I only knew that sesame oil is fragrant, but I didn’t expect that its nutritional value is so amazing?!

This year, the top journal Nature published a new article analyzing the nutritional advantages of the popular foods on the Chinese table. From tea to tofu, they are all familiar to us, but it also specifically mentioned a type of substance that may be a little surprising - sesame oil .

The article mentioned a study jointly published by scholars from Nanjing Medical University and Zhejiang University in 2020. Through a dietary health survey of 15,000 Chinese adults, it was found that eating too much of the common cooking oils we eat, whether lard or vegetable oil, will increase the risk of diabetes by 31-42%. However, for people who eat a lot of sesame oil, the risk of diabetes is basically unchanged . A major contributor to this may be the physiological activity of the oil concomitants in sesame oil, mainly sesame lignans . Current research has found that sesame lignans not only have strong antioxidant properties, but can also protect the cardiovascular system by regulating lipids [1].

Sesame is one of the oldest oil crops in the world. According to records, when Zhang Qian was on a diplomatic mission to the Western Regions, he brought back many plants from the Hu lands of the Western Regions, including "Hu Ma", which is now sesame, and is often recorded in various historical books in ancient China. Later, it was also known as "You Ma" and "Zhi Ma". When Zhi Ma appeared and became popular, its homophonic word "Zhi Ma" was also born and successfully replaced other names.

After sesame was introduced, its popularity was unstoppable. In ancient times, there were not many edible oil crops to choose from, and oil extraction technology was not mature, so plant oils were relatively scarce. However, sesame has a high oil content and high oil yield, and it can adapt to my country's climate and environment. It was very popular and its planting area continued to expand, especially in the north. Sesame oil became the most popular food in the kitchen, and the geographical pattern of "sesame in the north and rapeseed in the south" was formed for a time [2].

According to Shen Kuo’s Mengxi Bitan (Dream Pool Essays) from the Northern Song Dynasty, “Northerners today like to fry things with sesame oil. No matter what the food is, they fry it all with sesame oil.” This shows how popular sesame oil is.[3]

In addition to being used as a nutritional supplement and food, sesame oil is also used in skin care, beauty, and medical care, and is a kind of food and medicine.

Today, sesame oil has become an irreplaceable seasoning oil in the kitchen due to its unique flavor. Just a few drops can add a rich aroma, and it is the "finishing touch" of many delicious dishes. So far, among so many edible oils, only sesame oil can be called "fragrant". However, this should not cover up its own nutrition, especially the presence of lignans, a fat companion, which gives sesame oil a higher health value.

01

Lignans, the main antioxidant in sesame oil

Sesame oil is an edible oil of the oleic acid-linoleic acid type. These two are the main fatty acid components, and the total unsaturated fatty acid content is as high as over 80%. Although the unsaturated fat content is high, sesame oil is not easily oxidized and rancid, and its stability is better than other vegetable oils, which is mainly due to a unique oil accompaniment in sesame oil - lignans.

Natural lignans are distributed in various parts of plants. They are named because they were first discovered and distributed in large quantities in xylem and resin.

Among plant foods, sesame is one of the foods with the highest lignan content, up to 834.57 mg/100g . If it is pressed into sesame oil, the lignan content will be further enriched and the content will be even higher. Flaxseed and cashew nuts are also relatively rich, with 257.6 and 56.33 mg/100g respectively. Cruciferous vegetables and fruits are also one of the sources of lignans, but the lignan content in grains may be relatively low, and most of it is concentrated in the epidermis (seed coat or pericarp) and endosperm. It can be seen that when eating grains, it is better to eat more whole grains [4].

In addition, some scientists have found trace amounts of lignans in milk and its products, which was the first time that lignans were found to be of animal origin. Later, they were also found in chicken, pork, beef, mutton, and eggs[5].

Lignans are a collection of complex compounds. In sesame oil, the majority are sesamin and sesaminol . Although the content of other ingredients, such as sesamol and sesaminophenol, is very small, they have extremely strong antioxidant properties.

Structures of several main sesame lignans

Lignans are important guardians of sesame oil's oxidative stability.

The antioxidant advantages of sesame oil can be intuitively felt through an edible oil oxidation induction experiment.

Different edible oils were placed in an environment of 60°C for automatic oxidation. Generally, edible oils began to oxidize after 5-20 days of induction, while sesame salad oil began to oxidize after 35 days, and roasted sesame oil remained unchanged after 50 days. At least no oxidation was observed during the experimental period.

Antioxidant properties of different vegetable oils | [6]

When lignans enter the body with sesame oil, this antioxidant ability can continue to work, removing free radicals in the body and reducing the risk of chronic diseases and degenerative diseases related to oxidative stress, such as cancer, cardiovascular disease, and neurodegeneration.

02

Lignans effectively regulate lipid and cholesterol metabolism

In addition to its powerful antioxidant capacity, lignans can also regulate lipid and cholesterol metabolism, maintain cardiovascular health, and protect the heart, liver, and kidneys.

In a clinical study with a small sample size (48 people), by comparing the lipid-lowering effects of sesame oil and olive oil, it was found that in patients with hypercholesterolemia, sesame oil can effectively lower LDL-C and blood lipid levels, and the regulatory effect is better than olive oil.

Changes in blood lipids and body weight after sesame oil/olive oil intervention | [7]

Some components of lignans, such as sesamin, may improve blood lipid levels and reduce tissue lipid accumulation by inhibiting the synthesis of fatty acids and triglycerides, promoting fatty acid uptake, triglyceride decomposition and fatty acid oxidation.

In addition, lignans can inhibit the absorption of dietary cholesterol and the synthesis of cholesterol, and promote the excretion of cholesterol, thereby lowering serum cholesterol levels, especially the level of low-density lipoprotein cholesterol (LDL-C), a risk factor for atherosclerosis, while increasing the level of beneficial cholesterol - high-density lipoprotein (HDL).

The current research on the mechanism of action of lignans is incomplete, and the following figure can be used as a reference.

SREBP-1c: sterol regulatory element binding protein-1c; FASN: fatty acid synthase; LPL: lipoprotein lipase; CD36: leukocyte differentiation antigen 36; p-HSL: phosphorylated hormone-sensitive lipase; PPARα: peroxisome proliferator-activated receptor α; ACOX: acyl-CoA oxidase; WAT: white adipose tissue; BAT: brown adipose tissue; UCP1: uncoupling protein 1; ABCG: adenosine triphosphate-binding cassette transporter; SREBP-2: cholesterol regulatory element binding protein-2; HMGR: 3-hydroxy-3-methylglutaryl-CoA reductase; ACAT: cholesterol acyltransferase; ApoA-I: apolipoprotein AI; ApoB: apolipoprotein B; CYP7A1: cholesterol-7α-hydroxylase | [8]

The mechanism of sesame lignans regulating cholesterol sounds familiar, and it is easy to associate it with another substance - phytosterols. Phytosterols also inhibit the absorption of exogenous cholesterol, reduce synthesis in the body, and promote cholesterol excretion, ultimately playing a role in lowering cholesterol.

An animal experiment once compared the two and found that β-sitosterol seemed to have a stronger inhibitory effect on cholesterol and may be better than sesamin in lowering cholesterol[9]. However, this point needs to be verified by more experiments in the future!

In any case, increasing the intake of lignans in daily life will always add points to your health. Of course, this does not encourage you to eat sesame oil without restraint in the future. It just means that next time when you go to buy sesame oil, you can pay more attention and choose the one with higher lignan content.

In addition, the content of lignans in other common foods is also listed here for your reference.

Lignan content in common foods (mg/100g)

Note: Due to the limitations of the test samples, the data between different experimental analyses may differ. [4]

References:

[1] Eisenstein M. From tea to tofu: why Chinese dietary staples are rich pickings for research. Nature. 2023 Jun;618(7965):S15-S17.

[2] Qiu Liang. Talking about edible oil in ancient times [J]. Food and Health, 2013(04):52-53.

[3] Mengxi Bitan, Northern Song Dynasty, Shen Kuo.

[4]Rodríguez-García C et al. Naturally Lignan-Rich Foods: A Dietary Tool for Health Promotion? Molecules. 2019 Mar 6;24(5):917.

[5]Durazzo A et al. Dietary Lignans: Definition, Description and Research Trends in Databases Development. Molecules. 2018 Dec 8;23(12):3251.

[6]Fukuda Y, et al. Chemistry of lignan antioxidants in sesame seed and oil [A]. Food Phytochemicals for cancer II: teas, spices, and HERBs [C]. Washingtong DC: American Chenical Society, 1994: 264-274.

[7]Namayandeh SM, et al. Olive and sesame oil effect on lipid profile in hypercholesterolemic patients, which better? Int J Prev Med. 2013 Sep;4(9):1059-62.

[8] Hu Minmin, et al. Research progress on the mechanism of sesame lignans in regulating lipid metabolism[J]. Health Research, 2021, 50(05): 859-863+867.

[9] Lin Lei ,et al. Dietary β-sitosterol is more potent in reducing plasma cholesterol than sesamin in hypercholesterolemia hamsters. European Journal of Lipid Science and Technology, Eur. J. Lipid Sci. Technol. 2017. https://doi.org/10.1002/ejlt.201600349