Indeed, a considerable number of people in modern society are strict vegetarians, mainly because many studies have linked eating meat, especially red meat, with total mortality, cardiovascular disease incidence and cancer incidence. Red meat is specially labeled as unhealthy food, and some people even list meat as one of the driving factors of the global crisis system related to health and environment. So, can we still eat meat well?
Contemporary arguments against eating meat mainly focus on nutrition, environment and ethics. We mainly want to discuss strict meat restriction or avoidance and the potential impact of this dietary restriction on health from the perspective of nutrition. We believe that the statement that red meat is harmful to health is not only impossible from our evolutionary history, but also far from strong scientific evidence. Recently, Food Science and Nutrition Review published "Should dietary guidelines recommend low intake of red meat?" This was discussed in a scientific paper in. Their summary can be said to hit the nail on the head. The following are some key points of the article to share with you.
Meat has always been an important part of people's diet all over the world.
For millions of years, meat has been an important part of human diet all over the world. Archaeological findings show that 2.5 million years ago, ancient humans slaughtered animals with stone tools. Biologically speaking, human beings have adapted to a diet including meat.
The fact that we have been physiologically adapted to a diet containing a lot of meat does not in itself prove that a low-meat diet is unhealthy. However, almost all species are in the best health condition when their diet is roughly similar to the diet to which they are adapted. In theory, human beings are no exception.
However, mainstream nutrition often describes meat as a health disaster and thinks that it can be easily replaced by beans and vitamin B 12 supplements. In addition, a large number of international and peer-reviewed scientific data have also become the basis for many people to oppose eating meat. It has been repeatedly pointed out in various academic documents that high meat intake is related to high mortality, cardiac metabolic diseases, various types of cancer and intestinal diseases. 20 19 65438+ 10/6, The Lancet officials expressed their hope to change the diet to plant food and suggested reducing the intake of meat. They think that a stricter vegetarian diet or even a vegan diet is a more beneficial choice. Is that really the case? In fact, most of these data come from observational studies in the field of nutritional epidemiology, which has great limitations. Next, let's have a good analysis.
Evidence evaluation of meat intake and chronic diseases
Although epidemiology has many advantages as a scientific discipline, in the past decades, a large number of usually unreliable and exaggerated observational research results have been accumulated in the field of nutrition. The explanation of these findings is often exaggerated by the media and affects our nutrition guidelines.
First of all, the data about meat intake is obtained through the food frequency questionnaire, and the data about diet obtained from the food frequency questionnaire should be interpreted carefully. For various reasons, such as memory deviation, they may have problems and be less accurate.
Secondly, diet is difficult to be independent of other lifestyle factors. Studies show that people who eat meat are usually accompanied by unhealthy living habits such as insufficient dietary fiber intake, drinking, smoking and lack of exercise. In addition, the relationship between eating meat and diseases seems to be different in different cultural backgrounds. In North America, the relationship between eating meat and diseases is often higher than that in Europe or Asia. For example, a comprehensive analysis of a prospective cohort study in South Korea even shows that red meat intake is related to the reduction of cardiovascular disease mortality in men and cancer mortality in women. Similarly, if the Seventh-day Adventist research is excluded from the meta-analysis, the beneficial relationship between vegetarian diet and cardiovascular health is either not so obvious or does not exist, which indicates that this may be due to the influence of healthy lifestyle, not the low meat intake itself. This is very important, because the Seventh-Day Adventist will have a considerable influence on the dietary advice all over the world.
Third, the relative risk rate obtained from observational studies is generally low, far below 2. Relative risk rate refers to the ratio of the probability that a group is exposed to a certain risk and the probability that an event is not exposed to that risk occurs. In view of a large number of false positive findings and the huge uncertainty and deviation of the data caused by the above problems, such a low relative risk rate cannot be used as strong evidence alone in most epidemiological studies except nutrition. The results of observational studies with a relative risk rate below 2 are easily influenced by other factors and should be verified by other means, such as randomized placebo-controlled trials. For example, the relative risk rate of meat consumption associated with colorectal cancer is 1.2, while the relative risk rate of visceral fat associated with colorectal cancer is 5.9, so the latter is more worthy of priority.
In short, the current dietary recommendations on reducing meat intake are basically based on observational studies with a relative risk rate far below 2. It is not a good practice to infer the harm of eating meat from this weak correlation data, and it is often one-sided and inaccurate to incorporate observational research data into the formulation of diet policy. The conclusion of observational epidemiology is often untenable in randomized controlled trials. Nutritional epidemiology is a useful tool to put forward hypotheses, but its results can not provide a strong basis for policy making without further confirmation. The analysis of most observation data, no matter how complicated, can only be regarded as the basis of a hypothesis. This is especially true when the results are counterintuitive, just like eating meat. After all, meat has always been an important part of human diet.
Because of the highly heterogeneous results and the possibility of other confounding factors seen in most observation and analysis, we should carefully explain the epidemiological findings about meat intake. The interaction among meat, holistic diet, human physiology and health outcomes is very complex. The current epidemiological data can not prove that there is a consistent causal relationship between red meat intake and chronic diseases.
Randomized placebo-controlled trials play an important role in establishing causality, and usually the evidence they provide is stronger than the observed data. The existing evidence generally shows that red meat intervention will not lead to the increase of oxidative stress and inflammation in the body, and the increase of oxidative stress and inflammation is usually considered as a part of the potential mechanism of chronic diseases. In addition, the meta-analysis of randomized controlled trials shows that eating meat will not lead to the deterioration of cardiovascular risk markers. Although it seems that plant-based diets can indeed reduce the levels of total cholesterol and low-density lipoprotein cholesterol in intervention studies, they may also increase the level of triglycerides and reduce the level of high-density lipoprotein cholesterol, which are now generally considered as important indicators of cardiovascular risk.
Based on the above facts, we come to the conclusion that there is no strong evidence to prove that eating meat as a part of a healthy diet is clearly related to the occurrence of chronic diseases. It is very important to rate the existing evidence before providing dietary advice and formulating dietary guidelines. One of the founders of the evidence recommendation grading assessment, formulation and evaluation (GRADE) system warned the public that the scientific basis of the World Health Organization's International Agency for Research on Cancer on red meat was exaggerated, which was harmful to the public. The International Agency for Research on Cancer claims that red meat may cause cancer, but this claim has never been confirmed.
Dietary suggestions that meat is the internal cause of chronic diseases often seem to find fault with the research data and ignore some contradictory data.
A fact that is often overlooked is that most hunter-gatherers do not have heart metabolic diseases, but most of their energy comes from animal food, with an average of about two thirds, and some people even exceed 85%. In contrast, in modern society, we can only get about 30% calories from animal food.
In addition, although global meat consumption has been declining for more than a decade, heart metabolic diseases such as type 2 diabetes are increasing rapidly. Although this discovery can't solve the problem of causality, it should make people question the statement that meat is the culprit. In addition, some studies have found that meat intake has nothing to do with mortality/morbidity, while limiting meat intake is related to various negative health outcomes.
Another contradictory example is that epidemiological studies have pointed out that L-carnitine in meat will play a potential role in the occurrence of atherosclerosis by forming trimethylamine oxide (TMAO), but this is inconsistent with the results of intervention studies. In addition, other epidemiological data show that the intake of fish can increase the level of TMAO by an order of magnitude, but the intake of fish can improve the levels of triglycerides and high density lipoprotein cholesterol.
Nutritional value of meat
Throughout human history, meat has provided a variety of valuable nutrients, which are usually not easy to obtain from plants.
One of the main features of meat is, of course, its high protein value. Although both plant food and animal food contain protein, their amino acid compositions are quite different. Animal protein contains more kinds of amino acids than plant protein. Generally speaking, the proportion of amino acids in animal protein is closer to the proportion of amino acids needed by human body, while plant protein lacks some amino acids, especially lysine, threonine and methionine.
Vitamin B 12 is an indispensable vitamin for human body, which is involved in making bone marrow red blood cells, preventing pernicious anemia and brain nerve damage. Higher animals and plants can't make vitamin B 12 by themselves, and vitamin B 12 in nature is synthesized by microorganisms. Animals can synthesize vitamin B 12 through bacteria in the body. Therefore, the main dietary source is animal food.
Vitamin B 12 is the only vitamin that can be absorbed with the help of intestinal secretions (endogenous factors). We humans have lost the ability of the large intestine to absorb vitamin B 12, and the absorption of vitamin B 12 mainly occurs in the ileum of the small intestine. Although bacteria in our large intestine can also synthesize vitamin B 12, it can be absorbed by human body very little, which makes human beings have to rely on vitamin B 12 from food sources. It is speculated that our ancestors were able to survive after losing this ability because they often ate meat rich in vitamin B 12.
1.5000 years ago, ancient human skeletal remains showed signs of porous bone hypertrophy, which was usually related to the deficiency of vitamin B 12, but this phenomenon hardly existed in chimpanzees who could obtain B 12 from intestinal bacteria. This provides some evidence that at least in the early Pleistocene (2,588,000 years ago to 1 1700 years ago), meat was so important to the normal function of human beings that the lack of meat led to harmful pathological conditions.
In addition to vitamin B 12, meat can also provide vitamins A, D, K, iron, zinc, selenium and other minerals.
In addition, over time, compared with other primates, the ability of human beings to transform ω-3 fatty acid α -linolenic acid into biologically important long-chain ω-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is greatly reduced, which makes plants not the best source.
In addition, although neglected in most nutritional assessments, meat also contains various bioactive components, such as taurine, creatine, carnosine, conjugated linoleic acid, carnitine, choline, coenzyme Q and glutathione. These ingredients can provide important nutritional benefits, for example, contributing to the optimal development of cognitive function.
Evolution has adapted us to meat.
Some people may say that monkeys and orangutans are vegetarians and they are healthy. In fact, in evolution, the change from human food to high-energy meat has led to our intestines being much shorter than those of apes, especially the large intestine. The proportion of human intestines is also suitable for eating meat. Our small intestine is responsible for absorbing most nutrients, accounting for 56% of the total intestinal volume, while the large intestine accounts for about 20%. In apes, the proportion is just the opposite. This means that the way we absorb and obtain nutrients has also changed.
Eating meat and the related shortening of energy-consuming intestinal size are considered to play a vital role in the increase of human brain size. Because the brain and intestine compete for energy, when the intestine becomes smaller, the brain will grow. Therefore, in order to build and maintain a more complex brain, our ancestors may have used ingredients mainly found in meat, including iron, zinc, vitamin B 12 and fatty acids. Although plant foods contain many of the same nutrients, their contents are very low and usually exist in a form that is not easy to be used by human beings.
Therefore, it is especially recommended that people with high nutritional needs eat enough animal food, which is helpful to provide adequate nutrition at all stages of life. It contributes to the physical and cognitive development of infants and children; In the elderly, adequate meat intake can prevent or improve malnutrition and sarcopenia, and also improve the quality of life related to health.
Not eating meat will lead to the loss of nutritional stability.
Lack of animal food in the diet may lead to various nutritional deficiencies. As described more than a century ago, pellagra is still related to poorly planned vegetarianism. Vegetarians usually admit that these diets must be carefully planned to succeed, including regular supplementation of vitamin B 12 and other nutrients; But the reality is that many people who eat vegetarian food do not make efforts to supplement these nutrients, and they often fall into nutritional deficiency. In this case, the result may be malnutrition, poor health and nutritional limitation. Lack of vitamin B 12 in pregnancy, childhood and adolescence is particularly dangerous.
Other micronutrients that people who eat a plant-based diet may lack include but are not limited to iodine, iron, selenium and zinc. Even if the plant-based diet contains α -linolenic acid, it cannot prevent the lack of long-chain ω-3 fatty acids EPA and DHA, which may cause serious risks to pregnant and growing children.
A large number of clinical case reports in medical literature also recorded the risk of nutritional deficiency, and serious and sometimes irreversible pathological symptoms were reported in infants, children, adolescents and adults. Irreversible pathological symptoms usually include developmental stagnation, hyperparathyroidism, megaloblastic anemia, nervous system diseases such as optic nerve, lethargy, spinal cord degeneration, brain atrophy and other serious problems. In addition, although the causal relationship is not clear, statistically speaking, not eating meat seems to be related to eating disorders and depression, and nervous system problems may occur.
Conclusion: We should eat some meat in moderation.
For millions of years, meat has been the core component of our diet, but some nutrition authorities often keep close contact with animal rights protectors or other ideological vegetarians (such as Seventh-Day Adventists) to promote the view that meat will cause a series of health problems, which is nothing to recommend. We believe that most cases against meat are based on carefully selected "evidence" and low-quality and unreliable observational research data. It is totally unfounded to claim that red meat is "unhealthy food".
The fact that some people eat little or no meat shows that it is entirely possible to be vegetarian. At least in this era, nutrients such as vitamin B 12 can be obtained in the form of tablets. Some people even claim that they thrive in such an environment, and enthusiastically share the fruits and health gains gained on the vegetarian road. This does not necessarily mean that this is an ideal way. From a scientific point of view, sporadic anecdotes can't explain anything. In order to truly understand what kind of diet is ideal, thorough evolution and nutritional analysis are necessary. In this regard, vegetarianism is obviously insufficient.
We don't want to attack vegetarians or those who feel that they have benefited from this nutritional path, but we want to emphasize that it may be an adventurous path. As we mentioned at the beginning of the article, many vegetarian internet celebrities overturned and began to eat meat secretly. Meat is not only an important part of human diet, but also an excellent source of many important nutrients. It is also problematic to ingest a large number of certain nutrients in the form of dietary supplements alone, and there are problems in the absorption and balance of nutrients. It is not enough to obtain protein from high-protein plant foods (such as soybeans). Their amino acid composition is still far from what our body needs, which may lead to the lack of some amino acids. In addition, evolution has also adapted our intestines to eating meat. In a word, it is unreasonable not to eat meat at all for health.
Of course, it is very important that we never object to eating more plant-based food, but we can't just eat plant-based food. We believe that it is very wise to add an appropriate amount of animal food to the diet, because it is considered to promote satiety, mental health and musculoskeletal strength. However, please note that antibiotics and hormones are widely used in most meat farming processes, and they will remain in meat products. This kind of meat is very unhealthy. Try to choose meat products with reliable sources, high quality and less processing.
Some people may still choose to stick to a vegetarian diet, so they must be carefully designed to ensure a balanced intake of various nutrients, and often monitor their health status to see if they lack certain nutrients. Remember, don't blindly adopt a vegan diet.
References: Frederick Leroy &; Should Nathan Cofnas (2020) dietary guidelines recommend low intake of red meat? Key comments in food science and nutrition, 60: 16, 2763-2772, doi:10.1080/1040898+09.1657438.
The pictures are all from the Internet.