Those seeking the keys to a healthy diet these days face a predicament. Decades of studies have produced vast stores of data about the foods and nutrients likely to enhance and extend life. But any attempt to retrieve this vital knowledge lands the public in an informational crossfire.
Of all dietary staples, none has created as much fury as fat. How much, and what kind, is good for you? In the spring, the Annals of Internal Medicine published a paper concluding that saturated fats do not increase the risk of coronary disease. It also found no statistically significant health benefits from eating polyunsaturated vegetable oils.
The study made news. Big, sexy, controversial news.
"Everyone loves the idea that everything you thought you knew about nutrition is wrong," said Marion Nestle, author of numerous books on food and a professor in the department of nutrition, food studies and public health at New York University.
The paper's authors were cast by some as a sort of nutritional Innocence Project who had finally exonerated butter, lard and marbled meats, those dietary fiends long condemned as murderers.
The verdict, however, was by no means unanimous or clear-cut.
Statisticians, doctors, nutritional experts, journalists, biochemists and even some of the paper's own authors continue to debate what the findings mean and what, if any, changes people should make in their diets.
They all agree on this much: Food pyramids that used to recommend restricting all fat intake to an ascetic minimum were misguided, and the result - a marked increase in the consumption of sugars and refined carbohydrates - has made Americans significantly less healthy.
Many of the same experts who established the previous national guidelines are advising the public to increase fat intake while cutting down on breads, cereals, potatoes, rice and especially "low-fat" products such as sodium-infused processed meats and salad dressings made with sugar and salt instead of vegetable oil.
Does this mean the road to cardiac health is paved with bacon-wrapped burgers?
Most nutritional authorities say, sorry, no.
"The message is not that butter is back, red meat is back," said Dariush Mozaffarian, dean of Tufts University's School of Nutrition Science and Policy and one of the coauthors of the Annals study. "No one said saturated fat is good for you, per se, as a class. No one is saying don't eat fruits and vegetables. That is an incorrect interpretation of the findings."
What the experts are saying, Mozaffarian explained, is that a healthful diet requires a wide variety of whole, natural foods, including many, such as cheese and nuts, that contain some saturated fat.
Nothing about the issue is simple, however.
For the "meta-analysis," Mozaffarian and his colleagues pooled results from scores of studies that had examined the association between dietary fats and coronary disease.
It was not the first paper to report that, at least statistically, saturated fats appear to be relatively benign.
The "relative" aspect, however, is key.
When one type of food is removed from a diet, it has to be replaced with something else, said Alice Lichtenstein, who also serves on the Tufts faculty, helped develop national nutritional guidelines, and is a member of the National Academy of Sciences.
The choice of those alternatives makes all the difference, Lichtenstein said. "If you use polyunsaturated fat to replace saturated fat, there is a clear benefit."
Concerned that the public would be confused by media coverage of the study, in May, Harvard University held a teach-in about saturated fats.
Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health, was highly critical of the meta-analysis and presented charts and graphs supporting the theme that "healthy" is a relative term.
Compared with carbohydrates, saturated fats appear to have a neutral effect on cardiac health and diabetes, he said. Compared with trans fats, sugar and refined carbohydrates, saturated fats almost surely are healthier. Compared with fats, they are less healthy.
The Annals study was misleading, he wrote, because it was a "statistical summary of published papers and could only look at saturated fat vs. other sources of calories combined ... when this is done, there is no apparent increase in the risk of heart disease because bad is being compared with bad. However, if saturated fat is compared to polyunsaturated fat (or nonhydrogenated vegetable fat in general), saturated fat increases risk."
Critics have cited other problems with the meta-analysis, including concerns about the accuracy of data provided by test subjects who were asked to remember what they ate. And because some of the studies looked at people with chronic illnesses such ascoronary disease, the results might be different for healthy people.
Stepping back from the fray, Mozaffarian, who has his own quibble with the study, said the underlying science was sound and had not been challenged.
But the comparison of saturated fats as a whole to other dietary elements does not take into account other important factors, he said. There are, for instance, many different forms of saturated fat, and some, such as those in dairy products, might be beneficial in preventing diabetes.
Which leads to one other point on which everyone can agree: The biochemistry of fats is irredeemably complicated.
Like many of his colleagues, Mozaffarian said he believed that, "as a practical tool for trying to improve the health of the population, the focus on reducing saturated fat is a failure. The only real disagreement is how do you message this to the public?"
That disagreement appears to be as intractable as it is nuanced.
As the Harvard School of Public Health website explains, "All foods contain a mix of fats. Even 'healthy' foods like chicken, fish, nuts, and oils do contribute some saturated fat to the diet, though they are much lower in saturated fat than beef, cheese, and ice cream. And it would be a mistake to cut back on nuts, oils, and fish to minimize saturated fat."
Because more than one-third of American adults are obese, however, there is still concern about high caloric intake, and many experts worry about how people will interpret advice to allow more fat into their diet.
The fundamental problem, said Mozaffarian, is that "when people are lowering saturated fat, they're not getting the healthy benefit because they are eating low-fat, low saturated-fat foods that are just as bad, if not worse."
Low-fat processed turkey? Lean protein, but too much sodium, he said. Baked potato chips? "One of the worst ideas ever," he said. "The only really healthy thing about potato chips is the vegetable oil." Tuna packed in water? Your body benefits more when the fish is packed in oil.
Nearly 10 years ago, when journalist Nina Teicholz began researching her book "The Big Fat Surprise; Why Butter, Meat and Cheese Belong in a Healthy Diet," she said she planned to "give a tour" of the various kinds of fat. As she was finishing the project, Teicholz said, her editor noted that saturated fat seemed to be the dominant theme, and so she sharpened the focus.
After reviewing the history of nutritional research, Teicholz came to a provocative conclusion.
Given the ample evidence that carbohydrates cause obesity, heart disease, and diabetes, she writes, "a beet salad with a fruit smoothie for lunch is ultimately less healthy for your waistline and your heart than a plate of eggs fried in butter. Steak salad is preferable to a plate of hummus and crackers. And a snack of full-fat cheese is better than fruit."
Teicholz, whose book includes nearly 1,000 footnotes, also argues that so-called healthy polyunsaturated oils produce toxic compounds when heated, and she challenges the value of the Mediterranean diet, which most experts believe is close to ideal.
"What's happening now is that nutrition experts are defending themselves against the last 30 years of advice that they've given Americans," she said. Having invested their careers in the catechism that saturated fats are unhealthy, she said, the academic "elites" suffer from "cognitive dissonance," and dismiss conflicting evidence.
In response, Willett said he was perplexed as to why someone with no scientific credentials should be taken seriously.
"She has zero credibility and appears to be only another journalist out to sell a book," he wrote in an email.
He also noted that, contrary to Teicholz's assertion that he "has bought into the saturated-fat-being-evil idea," he published a paper in the British Medical Journal in 1994 "that first showed that saturated fat was not associated with risk of heart disease when compared to the other sources of calories in the U.S. diet."
In many ways, dietary advice hasn't changed since the 1950s, said Nestle.
"It is still to eat lots of fruits and vegetables, don't eat too much junk food, and balance calories. Nobody has ever said this better than Michael Pollan: Eat food, mostly plants, not too much. What makes this all seem complicated is research based on single nutrients and vast fortunes thrown into trying to sell one food product or another."
Increasingly, research is showing that while scientists may isolate and analyze nutritional components, whole foods are greater - and more mysterious - than the sum of their biochemical parts.
"We need to think about these foods beyond a single nutrient," Mozaffarian said. "We shouldn't be making decisions about yogurt or cheese based on saturated fat content. ... Should we not eat nuts because of the saturated fat? No. We should eat nuts. Each 4 ounces per week is associated with about a 25 percent lower risk of heart disease and diabetes."
The U.S. Department of Agriculture has replaced the old food pyramid with graphics and guidelines that advise eating more fruits and vegetables, lean proteins, whole grains and dairy.
It advises minimizing "empty calories" from sugar and refined carbohydrates, but still puts a great deal of emphasis on choosing low-fat foods.
Those well-intentioned guidelines have led to some poor choices in federally mandated changes to school lunch programs, said Mozaffarian.
Efforts to combat childhood obesity are not advanced by replacing whole milk with sweetened low-fat chocolate milk, he said, or by removing wholesome vegetable oilsalad dressings in favor of low-fat, high-carb alternatives.
(As Teicholz chronicles in her book, politics and special interests long have influenced national food policy. This month, that clout was evident in the federal spending bill that weakened or eliminated requirements to increase whole grains and reduce sodium in school lunches, changes that virtually all nutritional experts believe would have been healthier.)
Describing the effort to lower saturated fat as a "failed public experiment," Mozaffarian said that in the interest of public health, the time had come to stop being afraid of fat.
But he cautioned that the public should also be wary of prophets who claim the new secret to a long, healthy life is to go whole hog on fats.
Of all dietary staples, none has created as much fury as fat. How much, and what kind, is good for you? In the spring, the Annals of Internal Medicine published a paper concluding that saturated fats do not increase the risk of coronary disease. It also found no statistically significant health benefits from eating polyunsaturated vegetable oils.
The study made news. Big, sexy, controversial news.
"Everyone loves the idea that everything you thought you knew about nutrition is wrong," said Marion Nestle, author of numerous books on food and a professor in the department of nutrition, food studies and public health at New York University.
The paper's authors were cast by some as a sort of nutritional Innocence Project who had finally exonerated butter, lard and marbled meats, those dietary fiends long condemned as murderers.
The verdict, however, was by no means unanimous or clear-cut.
Statisticians, doctors, nutritional experts, journalists, biochemists and even some of the paper's own authors continue to debate what the findings mean and what, if any, changes people should make in their diets.
They all agree on this much: Food pyramids that used to recommend restricting all fat intake to an ascetic minimum were misguided, and the result - a marked increase in the consumption of sugars and refined carbohydrates - has made Americans significantly less healthy.
Many of the same experts who established the previous national guidelines are advising the public to increase fat intake while cutting down on breads, cereals, potatoes, rice and especially "low-fat" products such as sodium-infused processed meats and salad dressings made with sugar and salt instead of vegetable oil.
Does this mean the road to cardiac health is paved with bacon-wrapped burgers?
Most nutritional authorities say, sorry, no.
"The message is not that butter is back, red meat is back," said Dariush Mozaffarian, dean of Tufts University's School of Nutrition Science and Policy and one of the coauthors of the Annals study. "No one said saturated fat is good for you, per se, as a class. No one is saying don't eat fruits and vegetables. That is an incorrect interpretation of the findings."
What the experts are saying, Mozaffarian explained, is that a healthful diet requires a wide variety of whole, natural foods, including many, such as cheese and nuts, that contain some saturated fat.
Nothing about the issue is simple, however.
For the "meta-analysis," Mozaffarian and his colleagues pooled results from scores of studies that had examined the association between dietary fats and coronary disease.
It was not the first paper to report that, at least statistically, saturated fats appear to be relatively benign.
The "relative" aspect, however, is key.
When one type of food is removed from a diet, it has to be replaced with something else, said Alice Lichtenstein, who also serves on the Tufts faculty, helped develop national nutritional guidelines, and is a member of the National Academy of Sciences.
The choice of those alternatives makes all the difference, Lichtenstein said. "If you use polyunsaturated fat to replace saturated fat, there is a clear benefit."
Concerned that the public would be confused by media coverage of the study, in May, Harvard University held a teach-in about saturated fats.
Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health, was highly critical of the meta-analysis and presented charts and graphs supporting the theme that "healthy" is a relative term.
Compared with carbohydrates, saturated fats appear to have a neutral effect on cardiac health and diabetes, he said. Compared with trans fats, sugar and refined carbohydrates, saturated fats almost surely are healthier. Compared with fats, they are less healthy.
The Annals study was misleading, he wrote, because it was a "statistical summary of published papers and could only look at saturated fat vs. other sources of calories combined ... when this is done, there is no apparent increase in the risk of heart disease because bad is being compared with bad. However, if saturated fat is compared to polyunsaturated fat (or nonhydrogenated vegetable fat in general), saturated fat increases risk."
Critics have cited other problems with the meta-analysis, including concerns about the accuracy of data provided by test subjects who were asked to remember what they ate. And because some of the studies looked at people with chronic illnesses such ascoronary disease, the results might be different for healthy people.
Stepping back from the fray, Mozaffarian, who has his own quibble with the study, said the underlying science was sound and had not been challenged.
But the comparison of saturated fats as a whole to other dietary elements does not take into account other important factors, he said. There are, for instance, many different forms of saturated fat, and some, such as those in dairy products, might be beneficial in preventing diabetes.
Which leads to one other point on which everyone can agree: The biochemistry of fats is irredeemably complicated.
Like many of his colleagues, Mozaffarian said he believed that, "as a practical tool for trying to improve the health of the population, the focus on reducing saturated fat is a failure. The only real disagreement is how do you message this to the public?"
That disagreement appears to be as intractable as it is nuanced.
As the Harvard School of Public Health website explains, "All foods contain a mix of fats. Even 'healthy' foods like chicken, fish, nuts, and oils do contribute some saturated fat to the diet, though they are much lower in saturated fat than beef, cheese, and ice cream. And it would be a mistake to cut back on nuts, oils, and fish to minimize saturated fat."
Because more than one-third of American adults are obese, however, there is still concern about high caloric intake, and many experts worry about how people will interpret advice to allow more fat into their diet.
The fundamental problem, said Mozaffarian, is that "when people are lowering saturated fat, they're not getting the healthy benefit because they are eating low-fat, low saturated-fat foods that are just as bad, if not worse."
Low-fat processed turkey? Lean protein, but too much sodium, he said. Baked potato chips? "One of the worst ideas ever," he said. "The only really healthy thing about potato chips is the vegetable oil." Tuna packed in water? Your body benefits more when the fish is packed in oil.
Nearly 10 years ago, when journalist Nina Teicholz began researching her book "The Big Fat Surprise; Why Butter, Meat and Cheese Belong in a Healthy Diet," she said she planned to "give a tour" of the various kinds of fat. As she was finishing the project, Teicholz said, her editor noted that saturated fat seemed to be the dominant theme, and so she sharpened the focus.
After reviewing the history of nutritional research, Teicholz came to a provocative conclusion.
Given the ample evidence that carbohydrates cause obesity, heart disease, and diabetes, she writes, "a beet salad with a fruit smoothie for lunch is ultimately less healthy for your waistline and your heart than a plate of eggs fried in butter. Steak salad is preferable to a plate of hummus and crackers. And a snack of full-fat cheese is better than fruit."
Teicholz, whose book includes nearly 1,000 footnotes, also argues that so-called healthy polyunsaturated oils produce toxic compounds when heated, and she challenges the value of the Mediterranean diet, which most experts believe is close to ideal.
"What's happening now is that nutrition experts are defending themselves against the last 30 years of advice that they've given Americans," she said. Having invested their careers in the catechism that saturated fats are unhealthy, she said, the academic "elites" suffer from "cognitive dissonance," and dismiss conflicting evidence.
In response, Willett said he was perplexed as to why someone with no scientific credentials should be taken seriously.
"She has zero credibility and appears to be only another journalist out to sell a book," he wrote in an email.
He also noted that, contrary to Teicholz's assertion that he "has bought into the saturated-fat-being-evil idea," he published a paper in the British Medical Journal in 1994 "that first showed that saturated fat was not associated with risk of heart disease when compared to the other sources of calories in the U.S. diet."
In many ways, dietary advice hasn't changed since the 1950s, said Nestle.
"It is still to eat lots of fruits and vegetables, don't eat too much junk food, and balance calories. Nobody has ever said this better than Michael Pollan: Eat food, mostly plants, not too much. What makes this all seem complicated is research based on single nutrients and vast fortunes thrown into trying to sell one food product or another."
Increasingly, research is showing that while scientists may isolate and analyze nutritional components, whole foods are greater - and more mysterious - than the sum of their biochemical parts.
"We need to think about these foods beyond a single nutrient," Mozaffarian said. "We shouldn't be making decisions about yogurt or cheese based on saturated fat content. ... Should we not eat nuts because of the saturated fat? No. We should eat nuts. Each 4 ounces per week is associated with about a 25 percent lower risk of heart disease and diabetes."
The U.S. Department of Agriculture has replaced the old food pyramid with graphics and guidelines that advise eating more fruits and vegetables, lean proteins, whole grains and dairy.
It advises minimizing "empty calories" from sugar and refined carbohydrates, but still puts a great deal of emphasis on choosing low-fat foods.
Those well-intentioned guidelines have led to some poor choices in federally mandated changes to school lunch programs, said Mozaffarian.
Efforts to combat childhood obesity are not advanced by replacing whole milk with sweetened low-fat chocolate milk, he said, or by removing wholesome vegetable oilsalad dressings in favor of low-fat, high-carb alternatives.
(As Teicholz chronicles in her book, politics and special interests long have influenced national food policy. This month, that clout was evident in the federal spending bill that weakened or eliminated requirements to increase whole grains and reduce sodium in school lunches, changes that virtually all nutritional experts believe would have been healthier.)
Describing the effort to lower saturated fat as a "failed public experiment," Mozaffarian said that in the interest of public health, the time had come to stop being afraid of fat.
But he cautioned that the public should also be wary of prophets who claim the new secret to a long, healthy life is to go whole hog on fats.
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