Sunday, August 17, 2008

Cardiovascular Risk Factors on Kitava, Part III: Insulin

The Kitava study continues to get more and more interesting in later publications. Dr. Lindeberg and his colleagues continued exploring disease markers in the Kitavans, perhaps because their blood lipid findings were not consistent with what one would expect to find in a modern Western population with a low prevalence of CVD.

In their next study, the researchers examined Kitavans' insulin levels compared to Swedish controls. This paper is short but very sweet. Young Kitavan men and women have a fasting serum insulin level considerably lower than their Swedish counterparts (KM 3.9 IU/mL; SM 5.7; KW 3.5; SW 6.2). Kitavan insulin is relatively stable with age, whereas Swedish insulin increases. In the 60-74 year old group, Kitavans have approximately half the fasting serum insulin of Swedes. One thing to keep in mind is that these are average numbers. There is some overlap between the Kitavan and Swedish numbers, with a few Kitavans above the Swedish mean.

In figure 2, they address the possibility that exercise is the reason for Kitavans' low insulin levels. Kitavans have an activity level comparable to a moderately active Swedish person. They divided the Swedes into three categories: low, medium, and high amounts of physical activity at work. The people in the "low" category had the highest insulin, followed by the "high" group and then the "medium" group. The differences were small, however, and Kitavans had far lower serum insulin, on average, than any of the three Swedish groups. These data show that exercise can not explain Kitavans' low insulin levels.

The researchers also found that they could accurately predict average Swedish and Kitavan insulin levels using an equation that factored in age, BMI and waist circumference. This shows that there is a strong correlation between body composition and insulin levels, which applies across cultures.

Now it's time to take a step back and do some interpreting. First of all, this paper is consistent with the idea (but does not prove) that elevated insulin is a central element of overweight, vascular disease and possibly the other diseases of civilization. While we saw previously that mainstream blood lipid markers do not correlate well with CVD or stroke on Kitava, insulin has withstood the cross-cultural test.

In my opinion, the most important finding in this paper is that a high-carbohydrate diet does not necessarily lead to elevated fasting insulin. This is why I think the statement "carbohydrate drives insulin drives fat" is an oversimplification. What drives fat accumulation is chronically high insulin (hyperinsulinemia), which the Kitavans do not have. With a properly-functioning pancreas and insulin-sensitive tissues (which many people in industrial societies do not have), a healthy person can eat a high-carbohydrate meal and keep blood glucose under control. Insulin definitely spikes, but it's temporary. The rest of the day, insulin is at basal levels. The Kitavans show that insulin spikes per se do not cause hyperinsulinemia.

So this leads to the Big Question: what causes hyperinsulinemia?? The best I can give you is informed speculation. Who has hyperinsulinemia? Industrial populations, especially the U.S. and native populations that have adopted Western foods. Who doesn't? Non-industrial populations that have not been affected by Western food habits, including the traditional Inuit, the Kuna, the traditional Masai and the Kitavans.

We can safely rule out that total fat, saturated fat and carbohydrate cause hyperinsulinemia, based on data from the Inuit, the Masai and the Kitavans, respectively. We can also safely rule out that there's some specific food that protects these populations, since they eat completely different things. Exercise is also not a compelling explanation, based on the data above and others. What does that leave us with? Western food habits. In my opinion, the trail of metabolic destruction that has followed Westerners throughout the world is probably due in large part to wheat and refined sugar.

I'm not the first person to come up with this idea, far from it. The idea that specific types of carbohydrate foods, rather than carbohydrate in general, are responsible for the diseases of civilization, has been around for at least a century. It was an inescapable conclusion in the time of Weston Price, when anthropologists and field physicians could observe the transitions of native people to Western diets all over the world. This information has gradually faded from our collective consciousness as native cultures have become increasingly rare. The Kitava study is a helpful modern-day reminder.

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