Should Americans Get Half Their Calories From Carbs? Two Camps Battle It Out
As the U.S. government revises its dietary recommendations, opposing groups are fighting over the healthiness of carbohydrates A food fight over carbohydrates is shaping up for control of Americans’ plates.
Years after low-carb eating gained attention with the Atkins diet, the low-carb movement is trying to gain wider mainstream acceptance and a nod of government endorsement. The latest battleground is the U.S. government’s dietary guidelines, which are being revised for the first time in five years. Low-carb advocates believe the current guidelines—which recommend Americans get about half their calories from carbohydrates—are partly to blame for America’s high rates of obesity and Type 2 diabetes. Lining up against them are supporters of plant-based diets, among others, who argue that low-carb diets often include too much saturated fat from meat and dairy products and neglect important sources of nutrients like fruit, certain vegetables and whole grains.
During heated public hearings over the past 18 months, low-carb advocates pushed to include a low-carb diet option in the new dietary guidelines, which the government is expected to finalize in December. A federal advisory committee rejected that idea, saying evidence supporting that approach wasn’t conclusive. Now low-carb advocates have regrouped and are pushing the government to include a disclaimer with the final guidelines saying they are “only for healthy Americans”—marking them irrelevant for the majority of the country who are overweight or have diabetes or prediabetes.
For many such people, low-carb advocates say it’s unhealthy to follow the current guidelines and better to follow a low-carb approach. “About half of the country has either diabetes or prediabetes, 40% are obese, and if you include overweight Americans it’s about 70%,” says Mark Cucuzzella, director of an advocacy group called the Low-Carb Action Network and a professor and director of low-carb nutrition at the West Virginia University Center for Diabetes and Metabolic Health. “The people that are well, they really don’t need the government’s advice.”
The U.S. Department of Agriculture and the Department of Health and Human Services are currently reviewing recommendations from advisory committees on everything from carbohydrate levels to sugar intake to alcohol limits. The guidelines, which get updated every five years, have a broad impact. They help determine school lunch programs, shape state and local health promotion efforts, and influence what food companies make.
Seven percent of Americans report eating a low-carb diet this year, up from 5% in 2018, according to a survey conducted by the International Food Information Council, a nonprofit science communications and consumer research organization.
Low-carb advocates argue that the approach should be more widespread—and were vocal enough at hearings over the new dietary guidelines to get the federal advisory committee to review their case.
“This came out big at the first meeting that the public spoke,” says Carol Boushey, a registered dietitian and associate research professor in the epidemiology program at the University of Hawaii Cancer Center who chaired the dietary patterns subcommittee.
One of the leaders in the low-carb lobby is the Low-Carb Action Network, which describes itself as a coalition of doctors, academics, advocates and consumers of low-carb diets. They say they have more than 550 members, about 230 of whom are medical professionals, and that they don’t take money from industry. The group believes a low carb diet should be defined as one where carbohydrates make up 25% or less of daily calories.
They argue that reducing carbohydrates can help prevent and even reverse Type 2 diabetes, help people lose weight, and reduce the risk of heart disease. Carbohydrates raise the level of glucose in a person’s blood; the body produces insulin to reduce and regulate glucose levels. Low-carb advocates cite research suggesting that when blood sugar spikes too high too often, the resulting increases in insulin levels can make the body resistant to insulin and contribute to Type 2 diabetes and obesity. They also say carbohydrates increase the risk of heart disease by raising blood levels of triglycerides and small LDL particles, and high sugar intake increases blood pressure. There is some research on their side. An American Diabetes Association panel published a report last year that found sufficient evidence that a low and very low carbohydrate diet can be helpful in lowering blood sugar levels and even lowering medication use. The benefits were more pronounced for the very low carbohydrate diets. The ADA review defined low carbohydrate diets as having less than 45% of calories from carbs and a very low carbohydrate diet as less than 26%. Ronald M. Krauss, a professor of pediatrics and medicine at the University of California, San Francisco, says there is a growing body of evidence supporting low-carb diets to improve insulin resistance and cholesterol levels, which reduce the risk of heart disease and diabetes. Dr. Krauss is on the scientific advisory board of Virta Health, a company that provides very low-carbohydrate diet counseling for people with diabetes and has published data showing that prolonged treatment with a very low-carbohydrate diet reduces insulin resistance and a number of cardiovascular risk factors in Type 2 diabetes patients.
Low-carb diets are often higher in fat than higher-carb diets because people often eat more meat when they cut carbs. But the research on the cholesterol impact is mixed. William Yancy, a general internist and obesity medicine specialist at Duke University, says studies have shown that on average low-carbohydrate diets increase the levels of good HDL cholesterol and reduce triglyceride levels compared with low fat diets. Furthermore, levels of bad LDL cholesterol do not on average significantly increase in people losing weight on a low-carbohydrate diet.
“In head-to-head trials, low fat diets might be more effective for lowering LDL cholesterol but there are other advantages of low carb diets,” which are generally higher in fat, says Dr. Yancy, who has been studying low carb diets for nearly 20 years. “What happens is people aren’t as hungry if they eat a low carbohydrate eating pattern so they end up self-restricting spontaneously.”
Opponents of a low-carb approach say it’s important to distinguish between different types of carbohydrates. While highly processed carbs like white bread, sugar-laden packaged foods and sodas spike blood sugar quickly, other foods that contain carbohydrates like fruits, certain vegetables, whole grains and beans also contain fiber, which helps glucose release more steadily into the bloodstream. Those foods also contain beneficial nutrients and are low in cholesterol and unhealthy fats, like saturated and trans fats. “We think Americans already consume too few carbohydrates in the form of helpful carbohydrates,” says Susan Levin, director of nutrition education for the Physicians Committee for Responsible Medicine, an advocacy group that supports plant-based diets.
Shivam Joshi, a primary care and lifestyle medicine physician at NYU Langone Health and Bellevue Hospital in Manhattan, sees patients at Bellevue’s Plant-based Lifestyle Medicine Program. Started about two years ago, the program aims to help patients with chronic diseases get healthier with lifestyle changes, primarily following a plant-based diet consisting largely of whole, unprocessed plant foods.
“The demonization of healthy carbs is because of our inability to separate unhealthy carbs from healthy carbs,” says Dr. Joshi, who cites foods like whole grains and oats, quinoa, and bananas as healthy carbs. “People are now afraid to eat bananas because they think it will cause diabetes but a banana is very different from banana bread.” Some experts also say it’s difficult to tell whether the health benefits noted in low-carb research come from reducing carbohydrates or simply from reducing calories—people often consume fewer calories when they eat fewer carbs.
Alice H. Lichtenstein, director of the Cardiovascular Nutrition Laboratory and professor of nutrition at the Friedman School of Nutrition Science and Policy at Tufts University, says there’s no evidence that low-carb diets reduce the risk of heart disease and diabetes more than other types of weight-loss diets.
Dr. Lichtenstein was vice-chair of the 2015 dietary guidelines advisory committee that issued recommendations to the government five years ago. “We have two long-term studies that indicate the level of carbs alone has little effect in terms of weight loss or cardiometabolic risk factors,” she says.
This year’s dietary patterns subcommittee also found it difficult to draw conclusions. Jamy Ard, a member of the dietary patterns subcommittee and a professor in the department of epidemiology and prevention at Wake Forest School of Medicine, said the biggest challenge the subcommittee had was isolating the health impact of low-carb diets when they’re not being used for weight loss or cutting calories.
The low-carb camp is undaunted, firing off a letter earlier this month criticizing the subcommittee’s failure to endorse a low-carb diet option to the U.S. secretaries of agriculture and health and human services, where recommendations for the final guidelines are under review. Advocates requested that the final guidelines should “include a prominent statement that its recommendations are ‘Only for Healthy Americans’ so that those with diet-related chronic diseases will know that these Guidelines are not appropriate for them.” A USDA spokesperson says the dietary guidelines are “intended to be generalizable to the American population at large” and that it’s “beyond the scope of the dietary guidelines to be tailored to specific groups or treat specific diseases.” But organizations often build on the guidelines to tailor advice to particular needs and conditions, the spokesperson noted: “The dietary guidelines serve as one piece of America’s larger nutrition guidance landscape.”
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