Is Meat Unhealthy? Part VII

Looking at individual diseases is informative, but it can cause us to become myopic, making broad health-related decisions based on narrow information. It can cause us to miss the forest for the trees. In this case, the "trees" are individual diseases and the "forest" is total mortality: the overall risk of dying from any cause. Does eating meat increase total mortality, shortening our lifespans?

Non-industrial cultures

Traditionally-living cultures such as hunter-gatherers and non-industrial agriculturalists are not the best way to answer this question, because their mean lifespans tend to be short regardless of diet. This is due to ~30 percent infant mortality, which drags down the average, as well as a high risk of death in adulthood from infectious disease, accidents, and homicide/warfare. It can also be difficult to accurately measure the age of such people, although there are reasonably good methods available.

However, there are semi-industrialized cultures that can help us answer this question, because they feature a somewhat traditional diet and lifestyle, combined with modern medicine and the rule of law. The so-called Blue Zones, areas of exceptional health and longevity, fall into this category. These include Sardinia, Italy; Okinawa, Japan; Loma Linda, California; Nicoya Peninsula, Costa Rica; and Icaria, Greece.

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Is Meat Unhealthy? Part VI

In this post, I'll examine the possible relationship between meat consumption and cancer risk.

Is cancer risk even modifiable?

Cancer is caused by the uncontrolled division of a population of rogue cells in the body. These cells essentially evolve by natural selection to escape the body's multiple anti-cancer mechanisms.

To a large extent, cancer appears to be a numbers game. The human body contains about 37 trillion cells. To get cancer, all you need is one cell that develops key mutations that allow it to shed its built-in restrictions on cell division. The older you are, the more time you have to accumulate mutations, explaining why cancer risk rises sharply with age.

Unlike other common non-communicable diseases, we don't know to what extent cancer is caused by modifiable diet and lifestyle factors vs. bad luck that's completely outside our control. Some cancers, such as lung cancer, are typically linked to lifestyle factors like cigarette smoking-- yet the majority of cancers aren't so easily understood.

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Is Meat Unhealthy? Part V

In this post, I'll examine the possible relationship between meat intake and type 2 diabetes. Type 2 diabetes is the most common form of diabetes, and it is strongly linked to lifestyle factors.

Non-industrial cultures

Non-industrial cultures have an extremely low prevalence of diabetes, whether they are near-vegan or near-carnivorous. This is supported by blood glucose measurements in a variety of cultures, from the sweet potato farmers of the New Guinea highlands to the arctic Inuit hunters. Here is what Otto Schaefer, director of the Northern Medical Research Unit at Charles Camsell hospital in Edmonton, Canada, had to say about the Inuit in the excellent book Western Diseases (Trowell and Burkitt, 1981):
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Is Meat Unhealthy? Part IV

In this post, I'll address the question: does eating meat contribute to weight gain?

Non-industrial cultures

I'll get right to the point: humans living in a non-industrialized setting tend to be lean, regardless of how much meat they eat. This applies equally to hunter-gatherers, herders, and farmers.

One of the leanest populations I've encountered in my reading is the 1960s Papua New Guinea highland farmers of Tukisenta. They ate a nearly vegan diet composed almost exclusively of sweet potatoes, occasionally punctuated by feasts including large amounts of pork. On average, they ate very little animal food. Visiting researchers noted that the residents of Tukisenta were "muscular and mostly very lean", and did not gain fat with age (1, Western Diseases, Trowell and Burkitt, 1981).

!Kung man gathering mongongo fruit/nuts.
From The !Kung San, by Richard B. Lee.

Another remarkably lean hunter-gatherer population is the !Kung San foragers of the Kalahari desert. The !Kung San are so lean that many of them would be considered underweight on the standard body mass index scale (BMI less than 18.5). Average BMI doesn't exceed 20 in any age category (The !Kung San, Richard Lee, 1979). Is this simply because they're starving? It is true that they don't always get as much food as they'd like, but on most days, they have the ability to gather more food than they need. The fact that they are able to reproduce normally suggests that they aren't starving. Richard Lee's detailed work with the !Kung San indicates that approximately 40 percent of their calories came from animal foods during his study period in the 1960s. This was mostly meat, with occasional eggs when available.

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Is Meat Unhealthy? Part III

When we consider the health impacts of eating meat, cardiovascular disease is the first thing that comes to mind. Popular diet advocates often hold diametrically opposed views on the role of meat in cardiovascular disease. Even among researchers and public health officials, opinions vary. In this post, I'll do my best to sort through the literature and determine what the weight of the evidence suggests.

Ancel Keys and the Seven Countries Study

Ancel Keys was one of the first researchers to contribute substantially to the study of the link between diet and cardiovascular disease. Sadly, there is a lot of low-quality information circulating about Ancel Keys and his research (1). The truth is that Keys was a pioneering researcher who conducted some of the most impressive nutritional science of his time. The military "K ration" was designed by Keys, much of what we know about the physiology of starvation comes from his detailed studies during World War II, and he was the original Mediterranean Diet researcher. Science marches on, and not all discoveries are buttressed by additional research, but Keys' work was among the best of his day and must be taken seriously.

One of Keys' earliest contributions to the study of diet and cardiovascular disease appeared in an obscure 1953 paper titled "Atherosclerosis: A Problem in Newer Public Health" (2). This paper is worth reading if you get a chance (freely available online if you poke around a bit). He presents a number of different arguments and supporting data, most of which are widely accepted today, but one graph in particular has remained controversial. This graph shows the association between total fat intake and heart disease mortality in six countries. Keys collected the data from publicly available databases on global health and diet:

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Is Meat Unhealthy? Part II

Over time, animals adapt to the foods they regularly consume. This is how archaeologists can, for example, determine that Triceratops was an herbivore and Tyrannosaurus was a carnivore just by looking at the structure of the skeleton. Adaptations to diet extend beyond skeletal structure, into digestion, metabolism, the brain, musculature, and other aspects of physical function. What is our evolutionary history with meat?

Human Evolutionary History with Meat: 200 to 2.6 Million Years Ago

Mammals evolved from ancestral "mammal-like reptiles" (therapsids, then cynodonts) approximately 220 million years ago (Richard Klein. The Human Career. 2009). Roughly 100 million years ago, placental mammals emerged. The earliest placental mammals are thought to have been nocturnal shrew-like beasts that subsisted primarily on insects, similar to modern shrews and moles. Mammalian teeth continued to show features specialized for insect consumption until the rise of the primates.

65 million years ago, coinciding with the evolution of the first fruiting plants, our ancestors took to the trees and became primates. For most of the time between then and now, our ancestors likely ate the prototypical primate diet of fruit, seeds, leaves/stems, and insects (1). Some primates also hunt smaller animals and thus eat the flesh of mammals, birds, reptiles, amphibians, and fish in addition to insects. However, the contribution of non-insect meat to the diet is usually small.

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Is Meat Unhealthy? Part I

Introduction

At Dr. McDougall's Advanced Study Weekend, I had the opportunity to hear a number of researchers and advocates make the case for a "plant-based diet", which is a diet containing little or no animal foods. Many of them voiced the opinion that animal foods contribute substantially to the primary killers in the US, such as heart disease and cancer. Some of the evidence they presented was provocative and compelling, so it stimulated me to take a deeper look and come to my own conclusions.

No matter what the health implications of meat eating turn out to be, I respect vegetarians and vegans. Most of them are conscientious, responsible people who make daily personal sacrifices to try to make the world a better place for all of us.

My Experience with Vegetarian and Vegan Diets

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