013;28(11):845-858.
3. United States Department of Agriculture. Scientific Report of the 2015 Dietary Guidelines Advisory Committee. http://www.health.gov/dietaryguidelines/2015-scientific-report/PDFs/Scientific-Report-of-the-2015-Dietary-Guidelines-Advisory-Committee.pdf. February 2015.
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