The types of dietary fats we consume and cook with are critical to metabolic health. Over the past century, Western diets have undergone a profound transformation, shifting from traditional saturated fats to polyunsaturated fatty acids (PUFAs), predominantly from vegetable oils. This transition, initially driven by concerns about saturated fats’ cardiovascular impact, has been increasingly questioned by recent research.
Unsaturated and saturated fats have fundamentally different molecular structures, which directly impacts their metabolic effects. Specifically, a diet higher in monounsaturated fatty acids (MUFAs) and PUFAs relative to saturated fats may trigger hibernation-like signals in the body. These signals can lead to lower metabolic rates, increased reductive stress, and increased fat gain.
Fat selection is crucial for two primary reasons: metabolic signaling and minimizing toxic compound formation during cooking. Dietary fats are not merely energy sources but also serve as structural and signaling molecules that fundamentally influence our body’s internal environment and energy production.
The saturated fat to unsaturated fat (SFA/UFA) ratio plays a significant role in metabolic signaling. For instance, butter — a traditional fat consumed for millennia — has an SFA/UFA ratio greater than 1, which is metabolically favorable. In contrast, margarine has a ratio less than 1, indicating a less optimal metabolic profile.
This nuanced understanding challenges simplistic dietary recommendations and underscores the importance of choosing fats thoughtfully, considering both their chemical composition and traditional nutritional wisdom.
Choosing the Right Cooking Fats: Stability Matters
Different fatty acid structures behave uniquely under high-heat cooking, with unsaturated fats being particularly unstable molecules. While vegetable oils are often marketed for their high smoke points, smoke point alone is a misleading indicator of cooking oil safety.
The key factors in determining an oil’s suitability for cooking are oxidative stability and polyunsaturated fatty acid (PUFA) content. Oils with high-PUFA levels and low oxidative stability are potentially the most harmful for health. As the degree of unsaturation increases, so does the rate of oxidation, leading to the production of toxic byproducts that can cause widespread cellular damage. Critical considerations for cooking oils:
- Smoke point is not a reliable measure of oil safety. Instead, Oxidative stability and Polyunsaturated Fatty Acid (PUFA) content are the best predictors of oil safety at high temps1
- Higher PUFA content correlates with faster oxidation2,3
- Oxidation produces harmful compounds that can damage body tissues
- Saturated and monounsaturated fats are generally more stable for cooking
When selecting a cooking fat, prioritize stability over marketing claims, focusing on oils that maintain their chemical integrity at high temperatures.
PUFAs contain two or more double bonds, which makes them prone to oxidizing under heat.4,5,6,7,8 This lipid peroxidation process is a chain reaction that produces multiple breakdown molecules called Lipid Oxidation Products (LOPs),9 which both react with other lipids and amplify the damage effect of lipid peroxidation.
One of the most well studied aldehydes is 4-HNE, derived from the breakdown of PUFAS such as linoleic acid, during oxidative stress. Elevated 4-HNE levels is toxic and can cause cell damage, inflammation, and apoptosis (programmed cell death).
4-HNE readily reacts with proteins, DNA, and phospholipids, leading to cellular dysfunction and contributing to various diseases. And this is actually very well documented in the literature. Elevated levels of 4-HNE and other toxic LOPs are associated with:
- Neurodegenerative diseases (e.g., Alzheimer’s and Parkinson’s diseases)
- Cardiovascular diseases
- Cancer
- Chronic inflammatory conditions
Here are some important quotes from the literature:10
“Human ingestion of cytotoxic and genotoxic aldehydes potentially induces deleterious health effects, and high concentrations of these secondary lipid oxidation products (LOPs) are generated in polyunsaturated fatty acid (PUFA)-rich culinary oils during high temperature frying practices.
[T]he order and extent of toxic LOP (lipid oxidation products) production in culinary oils is PUFAs > MUFAs >>> saturated fatty acids (SFAs), and the relative oxidative susceptibilities of 18-carbon chain length fatty acids (FAs) containing 0, 1, 2 and 3 carbon-carbon double bonds (i.e. >C=C< functions) are 1:100:1,200:2,500, respectively.
Previous NMR-based investigations focused on the peroxidative degradation of culinary oil UFAs during standard frying practices … have demonstrated the thermally promoted generation of very high levels of highly toxic aldehydes and their hydroperoxide precursors in such products (particularly those rich in PUFAs), and these results have been available to the scientific, food and public health research communities since 1994.”
“Vegetable oil” is a general term used to refer to a variety of oils that may include corn, soy, safflower, sunflower and cottonseed oil, all of which are high in PUFAs, meaning they are unstable and should not be exposed to heat. Yet, these highly refined oils form the basis of modern food manufacturing and are used at most restaurants! Many of these oils are also highly refined, sourced from GMO plants and are extracted using high heat, solvents and other chemicals.
Nature is smart and protects PUFAs in nuts/seeds with antioxidants like vitamin E. However, the harsh oil extraction process used to make seed oils requires high heat, so some of the natural antioxidants are used up to protect from oxidation. We then expose the oils to more heat during cooking, where more antioxidants are used up. The oils are again exposed to heat inside of our bodies (@ 98 degrees F +), with little remaining antioxidants to protect from oxidation.
When it comes to cooking, you should prioritize a cooking oil that is stable and produces the lowest number of harmful compounds when heated.
Dietary fats that are higher in PUFAs are the least stable, and dietary fats that are higher in SFAs are the most stable. The more an oil can resist reacting with oxygen and breaking down, the safer and more stable the oil is to cook with.
In the image below, prioritize cooking with the bottom four fat sources. Lard can also be used, if the hogs were fed a low-PUFA, ancestrally consistent diet. However, modern pork lard can have the same fatty acid composition as canola oil.11
Olive oil offers health benefits through its rich polyphenol content, but its high monounsaturated fatty acid (MUFA) content requires mindful consumption. Excessive MUFA intake can activate PPAR-alpha, a key fat metabolism regulator, potentially disrupting metabolic processes. Remember, total dietary fat balance is crucial: aim for a higher saturated to unsaturated fat ratio. Best practices for olive oil:
- Use in moderation
- Ideal for low to moderate heat cooking
- Excellent for marinades, dressings, and finishing dishes
- Prioritize high-quality, unadulterated sources (be aware of potential vegetable oil adulterations)
Remember, dietary fat balance is crucial: aim for a higher saturated to unsaturated fat ratio. For high-heat cooking, tallow (from beef or lamb) and ghee are superior options. These fats have high smoke points and are rich in stable saturated fats, making them more suitable for intense cooking methods.
For high-heat cooking, tallow (from beef or lamb) and ghee are superior options. These fats have high smoke points and are rich in stable saturated fats, making them more suitable for intense cooking methods.
Then for more medium heat cooking (like sauteing, pan frying, or baking) butter and coconut oil are great choices. These have lower smoke points relative to tallow or ghee, but are rich in stable saturated fats. Now of course ghee and tallow can be used for these applications as well.
Avoid: Fried Foods at Restaurants
An alarming example of why fat choices matter for cooking fats is research studies documenting the toxic Lipid Oxidation Products (LOPs) in fried foods at restaurants. Typical fast-food restaurants serve 100+ orders of fried food in a matter of a few hours, and replace their fryer oil over the course of days or weeks, not hours. In a questionnaire at restaurants, frequency of fryer oil change varied from weekly to monthly.12
At many restaurants, the same vegetable oil is reused hundreds of times for frying before being replaced! That is very bad news. Each cycle of heating degrades the oil further, increasing the accumulation of harmful LOPs.
These harmful LOPs are then directly transferred to fried foods, meaning consumers ingest these toxic substances with each bite.
“The level of HNE in the oil extracted from the potato was found to be similar to the level of HNE in the frying oil … These results indicate that toxic HNE was readily incorporated into food fried in thermally oxidized oil; extensive consumption of such fried foods could be a health concern.”13
“In this study, it has been demonstrated that HNE, a toxic aldehyde which is produced during the heat treatment of frying oils, was incorporated into commercially available FF purchased from 6 fast food restaurants in the Twin Cities, MN.
It is believed that frequently consumed fried foods containing considerable amounts of HNE, which is readily absorbed from the diet and incorporated into tissues, may be a public health concern since HNE toxicity has been related to a number of common pathological conditions in the literature.”14
When oils are repeatedly reused for frying, their trans fat content can also increase. This happens because the oil undergoes repeated cycles of heating, cooling, and exposure to oxygen, which further promotes chemical reactions that generate trans fats and other harmful compounds like free radicals and aldehydes.
While there are no long-term studies in humans, the known health consequences of LOPs suggest significant risks of long-term use of vegetable oils as cooking fats. So we don’t know the long-term effects. But it is safe to assume it will be pretty bad due to the well-known health consequences of elevated levels of 4-HNE and other LOPs.
The current absence of comprehensive research likely stems from industry interests — removing PUFA rich vegetable oils (which are ‘heart healthy’ and ‘lower cholesterol’) would be disastrous for the conventional agriculture food system and Big Pharma.
PUFAs-rich vegetable oils and processed foods are primary sources of 4-HNE and LOPs, potentially contributing to widespread health problems. The lack of definitive long-term studies underscores the need for cautious consumption of these products.
“The potential contributions of toxic aldehydic LOPs to the pathogenesis and incidences of NCDs are supported by a plethora of evidence available, and a full outline of this is provided in Moumtaz et al. (47). One example is strong causal associations between the risk of coronary heart disease (CHD) and the recurrent consumption of fried food meals, specifically ≥ 4 times per week (157).
Moreover, linkages between deep-fried food consumption and prostate cancer risk have been demonstrated (3), and a meta-analysis of published data found that an increased fried food intake engendered an estimated 35% enhanced risk of this condition (158).”15
You may be wondering — well isn’t it fine to use these PUFA rich vegetable oils at lower temp cooking below their smoke point? No, as mentioned above and discussed in a number of other articles,16,17,18 a diet higher in unsaturated fats (even if they aren’t already oxidized) will negatively impact metabolism.
On top of that, lipid oxidation can occur at room temperature (but the process is a little slower relative to high heat) and is initiated by the presence of light, oxygen, and trace metals. Over time, secondary oxidation products like 4-HNE will form, especially if fats are exposed to air or heat. At moderate heat (104 to 212 degrees F, common cooking temps), lipid peroxidation rates increase significantly.
PUFAs will degrade and reactive LOPs will be formed. Above 300 degrees F, which again is common for cooking, frying or roasting, PUFA rich oils generate substantial amounts of 4-HNE and other toxic LOPs.
Even if you were to drink the vegetable oil from the bottle at room temperature in it’s “raw form” (vegetable oils are HIGHLY refined), PUFA rich oils have the potential to oxidize during digestion19,20 since your digestive tract provides an environment that will promote lipid oxidation (oxygen, high temperature (98.6 degrees F or above), iron and other pro-oxidants, enzymes, and even acidic pH in the stomach).
Avoid fried food when going out to eat. And when you are cooking at home, prioritize butter, coconut oil, ghee and tallow.
Fat Consumption Summary: Health-Conscious Choices
Dietary fat selection critically impacts metabolic health and determines your exposure to toxic LOPs. Key insights:
• Risks of modern diets
◦ Shift from traditional saturated fats to PUFA-rich vegetable oils
◦ Unsaturated fats can trigger metabolic slowdown and increased fat storage
◦ High heat cooking of unstable oils produces toxic lipid oxidation products
• Recommended cooking fats
◦ High heat — Tallow, ghee
◦ Medium heat — Butter, coconut oil
◦ Use sparingly — Olive oil
• Practical advice
◦ Avoid restaurant fried foods
◦ At home, prioritize butter, coconut oil, ghee, and tallow
◦ Choose fats with higher saturated to unsaturated fat ratios
About the Author
Ashley Armstrong is the co-founder of Angel Acres Egg Club, which specializes in and ships low-PUFA eggs directly to your door. Armstrong also co-founded a sister organization, Nourish Cooperative, which ships low-PUFA chicken, low-PUFA pork, beef, A2 cheese and dairy and traditional sourdough to all 50 states.
Dr. Mercola and Ashley discussed the importance of low-PUFA eggs in a previous interview, embedded below for your convenience.
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