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New Research Links Red Meat to Higher Risk of Heart Disease and Poor Kidney Health

New Research Links Red Meat to Higher Risk of Heart Disease and Poor Kidney Health

But there is a way to reverse the effects.

New research is giving us yet another reason to limit red meat consumption: its impact on heart disease risk. A study conducted by the National Heart, Lung, and Blood Institute (published in the European Heart Journal) found that both heart and gut health is impacted by a chemical called trimethylamine N-oxide (also known as TMAO)—which is a chemical byproduct derived in part from nutrients found in red meat.

Scientists discovered those who eat a diet rich in red meat have three times the TMAO levels compared to those who eat mostly white meat or plant-based protein sources. But the research also found that high TMAO levels can be reversed by replacing red meat with increased white meat or plant-based proteins.

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“This study shows for the first time what a dramatic effect changing your diet has on levels of TMAO, which is increasingly linked to heart disease,” said Stanley L. Hazen, M.D., Ph.D., in a press release. Hazen is the senior author of the study and a Preventive Cardiology & Rehabilitation section head at the Cleveland Clinic.

Hazen noted as many as a quarter of Americans have naturally elevated TMAO levels, which are made worse by excessive red meat consumption. The study suggests that measuring and targeting TMAO levels—which can be done with a simple blood test—could be a promising way to prevent heart disease, along with individualized diet plans.

The study examined 113 healthy men and women by having them follow a standard American diet—49 percent of their calories came from carbohydrates, 14 percent from protein, and 37 percent from fat for a period of two weeks. Participants were then randomly placed on a variety of diets based on varying protein consumption, and were expected to obtain 25 percent of their calories from protein each day.

One group ate a diet heavily based in red meat for protein, whereas another consumed mostly white meat, and the third ate mostly plant-based protein sources. From there, half of each group were put on a high-fat diet so that the effects of each protein source on TMAO were independent of dietary fat intake.

Easy recipes to incorporate more plant-based protein into your diet:

The red meat-centric diet allowed for participants to eat about eight ounces daily, either a steak or two quarter-pound beef patties. After one month, researchers found, on average, blood levels of TMAO in these participants tripled in comparison to those eating diets rich in white meat or non-meat protein sources.

The good news? It only took four weeks to reduce high TMAO levels after discontinuing red meat consumption.

“These findings reinforce current dietary recommendations that encourage all ages to follow a heart-healthy eating plan that limits red meat,” said Charlotte Pratt, Ph.D., a nutrition researcher at the National Heart, Lung, and Blood Institute. “This means eating a variety of foods, including more vegetables, fruits, whole grains, low-fat dairy foods, and plant-based protein sources such as beans and peas.”

How exactly TMAO affects heart disease is still unclear. Research has shown TMAO can affect cholesterol deposits on the artery wall, creating “clogged arteries.” TMAO has also been shown to interact with platelets in a way that can lead to clotting-related activities, including heart attack and stroke.


Study links frequent red meat consumption to high levels of chemical associated with heart disease

Researchers have identified another reason to limit red meat consumption: high levels of a gut-generated chemical called trimethylamine N-oxide (TMAO), that also is linked to heart disease. Scientists found that people who eat a diet rich in red meat have triple the TMAO levels of those who eat a diet rich in either white meat or mostly plant-based proteins, but discontinuation of red meat eventually lowers those TMAO levels.

TMAO is a dietary byproduct that is formed by gut bacteria during digestion and is derived in part from nutrients that are abundant in red meat. While high saturated fat levels in red meat have long been known to contribute to heart disease—the leading cause of death in the United States—a growing number of studies have identified TMAO as another culprit. Until now, researchers knew little about how typical dietary patterns influence TMAO production or elimination.

The findings suggest that measuring and targeting TMAO levels—something doctors can do with a simple blood test—may be a promising new strategy for individualizing diets and helping to prevent heart disease. The study was funded largely by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health. It will be published Dec. 10 in the European Heart Journal, a publication of the European Society of Cardiology.

“These findings reinforce current dietary recommendations that encourage all ages to follow a heart-healthy eating plan that limits red meat,” said Charlotte Pratt, Ph.D., the NHLBI project officer for the study and a nutrition researcher and Deputy Chief of the Clinical Applications & Prevention Branch, Division of Cardiovascular Sciences, NHLBI. “This means eating a variety of foods, including more vegetables, fruits, whole grains, low-fat dairy foods, and plant-based protein sources such as beans and peas.”

“This study shows for the first time what a dramatic effect changing your diet has on levels of TMAO, which is increasingly linked to heart disease,” said Stanley L. Hazen, M.D., Ph.D., senior author of the study and section head of Preventive Cardiology & Rehabilitation at the Cleveland Clinic. “It suggests that you can lower your heart disease risk by lowering TMAO.”

Hazen estimated that as many as a quarter of middle-aged Americans have naturally elevated TMAO levels, which are made worse by chronic red meat consumption. However, every person’s TMAO profile appears to be different, so tracking this chemical marker, Hazen suggested, could be an important step in using personalized medicine to fight heart disease.

For the study, researchers enrolled 113 healthy men and women in a clinical trial to examine the effects of dietary protein—in the form of red meat, white meat, or non-meat sources—on TMAO production. All subjects were placed on each diet for a month in random order. When on the red meat diet, the participants consumed roughly the equivalent of about 8 ounces of steak daily, or two quarter-pound beef patties. After one month, researchers found that, on average, blood levels of TMAO in these participants tripled, compared to when they were on the diets high in either white meat or non-meat protein sources.

While all diets contained equal amounts of calories, half of the participants were also placed on high-fat versions of the three diets, and the researchers observed similar results. Thus, the effects of the protein source on TMAO levels were independent of dietary fat intake.

Importantly, the researchers discovered that the TMAO increases were reversible. When the subjects discontinued their red meat diet and moved to either a white meat or non-meat diet for another month, their TMAO levels decreased significantly.

The exact mechanisms by which TMAO affects heart disease is complex. Prior research has shown TMAO enhances cholesterol deposits into cells of the artery wall. Studies by the researchers also suggest that the chemical interacts with platelets—blood cells that are responsible for normal clotting responses—in a way that increases the risk for clot-related events such as heart attack and stroke.

TMAO measurement is currently available as a quick, simple blood test first developed by Hazen’s laboratory. In recent published studies, he and his colleagues reported development of a new class of drugs that are capable of lowering TMAO levels in the blood and reducing atherosclerosis and clotting risks in animal models, but those drugs are still experimental and not yet available to the public.

The study was supported by grants from the NHLBI and the Office of Dietary Supplements (HL103866, HL126827, HL106003, HL130819) and the National Institute of Diabetes and Digestive and Kidney Diseases (DK106000). The study was also supported by UCSF Clinical and Translational Science Unit.


Related Links

References: Impact of chronic dietary red meat, white meat, or non-meat protein on trimethylamine N-oxide metabolism and renal excretion in healthy men and women. Wang Z, Bergeron N, Levison BS, Li XS, Chiu S, Jia X, Koeth RA, Li L, Wu Y, Tang WHW, Krauss RM, Hazen SL. Eur Heart J. 2018 Dec 10. doi: 10.1093/eurheartj/ehy799. [Epub ahead of print]. PMID: 30535398.

Funding: NIH’s National Heart, Lung, and Blood Institute (NHLBI) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) Leducq Foundation and University of California, San Francisco.


Is Red Meat Bad for Your Heart … or Not?

For decades, scientific studies have shown a connection between eating red meat — like beef, pork, veal and lamb — and getting heart disease. That’s why the American Heart Association encourages limiting the amount of red meat you eat. (The right amount is different for everybody, but think deck-of-cards-size portions and not every day.)

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And many doctors, like Stanley Hazen, MD, PhD, Co-Section Head of Preventive Cardiology, recommend the Mediterranean diet, which allows little if any red meat.

However, new analysis published in the Annals of Internal Medicine (including here and here) questions everything we’ve believed about red meat.

Authors of these new reports say that evidence linking red meat to heart disease (and cancer and other diseases) is relatively weak. They say the data isn’t strong enough to make dietary recommendations. That has launched a barrage of news stories claiming that red meat has gotten a bad rap.

But take this news with a grain of salt. Don’t go restocking your freezer with steaks and burgers just yet. Dr. Hazen explains in this Q&A.

Q: Why has beef and other red meat been linked to heart disease?

Dr. Hazen: There have been innumerable studies — looking at hundreds of thousands of patients with millions of years of follow-up — that show a connection between eating red meat, getting heart disease and dying from heart disease. It’s remarkably consistent.

Exactly how red meat contributes to heart disease is debated. There probably are multiple reasons. Two likely contributors are the higher cholesterol and saturated fat content in red meat.

New data also points to choline and carnitine, other nutrients in red meat. Microbes in your gut break down these nutrients, generating TMAO (trimethylamine-N-oxide). High levels of TMAO in your blood increase your risk of hardened arteries, heart attack and stroke. There also may be other genetic or environmental factors, or a combination of factors, we haven’t uncovered yet.

Regardless, there is a connection. I totally disagree with the new reports that downplay past dietary studies. This is unfortunate and, I believe, irresponsible.

Q: Why do new reports in the Annals of Internal Medicine discredit earlier studies?

Dr. Hazen: Scientific studies come in different forms. Medical and research professionals view “prospective randomized trials” as the strongest and best quality. These trials randomly assign some participants to perform one set of behaviors and some to perform another.

Ideally, everything is the same except the single thing being tested. There are extremely few long-term randomized trials that have studied human diets with hard outcomes like heart attack, stroke and death. It’s hard to do because we humans are free-ranging animals. Studies like these would require controlling exactly what and how much a group of people eats day in and day out for many years.

For this reason, most diet studies are observational. They typically require people to fill out questionnaires about their eating habits. Researchers then analyze responses to determine risk of disease, for example, while adjusting for other factors (such as, “Do meat eaters exercise less? Do they eat more salt?”). This type of study isn’t as reliable as a randomized trial because people sometimes forget what they ate or miscalculate how much. But it still can give valuable information.

The authors who published the new reports in the Annals of Internal Medicine didn’t conduct a new trial. They instead reviewed previous studies and passed judgment on the quality of data. They determined that, because most studies on the health effects of eating red meat were observational, they’re not strong enough to guide dietary recommendations.

Q: Why do you disagree with them?

Dr. Hazen: Regardless of the type of study, research consistently shows that the more red meat you eat, the higher your long-term risk of getting and dying from cardiovascular disease. There is a clear association. And it’s been seen over and over in both men and women in various populations in various countries.

True, strictly speaking, we don’t know if the higher risk is caused by the red meat or associated factors (like the ketchup on the burger, the french fries on the side, eating meat instead of salad). But study after study has tried to adjust for these potential confounders. Just because these studies aren’t prospective randomized trials with hard outcomes doesn’t mean they should be ignored.

Q: Will there ever be a randomized dietary trial?

Dr. Hazen: Yes. There have been many, but they usually study things like weight, blood glucose or cholesterol. It would be very expensive and difficult to feed people a controlled diet for a decade or longer and count the heart attacks, for example.

The PREDIMED trial, published in 2013, is probably the closest we’ve come. It studied more than 7,000 people at a higher risk of heart disease. Each person was randomly assigned to one of three diets and followed for many years.

Researchers found that people eating a Mediterranean diet were 30-35% less likely to have a heart attack or stroke than people eating a standard low-fat diet. Notably, people following the Mediterranean diet in this study were urged to eat no red meat. However, the diet did include other protein sources — like fish and lean chicken — and plenty of vegetables, grains, some fruits, extra-virgin olive oil and nuts.

It’s true that instead of reduction in red meat, any one or more of these items could have contributed to the remarkable reduction in heart disease.

Q: Once and for all, what is your advice on eating red meat?

Dr. Hazen: According to most scientific studies, people who eat more red meat have a higher risk of heart disease. Even though I’m begrudgingly a meat lover, I advise people to reduce their heart risk by eating less red meat.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy


Eating red meat and processed meat hikes heart disease, death risk: study

Credit: CC0 Public Domain

Drop the steak knife. After a controversial study last fall recommending that it was not necessary for people to change their diet in terms of red meat and processed meat, a large, carefully analyzed new study links red and processed meat consumption with slightly higher risk of heart disease and death, according to a new study from Northwestern Medicine and Cornell University.

Eating two servings of red meat, processed meat or poultry—but not fish—per week was linked to a 3 to 7% higher risk of cardiovascular disease, the study found. Eating two servings of red meat or processed meat—but not poultry or fish—per week was associated with a 3% higher risk of all causes of death.

"It's a small difference, but it's worth trying to reduce red meat and processed meat like pepperoni, bologna and deli meats," said senior study author Norrina Allen, associate professor of preventive medicine at Northwestern University Feinberg School of Medicine. "Red meat consumption also is consistently linked to other health problems like cancer."

"Modifying intake of these animal protein foods may be an important strategy to help reduce the risk of cardiovascular disease and premature death at a population level," said lead study author Victor Zhong, assistant professor of nutritional sciences at Cornell, who did the research when he was a postdoctoral fellow in Allen's lab.

The paper will be published Feb. 3 in JAMA Internal Medicine.

The new findings come on the heels of a controversial meta-analysis published last November that recommended people not reduce the amount of red meat and processed meat they eat. "Everyone interpreted that it was OK to eat red meat, but I don't think that is what the science supports," Allen said.

"Our study shows the link to cardiovascular disease and mortality was robust," Zhong said.

"Fish, seafood and plant-based sources of protein such as nuts and legumes, including beans and peas, are excellent alternatives to meat and are under-consumed in the U.S.," said study coauthor Linda Van Horn, professor of preventive medicine at Feinberg who also is a member of the 2020 U.S. Dietary Guidelines Advisory committee.

The study found a positive association between poultry intake and cardiovascular disease, but the evidence so far isn't sufficient to make a clear recommendation about poultry intake, Zhong said. Still, fried chicken is not recommended.

The new study pooled together a large diverse sample from six cohorts, included long follow-up data up to three decades, harmonized diet data to reduce heterogeneity, adjusted a comprehensive set of confounders and conducted multiple sensitivity analyses. The study included 29,682 participants (mean age of 53.7 years at baseline, 44.4% men and 30.7% non-white). Diet data were self-reported by participants, who were asked a long list of what they ate for the previous year or month.

  • A 3 to 7% higher risk of cardiovascular disease and premature death for people who ate red meat and processed meat two servings a week.
  • A 4% higher risk of cardiovascular disease for people who ate two servings per week of poultry, but the evidence so far is not sufficient to make a clear recommendation about poultry intake. And the relationship may be related to the method of cooking the chicken and consumption of the skin rather than the chicken meat itself.
  • No association between eating fish and cardiovascular disease or mortality.

Limitations of the study are participants' dietary intake was assessed once, and dietary behaviors may have changed over time. In addition, cooking methods were not considered. Fried chicken, especially deep fat-fried sources that contribute trans-fatty acids, and fried fish intake have been positively linked to chronic diseases, Zhong said.


Study strengthens links between red meat and heart disease

Credit: CC0 Public Domain

An observational study in nearly 20,000 individuals has found that greater intake of red and processed meat is associated with worse heart function. The research is presented at ESC Preventive Cardiology 2021, an online scientific congress of the European Society of Cardiology (ESC).

"Previous studies have shown links between greater red meat consumption and increased risk of heart attacks or dying from heart disease," said study author Dr. Zahra Raisi-Estabragh of Queen Mary University of London, UK. "For the first time, we examined the relationships between meat consumption and imaging measures of heart health. This may help us to understand the mechanisms underlying the previously observed connections with cardiovascular disease."

The study included 19,408 participants of the UK Biobank. The researchers examined associations of self-reported intake of red and processed meat with heart anatomy and function.

Three types of heart measures were analysed. First, cardiovascular magnetic resonance (CMR) assessments of heart function used in clinical practice such as volume of the ventricles and measures of the pumping function of the ventricles. Second, novel CMR radiomics used in research to extract detailed information from heart images such as shape and texture (which indicates health of the heart muscle). Third, elasticity of the blood vessels (stretchy arteries are healthier).

The analysis was adjusted for other factors that might influence the relationship including age, sex, deprivation, education, smoking, alcohol, exercise, high blood pressure, high cholesterol, diabetes, and body mass index (BMI) as a measure of obesity.

The researchers found that greater intake of red and processed meat was associated with worse imaging measures of heart health, across all measures studied. Specifically, individuals with higher meat intake had smaller ventricles, poorer heart function, and stiffer arteries—all markers of worse cardiovascular health.

As a comparison, the researchers also tested the relationships between heart imaging measures and intake of oily fish, which has previously been linked with better heart health. They found that as the amount of oily fish consumption rose, heart function improved, and arteries were stretchier.

Dr. Raisi-Estabragh said: "The findings support prior observations linking red and processed meat consumption with heart disease and provide unique insights into links with heart and vascular structure and function."

The associations between imaging measures of heart health and meat intake were only partially explained by high blood pressure, high cholesterol, diabetes, and obesity.

"It has been suggested that these factors could be the reason for the observed relationship between meat and heart disease," said Dr. Raisi-Estabragh. "For example, it is possible that greater red meat intake leads to raised blood cholesterol and this in turn causes heart disease. Our study suggests that these four factors do play a role in the links between meat intake and heart health, but they are not the full story."

She noted that the study did not look into alternative mechanisms. But she said: "There is some evidence that red meat alters the gut microbiome, leading to higher levels of certain metabolites in the blood, which have in turn been linked to greater risk of heart disease."

Dr. Raisi-Estabragh said: "This was an observational study and causation cannot be assumed. But in general, it seems sensible to limit intake of red and processed meat for heart health reasons."


Study: Red meat, processed meat hike heart disease risk

Drop the steak knife: Unprocessed red meat and processed meat consumption leads to a slightly higher risk of heart disease and premature death, according to a new study from researchers at Cornell and Northwestern University.

Their paper, Associations of Processed Meat, Unprocessed Red Meat, Poultry or Fish Intake With Incident Cardiovascular Disease and All-Cause Mortality, was published Feb. 3 in JAMA Internal Medicine. The lead author is Victor Zhong, assistant professor of nutritional sciences at Cornell.

The study found that eating two servings per week of unprocessed red meat, processed meat or poultry was linked to a 3% to 7% higher risk of cardiovascular disease. Eating two servings per week of unprocessed red meat or processed meat was associated with a 3% higher risk of all causes of death.

“Modifying intake of these animal protein foods may be an important dietary strategy to help reduce risk of cardiovascular disease and premature death at population level,” Zhong said.

“It’s a small difference, but it’s worth trying to reduce [consumption of] red meat and processed meat,” said senior author Norrina Allen, associate professor of preventive medicine at Northwestern’s Feinberg School of Medicine. “Red meat consumption is also consistently linked to other health problems like cancer.”

The new findings come on the heels of a controversial meta-analysis published last November that recommended people not reduce their consumption of unprocessed red meat and processed meat. “Everyone interpreted that it was OK to eat red meat,” Allen said, “but I don’t think that is what the science supports.”

Said Zhong: “Our study shows the link to cardiovascular disease and mortality was robust.”

Within this study, they found a 4% higher risk of cardiovascular disease for people who ate two servings per week of poultry, but the evidence so far is not sufficient to make a clear recommendation about poultry intake, Zhong said. The relationship may be related to the method of cooking the chicken and consumption of the skin rather than the chicken meat itself. Fried chicken and fish have been positively linked to chronic diseases, Zhong said.

The researchers suggest dietary alternatives such as seafood and plant-based sources of protein and other key nutrients to lessen one’s risk of heart disease and premature death. “Our study findings support current dietary guidelines that recommend limiting processed meat and unprocessed red meat intake,” Zhong said. “People can get needed nutrients from various other foods. Take protein for example: People can choose egg whites, fish, legumes, whole grains, and nuts to replace processed meat and unprocessed red meat.”

The study featured a large, diverse sample from six cohorts and included follow-up data from up to three decades. There were 29,682 participants (44.4% men, 30.7% non-white) the participants’ mean age at the start of the study was 53.7.

The study was funded by grants from the National Institutes of Health, the American Heart Association and the Feinberg School of Medicine.

Stephen D’Angelo is assistant director for communications for the College of Human Ecology.


Meat Consumption Raises Risk of Heart Disease and Death

Norrina Allen, PhD, associate professor of Preventive Medicine in the Division of Epidemiology, was the senior author of the study that linked the consumption of red and processed meat with a higher risk of heart disease.

Drop the steak knife. After a controversial study last fall recommending that it was not necessary for people to change their diet in terms of red meat and processed meat, a large, carefully analyzed new study links red and processed meat consumption with slightly higher risk of heart disease and death, according to a new publication from Northwestern Medicine and Cornell University.

Eating two servings of red meat, processed meat or poultry – but not fish – per week was linked to a 3 to 7 percent higher risk of cardiovascular disease, the study, published in JAMA Internal Medicine, found. Eating two servings of red meat or processed meat – but not poultry or fish – per week was associated with a 3 percent higher risk of all causes of death.

“It’s a small difference, but it’s worth trying to reduce red meat and processed meat like pepperoni, bologna and deli meats,” said senior study author Norrina Allen, PhD, associate professor of Preventive Medicine in the Division of Epidemiology and director of the Center for Epidemiology and Population Health. “Red meat consumption also is consistently linked to other health problems like cancer.”

Listen to an episode of the Breakthroughs Podcast on this research:

“Modifying intake of these animal protein foods may be an important strategy to help reduce the risk of cardiovascular disease and premature death at a population level,” said lead study author Victor Zhong, assistant professor of Nutritional Sciences at Cornell, who did the research when he was a postdoctoral fellow in Allen’s lab.

The new findings come on the heels of a controversial meta-analysis published last November that recommended people not to reduce the amount of red meat and processed meat they eat. “Everyone interpreted that it was OK to eat red meat, but I don’t think that is what the science supports,” Allen said.

“Our study shows the link to cardiovascular disease and mortality was robust,” Zhong said.

What should we eat?

“Fish, seafood and plant-based sources of protein such as nuts and legumes, including beans and peas, are excellent alternatives to meat and are under-consumed in the U.S.,” said study coauthor Linda Van Horn, PhD, RD, chief of Nutrition in the Department of Preventive Medicine, who also is a member of the 2020 U.S. Dietary Guidelines Advisory committee.

The study found a positive association between poultry intake and cardiovascular disease, but the evidence so far isn’t sufficient to make a clear recommendation about poultry intake, Zhong said. Still, fried chicken is not recommended.

The new study pooled together a large diverse sample from six cohorts, included long follow-up data up to three decades, harmonized diet data to reduce heterogeneity, adjusted a comprehensive set of confounders and conducted multiple sensitivity analyses. The study included 29,682 participants (mean age of 53.7 years at baseline, 44.4 percent men and 30.7 percent non-white). Diet data were self-reported by participants, who were asked a long list of what they ate for the previous year or month.

Key findings:

  • A 3 to 7 percent higher risk of cardiovascular disease and premature death for people who ate red meat and processed meat two servings a week.
  • A 4 percent higher risk of cardiovascular disease for people who ate two servings per week of poultry, but the evidence so far is not sufficient to make a clear recommendation about poultry intake. And the relationship may be related to the method of cooking the chicken and consumption of the skin rather than the chicken meat itself.
  • No association between eating fish and cardiovascular disease or mortality.

Limitations of the study are participants’ dietary intake was assessed once, and dietary behaviors may have changed over time. In addition, cooking methods were not considered. Fried chicken, especially deep fat-fried sources that contribute trans-fatty acids, and fried fish intake have been positively linked to chronic diseases, Zhong said.

Other Northwestern authors are Donald Lloyd-Jones, MD, ScM, senior associate dean for Clinical and Translational Research and chair of the Department of Preventive Medicine Philip Greenland, MD, the Harry W. Dingman Professor of Cardiology Mercedes Carnethon, PhD, the Mary Harris Thompson Professor and vice chair of the Department of Preventive Medicine Hongyan Ning, MD and John Wilkins, MD, ’11 MS, ’12 GME, associate professor of Medicine in the Division of Cardiology and of Preventive Medicine in the Division of Epidemiology.

The study was funded by National Institutes of Health/National Heart, Lung, and Blood Institute (R21 HL085375), American Heart Association Strategically Focused Research Networks and the Feinberg School of Medicine.


Heart Disease and Diabetes Risks Tied to Carbs, Not Fat, Study Finds

Is the pendulum swinging back? In what seems contrary to mainstream dietary advice, a small new study shows that doubling the saturated fat in a person's diet does not drive up the levels of saturated fat in the blood.

Rather, the study found that it was the carbohydrates in people's diets that were linked with increased levels of a type of fatty acid linked to heart disease and type-2 diabetes. The results of the study, which followed 16 middle-aged, obese adults for 21 weeks, were published Nov. 21 in the journal PLOS ONE.

Saturated fats, largely from meat and dairy products, have been vilified for decades as a primary culprit in promoting heart disease. And most health authorities maintain this stance.

However, in recent years, scientists have seen the ill effects of completely replacing saturated fat with carbohydrates, particularly the simple carbs that are found so commonly in processed foods. A large analysis published in 2009 in the American Journal of Clinical Nutrition found that swapping saturated fats with carbs had no benefit in reducing people's risk of heart disease. But replacing those so-called bad fats with polyunsaturated fats &mdash found in fish, olives and nuts &mdash did.

"The unintended consequence of telling everyone to restrict fat was that people ate an even greater amount of carbohydrates," said Jeff Volek, senior author on the new study and a professor of human sciences at The Ohio State University. "This is a fact. It's not a stretch to make the connection between overconsumption of carbs and the obesity and diabetes epidemic."

The new study "challenges the conventional wisdom that has demonized saturated fat," Volek said, because it shows that saturated fats don't need to be replaced at all, neither with carbs nor polyunsaturated fats. [7 Foods You Can Overdose On]

The study, it should be noted, was funded by a grant from the Dairy Research Institute, the National Cattlemen's Beef Association, the Egg Nutrition Center, and the Robert C. and Veronica Atkins Foundation, although the researchers reported that the funders had no role in the study design or decision to publish the research.

For the analysis, researchers placed 16 participants on a tightly controlled diet of fats and carbs. The participants were on their own high-carb, low-fat diets before entering the study. For the first three weeks of the study, they doubled or tripled their saturated-fat intake, consuming 84 grams of saturated fats, and 47 grams of carbs per day. Researchers found no jump in the levels of saturated fat in the blood during this phase.

Then, every three weeks after this, the dieters decreased the fat and increased their carb intake, ending the study on a diet of 32 grams of saturated fat and 346 grams of carbs per day. The final phase modeled U.S. dietary recommendations for carbs and included whole grains.

"You can sort of think of this experiment as a dose-response study, where we exposed individuals to a range of dietary carb levels and monitored their fatty-acid levels to determine if they were accumulating saturated fatty acids and turning carbs into fat," Volek told Live Science.

The researchers found that as the amount of dietary fat was decreased, there were no changes in the levels of saturated fat in the participants' blood. But one kind of fatty acid, called palmitoleic acid, did progressively increase.

"Higher proportions of palmitoleic acid in blood or adipose tissue are consistently associated with a myriad of undesirable outcomes, such as obesity, …inflammation, metabolic syndrome, type 2 diabetes, coronary disease, heart failure, and incidence and aggressiveness of prostate cancer," the researchers wrote.

Dr. Dariush Mozaffarian, dean of the Friedman School of Nutrition Science & Policy at Tufts University, who was not involved in the research, described the work as a well-controlled interventional study confirming that dietary refined carbohydrate is the primary driver of circulating saturated fatty acids in the bloodstream.

"White bread, rice, cereals, potatoes, and sugars &mdash not saturated fat &mdash are the real culprits in our food supply," he Mozaffarian.

Dr. Walter Willett, the chair of the Department of Nutrition at Harvard School of Public Health, also thought this was a reasonably done study, but he added it is difficult to make conclusions about the risk of heart disease from a study so small and short.

"Basically in their study they are comparing two bad diets, and the adverse of carbohydrates is likely to be particularly serious in the obese and insulin resistant population that they studied," Willett said.

We know from many long-term studies, Willet added, that replacing saturated fats from red meat and dairy with vegetable fats high in polyunsaturated and monounsaturated fats will reduce risks of heart disease. This is characteristic of the Mediterranean diet.

Also, other studies have shown beneficial properties of dietary palmitoleic acid, and its role in health remains an open question.

Follow Christopher Wanjek @wanjek for daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, Bad Medicine, appears regularly on LiveScience.


A look at the evidence

The study and its widespread reaction have once again brought up the question of whether red meat and processed meat are bad for your health and if people should cut them out or simply cut back.

So what are the facts? Here's a look at the main issues and questions regarding the role of red and processed meats in your diet.

Red and processed meats do increase health risks. In spite of what the Annals of Internal Medicine study suggests, Dr. Hu says that an accumulated body of evidence shows a clear link between high intake of red and processed meats and a higher risk for heart disease, cancer, diabetes, and premature death. "The evidence is consistent across different studies," he says.

But the key word here is "high." Dr. Hu points out that the exact amounts for safely consuming red meat are open to debate.

"The evidence shows that people with a relatively low intake have lower health risks," he says. "A general recommendation is that people should stick to no more than two to three servings per week."

Dr. Hu suggests that people focus not so much on actual serving sizes, but rather on red meat's placement in meals. "Instead of the main course, use red meat as a side dish," he says. "Consider red meat a luxury and not a staple food.

For processed meat, Dr. Hu says there is a much stronger association with a higher risk of heart disease and cancer (especially colon cancer).

Processed meat products contain high amounts of additives and chemicals, which may contribute to health risks. "Again, there is not a specific amount that is considered safe, so you should keep processed meat intake to a minimum," he says.

You don't need to eat red meat. Red meat has high amounts of protein, which helps promote muscle growth, and vitamin B12 to make red blood cells. For example, a 3-ounce serving has about 45% of the Daily Value (DV) of protein and 35% of the DV for B12. A serving of red meat is also a good source of zinc, which can help the body produce testosterone, and selenium, a powerful antioxidant. Plus, red meat is rich in iron. However, Dr. Hu says that you don't need to eat red meat to get these essential nutrients. "You can get the same amounts — and in some cases even more — from poultry, fish, eggs, and nuts, and as well as by following a plant-based diet."

Some kinds of red meat are not necessarily healthier. There are no firm studies that have shown nutritional or health advantages from eating organic or grass-fed beef.

"These types of red meat are often more desirable as they contain low or no growth hormones compared with grain-fed beef, but it's still not clear if they offer any health benefits," says Dr. Hu.

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