A week after the federal government released its latest recommendations for healthful eating, the 2015-20 Dietary Guidelines have touched off a food fight.
Acknowledging that the "scientific integrity" of the drafting process has been called into question, Congress has asked the National Academies of Science to review "whether balanced nutrition information is reaching the public," and set aside $1 million for the effort.
Meanwhile, nutritionists, public health specialists and experts in preventive health are vying to critique the government document, fill in its gaps and "spin" the guidelines to support their interests.
Steven Nissen, perhaps the nation's most influential cardiologist, took aim Monday at the new Dietary Guidelines for sowing public confusion and for lacking the support of rigorous scientific evidence.
Writing in the Annals of Internal Medicine, Nissen scolded the drafters of the guidelines for lifting the longstanding advice on consuming foods high in cholesterol but also suggesting Americans "should eat as little dietary cholesterol as possible."
"Which version should we believe? How can the same committee arrive at diametrically opposite conclusions?" he wrote.
Nissen also faulted the guidelines' recommendation for Americans to limit their intake of saturated fat, writing "the best available evidence does not clearly support the widely held belief that Americans should limit saturated fat" in their diets.
The problem, Nissen suggested, is lousy science undergirding good advice on nutrition. He called on the federal government to conduct and underwrite the cost of rigorous clinical trials to determine, for instance, whether saturated fat intake affects such health outcomes as cardiovascular disease.
"Properly performed studies may demonstrate that saturated fat and cholesterol are indeed nutrients of concern, but the opposite conclusion is also possible," Nissen wrote. "It is time to transition from the current evidence-free zone to an era where dietary recommendations are based on the same quality evidence that we demand in other fields of medicine."
In an interview, Nissen said the government should stop making dietary recommendations until it has its scientific act together.
"I believe it is better to say nothing than to give advice that's wrong," Nissen said. "And I think there's a very good chance that much of the Dietary Guidelines' advice is wrong."
Nutrition scientists fired back at Nissen, saying the guidelines were tainted by politics, not hampered by poor science. They charge that by suggesting there's no solid evidence to support good dietary advice, Nissen has strengthened the hands of commercial and political interests who would prefer to let Americans' penchant for poor dietary choices go unchecked.
"It's just going to be another argument that these guys don't know what they're talking about," said Dr. David L. Katz, director of Yale University's Prevention Research Center and founder of a new consortium of nutrition experts called the True Health Initiative. "It tells people, 'Don't listen to anybody and keep on eating double bacon cheeseburgers and don't worry about it.' But that's calamitous."
Yale University epidemiologist Rafael Perez-Escamilla acknowledged that clinical trials were rare in the science of nutrition because they are difficult and expensive to conduct. Instead, he said, nutrition recommendations for the public "rely heavily on triangulating evidence" from long-term population studies and short-term trials.
But both Katz and Perez-Escamilla said the science of nutrition had generated plenty of reliable advice on healthful eating -- none of which has been overturned by good clinical trials.
That "massive confluence of science and sense" on healthful eating was clearly reflected in an advisory report written by 14 independent scientists and delivered last February to the federal drafters of the Dietary Guidelines, Katz said. But when it came time to carry that scientific advice forward, Katz said, "food industry elements prevailed over scientists. This process was stolen from us."
The result, he said, was that good recommendations made by the scientific advisory committee were obfuscated or diluted to the point of contradiction in the final Dietary Guidelines.
Tufts University nutrition specialist Miriam Nelson said that political influence was nowhere more evident than in the Dietary Guidelines' recommendations on sources of protein. The scientific advisory committee -- of which Nelson was a member -- had recommended that the Dietary Guidelines advise Americans to get most of their protein from poultry, fish and plant-based foods such as nuts, seed and legumes, and eat less red meat and processed meats.
That advice, Nelson said, was founded in strong research -- studies that tracked health in broad populations over time (which Nissen has criticized) and the kinds of clinical trials that have been the gold standard in pharmaceutical research.
But in the roughly 10-month comment period, she said, "the beef industry mounted a highly orchestrated campaign to discredit the really strong science and the scientists who conducted it," much as the tobacco industry did decades ago as evidence of tobacco's harms mounted. The industry's congressional allies leaned on the secretaries of Agriculture and of Health and Human Services to dilute the language recommended by the independent scientists.
The result: The final Dietary Guidelines urge Americans to eat "a variety of protein foods ... from both animal and plant sources," and making no suggestion to limit red meats.
"It was not in the population's health best interest," Nelson said.
This is where a review by the National Academies of Science should help, said Frank Hu, professor of nutrition and epidemiology at Harvard's School of Public Health.
"The main issue is that the process of developing the Dietary Guidelines should not be politicized," Hu said in an interview. After the release of the scientific advisory report, which urged language limiting red meat consumption, "there was a lot of pushback or interference by the food industry, Congress and special interest groups," Hu said. "That has certainly influenced the translation of the scientific evidence into the policy document."