This paper is a fucking banger, i recommend reading it, at least the introduction, and the discussion.

Over the last 50 years, although the associations between meat eating and illness are circumstantial and controversial to some extent, they have prompted the spread of vegetarianism and veganism, based on the assumption that non-meat diets provide more health benefits than diets that include meat.

One might say it has been political

there has been prevailing research stating that vegetarians tend to have greater life expectancy compared with non-vegetarians in some populations, particularly among Seventh-day Adventists. However, lack of population representativeness and failure to remove the influence of lifestyle in these studies have been heavily criticised. Thus, the suggestion that vegetarian diet improves longevity is questionable. For example, several studies with large sample sizes conducted in Australia and the United Kingdom did not show that meat eating correlated negatively with life expectancy after controlling for health-related elements of lifestyles.

Meat intake has been associated with adverse health issues, but the evidence in support of this hypothesis is limited and reliant on epidemiologic associations as opposed to clinical trials, which are supposed to reveal a cause-and-effect relation

This population-based study, using data collected by the United Nations and its agencies, tests the hypothesis that, worldwide, populations with more meat consumption have greater life expectancies.

Cereals, starchy roots and sugars are primarily energy sources that do not provide a large nutrient range. They have been clustered and new variable “carbohydrate crops” was created as the independent contrast variable to meat. Another reason for clustering is that meat used to provide over 50% energy needs before the introduction of agriculture circa 11–9000 years ago, while carbohydrate foods eventually became a source of over 50% of current human energy needs

it is necessary to highlight that, in order to reflect the real meat consumption in human diet, we included total meat intake, instead of a particular animal meat or a particular group of animal meat as the predicting variable. As per the FAO, meat is defined as “flesh of animals used for food”, and total meat includes beef and veal, buffalo meat, pig meat, mutton and lamb, goat meat, horse meat, chicken meat, goose meat, duck meat, turkey meat, rabbit meat, game meat and offal.

They took into account population vegetarian levels https://en.wikipedia.org/wiki/Vegetarianism_by_country#Summary_table wow... china has 14% vegetarians?

Figure 2 SEARO is bucking the trend, i wonder why

However, with meat intake and the same potential confounding factors being kept constant, carbohydrate crops do not correlate with life expectancy and child mortality at all. This may imply that meat intake correlates with life expectancy not because of its energy contribution, but rather due to other nutrient effects.

This might be a indicator that carbohydrates are a net negative on their own, "empty calories" pushing out nutritious food.

Statistically, the finding of this study unequivocally indicates that meat eating benefits life expectancy independently.

1. Health effects of a vegetarian diet may be only a perceived benefit. The correlation identified between vegetarian-ism and high life expectancy may not necessarily depend on their diets, but rather on the lifestyles that vegetarians maintain. 18 It is important to acknowledge that vegetarians (especially in western countries) tend to be more “health-conscious”, with overall healthier lifestyle patterns than other people. Two studies conducted among British people have shown that vegetarians and non-vegetarians had very little20 and even no difference 19 in life expectancy if other healthy lifestyle factors were considered. A study on the cohort consisting of 243,096 adults in Australia revealed that the protective effects of variations of vegetarian diets (semi-vegetarians or pesco-vegetarians) on life expectancy depended on multiple potential confounding factors, such as age, smoking and alcohol consumption, history of type 2 diabetes and cardiovascular diseases.18 Therefore, it is apparent that the advocacy of vegetarianism to increase longevity may have been biased

2. Vegetarianism study designs were flawed in that research subjects were not representative of the general population. 86 With the exception of India and some Buddhist cultures, vegetarianism is practiced by a small percentage of world population. On this note, the Seventh-day Adventist cohort has been over researched in order to demonstrate the relationship between vegetarianism and life expectancy. 12–14 However, studies in non-Adventist vegetarians have shown nil or very weak correlation between vegetarian diet and longevity. 86 Importantly, the Seventh-day Adventist population engages in a beneficial life-style, which includes non-smoking, marital maintenance, regular exercise and maintaining normal body weight.

The healthy user bias we always talk about. India has the highest rate of vegetarians 39% in the world AND the highest rate of type 2 diabetes (30%)

Eating a vegetarian diet and identifying as vegetarian are two different things. Ruby (2012) and Rosenfeld and Burrow 3,69 have concluded that the majority of self-identified vegetarians may still eat meat occasionally. This would allow them to absorb the unique nutrients from meat

That is a hell of a confounder, some vegetarians are secretly eating meat and not reporting it... one of the major dangers of FFQ (food frequency questionnaires)

We are advancing the correlation between total meat, instead of red meat, and life expectancy. This hypothesis is supported by a systematic review concluding that total meat consumption did not facilitate the onset of atherosclerosis

2. Populations across the globe (representing about 90% of extant humans) were considered in this study as units. Data included in this study were aggregated at the population level, so that they include information relevant for all people in each population. Thus, we did not study a “sample” but practically the whole population. This had the advantage in overcoming the common biases in studies of limited sample size.

It's hard to argue 90% of all living humans isn't a large enough sample size.

The argument that vegetarians have long life spans is questionable since most of the studies supporting this statement were conducted within the specific groups of people, such as Seventh-day Adventists. This argument may also be biased due to the “healthy cohort effect”, which drives health conscious people to be more likely to be recruited and remain in the study cohort than non-health conscious people.

This cannot be repeated enough, observational studies have a huge problem with healthy user bias. That is why they are hypothesis generating and cannot prove causation.

Reporting bias in nutrition studies has been a constant issue as food intake data must be reported by volunteers accurately and truthfully. However, a number of studies have shown that people tend to underreport energy intake 121 and overreport healthy food consumption

i.e. vegetarians who eat meat.

the food group variables included in this study should be the true consumed quantities, rather than their supply quantity as food wastage was not considered during data collection.

here is the tradeoff, no FFQs, but not all food is eaten by populations so we have be over estimating the consumption.

This study has shown that meat intake is positively associated with life expectancy at national level. The underlying reasons may be that meat not only provides energy but also complete nutrients to human body. From the evolutionary point of view, meat has arguably been an indispensable component in human diet for millions of years, which is evidenced, genetically, by meat digesting enzymes and digestive tract anatomy. The complete nutritional profile of meat and human adaptation to meat eating have enabled humans to gain many physical benefits, including greater life expectancy. Meat intake, or its adequate replacement, should be incorporated into nutritional science to improve human life expectancy.

Thoughts :

• Great paper
• not dependent on FFQs
• hard outcomes (death), and hard data (food in a country)