Tuesday, December 16, 2014

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):

Friday, December 5, 2014

Wednesday, December 3, 2014

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.

Monday, December 1, 2014

Recent Interviews

For those who don't follow my Twitter account (@whsource), here are links to my two most recent interviews.

Smash the Fat with Sam Feltham.  We discuss the eternally controversial question, "is a calorie a calorie"?  Like many other advocates of the low-carbohydrate diet, Feltham believes that the metabolic effects of food (particularly on insulin), rather than calorie intake per se, are the primary determinants of body fatness.  I explain the perspective that my field of research has provided on this question.  We also discussed why some lean people become diabetic.  Feltham was a gracious host.

Nourish, Balance, Thrive with Christopher Kelly.  Kelly is also an advocate of the low-carbohydrate diet for fat loss.  This interview covered a lot of ground, including the insulin-obesity hypothesis, regulation of body fatness by the leptin-brain axis, how food reward works to increase calorie intake, and the impact of the food environment on food intake.  I explain why I think proponents of the insulin-obesity hypothesis have mistaken association for causation, and what I believe the true relationship is between insulin biology and obesity.  Kelly was also a gracious host.  He provides a transcript if you'd rather read the interview in text form.

Monday, November 24, 2014

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:


Monday, October 27, 2014

Is Meat Unhealthy? Part II

In the last post, I said Part II would be about cardiovascular disease.  Shortly after publishing that, I realized that before we move on to diseases, we need to set the stage by considering our evolutionary history with meat.  So here we go.

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

Mammals evolved from ancestral therapsids 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.