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Cholesterol Myths by Uffe Ravnskov MD, PhD: Myth 3: High-Fat Foods Raise Blood Cholesterol
Wednesday, November 12, 2014 10:28 am Email this article
“Ye shall eat the fat of the land.”
— Genesis 45:18
Food and fat in various populations
Why do levels of cholesterol vary in different people? Because of their food! This is the answer from Ancel Keys, stated over and over again in his papers. No alternative explanations are ever mentioned; Keys’s hand never trembles when he writes about the influence of diet on blood cholesterol.
One of his arguments is that the average blood cholesterol is high in countries where people eat lots of high-fat food, especially foods high in animal fat, and low in countries where people eat little fat. And, asserts Keys, if an individual with low cholesterol moves to an area where people’s cholesterol is high, then his cholesterol will also rise.
In 1958 Keys illustrated his idea with a diagram demonstrating the relationship between the amount of fat in the food and the cholesterol level of the blood in various populations (fig. 3A).
Figure 3A. Correlation between dietary fat and blood cholesterol in various populations. After Keys.
Fig. 3B. Same diagram as figure 3A, but including populations that Keys had ignored.
It is possible to draw an even curve through almost all points, an amazing result considering the uncertainties associated with the figures behind the individual points. It is highly unusual to find such a strong correlation in medical or biological science because observations of living creatures are much more imprecise than observations in physics and chemistry.
Note also that the figure gives the blood cholesterol related to the total amount of dietary fat. In his later study Seven Countries Professor Keys claimed that the correlation is far better if cholesterol is related to the intake of animal fat. Possibly you wonder how it could be better than shown in figure 3A. The reason is that in Seven Countries Keys found no correlation at all between total fat and heart mortality.
How come that in the first study Keys found a strong correlation, but in Seven Countries there was no correlation at all? The explanation is that in his first study Keys had ignored some remarkable populations.
Camels, cows and cholesterol
I have already discussed the discrepancies between the low blood cholesterol of the Masai and the Samburu cattle herders and their rich, high-fat food. Why didn’t Keys include the Samburu people in his elegant diagram? Wasn’t it interesting that for long periods they drank almost two gallons of milk each day. Milk from the African Zebu cattle is much fatter than our cow’s milk, which means that the Samburus consume more than twice the amount of animal fat than the average American, and yet their cholesterol is much lower, about 170 mg/dl (4.36 mmol/l).
Shepherds in Somalia eat almost nothing but milk from their camels. About a gallon and a half a day is normal, which amounts to almost one pound of butter fat, because camel’s milk is much fatter than cow’s milk.
But although more than sixty percent of their energy consumption comes from animal fat, their mean cholesterol is only about 150 mg/dl (3.85 mmol/l), far lower than that of most Western people.
Cholesterol and coconuts
Dr. Ian Prior and his team from Wellington, New Zealand, studied the population of the Tokelau Islands and the Pukapuka atolls. Here the main food is coconuts prepared in various ways, but seafood and chicken are also on the menu. Coconuts contain great amounts of coconut butter. Unlike most other types of vegetable fat coconut butter has a high content of saturated fatty acids, even higher than in animal fat.
On the Tokelau Islands the amount of saturated fat was almost twice that of Pukapuka and even higher than in the US, while the consumption of polyunsaturated oil was small on all islands.
The scientists confirmed that the Polynesian people really ate this great amount of saturated fatty acids by analyzing the fat beneath their skin. With a syringe they sucked out a little of this fat and found that its content of saturated fatty acids was twice that of Western people. Also, the chickens these Pacific islanders ate had a high content of saturated fatty acids in their tissue, probably because they ate a considerable amount of coconut.
The cholesterol of the Tokelauans was higher than that of the Pukapuka inhabitants as expected according to the diet-heart idea, but it was at least 20 percent lower than it should have been if Keys’s calculations were correct. Now to the most interesting point.
In 1966 a tornado pulled up a great number of coconut trees on the islands. The atolls could no longer feed their inhabitants and one thousand Tokelauans migrated to New Zealand. In New Zealand their diet changed markedly; the amount of calories from saturated fat was halved while the intake of polyunsaturated fat increased a little.
Here was the perfect opportunity to prove the diet-heart hypothesis, but the results of this so-called “favorable” change n diet did not live up to expectations. Instead of going down as expected, the cholesterol of the Tokelauans increased by about 10 percent as seen in Table 3A.
Table 3A. Fat content of the food of Tokelau inhabitants and Tokelau emigrants in New Zealand, and their blood cholesterol level.
Men, 45-54 years
Women, 45-54 years
Thus, something in the environment or lifestyle in New Zealand had such a great impact of the Tokelauans that their cholesterol increased, although their consumption of saturated fat was reduced by half.
Experiments and reality
Another of Keys’s arguments derives from the results of laboratory experiments to lower cholesterol by diet. The experiments are summarized as follows.
If energy is supplied mainly by saturated fatty acids, those dominating in animal fat and in coconut butter, blood cholesterol goes up a little.
If energy is supplied mainly by polyunsaturated fatty acids, those dominating in most vegetable fat and fat from seafood, blood cholesterol goes down a little.
Oddly, cholesterol in the diet has only a marginal influence on the cholesterol in the blood. The explanation is that we regulate our own production of cholesterol according to our needs. When we eat much cholesterol, the body’s production goes down; when we eat only little, it goes up.
The fact that a suitable diet may change the blood cholesterol level has been demonstrated by the cholesterol-lowering trials. An extreme diet may lower the level by about ten percent; a more palatable diet only a few percent.
Now to one of the cholesterol paradoxes. Although it is possible to change blood cholesterol a little in laboratory experiments and clinical trials by dieting, it is impossible to find any relationship between the make up of the diet and the blood cholesterol of individuals who are not participating in a medical experiment. In other words, individuals who live as usual and eat their food without listening to doctors or dieticians show no connection between what they eat and the level of their blood cholesterol.
If the diet-heart idea were correct individuals who eat great amounts of animal fat would have higher cholesterol than those who eat small amounts; and individuals who eat small amounts of vegetable fat should have higher cholesterol than those who eat great amounts. If not, there is no reason to meddle with people’s diet.
Counting money and counting food
Even in the early 1950s the Framingham study included dietary analyses. Almost one thousand individuals were questioned in detail about their eating habits. No connection was found between the composition of the food and the cholesterol level of the blood. Wrote Drs. William Kannel and Tavia Gordon, authors of the report: “These findings suggest a cautionary note with respect to hypotheses relating diet to serum cholesterol levels. There is a considerable range of serum cholesterol levels within the Framingham Study Group. Something explains this inter-individual variation, but it is not the diet.”
For unknown reasons, their results were never published. The manuscript is still lying in a basement in Washington.
In a small American town called Tecumseh, Michigan a similar study was performed by a team of researchers from the University of Michigan headed by Dr. Allen Nichols. Experienced dieticians asked in great detail more than two thousand individuals what they had eaten during a twenty-four hour period. The dieticians also asked about the ingredients of the food, analyzed the recipes of home-cooked dishes, and exerted great care to find out what kind of fat was used in the kitchen. Calculations were then performed using an elaborate list of the composition of almost 3000 American food items. Finally the participants were divided into three groups, a high, a middle, and a low level group, according to their blood cholesterol.
No difference was found between the amounts of any food item in the three groups. Of special interest was that the low-cholesterol group ate just as much saturated fat as did the high-cholesterol group.
These studies concerned adults, but no association has been found in children either. At the famous Mayo Clinic in Rochester, New York, for instance, Dr. William Weidman and his team analyzed the diet of about one hundred school children. Great differences were found between the amount of various food items eaten by these children, and also great differences between their blood cholesterol values, but there wasn’t the slightest connection between the two. The children who ate lots of animal fat had just as much or just as little cholesterol in their blood as the children who ate very little animal fat.
A similar investigation of 185 children was performed in New Orleans with the same result.
Even if no pains are spared to investigate the diet of people the information gathered is of course uncertain. Who can recall everything that he has eaten in the last twenty-four hours? And the diet of one 24-hour period may not be representative of the usual diet of the individual. A better result can be achieved by studying the diet over several days, preferably during various seasons of the year. In London professor Jeremy Morris and his team used this method and asked ninety-nine middle-aged male bank staff members to weigh and record what they ate over two weeks.
Have you ever bargained in a bank? Maybe you will succeed in the director’s office, but certainly not at the teller’s counter. If anyone is scrupulous with nickels and dimes, it is those sitting behind the glass of the bank.
Ninety-nine of these honorable men were asked to sit at home with a letter balance and weigh every morsel they ate for a whole week. But again, this meticulous method revealed no connection either between the food and the blood cholesterol level.
To be certain, seventy-six of the bank men repeated the procedure for another week at another time of the year: no connection was found, once again.
To be absolutely certain the researchers selected those whose records were especially detailed and accurate. Once more, no connection was found.
Another look at Finland
On average Finnish people have the highest cholesterol in the world. According to the diet-heart idea’s proponents, this is due to the fat-rich Finnish food. The answer is not that simple, however. This was demonstrated by Dr. Rolf Kroneld and his team at the University of Turku.
They studied all inhabitants of the village of Iniö near Turku, and twice as many randomly selected individuals of the same age and sex in North Karelia and in southwest Finland.
Apparently a health campaign had struck Iniö. There the consumption of margarine was twice as great and the consumption of butter only half as what it was in the other places. Also, the people of Iniö preferred skimmed over whole milk; the residents of the other districts did not. But the highest cholesterol values were found in Iniö.
The average value for male Iniö inhabitants was 283 mg/dl, on the two other places it was 239 and 243 mg/dl. Regarding women, the difference was even greater.
Threshold on trial
Is it really wise to meddle with people’s dietary habits if their food has no influence on their cholesterol? And how do those who believe that fat food is dangerous explain all these negative results?
Most often they argue that information about dietary habits is inaccurate—and it is. But this explanation is not applied consistently. It is never used against the studies mentioned in chapter 1, those that claimed a connection between fat intake and heart mortality in various countries, although the uncertainty in these studies was much higher. The researchers did not determine dietary information by any questionnaires or surveys at all, but instead on estimates of the average intake of fat based on the highly uncertain assumption that people eat what is available. Such soft evidence should be treated with the utmost care but diet-heart supporters refuse to do more than applaud investigations that support their theories
But even information gathered through direct questioning is inaccurate. A crude relationship should appear if a sufficiently large number of individuals are meticulously questioned. If not, the influence of the diet, if any, must be so weak that it cannot possibly have any importance.
Diet-heart supporters also argue that most people in Western communities already eat great amounts of fat and cholesterol. This argument declares that we have already crossed a threshold of too much animal fat in the diet so that more fat does not make any impact on our blood cholesterol.
The argument is in conflict with the studies I have mentioned above. Dr. Nichols and his team, for instance, declared “The distribution of daily intake of total fat, saturated fat, and cholesterol by the individuals in this study was quite broad.” And indeed it was. For about 15 percent of the men less than 12.8 percent of the calories came from animal fat, and for about 15 percent of the men more than 20 percent of the calories came from animal fat.
Consider now that it is the goal of the National Cholesterol Education Program to lower the intake of animal fat of all Americans to about ten percent of their caloric intake. Almost 15 percent of the participants in the Tecumseh study already ate that amount of animal fat that low, and yet it was impossible to see a difference between the blood cholesterol of those who ate small amounts of animal fat and of those who ate much more. Does it make sense to recommend this drastic reduction of animal fat if the cholesterol of those who already eat that little is just as that of the epicure?
The Mayo Clinic study also revealed a wide range of fat intake. The lowest intake of animal fat was 15 grams per day (less than 10 percent of the caloric intake); the highest was 60 grams per day. In the Bogalusa study, the range was still broader. The lowest intake of all fats was 17 grams per day, the highest 325 grams per day. (No information was given about the relative proportion of animal fat to vegetable oils.)
In Jerusalem a team of researchers, led by Dr. Harold Kahn studied the diet and blood cholesterol of ten thousand male Israeli civil servants. The dietary habits varied considerably between people from Israel, Eastern Europe, Central Europe, Southern Europe, Asia and Africa. The intake of animal fat varied from ten grams up to two hundred grams daily, and there were also considerable differences between their cholesterol values.
If the intake of animal fat were of major importance for the cholesterol level in the blood it should be possible to find some kind of relationship from a study of so many individuals with such great variations in blood cholesterol and dietary habits. But there was no relation in this Israeli study either. Extremely low cholesterol values were seen both in those who ate small amounts of animal fat and in those who ate the most animal fat, and high cholesterol values were seen at all levels of animal fat intake.
The scientists from Israel also studied the value of various ways of dietary questioning. Many studies have recorded the diet during only one 24 hour period only. Even if this information were accurate it may not be representative of the diet for the rest of the year, far less for a whole life-time. The Israeli scientists found that the best information came from a questioning over several days and during different seasons of the year, the method used in the study of the bank tellers. Using this expensive and time-consuming method in a smaller study of sixty-two individuals they could not find a correlation either; the correlation coefficient between animal fat intake and blood cholesterol was zero point zero.
Vegetarians usually have lower cholesterol than other people and they eat little animal fat. But vegetarians differ from the rest of the human population in more than their diet. They are usually more interested in their health, they usually smoke less, they are usually thinner, and they usually exercise more often than other people. Whether it is their diet, or their other living habits, or perhaps something else that lowers their blood cholesterol is unknown.
The fact that blood cholesterol is influenced by the diet in laboratory experiments and clinical trials but not in people who live without the interference of scientists and dieticians has a simple explanation: Blood cholesterol is controlled by more powerful factors than the diet. If these factors are kept reasonably constant in a laboratory experiment or a clinical trial, it is possible to see the influence of the diet alone.
The question, however, is whether a lowering of blood cholesterol by diet is permanent. As mentioned above, the body tends to keep blood cholesterol at a fairly constant level. The dietary experiments mentioned above went on for a few months at most. The cholesterol control mechanisms of the human body probably needs more time to adapt to a fat intake that differs from the usual one. Over millions of years mammals, including homo sapiens (our kind of men), have developed effective mechanisms to counteract unfavorable changes in all blood constituents. Salt and water, for instance, are regulated rapidly within narrow limits, because even small deviations may have a strong influence on the functions of the body. Extreme variations of other substances, such as proteins and fats, have no serious consequences in the short run; the adaptation is thus slow. But in due time also these deviations may be counteracted; this has been demonstrated by the Masais, the Samburus, the Somalian shepherds, and many others.
Food and blood cholesterol
You may ask why I have written so much about fats. After all, it is blood cholesterol levels that matter, not the level of fats in the blood, and the most important thing should be how much cholesterol we eat, not how much fat. If we eat lots of cholesterol, doesn’t our blood cholesterol increase? It is not that simple.
Have you limited your daily consumption of eggs, the richest source of cholesterol in our food? If so, the following statement will either make you angry or allow you to breathe a sigh of relief. The cholesterol in your food has little or no influence at all on the cholesterol in your blood.
Even the most zealous proponents of the diet-heart idea know this very well, but they keep silent, because how on earth can you promote the idea that high blood cholesterol is a threat while allowing people to eat as much cholesterol as they like? The truth is that cholesterol in your food can’t influence your blood cholesterol by more than a few percent.
Numerous studies have shown that in people who eat a normal Western diet, the effect on blood cholesterol of eating two or three extra eggs per day over a long period of time can hardy be measured.
To find out how eating eggs influenced my own cholesterol, I once used myself as a human guinea pig without asking for permission from the ethics committee. Before and during the experiment I analyzed my blood cholesterol. My cholesterol at the start of the experiment was 278 (7.13), close to a determination made ten years earlier. The results are shown in Table 3B.
Table 3B. Egg consumption and cholesterol values in one skeptical Swedish doctor.
||Number of eggs consumed
||Blood cholesterol (mg/l)
The data from my daring experiment showed that instead of going up, my cholesterol went down a little, even though I was eating two or three times more cholesterol than my body normally produces itself. Why didn’t my cholesterol go up?
Of course, one should be careful about drawing conclusions from an experiment on a single individual. However, it is not forbidden to speculate a little; after all, eight eggs a day represents a substantial amount of cholesterol.
Most probably, no change took place at all. Cholesterol measurements can never be as exact as measurements of your weight or height. If you take a blood sample, divide it between ten test tubes and analyze the cholesterol concentration of each tube, you will probably get ten different values. The difference between the lowest and the highest can be as great as 15 percent or more, although the true concentration is, of course, identical in all nine samples. Normal day-to-day cholesterol variations make it even more difficult to get an accurate measurement. The small decline in my cholesterol level could simply have been due to imprecise measurements.
What we do know is that when we eat large amounts of cholesterol, our cells slow down their own production of this vital substance. Part of the surplus in the blood is temporarily stored in the liver and part is excreted with the bile. In my case, this regulation was performed so efficiently that my blood cholesterol did not rise, in spite of a substantial increase in my daily cholesterol intake. Perhaps my cholesterol would have finally gone up if I had continued longer with my experiment, but even if eggs are a good and nutritious food, who wants to eat eight eggs a day?
Proponents of the diet-heart idea would argue that I am what they call a “non-responder.” According to this view, some members of the human race are able to maintain the same blood cholesterol level even after having eaten large amounts of cholesterol. Maybe so, but in that case, most of mankind are non-responders. This can be deduced from a study performed by Dr. Martijn Katan and his group at the Agricultural University in De Dreijen, the Netherlands. They gave test individuals a low-cholesterol diet for two weeks, followed by a high-cholesterol diet for another two weeks.
In some of the test individuals, called the hyper-responders, the cholesterol rose by 11 to 42 percent, whereas in others, called the hypo-responders, the cholesterol change varied from a decrease of 11 percent to an increase of 4 percent. These two groups, the hypo- and the hyper-responders, then participated in a second experiment, again with a high-cholesterol diet for two weeks. But this time their cholesterol levels changed very little, and the change was about the same in each group. Thus, the experiment did not support the idea about hypo and hyper-responders.
Surprised and disappointed with this unexpected result, the researchers decided to perform yet another experiment, this time with a total intake of almost one gram of cholesterol per day, and for three weeks instead of two. This time it was a little better, but there was a lot of individual variation. As the authors wrote: “Quite a number of subjects who appeared hyper-responsive in one experiment proved to be hypo-responsive in another experiment.”
To get a significant difference between the two groups, the researchers resorted to the so-called one-tailed t-test—a less stringent parameter that is not accepted among scientists for use in research where the expected result can go in either direction—and here the result certainly went in both directions. It is not particularly scientific either to continue an experiment until you get an outcome that suits your hypothesis, because sooner or later chance will produce a suitable result. The explanation for the haphazard results is, of course, that good friend of uncritical researchers, Mr. Chance.
Obviously, cholesterol in the diet has only a marginal influence on cholesterol in the blood. Why? Because we regulate our own production of cholesterol according to our needs. When we eat large amounts of cholesterol, our body’s production goes down; when we eat small amounts, it goes up.
But even if dietary saturated fat or cholesterol raises cholesterol in the blood a little, this effect is not particularly important—this is what scientists call a surrogate outcome. The crucial question is whether a high intake of saturated fat leads to cardiovascular disease, and whether you can prevent such disease by lowering the intake. In the next chapter you will see that both assumptions are false.
Here are links to the other chapters in the book.
- Cholesterol Myths by Uffe Ravnskov, MD, PhD: Forward to Book by Michael Gurr, PhD
- Cholesterol Myths by Uffe Ravnskov, MD, PhD: Author’s Foreword
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Introduction: The Diet-Heart Idea: A Die-Hard Hypothesis
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Myth 1: High-Fat Foods Cause Heart Disease
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Triglycerides
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Myth 2: High Cholesterol Causes Heart Disease
- Cholesterol Myths by Uffe Ravnskov MD: Familial hypercholesterolemia—not as risky as you may think
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Myth 3: High-Fat Foods Raise Blood Cholesterol
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Myth 4: High Cholesterol Blocks Arteries
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Myth 5: Animal Studies Prove the Diet-Heart Idea
- Cholesterol Myths by Uffe Ravnskov MD, PhD: Cholesterol lowering in children
- Cholesterol Myths by Uffe Ravnskov MD: Myth 6: Lowering Cholesterol Will Lengthen Your Life (Part 1)
- Cholesterol Myths by Uffe Ravnskov MD: Myth 6: Lowering Cholesterol Will Lengthen Your Life (Part 2)
- Cholesterol Myths by Uffe Ravnskov MD PhD: Myth 7: The Statins — Gift to Mankind (Part 1)
- Cholesterol Myths by Uffe Ravnskov MD PhD: Myth 7: The Statins — Gift to Mankind (Part 2)
- Cholesterol Myths by Uffe Ravnskov MD PhD: “The most exact data base”—the screenee
- Cholesterol Myths by Uffe Ravnskov MD PhD: Myth 8: Polyunsaturated Oils are Good for You
- Cholesterol Myths by Uffe Ravnskov MD PhD: Dr. Ornish and The Lifestyle Heart trial
- Cholesterol Myths by Uffe Ravnskov MD PhD: Myth 9: The Cholesterol Campaign is Based on Good Science
- Cholesterol Myths by Uffe Ravnskov MD PhD: Insider Insight
- Cholesterol Myths by Uffe Ravnskov MD PhD: Myth 10: All Scientists Support the Diet-Heart Idea
- Cholesterol Myths by Uffe Ravnskov MD PhD: Epilogue
- Cholesterol Myths by Uffe Ravnskov MD PhD: References
This chapter is from the book
The Cholesterol Myths: Exposing the Fallacy that Saturated Fat and Cholesterol Cause Heart Disease
by Uffe Ravnskov, MD, PhD.
Dr. Ravnskov has given me the permission to share this version of his book to help educate the world about the cholesterol campaign.
Information about Uffe Ravnskov, MD, PhD is posted here.
More information about Cholesterol Myths is posted on his website here.
Dr. Ravnskov posted his book for free here.
Uffe Ravnskov, MD, PhD is the founder of The International Network of Cholesterol Skeptics (THINCS.org) which can be found here.
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