How to take fats as food

Latest truth of saturated fatty acids

Beef for Sukiyaki. Maybe too much saturated fat 

by eating ten pieces, but how about five pieces?

Ingestion or intake of saturated fatty acids is not bad for your health. Such research results have recently appeared in reputable medical journals. Saturated fatty acids are fat often found in animal meat, butter, dairy products, etc. Also included are coconut, and cocoa. Good news for those who like these foods.

Until now, ingestion of saturated fatty acid has been recognized to raise the blood concentration of Low Density Lipoprotein (LDL) cholesterol (bad cholesterol), and therefore it would be a risk for arteriosclerosis (hardening of the walls of the arteries) and thus promoting heart attack and stroke. Certainly, the higher the LDL cholesterol level, the higher the risk of arteriosclerosis.

However, it has not been proven if the LDL cholesterol level would rise due to ingestion of saturated fatty acids. Since not all of the metabolic phenomena in the human body have been elucidated, the "premature" medical theory and real data may not always match. In recent scientific literature, the importance of these "real-world" data is increasing.

Meta-analysis is a method of integrating and analyzing real-world data obtained from various clinical studies. A meta-analysis integrating several major studies with a total combined number of some hundreds of thousand subjects on saturated fatty acids and various health risks have been published. It was shown that there is no relation to the risk of total number of deaths, heart attack, stroke, diabetes, of saturated fatty acid intake.

Latest truth about trans fatty acids

While saturated fatty acids are not bad, trans fatty acids are not good for the body and health. That is the results of meta-analysis coming out recently in peer-review journals. Trans fatty acids are the fat contained in margarine, confectionery, snacks, fresh cream, etc. It is the fatty acid that is artificially produced by loading with hydrogen. If you like such foods, it's important information that could prevent premature diseases.

Well, to understand more in details, let's review about fatty acids here. There are liquid oil and solid fat at room temperature collectively called oils. Fat or oil molecule consists of three fatty acid molecules and one glycerin molecule. Fatty acids are molecules in which carbon atoms are linked in a chain. There are two types of fatty acids: saturated fatty acids with no carbon double bonds and unsaturated fatty acids with carbon double bonds. Unsaturated fatty acids are classified into two types, cis and trans, based on differences in structure around the carbon double bonds. Cis means "on the same side", with hydrogen atoms on the same side across double bonds of carbon atoms. Most natural unsaturated fatty acids are cis type.

Trans means "over there", with hydrogen atoms on opposite sides of the carbon atom double bonds. Unsaturated fatty acids with one or more trans (double) double bonds are collectively called "trans fatty acids". There are some trans fatty acids that are naturally contained in foods and those that can be produced in the process of processing and refining oils and fats.

In animals such as cows, trans fatty acids are made by the action of microorganisms in the stomach, so trace amounts of natural trans fatty acids are contained in beef, milk and dairy products. With the processing technology of "hydrogenation", it is possible to produce semisolid or solid trans fatty acids from liquid vegetable oils or fish oils at room temperature. Foods containing trans fatty acids produced artificially by such hydrogenation include margarine, fat spreads, shortening, and breads, cakes, donuts and other types of confectionery such as fried foods using them as raw materials.

So, in meta-analysis that integrated real-world data, how much was trans fatty acid intake that could lead to various health risks? Six research data were integrated, and the results showed that there is a correlation between intake of trans fatty acids for total mortality and the incidence of heart attack. There was no correlation with the risk of stroke and diabetes.

How to go with trans fatty acids

If you take a lot of trans fatty acids, not only does LDL cholesterol increase in the blood, but HDL cholesterol (good cholesterol) decreases. However, here again there is a possibility of a difference between theory and reality. There are still unknown problems. It is obvious that trans fatty acids made artificially will harm health, but the effect on health on natural trans fatty acids is unknown. Also, no research has been done on which trans fatty acids have a bad influence among many types of trans fatty acids.

So, to what extent can trans-fatty acids be consumed from the findings known to date? WHO recommends that intake of trans fatty acids should be less than 1% of total energy intake. On a weight basis, it is less than about 2 g per person per day. The Ministry of Health, Labor and Welfare of Japan has not yet established the target value of trans fatty acid intake and there is no reference value and obligation to display the content of the trans fatty acids in food in Japan.

Regarding the amount of intake in Japanese, in the survey conducted by the Ministry of Agriculture, Forestry and Fisheries in 2008, the average amount of trans fatty acids consumed per person is estimated to be 0.92 to 0.96 g. However, people who consume more processed foods are likely to exceed 2 grams. It is advisable to avoid intake of foods containing a lot of trans fatty acids as much as possible.

Finally, how much fat intake is ideal for health?

If asked, we would like to answer like this manner. First, artificial trans fatty acids intake should be reduced. Monounsaturated fatty acids intake such as nuts should be increased. And saturated fatty acids such as meat and milk intake should be reasonable in amount.

Yasuharu Tokuda, MD, MPH & David Itokazu, MD