In Part 1 of the series, I've shared that there were two theories to prove what diet would lead to heart diseases. First was carbohydrate being related to heart disease by Dr. John Gofman, and second was lipid hypothesis where fat is the cause of heart disease by Dr. Ancel Keys.
I've also shared information on how Ancel Key got his data and manipulated to make his hypothesis more realistic for the government to buy into his idea in 1960s and government made Dietary Guideline for American in 1980. As you can observe, since then, American population whom have followed this guideline has been getting obese, diabetes, heart diseases, and even cancer.
But what were the data actually suggesting? Well let's look at it.
Japan Studies
Japan has been viewed as one of the very healthy countries and often compared with other countries to determine what Japanese people are doing that other countries are not. Japan is very interesting country because when it comes to heart disease they are the lowest country in the world but highest in stroke (1). So what did Japan do to keep the heart diseases lower? Looking at the figure 1 to the right, you can see the trend of how Japanese diet changed from 1946-1990.
When you look at the third graph, you can see that Japanese lowered their carbohydrate intake. In the fourth graph you can see that carbohydrate intake dropped and fat intake got higher, which is complete opposite from what Dr. Ancel Keys and
government has been suggesting U.S. population to eat. Figure 2 shows type of food sources that Japanese ate and changed over the few decades.
Chart at the top shows that Japan has lowered the consumption of grain, rice, and potatoes. Fruits consumption at one point increase drastically but trending down starting around 1980s. Since 1965 sugar consumption has been lowered. Fish, meat, eggs, and dairy products has been increasing since 1946 or even earlier.
Japan tend to get a image of eating lots of vegetables, rice and fish and keeping the fat intake lower than other countries, however, we do consume higher amount of fat, especially animal fat.
So, for Dr. Keys using Japan as low fat diet example to lower the heart disease was a mistake because Japan has done complete opposite and decrease the number of heart disease patient.
When I look at this, I had to ask, how their cholesterol level was. Figure 3 shows comparison between 8 different countries for their trend in cholesterol for both men and women. In 1980, Japan had lowest blood cholesterol concentration in both men and women, and as the diet changed, the cholesterol level went up. What is interesting is Japan is the only country that increased their cholesterol level substantially to even out with the other countries and still kept the heart diseases lower than any other countries.
U.S. Studies
Let's look at what U.S. studies have shown. There was 26 country studies published in 1985(5) where comparing death rates for heart disease in men and women from 1950-1978. When you look at U.S. in Figure 4, both men and women were on down trend. Women seem to have dropped more than men but still mortality rate for heart disease was lowering.
This figure shows something else that is interesting. Both Finland and Czechoslovakia, both showed opposite trend in men and women. They should have been eating similar diet in each countries but the trends were different. This confirms that one element cannot be a cause for there can be so many other factor involved. In other words, cookie cutter approach does not work, not only in exercise but also diet as well because everybody is different.
Let's go more deeper with U.S. studies.
Figure 5 (6) shows number of death from heart disease is the U.S. between 1900 to 2010. You can see that the trend has started to rise around 1910 and started to skyrocket in 1930 then peaked out around 1960. Ischemic heart disease or coronary heart disease has peaked at 1969.
What's interesting is we were taught that heart disease and stroke or cerebrovascular disease happened for same dietary reasons. However, the Figure 5 shows otherwise because the same dietary trend lowered stroke and raised heart diseases.
In the book, The Big Fat Surprise, Nina Teicholz illustrated that U.S. population mainly ate animal meat in 1800s. There may have not been enough sources for grain, fruits and vegetable simply because U.S. population has not established agriculture as much as we have today in 1800s. Trend for eating red meat has declined from 1800s to about 1940s and this is when the heart disease started to elevate. After 1940s red meat consumption increased but started to drop in about 1980s. Other meat consumption that trended up after 1940s was poultry and trend is still on the rise.
The study that viewed a changes in daily nutrient fat in take in the U.S. between 1909 - 1972(7). Study have showed that total fat consumption has increased 1909 however, saturated fat stayed consistent and animal fat trending down. What was on the rise was vegetable fats especially with soybeans, cotton seed, corn and so on.
Figure 6 (8) is from the study done to find the changes in types of fat consumption in the U.S. Huge change is in poultry, shortening, and margarine although margarine consumption started to decrease in 1990. Another up trend you can see is soybean and canola oil. Why is this an issue? Vegetable oils are mainly polyunsaturated fats. Although not all polyunsaturated fat is bad but huge increase was in omega 6 fatty acid, which is a inflammatory fat. With omega 3 fatty acids, which you can find more in animal sources, stayed the same or many are on down trend, our body is becoming more susceptible to inflammation. Omega 3 can be obtained in vegetables too, however, with omega 6 being incredibly high, amount of omega 3 you can get from vegetables may not be sufficient.
Carbohydrate supplies have also changed. From late 1800s to 1961 consumption of sugar and syrup has increased drastically while complex carbohydrates decreased. Therefore, if the carbohydrate is the link to the increase in heart disease, the strongest link is with sugar and syrup consumption and reduction in complex carbohydrate.
We can see this trend in study published in American Journal of Clinical Nutrition(10). Started in 1909, U.S. population was already consuming diet high polyunsaturated fat and lower in the saturated fat while the heart disease was on the rise. By the 1960s U.S. population was consuming way more polyunsaturated fat than saturated fat. However, Dr. Keys and government ignored those evidence and kept suggesting Americans to consume more vegetable fats, mainly linoleic acid, lower the animal fats and increase in carbohydrate and sugar consumption which has been leading to heart disease, cancer, stroke, diabetes, still being top 10 causes of death in the U.S. (9).
There is enough evidence and study done to show that diet with saturated fat or elevated cholesterol alone is not linked to heart disease. What is more directly related to heart health and other leading cause of death is diet high in polyunsaturated fat and carbohydrate, especially in sugar and syrup. Something else can see from data is that diet alone, although it plays huge role, cannot be the only link to diseases.
In part 3 of this series, we will look into what we should be eating to stay healthy and what are some considerations need to be made for your dietary guideline.
Kota Shimada
Reference
http://library.crossfit.com/free/pdf/1957_Yerushalmy_Hilleboe_Fat_Diet_Mortality_Heart_Disease.pdf
https://www.jstage.jst.go.jp/article/jea1991/6/3sup/6_3sup_189/_pdf/-char/en
https://academic.oup.com/aje/article-abstract/102/6/514/72078?redirectedFrom=fulltext
https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm
https://www.sciencedirect.com/science/article/abs/pii/0021915070900572
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