Trans Fatty Acids

Trans-fats or Trans fatty acid is a type of unsaturated fat, that occurs naturally and large proportion is industrially produced. Trans-fat is produced by reacting unsaturated fat with hydrogen gas in the presence of catalyst in a process called partial hydrogenation. Partial hydrogenation of oil gives it a semisolid to solid texture (depending upon the degree of saturation), higher shelf life, and inertness in air (no rancidity). Due to these properties, trans-fats are useful in the food industry.

Trans-fats occur naturally in animal fat as a result of anaerobic bacterial fermentation in the rumen. These Trans-fats are absorbed from the gut and ultimately distributed to fat deposits of the animal. Therefore, animal fats, such as meat and dairy fats, contribute to the trans-fatty acid content of the diet.

Foods that Contain Industrially Produced Trans-fats

Partially hydrogenated oils (PHO) are the primary source of industrially-produced trans-fat. PHO is an ingredient in many foods, including margarine, vegetable shortening, and Vanaspati ghee; fried foods and doughnuts; baked goods such as crackers, biscuits, and pies; and pre-mixed products such as the pancake and hot chocolate mix. Baked and fried street and restaurant foods often contain industrially-produced trans-fat. All of these products can be made without industrially-produced trans-fat.

Effects of Partially Hydrogenated oil (PHO) on Health

1. Increased plasma low-density lipoprotein (LDL) concentration and decreased high-density lipoprotein (HDL). High LDL and low HDL are associated with a higher risk of cardiovascular disease.
2. Increased consumption of PHO is associated with an increased risk of type 2 diabetes, insulin resistance, and inflammation.  
3. Small amounts of PHO also have harmful health effects, for each additional 2% of calories from trans-fat consumed daily, the risk of coronary heart disease increases by 23%.

Is Natural Trans-fat Harmful?

The effect on blood lipids resulting from changes in natural trans-fats (ruminant) or industrially-produced trans-fat appear to be similar. Health authorities recommend limiting consumption of trans-fat (industrially-produced and ruminant) to less than 1% of total energy intake, which translates to less than 2.2 g/day for a 2,000-calorie diet.

Heating and Reheating of Oils

Heating, frying and reusing edible fats/oils increase the formation of trans-fats. A study has confirmed that heating to temperatures <200 °C had no appreciable impact on trans-fats levels. However, between 200 and 240 °C, trans-fats levels increase with the increase in temperature and the level of trans-fats increases further, with prolonged heating between 200 and 240 °C. Therefore, heating edible oils to common cooking temperatures (≤200 °C) has minimal effect on trans-fat generation whereas heating to higher temperatures can increase trans-fat levels. However, the amount of trans-fat generated during heating and frying is low when compared with the amount of trans-fat in partially hydrogenated oils (PHO).

Alternate to Tans-fats

The elimination of partially hydrogenated oils results in significant health benefits, with the greatest advantage obtained when PHOs are replaced by oils rich in polyunsaturated fatty- acids (PUFA), and oils rich in monounsaturated fatty acids (MUFA). Oils rich in PUFA include safflower oil, corn oil, sunflower oil, soybean oil, fatty fish, walnuts, and seeds; oils rich in MUFA include canola oil, olive oil, peanut oil, and oils from nuts and avocados.

Sources

[1] https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/fats-and-cholesterol/types-of-fat/#ref16

[2] Risérus U, Willett WC, Hu FB. Dietary fats and prevention of type 2 diabetes. Prog Lipid Res. 2009 Jan;48(1):44-51. doi: 10.1016/j.plipres.2008.10.002. Epub 2008 Nov 7. PMID: 19032965; PMCID: PMC2654180.

[3] Bhat S, Maganja D, Huang L, Wu JHY, Marklund M. Influence of Heating during Cooking on Trans Fatty Acid Content of Edible Oils: A Systematic Review and Meta-Analysis. Nutrients. 2022 Apr 2;14(7):1489. doi: 10.3390/nu14071489. PMID: 35406103; PMCID: PMC9002916.