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A groundbreaking study has revealed that cooking garlic and onions at high temperatures can produce trans-fatty acids (TFAs), harmful fats known to contribute to cardiovascular diseases. The findings, published in the journal Food Research International on November 27, 2024, shed light on how common cooking practices may inadvertently increase TFA consumption, even in households avoiding processed foods.
TFAs are a major public health concern, causing over 278,000 deaths annually, according to the World Health Organization (WHO). They accumulate along artery walls, restricting blood flow and heightening the risk of heart attacks. WHO recommends that TFAs should account for less than 1% of daily energy intake.
Trans Fats in Everyday Cooking
While TFAs are widely known to form in processed foods through the hydrogenation of vegetable oils, the new study highlights that they can also form at home. A research team led by Junji Obi of Nissui Corporation and Dr. Masaki Honda of Meijo University explored how natural sulfur-containing compounds in vegetables like garlic and onions promote the trans-isomerization of unsaturated fatty acids (UFAs) in cooking oils.
The process, which occurs at temperatures above 140°C, transforms healthy UFAs into TFAs through a molecular reconfiguration.
How Sulfur Compounds Contribute
The researchers tested a variety of vegetables, including garlic, onion, leek, cabbage, horseradish, and broccoli sprouts, alongside oils like soybean and olive oils. They found that sulfur compounds such as isothiocyanates and polysulfides significantly increased the trans-isomerization of UFAs during high-heat cooking.
“Polysulfides in garlic and onions were particularly effective at promoting the formation of TFAs,” said Junji Obi. “However, the extent of TFA production under normal cooking conditions is expected to be minimal.”
Role of Antioxidants
The study also examined whether antioxidants could mitigate TFA formation. Antioxidants like α-tocopherol were found to reduce isomerization caused by isothiocyanates but were less effective against polysulfides.
Practical Implications
While the TFA increase from cooking garlic and onions is likely to be minimal under typical home cooking conditions, the study underscores the importance of awareness. “Excessive caution is unnecessary,” said Dr. Honda. “However, it’s valuable to recognize that ingredients rich in sulfur compounds may slightly elevate TFA levels.”
This research opens new avenues for understanding how natural compounds interact with cooking methods, potentially influencing dietary recommendations.
For more details, refer to the original study:
Junji Obi et al., Vegetables containing sulfur compounds promote trans-isomerization of unsaturated fatty acids in triacylglycerols during the cooking process, Food Research International (2024). DOI: 10.1016/j.foodres.2024.115425
