Trans fatty acids are trending again! Is it true that we can’t eat even a single bite?

On May 9, the “notorious” trans fatty acids became a hot topic again!

Screenshot of the network platform

There is news that "a well-known brand of dairy products contains trans fatty acids, which are harmful to health", and many bloggers have reminded parents to "be careful" and not give their children this product. We cannot make a judgment on the quality of this brand of products, but today we can talk about trans fatty acids in our food.

What are trans fatty acids?

Fat is a triglyceride formed by fatty acids and glycerol. Fatty acids have different names depending on their structure. Trans fatty acids are a type of fatty acid and are unsaturated fatty acids.

Existing research suggests that the main harm of trans fat is that it significantly increases the risk of cardiovascular disease because it can increase the level of low-density lipoprotein (LDL, or "bad cholesterol") in the blood while lowering the level of high-density lipoprotein (HDL, or "good cholesterol"), leading to an increased risk of arteriosclerosis and heart attack.

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As for other impacts, such as obesity, cancer, diabetes, growth and development, reproductive health, Alzheimer's disease, etc., there is insufficient evidence.

Some people also say that trans fats will accumulate in the body and cannot be metabolized, or that it takes 51 days for trans fats to be metabolized in the human body. In fact, these claims are wrong. In the human body, trans fats and ordinary fats are metabolized in the same way, and no difference has been found in the metabolic pathways of trans fats in infants, children, teenagers, and adults.

Which foods contain trans fatty acids?

1. Trans fatty acids are found in natural foods

Yes, you read that right. Trans fatty acids are also found in natural foods. They mainly come from meat, fat, milk and dairy products of ruminant animals such as cattle and sheep.

Trans fatty acids are also found in human breast milk. Studies have found that the trans fat content in breast milk is between 1% and 10% of the fat content in breast milk, such as 7.0±2.3% for American women and 7.19±3.03% for Canadian women.

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2. Hydrogenated vegetable oil

Hydrogenated vegetable oils are a notorious source of trans fatty acids. Hydrogenation of vegetable oils is an operation that adds hydrogen to unsaturated bonds to increase the melting point of the oil and improve its food processing properties.

Liquid vegetable oil is not very effective in shortening, but after hydrogenation, it is semi-solid at room temperature, which can meet the requirements of process and taste. Using hydrogenated vegetable oil can also improve the taste of food, such as making cookies more crispy and milk tea more lubricated.

In addition, its chemical properties are relatively stable, which can extend the shelf life, and it is lower in cost than animal fats such as natural butter. Therefore, hydrogenated oil is widely used in the food industry.

However, when vegetable oils are not fully hydrogenated, some double bonds are converted from the natural "cis structure" to the "trans structure", making the fats containing them "trans fats". In addition, frying food at too high an oil temperature and for too long will also produce a small amount of trans fatty acids.

But in fact, not all hydrogenated oils have trans fatty acids. Only incompletely hydrogenated oils produce trans fatty acids.

At present, with the development and innovation of food science and technology, trans fatty acids in edible oil products such as hydrogenated vegetable oils can be well controlled, and alternative products such as oil products using non-hydrogenated processes have also been applied. Now many hydrogenated vegetable oil products, non-dairy creamer, and cocoa butter substitutes can actually achieve "0 trans fatty acids", and the trans fatty acid content has also dropped significantly compared with the past.

Is it really true that we can’t eat any trans fatty acids?

As the classic saying goes, "It is foolish to talk about toxicity without considering the dosage." Whether trans fatty acids are harmful to our health depends on how much we eat.

At present, the dietary guidelines of the World Health Organization (WHO), my country, the United States and other countries all recommend that the energy supply ratio of trans fat should be less than 1%, which is equivalent to eating 2.2 grams of trans fat for an adult who needs to consume 8,400 kilojoules of energy per day. However, survey data in my country shows that the average trans fat consumed by Chinese people is 0.39 grams per day, which is equivalent to an energy supply ratio of 0.16%, far lower than the WHO's recommended value (less than 1%).

Therefore, as long as you do not consume a large amount of foods containing trans fatty acids, the health risk is very low and there is no need to panic too much about trans fats.

For example, trans fatty acids are naturally present in milk, but usually in very small amounts: the average trans fat content in liquid milk is 0.08 g/100 g, in milk powder is 0.26 g/100 g, and in yogurt is 0.07 g/100 g.

To put it in perspective, a person would need to drink 2.75 kg of milk a day to exceed the WHO's recommended value. For Chinese residents, whose per capita dairy product intake is less than 50 grams, there is obviously no need to worry about excessive trans fatty acids.

How to identify

Are there trans fatty acids?

1. These two types of food usually have high trans fatty acid content

There are two types of food that generally have relatively high trans fat content. One is natural and margarine cream and butter, with an average content of 2 grams per 100 grams; the other is vegetable oil, with an average content of 0.86 grams per 100 grams.

The average trans fat content in other foods is generally low, but the trans fat content in some individual products, such as chocolate with cocoa butter substitutes, French fries/potato chips, cakes, wafers, and sandwich biscuits, may be relatively high because some products use hydrogenated oils.

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2. Read the food ingredient list

First, you need to look at the ingredient list on the food label. There are many common "names" for hydrogenated fats in the ingredient list, including hydrogenated vegetable oil, partially hydrogenated vegetable oil, hydrogenated palm oil, hydrogenated soybean oil, vegetable shortening, margarine, non-dairy creamer, cocoa butter substitute, etc. Therefore, when you buy packaged food, if you see these things in the ingredient list, it means that there may be trans fatty acids.

Secondly, you should also look at the nutrition information table on the label and choose foods that do not contain trans fatty acids or have low trans fatty acid content.

my country's national food safety standard "General Rules for Nutrition Labeling of Prepackaged Foods" stipulates that if food ingredients contain or use hydrogenated and/or partially hydrogenated fats during production, the trans fatty acid content must be indicated in the nutrition information table on the food label. In other words, if the trans fatty acid content is not indicated on the label of the food you eat, it generally means that it does not contain hydrogenated oil.

my country's standards also stipulate that if the trans fatty acid content in 100 grams of food is less than 0.3 grams, it can be labeled as "0". In other words, if the trans fatty acid content is indicated in the nutrition information table of your food label, but its content is zero, it may contain trans fatty acids, and you should pay attention to the intake.

How to control in diet

Trans fatty acid intake?

1. The key to controlling trans fatty acids is cooking oil

According to surveys, (refined) vegetable oil is the main source of trans fatty acids for Chinese people. Therefore, to avoid consuming too much trans fatty acids, we must first pay attention to controlling the amount of vegetable oil used in cooking.

The Chinese Dietary Guidelines (2022) recommend that adults should control their daily cooking oil intake to 25-30 grams, but we actually eat nearly 40 grams on average per day, and many people exceed 40 grams. Therefore, if we want to control trans fatty acid intake, the first thing to do is to use less oil when cooking.

2. Don’t just focus on trans fatty acids and ignore total fat

I would like to remind everyone that sometimes we overestimate the harm of trans fatty acids to health, but ignore total fat and saturated fat.

Generally speaking, foods high in trans fats contain both total fat and saturated fat. Excessive intake of saturated fat can increase the risk of atherosclerosis, coronary heart disease, and hypercholesterolemia. Excessive intake of total fat can also increase the risk of obesity and cardiovascular disease.

You should know that the current total fat energy supply ratio of our residents is 34.6%, which has exceeded the health recommendation range (20% to 30%), and most of this comes from cooking oil used for cooking; nearly one-third of people's saturated fat intake energy supply ratio exceeds the health recommendation range (10%). However, our trans fatty acid intake is far below the health recommendation range and does not exceed it at all. Therefore, instead of always worrying about trans fatty acids, it is better to use less cooking oil and eat less fatty meat and fried foods.

References

[1] GB 15196-2015 National Food Safety Standard Edible Oils and Fats Products

[2] Dietary intake of trans fatty acids and its risk assessment among Chinese residents

[3]Effects of saturated fatty acids on serum lipids and lipoproteins: a systematic review and regression analysis

[4]Effect of trans-fatty acid intake on blood lipids and lipoproteins: a systematic review and meta-regression analysis

[5]Reduction in saturated fat intake for cardiovascular disease

[6]Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies

[7]Health effects of saturated and trans-fatty acid intake in children and adolescents: Systematic review and meta-analysis.

[8] Scientific understanding of the relationship between dietary total fat, saturated fat and health[J]. Journal of Nutrition, 2022, 44(04): 313-315. DOI: 10.13325/j.cnki.acta.nutr.sin.2022.04.014.

[9] National Health Commission, Department of Disease Control and Prevention. Report on the Nutrition and Chronic Disease Status of Chinese Residents (2020)[M]. Beijing: People's Medical Publishing House, 2021.

[10] Chinese Nutrition Society. Dietary Guidelines for Chinese Residents (2022)[M]. Beijing: People's Medical Publishing House, 2022.

[11] Zhao R, Zhao L, et al. Dietary Fat Intake among Chinese Adults and Their Relationships with Blood Lipids: Findings from China Nutrition and Health Surveillance and Comparison with the PURE Study. Nutrients. 2022; 14(24):5262. https://doi.org/10.3390/nu14245262

Author: Ruan Guangfeng, Deputy Director of Kexin Food and Health Information Exchange Center

Review丨Zhang Yu, Researcher, Chinese Center for Disease Control and Prevention, Doctor of Medicine