If you read the health section of your local newspaper or favorite online news aggregater last week, you no doubt saw the frightening headlines about eating meat being as bad as smoking, or how high-protein diets are now linked to cancer. Here are a few of them:

* Why High-Protein Diets May Be Linked To Cancer Risk
Forbes
* Too much protein as bad as smoking
Independent Online
* High-protein diet in middle age can lead to early death
eMaxHealth
* Are burgers as bad as cigarettes? Unravelling the truth about diet and disease
Telegraph.co.uk (blog)

The research involving humans is so badly conducted that it cannot be seen as representative of even a correlation, let alone causation. The mouse portion of the study is a little more interesting, but it's still not capable of showing cause and effect.

Fortunately, New Scientist has a short but sweet debunking of all those scare-tactic headlines. And National Geographic looks at the real issue, according to other research, which is blood levels of
insulin-like growth factor-1 (IGF-1).

I can has cheezburger? Protein cancer risk overblown

18 March 2014 by Catherine de Lange

Are you middle-aged and partial to cheeseburgers? If so, you may be concerned by a study suggesting you have a much greater risk of dying from cancer than your peers who favour a less protein-rich diet. But not all researchers agree with the study's findings.

Morgan Levine at the University of Southern California in Los Angeles and her colleagues analysed a dietary survey of more than 6300 people in the US aged over 50. Those aged 50-65 at the time of the survey and who had a high-protein diet – one where protein supplied a fifth of calories – were 75 per cent more likely to have died over the next 18 years than peers who only got 10 per cent of their calories from protein.

The high-protein eaters had a cancer death rate four times that of their low-protein peers. Statistical analyses showed that the findings only held for animal protein diets – in other words, protein from meat and dairy rather than beans and pulses.

In a follow-up study in mice, the team also found that animals fed a low-protein diet had a lower incidence of cancer than those on a high-protein diet. The low-protein mice that did develop the disease had slower-growing tumours.

Lots of leaps

But Tim Key, a Cancer Research UK epidemiologist based at the University of Oxford, says the dietary survey is too small to provide any robust conclusions.

Catherine Collins, chief dietician at St George's Hospital, London, doesn't dispute the results in mice, but says the authors make a lot of leaps when trying to apply the findings to humans. What's more, the conclusions are based on a single survey of what people reported eating in the preceding 24 hours. "As a dietician that's worrying," she says. "There are so many errors with the data collection. It implies people's diet doesn't change over 18 years."

Study co-author Valter Longo, also at the University of Southern California, counters that the participants said that the 24 hour period was representative of their diet. "Most people don't change their diet very often," he says.

Different health organisations recommend consuming different amounts of protein. Longo says that people in middle age should try to eat at the lower end of these recommendations.

Collins isn't convinced. "We don't need to do anything different, and nor should we be worried [on the strength of this study]," she says.

Journal reference: Cell Metabolism, DOI: 10.1016/j.cmet.2014.02.006

Here is the National Geographic article about IGF-1 and the health risks of having too high of levels of this growth factor (a molecule created by the metabolizing of human growth hormone).

Behind the News: Why a High-Protein Diet in Middle Age May Increase Risk of Death

Levels of a growth-related molecule in the blood may be key.

Eating a high-protein diet during middle age may be as harmful as smoking, a scientist says.  PHOTOGRAPH BY ANDREW SCRIVANI, THE NEW YORK TIMES/REDUX

Stephen S. Hall
for National Geographic
Published March 8, 2014

On March 4, scientists reported that people who ate a diet rich in protein during their middle-aged years (ages 50-65) were four times more likely to die from cancer than those who ate a low-protein diet, and had a 75 percent increase in overall mortality.

Valter Longo of the University of Southern California, who led the study, likened the risk of a high-protein diet to that of smoking. The key to these startling findings—underreported in many media accounts—is the role of a molecule called insulin-like growth factor-1 (IGF-1).

This same molecule was the prime player in a highly publicized study published three years ago by Longo, along with Jaime Guevara-Aguirre of the Institute of Endocrinology, Metabolism and Reproduction in Quito, Ecuador, and their colleagues, that looked at patients in a remote area of southern Ecuador. The subjects of the study had a rare mutation that interfered with the normal functioning of IGF-1, blocking the body's normal growth pathway. As a result, adults with the disease (known as Laron syndrome) rarely grew beyond 3 1/2 feet tall.

But the scientists observed an unusually beneficial side effect of the disease: The "Larons" did not get cancer, they claimed, and did not get diabetes, even though they were often obese. (Read "On Beyond 100" in National Geographic magazine.)

For the recent study, published in the journal Cell Metabolism, the scientists analyzed data from the Center for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES).

In an unexpected twist, the researchers also reported evidence that after age 65, a high-protein diet seemed to have the opposite effect: It protected against mortality.

In other words, a low-protein diet during middle age appears to be protective, but the same low-protein diet in older adults has deleterious effects.

To explore these puzzling results and the role of IGF-1, National Geographic spoke with Longo earlier this week.

For a number of years you've been studying a population in Ecuador with a growth disorder, and in 2011 you reported the relative absence of cancer and diabetes mortality in people with Laron syndrome. How does this new report tie in to that earlier research?

The Laron study was a continuation of our work that we started 20 years earlier. When we put it all together, the obvious thing was, in both in mice and humans, when they eat [a low-protein diet], we predicted that they would have low levels of IGF-1. So I started bugging everybody in the world that had any databases. It turned out that here at USC, downstairs from our lab, we had some people who had been studying NHANES for years. It was a perfect database to look at, because it was nationally representative; it's done by the CDC, and the sample and the measurements are considered to be very reliable.

There are several surprising claims in this new study, but let's talk about perhaps the biggest: A high-protein diet during middle age was associated with a much greater risk of dying of any cause, especially cancer, than a low-protein diet. In fact, you liken the mortality risk of the high-protein diet to that of smoking. How would you explain this association?

The more protein you eat—and this is very clearly shown by clinical work by others—the more IGF-1 activity you have. And we see the same in mice. There was a paper that came out in the same issue of Cell Metabolism, looking at all kinds of combinations of micronutrients, and in fact the best combination for longevity was low-protein, high carbs.

And just to be clear: When you say high-protein or medium-protein diet versus low protein, what exactly do you mean?

High protein means 20 percent or more of the calories is coming from protein; moderate is 10 to 20 percent; low is less than 10. We looked at animal-based and plant-based proteins.

One of the other surprises in the study is what you refer to as a "dramatic switch"—a point when a low-protein diet seems to stop being protective and starts having negative effects. How did you identify that shift, at what age does it occur, and why do you think it happens?

So when I first sat down with the epidemiologist, the analysis was done for the whole survey, from ages 50 on up. And we saw nothing. But we were seeing in mice that if you starve a young mouse or a middle-aged mouse, it does very well. But we started seeing that when we starved old mice in the same way, they were struggling. That's when I started thinking, "Hmm, I think that there are two major phases, if not more."

I went back to the epidemiologist and said, "Can you reanalyze the data and break it down into two groups? [Up to 65 years old, and after 65.] And sure enough, she came back and said to me, "Valter, it's incredible." Now we know why we didn't see it before. [In the original analysis] the effects in the old were offsetting the effects in the middle-aged.

You also conducted complementary studies of high-protein and low-protein diets in mice and yeast. Those studies suggested a role for IGF-1. Can you explain your working hypothesis about the possible role of IGF-1 in cancer, and in mortality in general?

We know that in either animals or humans, if the diet is low in protein, the level of IGF-1 goes down—or way down, depending how severely you restrict protein. If you look at humans, it's a pretty large change [in IGF-1 levels] between the high-protein group and the lowest-protein group, with the moderate-protein group in between.

So then how does it lead to cancer? Well, that was basically our paper three years ago on the Larons, which showed that if you take the blood from the Larons [which essentially has no IGF-1] and you expose human cells to it, and then you try to damage those cells to make them precancer cells, the absence of IGF-1 has a protective effect in two ways. First, as we have known for years from yeast, the lack of IGF-1 protects DNA from damage in the first place. Second, the lower IGF-1 now makes the mammalian cell more likely to go into what is called "programmed cell death," or apoptosis.

And the cell dying in that instance is a good thing?

Yes—because it's a cell that's about to become a cancer cell. So there's a dual protective effect. You try to prevent DNA damage from happening in the first place, but when the damage does happen, the [precancerous] cell is much more likely to die.

We showed this very clearly in this new study, where a cancer [in mice] progresses more slowly on the low-protein diet.

This new paper suggests that animal proteins, as in red meat, have a different effect on this biochemical pathway than plant proteins, as in vegetables. At the biochemical level, why would cells see a difference between animal proteins and plant proteins?

When we did the mouse studies, we did see a trend for decreasing IGF-1 with soy protein versus animal protein. We are doing more studies now, looking at different protein sources and IGF-1 levels. We suspect that the amino acid profile of plant proteins is going to control IGF-1 differently, but we need to test that more carefully.

Just to make sure the proper caveats are introduced here: This study finds an association between diet and mortality, but doesn't prove that a high-protein diet in middle age causes an increased risk of dying. And one of the limitations with the NHANES study is that it is based on a single, one-time recall of a person's diet over a 24-hour period, and then you're associating mortality up to 18 years later from that single dietary report.

Well, there's not many things you can do that are not going to have limitations. I think this needs to be viewed in the context of a number of other studies done, including the Laron study.

Frank Hu at Harvard looked at high animal proteins and fats in diets and low carbs, and even if he didn't break it down into age segments, he still saw that people eating high animal food diets and low carbs were the ones with the highest overall mortality risk, the highest cancer risk, the highest cardiovascular risk.

And certainly if you look at long-lived populations around the world, this is really consistent with that. So whether it's the California centenarians, the Okinawans, the southern Italians—the common denominator seems to be a low-protein, high-plant-food-based diet.

Every experimental result points to the next experiment. What's the next step here?

We're doing a clinical trial that we started a year ago, and in that clinical trial we're basically saying to people, "Don't change what you do in terms of diet." But we do ask them to switch once a month for five days to a diet that mimics fasting. We want to see if this periodic exposure to these more extreme diets can actually reprogram the system so the IGF-1 pathway is switched to a more beneficial mode, similar to what you would see in somebody having the perfect diet.

"Real" Men Eat Meat Because that Is What Manly Men Do

This story was meant to lead into the Thanksgiving holiday, a day when many men in the country will experience the "meat sweats" due to an over-consumption of turkey or ham (Joey on Friends coined the term "meat sweats" for the rise in metabolism that occurs as a result of massive protein intake).

It's past Thanksgiving now, but this is still an interesting article in that there is actual research (published in Psychology of Men & Masculinity, a journal of the American Psychological Association) showing that men eat meat because they associate meat with masculinity.

One caveat, the researcher in this article states that meat eating is associated with increased risk of cancer - which is only partially true. The way the meat is cooked and the type of meat makes all the difference. For example, beef is very unhealthy when cooked over a flame or in a frying pan, but not so when cooked in an oven. Furthermore, meat includes chicken, fish, and turkey, as well as ham, bison, elk, and any other protein source that once had eyes.

Why real men eat meat: It makes them feel manly

By Maggie Fox

NBC News

updated 11/21/2012

As red-blooded Americans dig into their Thanksgiving meals this week, it’s safe to say most are eating turkey. It’s also likely there will be some manly activities – watching football, maybe even playing some football. 

The two aren’t unrelated, says Hank Rothgerber of Bellarmine University in Louisville, Ky. In fact, some research he’s done suggests that eating meat is deeply intertwined with American perceptions of masculinity.

“There is a group of manly men who swear off what they call chick food, and they seek a double whopper to declare their manhood,” Rothgerber told NBCNews.

“It makes them feel like real men,” he writes in a study published in Psychology of Men & Masculinity, a journal of the American Psychological Association.

“Meat consumption is a symbol of patriarchy resulting from its long-held alliance with manhood, power, and virility.”

And Thanksgiving, with its celebration of deep-fried turkeys, Turduckens and other symbols of cooked-flesh overload, might just be the pinnacle of this manly display.

“When men consume meat in this way, especially when it’s public and it’s celebrated, they are validating their manhood and feeling good about what they are,” Rothgerber says.

Rothberger, who teaches psychology, has been trying to understand why so many Americans cling so desperately to their meat-eating habits despite a growing body of research that eating a lot of meat is not only bad for our bodies, but for the environment.

“Meat-eating contributes more to global warming than even auto emissions,” says Rothgerber. He cites a 266 report by the United Nations and a 2008 report by the Pew Commission on Industrial Farm Animal Production  that concluded that farmed animals contribute 40 percent more to global warming than all transport combined.

“A 2008 German study concluded that meat eaters contribute seven times as much greenhouse gas emissions as vegans,” he writes in his report.

Heavy meat-eaters have a higher risk of cancer, heart disease and other ills than people who eat little or no meat. 

“There’s a growing awareness that it’s not great to eat meat, but still, people are doing it,” Rothgerber said in a telephone interview.

So he conducted two studies to find out why. He surveyed 125 undergraduate psychology students for one study, and 89 for the second.

“Men expressed more favorable attitudes toward eating meat, denied animal suffering, believed that animals were lower in a hierarchy than humans, provided religious and health justifications for consuming animals, and believed that it was human destiny to eat meat,” he found. “These are direct, unapologetic strategies that embrace eating meat and justify the practice.”

The men said animals "just taste too good to not eat them,” he said. “Females -- they are more likely to take what I consider to be indirect and apologetic attitudes.”

Rothgerber is the first to admit his study is limited – the students he surveyed were mostly white and middle-class and they were in their late teens and early 20s. But he thinks if anything, this group would under-represent the effects of masculinity and meat-eating in our culture.

“It’s possible that in certain ethnic groups there could be even more pressure to prove manhood by eating more meat,” he said.

The idea that people think eating meat is manly is hardly revolutionary, but there have been very few studies done on it. Most have been done in Europe.

In the United States, where surveys suggest just over 3 percent of the population admits to being vegetarian or vegan, most research has been done by groups seeking to promote meat-eating, such as the National Pork Board, the National Cattlemen’s Beef Association and the U.S. Department of Agriculture.

Last March, a team including Paul Rozin of the University of Pennsylvania and Brian Wansink of Cornell University showed consumers link meat with masculinity. "To the strong, traditional, macho, bicep-flexing, All-American male, red meat is a strong, traditional, macho, bicep-flexing, all-American food," they wrote in the Journal of Consumer Research.

So what does a vegetarian like Rothgerber do on Thanksgiving? 

"I do feel personally that my manhood is a little more under scrutiny, especially because Thanksgiving is all about the turkey,” he says. “I think I really don’t need to validate my manhood.”