Eating steak causes cancer
Low health effects : Isn't red meat so unhealthy after all?
Few foods have such a bad reputation as meat and sausage. This is not only due to the fact that their massive production contributes to climate change and animals are kept and killed under sometimes catastrophic conditions. No, meat and sausages are also unhealthy, they can cause cancer and heart disease - they say.
That is why experts around the world have been recommending eating much less red and processed meat for years. The US health authorities, for example, are in favor of only one serving of meat per week (here as a PDF). In Great Britain, the guideline is 70 grams per day of meat and sausage products, and the German Nutrition Society (DGE) recommends that you rarely eat meat and sausage: in total, it should not be more than 300 to a maximum of 600 grams per week. Far less than it is eaten in Germany: According to the Federal Agency for Agriculture and Food, per capita consumption has been around 60 kilograms of meat and sausage per year for years. That is 1.15 kilograms per week, two to four times as much as recommended.
But what if that wasn't so bad after all? In what it claims to be the most extensive data analysis to date, an international research team has come to the conclusion that - at least in terms of health - there is very little benefit in going without meat.
The WHO classified processed meat as carcinogenic
The previous advice on abstinence is justified primarily with a higher risk of various diseases, primarily cancer. The DGE website reads: "Those who eat a lot of red meat and sausage have a higher risk of colon cancer." This assessment is based on scientific studies. In 2015, for example, a work by the International Agency for Cancer Research (IARC) of the World Health Organization (WHO) made headlines (summary as PDF).
Researchers evaluated more than 800 studies for this. At the end of their meeting, they saw enough evidence to classify processed meat - that is, cured, salted, fermented or smoked meat - as "carcinogenic". In contrast, unprocessed red meat, which in addition to beef also includes muscle meat from pork, sheep, veal, lamb, horse or goat, was classified as "probably carcinogenic". The risk of colon cancer increases by 18 percent if you eat 50 grams of processed meat a day, and by 17 percent for every 100 grams of unprocessed red meat, according to the result.
The researchers contradict almost all recommendations that exist
But now everything could be very different. Scientists from several countries have come together to fundamentally re-evaluate the study situation on the health effects of meat. The aim of this association - called NutriRECS - is to create scientifically sound recommendations in the area of nutrition - first of all for meat consumption.
To put it bluntly, one could interpret this as follows: The previous recommendations are not good enough, so we are now making our own. And this recommendation has it all: The group comes to the conclusion that adults can continue to eat as much meat and sausage as before. From a health point of view, doing without it probably makes little sense. This advice contradicts the vast majority of recommendations on meat consumption around the world.
The team consisted of researchers from the Canadian universities of Dalhousie and McMaster as well as experts from the Spanish and Polish Cochrane centers. Cochrane is an international network that has long been committed to science-based decisions in the healthcare system.
The scientists proceeded accordingly carefully in their analysis of the existing literature. They systematically examined the available information in four parallel studies. Their main focus was the possible influence of red and processed meat on heart disease, cancer and diabetes. In another study, they also analyzed people's attitudes towards their meat consumption.
Based on these results, 14 scientists from seven countries developed recommendations for the consumption of red and processed meat. The researchers published these six scientific papers on Monday in the renowned journal "Annals of Internal Medicine". This unusually concerted approach alone suggests that the researchers hope their results will have a resounding effect.
Many studies had methodological flaws
It is important to understand that there are no fundamentally new insights into how dangerous meat is for humans. The authors merely reevaluated the existing studies - more rigorously than most groups have done so far. For example, the IARC was based solely on observational studies when it classified processed meat as carcinogenic.
"That has always been the basic problem of nutrition studies," says Stefan Kabisch, study doctor at the German Institute for Nutrition Research (DIfE) in Potsdam-Rehbrücke. In such studies, for example, a retrospective questioning is used to determine how much meat people have eaten on average over the past few years. Researchers then use mathematical calculations to establish relationships between meat consumption and possible health effects. "In principle, however, you cannot prove that there is a cause-and-effect relationship, for example that meat consumption triggers cancer," says Kabisch.
Nevertheless, most studies are still structured in this way, because only with them can long periods of time be overlooked. In three of the four current papers, the researchers are analyzing those cohort studies in which a total of several million participants were examined.
But they also looked specifically for studies in which the participants had to adhere to a certain diet, about three less servings of meat per week than before. Such studies then examine whether people from this group, for example, develop cancer less often than those who continue to eat as before.
However, the researchers found a surprisingly small number of studies that matched their search criteria. In the end, only twelve out of more than 13,000 were eligible. Many of them also had methodological deficiencies. In some cases, for example, it was not explicitly stated whether the participants were diagnosed with cancer or had a heart attack; instead, the researchers had to be content with substitute parameters, such as the blood lipid level. Most of them also did not distinguish between red and processed meat. This made the analyzes even more difficult.
You can't trust the results
Overall, there was no statistically significant association between meat consumption and 13 different types of cancer, diabetes or heart disease. Specifically, this meant, for example, in relation to the risk of dying from cancer: If 1,000 people eat three less servings of red meat than usual each week for their entire life, only seven fewer will die from cancer than before.
"This means that only about one percent of people benefit from such a far-reaching change in behavior to such an extent that they do not die prematurely from cancer," says Jörg Meerpohl. The doctor heads the Institute for Evidence in Medicine at the University of Freiburg and contributed to the recommendation of the NutriRECS group. The numbers are similar for type 2 diabetes and the risk of dying from heart disease. Only with sausage and diabetes was the connection somewhat stronger.
In addition - and this is different from previous studies - the researchers rated how much one can trust these results. Very little is the answer. Because they rarely found high-quality studies, the authors rated their results as uncertain or extremely uncertain. This could mean that meat consumption has a slightly larger impact on health than stated, or a slightly smaller one. Above all, however, it means: The study situation is catastrophic, and no one can make sensible recommendations from it - actually.
Criticism of the researchers' approach
This is where the only one of the five studies comes into play that does not deal with risks, but with what people think about meat consumption. The result in a nutshell: People eat meat because they think it is delicious, because they think it is healthy and it should be part of their daily diet, or because they are unsure of what to replace it with. In any case, the authors write, most people do not want to do without meat at all. Not even if you tell them it is bad for their health.
Usually, such settings are irrelevant for recommendations. For the authors, however, they were the key to guessing: You can keep eating meat. Because if the effect of meat consumption is as small as described, if this effect is also extremely uncertain and people do not want to do without meat and sausage anyway, then - so the argumentation - one could also recommend continuing to eat meat.
However, this approach provokes criticism. Bernhard Watzl, head of the Institute for Physiology and Biochemistry of Nutrition at the Max Rubner Institute, says he could not understand why the authors had devalued the results of the studies examined so much: "There is so much scientific evidence that a nutritional pattern is involved lots of meat increases the risk of colon cancer, heart disease and diabetes. "
It is unclear whether this is due to the meat itself. It is more likely that people who eat a lot of meat also eat unhealthily in other ways - for example, eat little fiber and a lot of sugar. "In 95 percent of cases, a lot of meat means an unhealthy diet," says Watzl.
"Pudding vegetarians" also live unhealthily
In fact, the authors have tried to take such dietary patterns into account. But many studies fail to consider what causes participants to replace the meat they remove from the menu. "It is not because a form of nutrition is meatless that it is healthier", says DIfE researcher Stefan Kabisch.
There is, for example, the "pudding vegetarian" who does not eat meat, but instead eats a lot of sugar. Conversely, a relatively meat-heavy diet does not necessarily have to be unhealthy if it is accompanied by low-refined carbohydrates, a lot of fruit, vegetables and whole grains.
And, even if a Mediterranean diet with little red meat and a lot of vegetables is generally considered beneficial in studies: Nobody can say whether this is due to the lack of red meat or rather to the food mix itself. "Because of all these factors, there is no data basis to give a precise recommendation on red meat," says Kabisch. He sees the researchers' analysis as a plea for better nutritional studies.
The climate doesn't matter
Another point, however, is quite controversial: that climate protection and animal ethics play no role in the recommendations. "I ask myself: What time do the authors live in?" Says Watzl. As a scientist you have a social responsibility. "You can't say I'm just looking at the effects on health."
Meerpohl emphasizes that when making the recommendation, they deliberately did not take a social perspective, but an individual one: What can one advise the individual on the basis of the database? Personally, however, he could partially understand the criticism. "It's mentally difficult for me to completely separate myself from ethical and climate considerations," says Meerpohl. For these reasons, too, he was one of three researchers who voted against the recommendation to continue eating meat to the usual extent.
He also ensures that the message is spread undifferentiated to the public. "It would be unfortunate if it just came across that everyone should just keep eating as much meat as before."
Eat meat or not?
So what should you do? It is questionable whether meat and sausage per se cause cancer, heart attacks or diabetes. It probably depends on what you eat with or instead of. Kabisch, Watzl and Meerpohl agree, but it cannot do any harm to consume less meat. However, the data does not provide enough information to insist on insisting on health reasons, as the guidelines do worldwide.
Perhaps, as the scientists Aaron Carroll and Tiffany Doherty write in an accompanying article in the "Annals of Internal Medicine", it is time to better communicate to the public how uncertain the results of nutritional studies actually are with regard to health effects. After all, ecological or ethical motives can also induce people to change their behavior - this is also a result of the study.
So if you - for whatever reason - are already trying to eat less meat, you don't have to stop. And for everyone else, there are more reasons than - perhaps - a slightly reduced risk of cancer, to put vegetables on your plate from time to time.
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