Reusing frying oil often can hasten the onset of brain damage

• Frying oil that have been deep-fried is associated with oxidative stress and inflammation, both of which are risk factors for neurodegenerative diseases and other chronic conditions.
• A recent study involving rats indicates a possible link between prolonged consumption of reheated cooking oils and heightened neurodegeneration.
• The gut-brain-liver axis seems essential for preserving neurological well-being, and the consumption of reheated oils might disturb this equilibrium.
• Professionals advise opting for diets abundant in antioxidants and omega-3 fatty acids while advising against regular consumption of fried foods.

In the latest Alzheimer’s Association 2024 Alzheimer’s Disease Facts and Figures report, it’s revealed that Alzheimer’s now impacts almost 7 million individuals aged 65 and above in the United States.

In the midst of this escalating neurodegenerative health challenge, a recent study on rats has brought attention to a potential correlation between prolonged consumption of reused deep-fried oil and heightened neurodegeneration.

Presented at Discover BMB 2024, the annual meeting of the American Society for Biochemistry and Molecular Biology, the abstract of the study will be published in a virtual supplement to the Journal of Biological Chemistry.

The fresh study discovered that rats fed diets containing reheated cooking oils displayed notably elevated levels of neurodegeneration compared to rats on a standard diet.

The findings imply that reheated oil might exacerbate neurodegeneration by interfering with the crucial liver-gut-brain axis, which plays a pivotal role in maintaining physiological equilibrium and has been associated with neurological disorders.

Frying oil when heated compared to when they are not heated.

Deep frying is a widely practiced cooking technique globally, commonly seen in fast-food eateries, street vendors, and households.

While studies have linked the consumption of deep-fried foods to cardiometabolic conditions and specific cancers, there has been limited exploration into the prolonged effects of ingesting reheated cooking oils on the metabolism of polyunsaturated fatty acids (PUFAs) and the development of diseases.

Heading the investigation, Dr. Kathiresan Shanmugam, PhD, an associate professor at the Central University of Tamil Nadu in Thiruvarur, India, led a research team to delve into this matter.

To address this issue, the study team divided female rats into five groups, providing them with either a standard diet (control group) or a standard diet supplemented with unheated sesame oil, unheated sunflower oil, reheated sesame oil, or reheated sunflower oil on a daily basis for a duration of 30 days.

This methodology aimed to replicate the circumstances surrounding the consumption of reused deep frying oil.

When compared to rats following different dietary patterns, those consuming diets containing reheated oils displayed increased levels of oxidative stress and inflammation in liver tissues.

Furthermore, these rats exhibited significant damage to the colon, resulting in changes in levels of endotoxins and lipopolysaccharides, indicating the presence of toxins produced by specific bacterial strains.

In subsequent experiments, monosodium glutamate (MSG) was utilized to induce neurotoxicity in offspring. Offspring fed diets containing reheated oils displayed heightened vulnerability to neuronal damage compared to the control group, which received no oils or diets with unheated oils.

In a statement to the press, Shanmugam clarified:

“As a result, liver lipid metabolism was significantly altered, and the transport of the important brain omega-3 fatty acid DHA was decreased. This, in turn, resulted in neurodegeneration, which was seen in the brain histology of the rats consuming the reheated oil as well as their offspring.”

The study demonstrated that diets containing reheated oils were associated with increased levels of cholesterol, LDL cholesterol, triglycerides, AST, and ALT, as well as inflammatory markers. This was accompanied by significant damage to the liver and colon structures, indicating potential cardiometabolic and organ damage.

Furthermore, the consumption of reheated oils led to specific brain damage, particularly in regions essential for regeneration, underscoring the neurological risks associated with reheated oil intake.

Conversely, rats fed unheated oils exhibited improved markers for brain health compared to those in the reheated oil groups.

What changes occur in the chemical composition of frying oils when they are reheated?

Subjecting oils to high temperatures leads to significant changes in their natural chemical composition, resulting in a reduction of beneficial antioxidants and the formation of harmful compounds such as trans fats, acrylamide, and aldehydes.

The process of reheating oils, particularly for deep-frying purposes, exacerbates this alteration as the oil becomes increasingly unstable, losing its health-promoting properties and producing more toxins with each subsequent use.

Alyssa Simpson, a registered dietitian and the owner of Nutrition Resolution, who was not involved in the study, clarified that repeated heating causes oils to degrade, leading to alterations in their fatty acid composition and increased levels of lipid oxidation products like reactive oxygen species (ROS).

An imbalance between ROS and biological antioxidants can provoke oxidative stress in the brain, potentially harming neurons and raising the risk of neurodegenerative diseases.

Additionally, Simpson underscored the presence of oxidized fats and advanced glycation end products (AGEs) in reheated frying oils, which are associated with chronic illnesses, including neurodegenerative conditions.

Dr. Alexandra Filingeri, a registered dietitian and doctor of clinical nutrition not affiliated with the study, concurred and elaborated on the detrimental effects of reheating cooking oil on its nutritional value.

“Reheating cooking oil repeatedly under heat exposure adversely affects its fatty acid composition, leading to a reduction in beneficial polyunsaturated fats and an increase in trans isomers and saturated fatty acids,” she explained.

What effects could consuming reheated oil have on human health?

While further investigation is necessary, consuming reheated frying oil has been associated with elevated levels of cholesterol and inflammation, both of which are known risk factors for cardiometabolic diseases and neurodegenerative disorders.

The liver, responsible for filtering and detoxifying substances in our bodies, may be particularly susceptible to damage caused by reheated oils.

According to Simpson, repeated consumption of oils exposed to high temperatures could disrupt liver lipid metabolism, potentially leading to nonalcoholic fatty liver disease (NAFLD) and accelerating liver diseases due to oxidative stress induced by reactive oxygen species (ROS).

Furthermore, Simpson and Filingeri expressed concerns regarding the impact of oxidized fats on gut microbiota and intestinal permeability, which could potentially result in dysbiosis, inflammation, and dysfunction of the gut barrier.

Filingeri emphasized the importance of maintaining a healthy gut microbiome for liver health, as an imbalance could allow harmful bacteria to penetrate the liver through increased intestinal permeability, thereby causing oxidative stress and inflammation.

This disturbance impacts the liver-gut-brain axis, which is crucial for neurological health as it involves metabolic, immune, and hormonal communication pathways. According to Simpson, this disruption could potentially result in neuroinflammatory conditions and neurological disorders.

Additionally, Simpson explained that alterations in the metabolism of certain lipids could interfere with brain cell communication and function, potentially causing damage to neurons.

Nutritional strategies to safeguard against neurodegeneration

To counteract the adverse effects of consuming reheated oil, Simpson suggests adopting diets abundant in omega-3 fatty acids and nutraceuticals such as curcumin and vitamin E, which are present in foods like turmeric, almonds, and other sources.

Simpson highlights that integrating antioxidants, fiber, and polyphenols from a variety of foods like fruits, berries, vegetables, nuts, and green tea can diminish oxidative stress and inflammation, thereby shielding the brain.

Furthermore, Filingeri underscores the significance of probiotics obtained from foods like kefir and kimchi for maintaining gut and liver health.

Adhering to healthy dietary patterns like the Mediterranean or MIND diet may aid in preventing neurodegeneration.

However, Simpson warns that frequent consumption of fried foods might contribute to weight gain, insulin resistance, and metabolic syndrome, consequently heightening the risk of chronic diseases.

Professional advice for enhancing the safety of cooking oils

When using oils for cooking, Filingeri emphasized the importance of selecting high-quality oils prior to exposing them to heat.

“When consumers are choosing cooking oils, they should opt for those high in polyunsaturated fats and opt for cooking methods that require low heat,” she advised. “It’s essential not to reuse frying oil for multiple cooking sessions and to avoid heating oils to high temperatures.”

Simpson suggested rotating cooking oils and monitoring oil temperature, particularly in establishments that utilize deep frying, to prevent overheating and excessive oxidation.

To steer clear of unhealthy oils, the experts recommended that consumers inquire about the types of cooking oils used in restaurants and opt for dishes prepared using healthier methods such as grilling or baking.

The relationship between diet and the risk of neurodegenerative conditions

This recent study indicates that frequent intake of reheated frying oil could disturb liver function and elevate oxidative stress, thereby increasing the susceptibility to neurodegenerative diseases.

While the study was performed on rats, its findings underscore the potential health risks associated with consuming reheated oils and emphasize the importance of making conscious dietary decisions.

Regarding future research avenues, Simpson concluded: