A recent warning from health experts has highlighted that a widespread kitchen habit—reusing cooking oil for frying—could unknowingly raise cholesterol levels, putting millions at risk of long-term heart disease. While many Thai families reuse their cooking oil as a way to save money and reduce waste, mounting scientific evidence reveals this common practice could be a silent contributor to elevated cholesterol and cardiovascular risk, making it an urgent public health concern.
In Thai households, street food stalls, and countless community kitchens, it is common to use the same batch of cooking oil several times for deep-frying popular dishes such as fried chicken (gai tod), spring rolls, or doughnuts. The advice comes on the back of new research and recent health news, including a widely-read article in the Hindustan Times, that highlights how reusing oil during cooking breaks down its chemical composition, leading to the creation of harmful trans fatty acids (TFAs) and oxidized compounds. These harmful substances are strongly linked to higher levels of low-density lipoprotein (LDL) cholesterol—the so-called “bad cholesterol”—and lower levels of high-density lipoprotein (HDL) cholesterol, which is protective for heart health (hindustantimes.com).
For years, cardiovascular diseases have been among the top causes of mortality in Thailand, with rising cholesterol levels contributing heavily to the burden. Many people believe that visible oil color changes or bad odor are the only signs oil should be discarded; however, research shows that dangerous chemical transformations, including TFA formation, happen well before the oil appears visibly degraded. This makes it difficult for ordinary cooks to detect, heightening the hidden risk.
A notable 2016 study published in Food Chemistry investigated how heating and repeated frying typical in Asian households leads to the increase of TFAs in commonly used oils such as palm oil, soybean oil, and canola oil. Researchers found that each additional round of reheating caused a significant rise in unhealthy trans fats, well above safe consumption limits recommended by the World Health Organization. The study concluded that “heating/frying and reuse of edible fats/oils induces chemical changes such as formation of trans fatty acids (TFAs),” and that regular intake can contribute to higher cholesterol levels, a leading risk factor for heart disease (PubMed).
Another relevant animal study conducted using canola oil, published in 2014, identified long-term consumption of foods fried in reused oil led to both increased abdominal fat and a rise in blood cholesterol and triglyceride levels. The study also documented impaired blood vessel function, which is an early marker of cardiovascular disease. While the research was conducted in Wistar rats, the findings support the hypothesis that continuous consumption of reused oil could have similar adverse effects in humans, particularly in populations with already high cholesterol diets (PubMed).
According to a senior cardiologist at Thailand’s Ministry of Public Health, “There is an urgent need to educate the public about the dangers of reusing cooking oil, especially as Thai cuisine involves many deep-fried dishes. The trans fats and oxidized compounds formed are invisible but can quietly increase your risk of heart attack and stroke.” This concern is echoed by nutritionists working in public hospitals, who observe a surprising rise in young adults and even children with elevated cholesterol—often attributed to dietary habits including frequent consumption of food fried in reused oil, particularly from street vendors.
Globally, the World Health Organization has urged member states, including Thailand, to phase out industrially produced trans fats from the food supply by 2023. Thailand took a step forward in 2018 by banning partially hydrogenated oils—the major source of industrial TFAs—in processed foods. However, these regulations do not extend to home kitchens or small restaurants, where the reuse of vegetable oil during cooking remains pervasive (WHO).
Historically, resource conservation and budgeting are part of Thai culinary practice, with oil traditionally perceived as a costly commodity not to be wasted. This habit, while rooted in pragmatism, has turned counterproductive in the modern era, given both the diversity of available oils and current scientific understanding. A nutrition researcher at a leading Bangkok university explains, “Before, we worried only about microbial contamination. Now, the bigger threat comes from chemical by-products invisible to the eye but harmful to the body.”
Looking forward, continued public awareness campaigns and health education efforts will be critical. New technologies—such as household oil-testing kits or community-based frying oil collection programmes—could provide practical solutions. Additionally, encouraging healthier cooking methods such as steaming, boiling, or grilling, and using fresh oil each time when frying, are highly recommended. For consumers who eat out regularly, choosing vendors who use fresh oil or display oil-change frequency certificates can make a significant difference to long-term heart health.
For Thai families, practical steps include using smaller quantities of oil to avoid the temptation to reuse, switching to oils with higher resistance to oxidation (such as rice bran oil), and regularly rotating frying methods with less oily alternatives. Local authorities are urged to step up both enforcement and education regarding oil safety, especially in school canteens and local food markets where children are key consumers.
In conclusion, while the tradition of reusing cooking oil is deeply ingrained in Thai culinary culture, embracing new knowledge about its health risks is vital. Avoiding the reuse of cooking oil, particularly for deep frying, is a simple but powerful way to reduce cholesterol and safeguard your heart—a message that resonates for every household in Thailand. For more practical tips, consult local public health offices or visit the Ministry of Public Health’s online portals for updated food safety guidelines (Ministry of Public Health).