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Rabu, 14 Januari 2009
The Tokelau Island Migrant Study: Cholesterol and Cardiovascular Health
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Let's get right to the meat of this study. It's a direct test of the idea that saturated fat is a cause of cardiovascular disease. If you were to design the perfect experiment to determine if saturated fat causes heart disease, and ethics were not a concern, how would you do it? You would stuff one group of people with as much saturated fat as they would eat for their entire lives, while feeding far less to a genetically identical group. Ideally, you would keep everything else about the diet and lifestyle the same. Then, you would measure some marker of cardiovascular disease, or even better, count actual heart attacks.
The Tokelau Island Migrant study isn't a perfect experiment, but it's about as close as we're going to get. Tokelauans traditionally obtained 40-50% of their calories from saturated fat, in the form of coconut meat. That's more than any other group I'm aware of, even topping the roughly 33% that the Masai get from their extremely fatty Zebu milk.
So are the Tokelauans dropping like flies of cardiovascular disease? I think most of the readers of this blog already know the answer to that question. I don't have access to the best data of all: actual heart attack incidence data. But we do have some telltale markers. In 1971-1982, researchers collected data from Tokelau and Tokelauan migrants to New Zealand on cholesterol levels, blood pressure and electrocardiogram (ECG) readings.
The Tokelauan diet, as I've described in detail in previous posts, is traditionally based on coconut, fish, starchy tubers and fruit. By 1982, their diet also contained a significant amount of imported flour and sugar. Migrants to New Zealand had a much more varied diet that was also more typically Western: more carbohydrate, coming chiefly from wheat, sugar and potatoes; more processed sweet foods and drinks; more red meat; more vegetables; more dairy and eggs. Sugar intake was 13 percent of calories, compared to 8 percent on Tokelau. Saturated fat intake in NZ was half of what it was on Tokelau, while total fat intake was similar. Polyunsaturated fat intake was higher in NZ, 4% as opposed to 2% in Tokelau. I don't have data to back this up, but I think it's likely that the n-6:n-3 ratio increased upon migration.
Blood pressure did not change significantly over time in Tokelau from 1971 to 1982, if anything it actually declined slightly. It was consistently higher in NZ than in Tokelau at all timepoints. Men were roughly three times more likely to be hypertensive in NZ than on Tokelau at all timepoints (4.0% vs. 12.0% in the early 1970s). Women were about twice as likely to be hypertensive (8.1% vs. 15.0%).
On to cholesterol. Total cholesterol in male Tokelauans was a bit lower on average than in New Zealand, but neither was particularly elevated (182 vs. 199 mg/dL). LDL was also a bit higher in NZ males (119 vs. 132 mg/dL). Get these guys on Lipitor!! Triglycerides were lower in Tokelauan men than in NZ (80 vs. 114 mg/dL). There were no differences in total cholesterol, LDL cholesterol or triglycerides between Tokelauan and NZ women.
These data would make Dr. Uffe Ravnskov smile (actually I'm sure he's aware of them). Much of the hoopla surrounding saturated fat is due to the fact that in controlled clinical trials, it seems to elevate blood cholesterol (by elevating both LDL and HDL). What Dr. Ravnskov and others have pointed out is that the correlation between saturated fat intake and blood cholesterol is weak, and in any case, so is the correlation between blood cholesterol and cardiovascular disease. This study lends support to the idea that saturated fat is not a major determinant of total cholesterol or LDL.
But does it cause heart attacks? The best data I have from this study are ECG readings. These use electrodes to monitor the electrical activity of the heart. There are certain ECG patterns that suggest that a person has had a heart attack (Minnesota codes 1-1 and 1-2). The data I am going to present here are all age-standardized, meaning they are comparing between groups of the same age. On Tokelau in 1982, 0.0% of men 40-69 years old showed ECG readings that indicated a probable past heart attack. In NZ in 1980-81, 1.0% of men 40-69 years old showed the same ECG readings. In Tecumseh U.S.A. in 1965, 3.5% of men 40-69 years old showed the same ECG pattern. I don't have data for women.
These data don't prove that no one ever has a heart attack on Tokelau. They do sometimes, and they also have strokes (at least in modern times). But they do allow us to compare in quantitative terms between genetically similar people living in two different environments.
This is consistent with what has been observed on Kitava and other traditional Pacific island cultures: a vanishingly small incidence of cardiovascular disease while they retain their traditional diet and lifestyle (and sometimes even when some processed Western food has been introduced). When diets and lifestyles become modern, there is invariably a rise in the incidence of chronic disease.
I don't believe that saturated fat contributes to cardiovascular disease. The best data available have never supported that hypothesis, even from the very beginning. The Tokelau Island Migrant study, among many others, should have put it out of its misery long ago. Tokelau underlines the fact that the most important determinant of health is a diet based on whole, natural foods that are familiar to the human metabolism, prepared in traditional ways that maximize their digestibility and nutritional value.
Unless otherwise noted, the data in this post are from the book Migration and Health in a Small Society: the Case of Tokelau.
The Tokelau Island Migrant study isn't a perfect experiment, but it's about as close as we're going to get. Tokelauans traditionally obtained 40-50% of their calories from saturated fat, in the form of coconut meat. That's more than any other group I'm aware of, even topping the roughly 33% that the Masai get from their extremely fatty Zebu milk.
So are the Tokelauans dropping like flies of cardiovascular disease? I think most of the readers of this blog already know the answer to that question. I don't have access to the best data of all: actual heart attack incidence data. But we do have some telltale markers. In 1971-1982, researchers collected data from Tokelau and Tokelauan migrants to New Zealand on cholesterol levels, blood pressure and electrocardiogram (ECG) readings.
The Tokelauan diet, as I've described in detail in previous posts, is traditionally based on coconut, fish, starchy tubers and fruit. By 1982, their diet also contained a significant amount of imported flour and sugar. Migrants to New Zealand had a much more varied diet that was also more typically Western: more carbohydrate, coming chiefly from wheat, sugar and potatoes; more processed sweet foods and drinks; more red meat; more vegetables; more dairy and eggs. Sugar intake was 13 percent of calories, compared to 8 percent on Tokelau. Saturated fat intake in NZ was half of what it was on Tokelau, while total fat intake was similar. Polyunsaturated fat intake was higher in NZ, 4% as opposed to 2% in Tokelau. I don't have data to back this up, but I think it's likely that the n-6:n-3 ratio increased upon migration.
Blood pressure did not change significantly over time in Tokelau from 1971 to 1982, if anything it actually declined slightly. It was consistently higher in NZ than in Tokelau at all timepoints. Men were roughly three times more likely to be hypertensive in NZ than on Tokelau at all timepoints (4.0% vs. 12.0% in the early 1970s). Women were about twice as likely to be hypertensive (8.1% vs. 15.0%).
On to cholesterol. Total cholesterol in male Tokelauans was a bit lower on average than in New Zealand, but neither was particularly elevated (182 vs. 199 mg/dL). LDL was also a bit higher in NZ males (119 vs. 132 mg/dL). Get these guys on Lipitor!! Triglycerides were lower in Tokelauan men than in NZ (80 vs. 114 mg/dL). There were no differences in total cholesterol, LDL cholesterol or triglycerides between Tokelauan and NZ women.
These data would make Dr. Uffe Ravnskov smile (actually I'm sure he's aware of them). Much of the hoopla surrounding saturated fat is due to the fact that in controlled clinical trials, it seems to elevate blood cholesterol (by elevating both LDL and HDL). What Dr. Ravnskov and others have pointed out is that the correlation between saturated fat intake and blood cholesterol is weak, and in any case, so is the correlation between blood cholesterol and cardiovascular disease. This study lends support to the idea that saturated fat is not a major determinant of total cholesterol or LDL.
But does it cause heart attacks? The best data I have from this study are ECG readings. These use electrodes to monitor the electrical activity of the heart. There are certain ECG patterns that suggest that a person has had a heart attack (Minnesota codes 1-1 and 1-2). The data I am going to present here are all age-standardized, meaning they are comparing between groups of the same age. On Tokelau in 1982, 0.0% of men 40-69 years old showed ECG readings that indicated a probable past heart attack. In NZ in 1980-81, 1.0% of men 40-69 years old showed the same ECG readings. In Tecumseh U.S.A. in 1965, 3.5% of men 40-69 years old showed the same ECG pattern. I don't have data for women.
These data don't prove that no one ever has a heart attack on Tokelau. They do sometimes, and they also have strokes (at least in modern times). But they do allow us to compare in quantitative terms between genetically similar people living in two different environments.
This is consistent with what has been observed on Kitava and other traditional Pacific island cultures: a vanishingly small incidence of cardiovascular disease while they retain their traditional diet and lifestyle (and sometimes even when some processed Western food has been introduced). When diets and lifestyles become modern, there is invariably a rise in the incidence of chronic disease.
I don't believe that saturated fat contributes to cardiovascular disease. The best data available have never supported that hypothesis, even from the very beginning. The Tokelau Island Migrant study, among many others, should have put it out of its misery long ago. Tokelau underlines the fact that the most important determinant of health is a diet based on whole, natural foods that are familiar to the human metabolism, prepared in traditional ways that maximize their digestibility and nutritional value.
Unless otherwise noted, the data in this post are from the book Migration and Health in a Small Society: the Case of Tokelau.
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