Good fats – bad fats?

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Dietary fats and their effect on our health have been the subject of a heated debate for decades now. Fats are subdivided into three different classes according to their chemical properties: saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA). In conjunction with obesity and heart disease mainly the "bad" saturated fats have been blamed – the recommendation to restrict those allegedly unhealthy fats was already given in 1961. This recommendation has not only been based on a high calory density, but also on the observation that SFAs raise the level of LDL-cholesterol, the "bad" cholesterol. This rise may play a role in the formation of arteriosclerosis.

Today, more than 50 years later, the success of this guideline is questioned more and more. The scientific evidence is still rather scarce, because there is simply too much conflicting data. The intake of saturated fatty acids only weakly correlates with the incidence of chronic heart disease. Several countries (e.g. Thailand, India or Sri Lanka) with a high dietary intake of SFAs seem to defy all findings as they all show a very low incidence of cardiovascular disease.

So saturated fats may not be the berated villains of our diets. Instead of demonizing them they should primarily be viewed as nutrients – nutrients that do not only provide energy, but can also fulfill physiological functions. For example, some SFAs inhibit intestinal inflammation or show a supportive effect in fighting cancer cells. There are many factors that play a role in the development of heart disease, such as genes, smoking, age, gender, weight, high blood pressure or diabetes, so the intake of saturated fats does not suffice as sole explanation. Saturated fats increase the levels of both good and bad cholesterol, and thus their overall health effect is most likely neutral.

Do fats play a role in cardiovascular disease?

There is growing evidence that the form of ingested carbohydrates and an elevated risk of heart disease are related. Carbohydrates with a high glycemic index can have a negative effect on the composition of blood lipids as they can increase the fraction of low value or detrimental fatty acids in the blood stream. If the goal is to reduce saturated fats it is important to consider which nutrients take their place – rapidly digestible carbohydrates from highly processed cereals and sugars are definitely not a suitable alternative, because they carry yet another risk: High glycemic index foods promote the formation of particularly small LDL cholesterol molecules that lead to plaques in the arteries.

What about polyunsaturated fatty acids?

PUFAs are said to be the "healthy" fats in our diet. They are subdivided into omega-6 fatty acids and omega-3 fatty acids. They are essential for us and need to be a part of our diet. Contrary to SFAs or MUFAs our body is not able to synthesize them.

Omega-3 fatty acids
Omega-3 fats are particulary beneficial to our health, especially eicosapentaenic acid (EPA) and docosahexaenic acid (DHA). They mainly occur in seafood and only to a minor degree in meat, milk or eggs. With the exception of algae they cannot be found in plant based foods. These omega-3s reduce countless risk factors associated with cardiovascular disease: They reduce blood pressure and inflammation, and they have a positive effect on asthma, arthritis, psoriasis, depression and are protective against cancer.

Omega-6 fatty acids
Omega-6 fats, of which linolic acid is the main source in our diet, are a fundamental component of our cell membranes and play an important role in forming metabolites that are necessary for inflammatory processes in the body. Omega-6 and omega-3 fats have a quite opposite effect. Therefore, it is necessary that the ratio between the two is in balance. An excessive intake of linolic acid promotes the formation of pro-inflammatory signaling molecules. Also, a diet overly rich in omega-6 and very low in omega-3 may be a factor in developing chronic disease. Recently the omega-6 to omega-3 ratio has received growing attention in research. It is still unknown how much linolic acid is actually too much, but it is estimated that a ratio of about 5:1 is favorable. However, currently the intake of omega-6 fats is 15 to 40 times higher than the intake of omega-3. Several vegetable oils, such as sunflower oil, that are used in large quantities in our diet, even show an extremely out of balance ratio of more than 200:1!

Some vegetable oils are subject to criticism for another reason: A big proportion of our omega-6 intake comes from deep-fat frying oils but polyunsaturated fatty acids are not resistant to heating. High temperature treatment, e.g. frying, may transform them into trans-fats or other harmful oxidation products. A substantial proportion of the residues in the arteries consists of those harmful by-products. Trans-fats show a strong correlation with cardiovascular disease and are about to be banned in the U.S.

How can you improve the ratio of omega-6 to omega-3?

Basically one could just reduce the intake of omega-6, as this would autmatically improve the omega-6 to omega-3 ratio. However, it's the absolute intake of omega-3 that is crucial. 250 mg EPA + DHA per day are necessary to prevent disease and ensure a proper physiological function. Several authorities even recommend twice that amount. Many countries all over the world have insufficient intakes of these two essential nutrients.

EPA and DHA can be found exclusively in animal products, with the exception of some algae. However, the body can synthesize them to a restricted extent from the omega-3 fatty acid α-linolenic acid. The conversion rate in men is very low, less than 5 %, women can convert between 5 and 10 %. The conversion rate is also strongly dependent on the omega-6 intake, as both classes of fatty acids compete with the same conversion enzymes: excessive omega-6 decreases the production of EPA and DHA. Therefore vegetarians should watch their intake of omega-3 very carefully and if necessary supplement with a plant based omega-3 source (e.g. algae oil extracts).

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