Wednesday, June 2, 2010
12:47 PM | Posted by Martin Berkhan | Edit Post
In many cases the mass media is to blame. Dumbed down translations of results, coupled with soundbites taken out of context and comments from "experts," can easily distort the true meaning of a study. Sensationalistic headlines like "fruit is fattening" sells more papers than "HFCS in refined foods may cause weight gain".
Sometimes we are to blame. When looking for the next cutting edge diet strategy or pill to optimize fat loss and muscle gain, we tend to look for stuff that validates our theories or fantasies. We are prone to readily accept any evidence, however weak and vaguely presented, as long as it jibes with our own thinking.
In this article series I am going to track the origin of diet myths and pinpoint where things got wrong. I thought it would be fitting to kick off with an old school myth that in some circles is still alive and kicking today. Even if it's old news to most of you, I hope you will find the origins of the myth interesting. It's an excellent example of how bias may warp the minds of scientists. Personally I find this stuff fascinating.
Future articles will reveal how people came to believe that breakfast is healthy, delve into the "30 g protein in one sitting"-myth, carbs and growth hormone, late night eating, among other things.
Fat, cholesterol and heart disease
I still see dietitians in the press media and television warning against the dangers of saturated fat. You have to wonder how long it's going to take until this myth finally dies completely.
The most notorious example of research gone wrong in the field of nutrition has to be that of Ancel Keys and his "Seven Countries" studies. I've mentioned Keys' groundbreaking work on starvation in the past: "The Minnesota Starvation Experiment", which resulted in the two-volume Biology of Human Starvation. Perhaps it was those impressive credentials that bought him so much trust and good will in the scientific community. As history would come to prove, even a brilliant mind like Keys's is susceptible to bias and error.
The birth of the fat fallacy goes back to the 1960's, when Keys started promoting a low fat diet to lower cholesterol levels. At that time he was in the process of finishing up the first study on cholesterol and heart disease. At this point he had convinced himself that there was a connection between fat intake, cholesterol and heart disease. He changed his stance slightly in the early 1970s , when he discovered that death in heart disease was best predicted by the intake of saturated fat specifically.
Keys needed stronger evidence for his hypothesis. Since he had already seen the connection in the "Seven Countries" study, it made sense to him that he would continue his work on the study over a longer time period. His findings were published in the 1980s and it was concluded that there was a connection between deaths from heart disease and serum cholesterol. Populations with a high saturated fat intake (U.S, Finland) had more deaths from heart disease, while populations with a low saturated fat intake (Greece, Italy) had fewer.
The fear of saturated fat had gradually been building up and reached its peak after the results of that study was made public. It was further compounded by studies showing a positive link between dietary fat, obesity and cancers in the early 1990s. By this time there seems to have been a mind shift in the public perception of fat - all fat was basically considered bad.
I wonder what Keys would think of the meal I had today: 1.2 lbs of fatty grilled pork rib goodness.
The mistake: Ancel Keys cherry picked his data to support a pre-existing notion he had about a connection between saturated fat, cholesterol and heart disease. Instead of choosing to continue his work in the seven countries from his original study, he should have selected other populations. When more and different data is added into the mix, the connection disappears. Keys seems to have been blinded by his own bias and wanted to validate, not investigate.
The consequences: Keys's findings resulted in the crusade against dietary fat in the 1980s and '90s. The message to the public was that dietary fat should be minimized and replaced with grains, and saturated fat replaced by unsaturated fat. Everyone started doing low fat, high-carb diets. On a related note, Keys's study also gave birth to the Mediterranean diet and the notion that people should adopt a diet rich in monounsaturated fat.
The truth: Many of the old theories about dietary fat and disease have now been contradicted by more rigorous studies that dispute the results, but it wasn't until about ten years ago the tide started to turn. It is now quite clearly established that there is no clear connection between fat intake, weight gain and many of the aforementioned disease states. Unfortunately Average Joes and Janes, especially those 40 years and older that don't spend their time debating nutrition on Internet forums, still think fat is "unhealthy". At least those I converse with.
Note: There are many nuances to Keys's story and I've only given a brief summary of the events which lead to the fear of cholesterol and fat. One book that covers the topic in great detail is Anthony Colpo's "The Great Cholesterol Con". It's an impressive piece of work and an excellent read.
Thoughts on dietary fat and diet
Fat gain, heart disease and other modern maladies has everything to do with caloric excess and much less to do with dietary fat or any other macronutrient. For those of you who spend time nitpicking about what fat sources to eat for optimal health, consider this.
1. Reach and maintain the lean state first and foremost
Because for health, everything else is secondary. Lean people nearly always have excellent health markers. If you focus primarily on reaching and maintaining a lean state, your metabolic profile will be much better than if you had focused on perfecting the fat composition of your diet. Unfortunately, I know many people for whom the priorities seem reversed. Barring extremes it's an indisputable fact that fat loss does more for your blood lipids than weight maintenance with better fat sources.
Use whatever means you want to reach the lean state; whether you use a low-fat or high-fat diet is secondary to you reaching that objective. Then, maintain the lean state by adding weight slowly. An added bonus of that approach is that more of it will be muscle and less of it will be fat.
Adopting a whole foods approach helps in this endeavour. As it happens, the fat composition of a whole-foods diet is also favorable for health.
Everything is a go if it's an unprocessed food. Dairy is also fine. But eat only food you like and can live with in the long term. Is it not self-evident why am I telling you this? It seems not, because I often hear about how people force oil down their throat even if they hate it. So, if you don't like fish, eat beef. Can't stand avocados, eat eggs. You get the point.
Refined foods with a high fat content should not be an everyday diet staple. Besides diet compliance, there's the issue with trans fats and industrially processed oils present in these foods (which is what people should be concerned about).
My ideas on how to best approach maintenance of the lean state has been outlined in this article.
2. Eat fish or add fish oil to your diet
Even if you get your fats from unprocessed foods for the most part, your omega-6/omega-3-ratio is likely to be skewed towards omega-6. Unless you eat fatty fish on a regular basis, I would advise to add 3 g of fish oil per day. Doing so is prudent and may have modest health benefits in the long term.
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