Industry-funded research feeds the confusion
"Butter is back.” “Eating cheese and red meat is actually good for you.” “Skim milk isn’t any better for you than whole milk, so go nuts.” An endless stream of headlines about new research—much of it industry funded—has fueled confusion about meat and dairy. Here are five myths that may trip you up.
MYTH: White meat or red meat? Doesn’t matter.
“White meat increases cholesterol levels similar to red meat,” declared U.S. News & World Report in June.
“When we planned this study, we expected red meat to have a more adverse effect on blood cholesterol levels than white meat, but we were surprised that this was not the case—their effects on cholesterol are identical when saturated fat levels are equivalent,” said the study’s senior author, according to U.S. News.
They were surprised? Since the researchers made sure that the red meat and white meat diets had the same levels of saturated fat, of course their effect on cholesterol—or more precisely, LDL (bad) cholesterol—was the same.
(Much of the author’s work has been funded by the dairy and beef industries, though this study, which also looked at TMAO, was funded by the National Institutes of Health.)
“Both the press release and the news reports were ridiculous,” says Marion Nestle, professor emerita of nutrition and food studies at New York University.
“The title made it sound like the study was about red or white meat. But if you look at the way it was designed, the researchers went to a lot of trouble to show that if you feed people diets with equivalent amounts of saturated fat, they’ll raise LDL levels equally. Well, duh.”
The study randomly assigned 113 people to eat diets made with red meat, white meat, or non-meat protein (beans, nuts, soy, etc.) for four weeks each.1
Here’s the catch: in order to make the red meat (beef) and white meat (chicken and turkey) diets equal in saturated fat, the researchers had to pick the very leanest cuts of beef, like top round and top sirloin.
But those lean cuts account for only a fraction of the beef we eat.
Hello-o-o. That’s precisely why experts advise people to eat more chicken and turkey than beef and pork.
“Because animal protein sources in the present study were restricted to lean cuts...we cannot extrapolate our findings to the lipid and lipoprotein effects of higher-fat red meat products in comparison with generally leaner white meats,” wrote the authors.
Too bad that didn’t end up in the press release. Nor did most press reports point out that LDL was higher when the researchers made all three diets—red meat, white meat, and non-meat—higher in saturated fat (by adding full-fat dairy and butter).
“Some people are arguing that saturated fat has no effect on heart disease risk,” says Nestle. “Here’s more evidence that saturated fat is really important.”
What’s more, we’ve seen this movie before. The beef industry has been funding studies using v-e-r-r-r-y lean meat since the 1990s.2
“It’s easy to design studies to give you the answer you want,” says Nestle. Her most recent book, Unsavory Truth, explores the food industry’s influence on scientists and their research.
Bottom Line: Most cuts of red meat raise LDL (“bad”) cholesterol more than white meat.
MYTH: Red meat is healthy if it’s lean.
“You might not have to give up (lean) red meat, after all,” reported the Washington Post last year. “Modest amounts of lean, unprocessed red meat don’t appear to have major health risks.”
The news: an industry-funded study found that, lo and behold, lean beef and pork don’t raise LDL if they’re part of a “Mediterranean” diet! Gosh!
“Our results are not generalizable to all cuts of beef and pork because only tenderloins were provided to subjects,” wrote the authors.3
But even lean red meat may boost the risk of heart disease and cancer.
In the white-vs-red-meat study, TMAO (trimethylamine N-oxide) levels tripled when people ate red meat rather than white meat or non-meat proteins.4
TMAO has been linked to a higher risk of heart disease in people.5 A key source: gut bacteria that dine on the carnitine in red meat (see “TMAO: Troublemaker from Meat?” below).
“Our 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,” says author Stanley Hazen, head of Preventive Cardiology and Rehabilitation at the Cleveland Clinic.
Though the evidence that TMAO harms the heart is still emerging, it could help explain why studies that track people for years find higher risks of heart disease and early death in people who eat more red meat.6
And then there’s colorectal cancer.
In 2015, the International Agency for Research on Cancer concluded that processed meats (like bacon, sausage, hot dogs, ham, and lunch meats) are carcinogenic to humans, and that unprocessed red meats (beef, pork, lamb, and veal) are probably carcinogenic.7
“The vast majority of observational studies show that people who consume the most processed or red meat have a higher risk of colorectal cancer,” says Amanda Cross, a cancer researcher at Imperial College London.
Several lines of evidence could explain the link.
“Heterocyclic amines, polycyclic aromatic hydrocarbons, and N-nitroso compounds are all carcinogenic in animals,” explains Cross.
“The first two are formed when meats are cooked at high temperatures until well done.” That means grilling, barbecuing, or pan-frying.
“N-nitroso compounds can come from the nitrite that’s added to processed meats, but they can also form in the gut,” says Cross. “The heme iron in red meat may catalyze the reaction.”
Bottom Line: Even lean red meat may raise the risk of heart disease and colorectal cancer.
MYTH: Full-fat dairy is heart healthy.
“For the love of all that is dairy, why are we still eating low-fat?” asked Bon Appetit last year. “Science has come around on full-fat dairy. Why haven’t we listened?”
The science has come around, according to Bon Appetit, because “better designed studies found that saturated fat increased both good and bad cholesterol,” and “when both were raised, the net effect is zero.”
Simple? Yes. Correct? No.
Four recent studies randomly assigned people to eat diets that were either high or low in saturated fat, largely from dairy.1,8-10 The results: LDL (bad) cholesterol was higher—and HDL (good) cholesterol didn’t budge—in people who ate more dairy fat.
“Dairy fat is high in palmitic acid, a saturated fat that has potent LDL-raising effects,” says Frank Hu, who chairs the nutrition department at the Harvard T.H. Chan School of Public Health.
And there’s no question that a higher LDL puts the heart at risk.
“LDL is a major cause of heart disease, and lowering it with diet or drugs prevents heart disease,” says Frank Sacks, professor of cardiovascular disease prevention at the Harvard T.H. Chan School of Public Health.
“LDL isn’t just a marker for a higher risk. It’s the real deal.”
Dairy fat doesn’t raise LDL in some industry-funded studies, but there’s usually a reason why.
For example, one study—funded by the Australian, Canadian, Danish, Dutch, French, and U.S. dairy industries—reported no difference in LDL when people were randomly assigned to eat regular versus lower-fat cheese.11
But the study was “underpowered”—that is, too small to see a difference from the change in sat fat—noted Jan Pedersen of the University of Oslo in a letter to the journal’s editor.12
A second industry-funded study reported no higher LDL on a high-cheese or high-meat diet than on a lower-fat, higher-carb diet.13
No surprise there.
“The cheese and meat diets were enriched with foods rich in polyunsaturated fats such as nuts, canola oil, and sunflower oil, which are known to lower LDL cholesterol,” wrote Peter Marckmann of the Roskilde Hospital in Denmark in a letter to the editor.
“The diets were apparently designed so that the possibly desired conclusion could be drawn.”14
That said, butter may raise LDL slightly more than cheese.
In the largest study—funded by the Canadian dairy industry—LDL was 4 points higher when people ate about 10 pats of butter than when they ate about 3 ounces of cheese a day. (The two foods supplied the same amount of sat fat.)
However, the researchers reported much bigger differences in LDL when they switched people from butter to polyunsaturated fat (18 points lower), monounsaturated fat (10 points lower), or carbs (7 points lower).15
“It’s conceivable that fermentation may mitigate the LDL-raising effect of the palmitic acid in cheese,” says Hu. “By how much, it’s hard to know.”
“But that doesn’t exonerate the palmitic acid and other saturated fats in cheese. It just means that when it comes to raising LDL, cheese is the lesser of two evils, and they’re both worse than unsaturated fats.”
That fits with studies that ask people what they eat and wait years to see who gets heart disease.16
“There’s certainly no good evidence that high-fat dairy is better than low-fat,” says Hu. And pushing high-fat dairy could also lead to worse diets.
“We eat much of our dairy in foods like cheeseburgers and pizza,” notes Hu.
“Promoting high-fat dairy would do more harm than good because when we eat those foods, we get not only saturated dairy fat but also processed meats, refined carbs, and sodium.”
Bottom Line: Dairy fat hasn’t earned a clean bill of health for your heart.
MYTH: Full-fat dairy wards off diabetes.
“Can type 2 diabetes be prevented by cheese?” asked the headline in Newsweek last year.
But something else about those people could have explained their lower risk.
And the biomarkers—primarily blood levels of two fats (pentadecanoic acid and heptadecanoic acid) that make up about 2 percent of dairy fat—aren’t perfect.
“Those biomarkers are not equivalent to full-fat dairy in the diet,” says Harvard’s Frank Hu. Among the reasons:
■ Lower-fat dairy: The biomarkers may identify people who consume the most lower-fat dairy. “Low- or reduced-fat milk, yogurt, and cheese have less fat, but if you consume enough, they could supply as much fat as a daily serving of full-fat dairy,” says Hu.
■ Fish & fiber: “You can get small amounts of those fats from some fish,” notes Hu. Eating some types of fiber may also raise blood levels.18
■ We may make them: “The amount in our bodies could refiect metabolic pathways that we don’t know or understand,” says Hu.19 In one study, when people were fed extra high-fat dairy, one of the biomarkers didn’t budge.20
What’s more, the results on blood fats don’t match the results from studies that track what people eat for years.
When Dutch researchers looked at 22 studies on nearly 580,000 people, each daily serving of any dairy was linked to only a barely significant 3 percent lower risk of type 2 diabetes.21
And there were hints that the risk of diabetes was lower only in people who ate low-fat dairy and only in Asian, not European, populations.
Was the risk lower when researchers looked at cheese alone? Nope. Ditto for milk. People who ate a small (1/6 cup) daily serving of yogurt had a 12 percent lower risk, but the risk didn’t drop further in those who ate more yogurt.
“In many studies, yogurt is a good marker for health-conscious people,” notes Hu. Could that or something else about yogurt or dairy eaters explain their lower risk?
To find out, a few studies have tested high-fat dairy on blood sugar and other surrogates for type 2 diabetes risk.
But when researchers randomly assigned people to diets that were higher or lower in dairy fat for a month, they saw no difference in blood sugar or insulin levels.22
The results of a three-month, industry-funded study are expected soon. Stay tuned.
Bottom Line: So far, there’s no solid evidence that full-fat dairy prevents type 2 diabetes.
MYTH: Full-fat dairy keeps the weight off.
“How full-fat dairy helps keep you lean,” ran the headline on Verywellfit.com in April.
“We have been brainwashed to believe these types of full-fat dairy foods contribute to weight gain and obesity,” declared the author. “According to more recent studies, eating full-fat dairy may actually keep you thin.”
How? “In order to make low-fat dairy products taste good, the fat has been replaced by sugar and other additives,” explains Verywellfit.com. Really?
We looked at 10 popular brands of yogurt—roughly 150 in all—that had both whole-milk and low-fat or fat-free flavors. Ounce per ounce, total sugars were typically no different.
Another key argument for full-fat dairy: it curbs hunger.
“But the evidence is very limited,” says Harvard’s Frank Hu. “In our studies, neither high-fat nor low-fat dairy is linked to less weight gain over time.”
His studies track people for years or decades. But why wait that long when you can give people high-fat or low-fat dairy for a few months to see what happens to their weight?
In one of the few good studies, Spanish researchers gave 45 college students 3½ servings a day of full-fat or low-fat milk and yogurt for two months each. They gained two pounds on the full-fat and zero on the low-fat dairy.23
A new three-month study, funded by the dairy industry, may help answer the question.
Even so, “the most troubling problem with dairy research is that so much of it is funded by the dairy industry,” says NYU’s Marion Nestle.
Bottom Line: Don’t assume that full-fat dairy helps keep you trim.
1Am. J. Clin. Nutr. 2019. doi:10.1093/ajcn/nqz035.
2Arch. Intern. Med. 154: 1261,1994.
3Am. J. Clin. Nutr. 108: 33, 2018.
4Eur. Heart J. 40: 583, 2019.
5J. Am. Heart Assoc. 2017. doi:10.1161/ JAHA.116.004947.
6Arch. Intern. Med. 172: 555, 2012.
8PLoS One 2017. doi:10.1371/journal.pone.0170664.
9J. Nutr. 141: 2180, 2011.
10Eur. J. Clin. Nutr. 66: 1229, 2012.
11Am. J. Clin. Nutr. 104: 973, 2016.
12Am. J. Clin. Nutr. 105: 1017, 2017.
13Am. J. Clin. Nutr. 102: 573, 2015.
14Am. J. Clin. Nutr. 103: 291, 2016.
15Am. J. Clin. Nutr. 105: 800, 2017.
16Am. J. Clin. Nutr. 104: 1209, 2016.
17PLoS Med. 15: e1002670, 2018.
18Am. J. Clin. Nutr. 105: 1544, 2017.
19Molecules 20: 2425, 2015.
20Sci. Rep. 2017. doi:10.1038/srep44845.
21Am. J. Clin. Nutr. 103: 1111, 2016.
22J. Nutr. 144: 1753, 2014.
23J. Hum. Nutr. Diet. 22: 336, 2009.
TMAO: Troublemaker from Meat?
Remember those misleading red-meat-is-no-different-than-white-meat headlines? In fact, red meat is worse, not only for cholesterol but also for TMAO.1
When microbes in our intestines “eat” carnitine or choline, they make TMA (trimethylamine), which gets converted to TMAO (trimethylamine N-oxide) in the liver.
Carnitine is found largely in red meat (beef, pork, lamb, and veal). Egg yolks and liver have the most choline.
“Higher blood levels of TMAO predict a heightened risk of heart attack or stroke,” says the Cleveland Clinic’s Stanley Hazen.
(As a co-developer of a TMAO blood test offered by Quest Diagnostics, Hazen could receive royalties from its use.)
If you lower TMAO levels, does the risk of a heart attack or stroke drop? So far, no human studies have looked. But other evidence on TMAO is troubling.
“TMAO not only increases atherosclerotic plaque in animals’ arteries,” says Hazen. In a pilot human study, “higher blood levels caused blood cells called platelets to become more sticky.”2
Sticky platelets are more apt to form the blood clots that trigger most heart attacks and strokes.
When people in the latest study ate lean beef (roughly 8 oz. a day) for a month, “blood levels in virtually every person moved into what we’d call the danger zone,” says Hazen. Why?
“Red meat increased the capacity of their gut microbiomes to make TMA.” It also made their kidneys excrete less TMAO.
What’s more, notes Hazen, “these people were all young and healthy.” TMAO may pose a greater risk for people with chronic kidney disease. On the upside, he adds, “TMAO came down after four weeks on either a white meat or non-meat diet.”
One quirk about TMAO: a few deep-sea fish—like cod, haddock, and halibut—have very high levels.
“It’s only in a subset of the deep-water fish that are harvested when they’re in cold waters,” says Hazen. “TMAO acts as an antifreeze, but enzymes chew it up when the fish reach warmer water.”
Bottom Line: TMAO aside, there’s plenty of reason to cut back on red meat. You can also avoid TMAO by ditching multivitamins or other supplements that contain carnitine, choline, or phosphatidylcholine (lecithin).
Photos: azurita/stock.adobe.com, Maksym Yemelyanov/stock.adobe.com (gut microbes). Diagram: Adapted from N. Engl. J. Med. 368: 1575, 2013.