Are Carbs the Culprit?

New evidence from a sweeping study of diet choices reinforces the old adage, “Everything in moderation.”

The research article, published in The Lancet Public Health journal, followed more than 15,000 U.S. adults for 25 years to determine how carbohydrate intake affects health and mortality. In addition, the authors conducted a meta-analysis that included data from an additional seven large studies–a total of more than 430,000 people from across the globe–to determine how the most recent study results fit into the evidence we already have about carbohydrates and health.

Both the study and meta-analysis drew a simple conclusion: Eating a moderate amount of carbohydrates is best for your health.

Before we go any further, it is important to note that nutrition research is fraught with difficulty. It’s typically not possible to do randomized-controlled trials–assigning people randomly to different diets for long periods of time–and that affects the quality of the research. Instead, nutrition studies use surveys to ask people what they have eaten, but it can be difficult to get specific answers or guarantee that people are filling them out correctly. (For example, did a participant have chocolate-flavored yogurt loaded with sugar or plain yogurt for breakfast?) That said, this recent study contains some sound evidence.

The research article used data from Atherosclerosis Risk in Communities, an ongoing observational study of disease across four communities in the U.S. Participants, who were recruited in the late 1980s, filled out questionnaires about their diets and then underwent physical examinations a total of six times between 1987 and 2017.

Research found that participants who consumed diets low in carbohydrates–meaning carbohydrates made up less than 40 percent of their total caloric intake–were more likely to die earlier. In addition, participants who consumed diets high in carbohydrates–more than 70 percent of their total calories–were more likely to die earlier.

While those are some clear findings, there is more to the story. Researchers also wanted to find out if the type of protein and fat in a low-carbohydrate diet made a difference in health outcomes. Their analysis revealed that eating more animal-based proteins and fats to replace carbohydrates–from sources such as beef, pork, chicken and cheese–is associated with shorter lifespans, whereas replacing carbohydrates with plant-based proteins and fats, such as those found in vegetables, nuts, peanut butter and whole-grain breads, leads to longer life spans.

One of the main messages is that extremes in a diet are “fraught with risk,” said Charles McCormick, an associate professor of nutrition at Cornell’s College of Human Ecology.

“I was struck by the magnitude of the effect in this study–far past the confidence limits at the extremes suggesting a strong effect,” he said. “The current evidence seems to support the idea of reducing processed meat and total red meat consumption reduces risk of mortality from heart disease. Moderate consumption of non-processed carbohydrates is most likely the best solution. That means lots of unprocessed vegetables. No one can provide any real evidence against that suggestion.”

The take-home message: Moderation is best, and focusing primarily on a plant-based diet can help you to live longer.

Please visit Cornell University’s Bronfenbrenner Center for Translational Research’s website for more information on our work solving human problems.

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