A Brief History of fat
Our relationship with fat and dietary cholesterol has just gotten more complicated. Or has it gotten easier? I guess it depends on how you look at it. What we once thought was an absolute truth now no longer seems to be true at all. It was supposedly well known science that dietary fat and cholesterol are dangerous and need to be avoided. We now know, however, that science tells us the opposite. Dietary fat and cholesterol are not inherently unhealthy. How could this be? Let’s take a look at the history of what brought us to this point.
The evidence that convinced nutritional and health experts that dietary fat and cholesterol were dangerous to our health consisted of three main areas.
1- Studies showed that feeding animals very high levels of dietary cholesterol increased plasma cholesterol and vascular plaque. This started back in 1843, when researchers analyzed atherosclerotic plaque and found it to contain cholesterol.(Am J Clin Nutr 1974;27:403-422). After that, studies in the early 1900s showed that rabbits who were fed cholesterol developed more atherosclerosis (Cardiovasc pathology 1999;8:177-178). Then other studies followed in a similar vein. However, it should be pointed out, that rabbits and other herbivores that were tested have never adapted to eating cholesterol in their diet. They have forever been herbivores and their bodies are not evolutionarily adapted to eating cholesterol. In addition, they were given extreme amounts of cholesterol. Therefore, the correlation to humans eating cholesterol and fat in food is questionable at best.
2- Clinical studies in humans showed that increased fat and cholesterol consumption raised total cholesterol levels. Unfortunately, total cholesterol is a poor marker for cardiovascular risk and has very little to do with the fat and cholesterol you eat. Studies that investigated changes in specific lipid subtypes in response to fat intake showed that LDL and HDL increased proportionally, thus keeping the HDL:LDL ratio the same, and likely NOT increasing the risk of cardiovascular disease. More recent studies have confirmed this by showing that dietary cholesterol intake had no effect on cardiovascular risk (biochem biophys acta 200, 1529, 310-320)
3- Epidemiological studies subsequently showed that increased dietary cholesterol and fat intake was associated with an increase in cardiovascular disease. This was the main area of research that captivated the public and experts alike.
Let’s look a little deeper into the epidemiological studies and how they came to influence nutritional guidelines. The big push for the low-fat craze came in the 1950’s when Ancel Keys embarked on his Seven Countries Study, which was essentially his quest to prove that dietary fat and cholesterol led to heart disease. His timing was ideal for having a maximal impact as heart disease was fresh on peoples’ minds. President Dwight Eisenhower had just had a heart attack in 1955, and the rates of heart disease in the US were rapidly rising as the nation’s number one cause of death.
Everyone was primed to find a scapegoat. Society wanted to find the one thing that causes heart disease, eliminate it, and the go back to feeling safe and protected. It is an overly simplistic way of thinking, but at the same time it is part of human nature to want to simplify things into an easily answered question. Dr. Keys believed that the countries that ate cholesterol and fat-containing foods had higher rates of coronary heart disease, and those that ate less had lower rates. Therefore, based on his logic, dietary fat and cholesterol caused heart disease, and suddenly society had their scapegoat. This line of thinking provides absolutely no proof, but that did not stop him from promoting it as such.
In 1968 the AHA recommended that all individuals should limit their dietary cholesterol and fat intake (Dr. Keys was on the board of this committee), and the American Government incorporated the same into the official dietary guidelines in 1977. Acta Cardiol 1999;54:155–158 JAMA 1961;175:389-391. Based on these guidelines, the medical profession preached the dogma that dietary fat and cholesterol were dangerous and by definition, a healthy diet was a low fat, low cholesterol diet. Food companies raced to the market with “healthy” low fat food, and a multi-million dollar food industry was born.
However, the problem lay with the details of Dr. Keys’ study. Most importantly, his study was purely observational. There was no control group, no randomization, and no controlling for variables. Therefore it did nothing to prove causation. It merely pointed out an observed coincidence. In addition, there have been numerous debates about whether he handpicked his countries to fit his hypothesis. It has been suggested that he started with 22 countries and only kept the ones that supported his hypothesis, discarding the rest. In addition, the main example of beneficial effects of low cholesterol intake correlating with low CHD risk was extrapolated from peasants from the Greek Island Crete. These individuals performed hard manual labor for the majority of their lives. Therefore they were much more active then the other populations studied. But he did not control for this variable of increased physical activity and its beneficial effect of reducing the risk of heart disease. In addition, Dr. Keys sampled their dietary patterns during lent. The majority of them were avoiding meat and cheeses, thus underestimating their true average consumption of saturated fat.
All that being said, however, those details matter less since the study as a whole was plain and simply bad science. The study did not prove anything, and it should be considered an interesting finding that required more investigation, not a cause and effect result around which governmental guidelines should be based. The study did not accurately control for other behaviors such as level of physical activity, sugar intake, vegetable intake etc. It is very plausible that the people who ate more saturated fat ate more burgers, so they also ate more French fries, more simple carbs (buns), and were not eating as many vegetables (ketchup was their vegetable), and maybe even had more milkshakes and soda. It is very shortsighted to say with certainty that the fat was the culprit, (thus one of my favorite sayings, “Don’t blame the butter for what the bun did.”). A well-designed scientific study would control for all that, including physical activity, smoking, stress management, etc. Dr. Keys’ study did not, but he stated his results with authority as if it had.
Interestingly, there was a dissenting voice during that time frame that got drowned out by Ancel Keys. A British physiologist, John Yudkin asserted that fat was not the main culprit, but rather sugar was the main cause of CHD and death. Like Keys, his data was observational and not conclusive. His theory, however, was shunned and was not adopted like Keys’. It is fascinating to read reports as to why this may have been. Keys is described as aggressive, charismatic and combative. Yudkin, on the other hand, is described as calm, reserved and quiet. Some, therefore, believe the past 50 years of misguided dietary guidelines all started because of differences in personalities. That may be an over-simplification, but it is a fascinating theory none-the-less.
Although it would be unfair to say our country’s entire low-fat craze came from Ancel Keys, he certainly promoted his hypothesis with enthusiasm and a fervor that gained a tremendous amount of attention. The subsequent national recommendations started an entire industry of “low-fat” food products ranging from cookies and cakes, to meat alternatives and even “Healthy” hydrogenated vegetable oils to replace anything that had dietary fat and cholesterol. The word “fat” became one of the most loaded and charged words in our language. Think about it. Sugar is a term of affection. You can hear the waitress with her southern drawl, “Hey, sugar. What can I get you?” We frequently use “sweet” to mean nice, caring, kind. “She is so sweet.” Fat, on the other hand, is a word you have to whisper for fear someone will hear you. The word fat has become associated with ugly, unpleasant, or even worse, death.
Unfortunately, our dialect and misguided dogma make an implicit assumption that eating fat makes us become fat. If cholesterol and fat are in arterial plaques, then it must get there by eating cholesterol. That way of thinking, however, ignores the fascinating and complex physiology that occurs in our bodies when we ingest food. In fact, it turns out that our bodies convert sugar to fat. This causes us to gain weight and can lead to fatty plaques in our arteries. Sugar increases insulin levels, and insulin is a hormone that causes our bodies to store more fat. Low-fat, higher carbohydrate diets have consistently shown less weight loss than higher fat, low carbohydrate diets. It seems contradictory, but eating fat can actually help us burn fat! As an example, a ketogenic diet, which is up to 80% from fat and less than 20 grams of carbohydrates, is one of the best diets for fat loss. Our bodies preferentially burn fat despite eating a high percentage of calories from fat. After all, from an evolutionary standpoint, we have been eating animal fats for 200,000 years. Grains have only been introduced over the past 10,000 years, and refined sugar (stripped of any fiber or nutritional components) over the past 300 years, a mere blink of the eye in evolutionary terms.
A big question that was not addressed as much during the past 50 years has been what do we eat instead of the fat? Once the government recommended a low-fat and low-cholesterol diet, society as a whole was not as concerned with what we replaced the fats with, so long as we got rid of the fat. Therefore, the high sugar, high fructose, processed foods reigned unchecked and became the new “healthy” staple of the American diet. Eggs for breakfast were replaced by sugar cereals, bagels, muffins and the like. Whole milk was replaced by orange juice and fructose containing drinks. Meat and chicken were replaced by white bread and white flour noodles. Since that time, the incidence of obesity and diabetes has increased dramatically. In 1950, 12% of Americans were obese. In 1980 it increased a little to 15%, and then sky rocketed to 35% by 2000. At the same time, rates heart disease and other chronic illnesses have also continued to climb. Again, this does not prove that the low-fat craze was the cause, but it certainly shows that the low-fat shift did not achieve the intended results of improving our health. At best it failed to make us healthy. At worst, it was the direct cause of an explosion of obesity, diabetes, autoimmune disease, and other chronic diseases.
More than 50 years have passed since the low-fat craze began, and there are still no randomized controlled trials to support the hypothesis that dietary fat and cholesterol increase the risk for heart disease (Am j clin nutr. 2010;91:535-546). In fact, multiple epidemiological studies and meta-analysis have subsequently shown no correlation between dietary cholesterol intake and cardiovascular risk. The American College of Cardiology (ACC) finally reversed their ban on dietary cholesterol in 2014 saying, “There is insufficient evidence to determine whether lowering dietary cholesterol reduces LDL-C” (JACC 2014,63,2960-2984.). In 2015, the American government guidelines followed suit saying, “Available evidence shows no appreciable relationship between consumption of dietary cholesterol and serum cholesterol.” (http://www.health.gov/dietaryguidelines/science-report) Taking this one step further, new research now suggests much more clearly that John Yudkin had the more plausible hypothesis that sugar is the main culprit leading to obesity, diabetes and CHD. It is fascinating to think how things could have been different if the sugar hypothesis, rather than the fat hypothesis, was adopted in the 1960s.
There remains no doubt that real, from the earth vegetables in a variety of colors should make up the majority of every meal. However, nutritional science has entered a new frontier, and all that was known in the past has to be questioned. When it comes to fat and animal based foods, many of the previous experts and authority figures who followed the conventional dogma have now begun to rethink their positions. Additionally, the rise of social media has given a voice to dissenters and supporters of the low-fat hypothesis alike.
If you choose to not eat animal products based on a moral belief about the treatment of animals, then the science does not matter as much as that is a very personal decision and is a matter of principal. If you choose to not eat animals based on environmental sustainability, that likewise has little to do with the science of how it affects your body. Even here, the science can get murky, but I will stick to what I know best and focus on the effects on our bodies.
There is no high level evidence proving that we should avoid animal based foods. Nutritional science is complicated, with mostly observational and epidemiological studies as opposed to studies showing a causative proof. That being said, however, large meta-analysis of most dietary trials have shown that there is no direct relationship between fat intake and heart disease. Period.
I would suggest, however, that quality matters. One of the problems may be that the quality of our animal based foods have deteriorated as a result of mass production and the associated use of corn feed, antibiotics and hormones. Studies have shown higher nutrient and lower toxin content in grass-fed as opposed to grain-fed meat, wild as opposed to farmed fish, pasture-raised as opposed to pen-raised chicken and hens (Nutr J 2010;9:10; J Nutr, 2005;135(11),2639-2643; Environ Health Prospect 2005;113(5), 552-556). From an evolutionary perspective, our ancestors only ate grass fed meat. They only caught wild fish. They only ate eggs from hens freely grazing grass. Our bodies have evolved over thousands of years to eat this way. If we could get back to those basics, we would take a huge step towards restoring a healthier dietary pattern.
So what can we conclude from the research we have available, good, bad or otherwise?
- Vegetables are the undisputed cornerstone of a healthy diet and should make up the majority of every meal. The debate over whether fats are “good” or “bad” should not overshadow the fact that all research points to the healthy power of fresh (preferably organic) vegetables. That is not synonymous with being vegetarian, but it holds true that veggies are king.
- Dietary cholesterol has been exonerated and no longer needs to be avoided. Eggs are the primary example. Since they are a widely available and affordable source of protein, choline, xanthophylls, vitamin K2, and other vital nutrients, we should now focus on eggs for their health benefits rather than avoiding them.
- Fat is not inherently unhealthy. All fat is not the same, and diets that have shown reduction in heart disease and strokes have had over 40% fat (Lyon heart study and PREDIMED study).
- Monounsaturated fats (avocado, nuts, olive oil etc.) are clearly beneficial to our health and help with reduction of chronic diseases.
- Trans-Fats (food made with hydrogenated oils like doughnuts, muffins, cookies, crackers etc.) are almost certainly associated with increased risk of CHD and cancer and should be avoided.
- Saturated fat is not as evil as initially thought. We may not have convincing evidence for its direct health benefits, but we also do not have any credible evidence for its health detriments. Therefore this one is “neutral,” and more controversial, but we can no longer say with certainty that it needs to be avoided. We can now start to explore its potential benefits and enjoyment.
- Polyunsaturated fats (mostly found in cooking oils such as soybean oil, corn oil, sunflower oil etc.) may not be as beneficial as initially thought. Risk of oil oxidation causing systemic inflammation may lead to potential deleterious health effects. Again, the science is mostly observational but certainly suggestive.
- Simple carbohydrates, sugars and processed grains are the most likely foods to cause obesity, diabetes and heart disease, and therefore should be minimized.
Practical tips:
Cooking oils are a vey common way we encounter fats in our diet. There are many choices, and it can be confusing to know which are “healthy” oils and which are less healthy. Here is a quick primer:
You want to pick a cooking oil that has :
- a higher amount of monounsaturated fatty acids (MUFAs)
- a high smoke point (the point at which heat starts to change the structure of the fat and can cause it to oxidize),
- it should be made with minimal processing and not be prone to toxin accumulation.
- Lower Omega 6 to Omega 3 ratio. Simplistically you can think of omega 3 fatty acids as “anti-inflammatory” and omega 6 as “potentially inflammatory.” As with most things, it is more complicated than this, but it still helps to have a convenient way of thinking.
Whatever you choose, choosing organic is best as it avoids GMOs and contaminants. Also, look for oils that are labeled as “cold pressed” or “expeller pressed” as this ensures that the oil retains more nutrients and has fewer chemical contaminants.
Best oils: Avocado oil, almond oil, olive oil (be careful with high cooking heat), canola oil (important to be organic)
Second line: Butter, Ghee, coconut oil or other medium chain triglyceride (MCT) oil
Avoid: Processed oils such as corn, cottonseed, sunflower and soy based products. Avoid any partially hydrogenated oil. In addition, grapeseed oil is prone to contamination and has a high proportion of omega 6, thus unfavorable altering your omega 6 to omega 3 ratio.
Whether you are in the “low-fat” or the “low-carb” camp, one thing is clear beyond reproach. Focusing on real foods, avoiding processed or refined foods, and avoiding added sugar is a great place to start to improve your health. Improve the quality of what you use to nourish your body, and your heath will improve. If that is the only change you make, then you are well on your way.