Oleic acid is a major component of olive oil greatly responsible for its beneficial effects on heart health, metabolism, mental health, and more. Besides olive oil, some other oils and fat sources also contain significant amounts of this monounsaturated fatty acid. Keep reading to learn about the benefits, food sources, and safety of oleic acid.
What Is Oleic Acid?
Oleic acid is a non-essential fatty acid, which means it is produced naturally by the human body .
It is the primary member of the omega-9 class of monounsaturated fatty acids (MUFAs). Oleic acid accounts for 92% of cis-isomer monounsaturated fats in the human diet .
Monounsaturated fats have only one double bond and are defined by the number of carbons in their omega side chain. Oleic acid is sometimes abbreviated as (C18:1), referring to its carbon structure .
Most naturally occurring monounsaturated fats are of the cis-isomer conformation, referring to the orientation of the double bond. Artificially produced trans-isomers are associated with negative health outcomes .
This article focuses on the cis oleic acid isomer.
Olive oil is the largest dietary contributor to human intake of omega-9 monounsaturated fats. Other good sources of oleic acid are in the following table .
|Fat Source||Oleic Acid|
|Rice bran oil||42.7%|
Oleic Acid in Olive Oil and the Mediterranean Diet
Olive oil is an important component of the Mediterranean diet .
In Mediterranean countries, olive oil is the main source of dietary monounsaturated fats. This is compared to the US and northern European countries where meat and dairy products (20 to 40% monounsaturated fats on average) are more common dietary sources, and also include higher levels of saturated fats .
The Mediterranean diet has been linked to a variety of health benefits, including improved heart health, lower blood pressure, lower rates of obesity, and lower incidence of type 2 diabetes [3, 5].
Oleic acid is responsible for some of the health benefits of this diet, but other potentially beneficial compounds in olive oil (squalene, antioxidant phenolic alcohols, polyphenols, and vitamin E) also contribute to these benefits .
Mechanism of Action
Oleic acid plays an active role in many body processes by changing cell membrane composition and altering which receptors are present on the membrane as a result.
By changing receptor presence at the cellular membrane, oleic acid has the following effects. It:
- Blocks transport of cholesterol in the small intestine by reducing cholesterol receptor production .
- Increases production of proteins to promote healthy blood vessel function (PKA and RhoA) .
- Assists immune cells (neutrophils) to identify inflammation [9, 10].
An increased level of oleic acid in the cell membrane reduces the oxidative damage caused by free radicals .
Oleic acid is an important building block of the brain and nervous system. It is required for the formation of myelin and for nerve growth and repair .
Potential Benefits of Oleic Acid
Please note: the majority of potential oleic acid benefits have been studied as a part of monounsaturated fat-rich diets. These benefits may be partly contributed to other MUFAs, too. Being the most abundant fatty acid in olive oil, oleic acid is mainly responsible for its beneficial effects.
Below we’ll outline the potential benefits of MUFA and olive oil-rich diets, as well as some health effects unique to oleic acid. It’s hard to distinguish the health effects of oleic acid from other biologically active compounds until more research is done.
1) Heart Health
According to preliminary research, a diet rich in MUFAs may improve heart health by reducing cholesterol and lipid levels, inflammation, and high blood pressure. The Mediterranean diet, with olive oil as the primary fat source, was particularly effective [13, 14, 15, 16].
165 patients who were at high risk for heart disease went on a diet including olive oil. Those patients had decreased blood pressure, total cholesterol, low-density cholesterol, and triglycerides .
Tomato sauce enriched with olive oil has a greater effect on heart risk factors than just raw tomato sauce .
In non-smoking women, olive oil decreased blood nitric oxide as well as endothelin-1. This explains the effect of olive oil lowering blood pressure among hypertensive women .
Rats with high blood pressure fed a different form of oleic acid (bioactive 2-hydroxyoleic acid) decreased their blood pressure to normal levels after 7 days of treatment .
Increased levels of oleic acid in the vessels of rats fed a high olive oil diet were associated with an increase in receptors that lower blood pressure .
2) Blood Sugar Control
A summary of clinical reviews concluded that high-MUFA diets reduce blood sugar and hemoglobin A1c in type 2 diabetic patients .
Diets high in monounsaturated fatty acids (MUFAs) may be healthier for diabetic patients than low-fat, high-carbohydrate diets. The Mediterranean diet, with olive oil as its main source of fat, improves glucose control and insulin sensitivity .
The ADA recommends using this diet to improve blood sugar control. By following this diet, there is a 20%-23% lower risk of developing type 2 diabetes .
Olive oil intake is associated with a decreased risk of developing type 2 diabetes, according to a meta-analysis of 29 trials. However, some other substances in olive oil other than oleic acid may also be responsible for these effects .
11 overweight and diabetic patients added olive oil to their diet, which significantly reduced fasting blood sugar. Daily consumption can also improve metabolic control in overweight type 2 diabetes patients .
3) Joint and Bone Health
The Mediterranean diet can help suppress rheumatoid arthritis (RA) symptoms. According to a study of 413 participants, high content of MUFA sources such as olive oil in this diet may be the key to beneficial effects on the joints .
In addition, olive oil consumption was associated with a lower risk of rheumatoid arthritis in a study of 330 subjects .
43 RA patients given fish oil (high in omega-3) and olive oil (high in MUFA/oleic acid) had the best improvements in both pain and mobility, compared to fish oil alone or a placebo (soy oil) .
In a study of 187 women, oleic acid status was associated with increased bone strength, while certain MUFAs showed the opposite connection .
Olive oil reduced bone loss in menopausal rats. In test tubes, it increased the formation of bone-building cells [29, 30].
4) Mood and Mental Health
Diets high in MUFA and olive oil correlated with lower levels of depression in a study of 12,059 Spanish students. On the other hand, total fat intake was positively associated with depression .
A Mediterranean-like diet rich in olive oil was inversely associated with depression in a trial of 1,362 participants .
14 young adults who consumed high amounts of oleic acid over the course of 3 weeks reported less anger compared to those in the high palmitic acid (a saturated fatty acid) group. However, it wasn’t clear if this was due to increased MUFAs or decreased saturated fatty acids .
In 20 adolescent boys with ADHD, oleic acid levels in the blood were positively linked with brain plasticity and extrovert personalities .
5) Skin Health
In nearly 3,000 volunteers, increased intake of MUFAs from olive oil was associated with a lower risk of severe skin damage from the sun. On the other hand, there was no association with MUFA intake from animal products .
Being the primary fatty acid in olive oil, oleic acid is mainly responsible for the observed skin benefits.
6) Anticancer Effects
In two studies of more than 5,000 women, those with high levels of oleic acid in their diets were less likely to have cancer [36, 37].
Mice with induced lung cancer (adenocarcinoma) fed an oleic acid-rich diet had increased rates of survival and longer disease-free periods .
According to a clinical review, diets high in oleic acid correlate with lower rates of breast cancer .
However, mice with salivary gland tumors fed an oleic acid-rich diet increased tumor progression, possibly due to a lack of other monounsaturated fats in the diet .
Despite the promising preliminary studies, olive oil and other sources of oleic acid can’t be proclaimed effective for cancer prevention or treatment.
Animal and Cellular Research (Lacking Evidence)
No clinical evidence supports the use of oleic acid for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
Chronic Nerve Pain
Oleic acid inhibits a receptor (TRVP1) involved in pain perception (sensing of spiciness, hot temperatures, and itchiness). This is part of oleic acid’s natural role in inflammation .
Injection of oleic acid and albumin at the injury site in mice reduced the pain and involuntary movements associated with paralysis after spinal injury .
Albumin and oleic acid also promoted new nerve cell (dendritic) growth in normal mice and in mice genetically modified to have human TRVP1 .
Injections of oleic acid in a mouse pain model reduced pain and inflammation .
Limitations and Caveats
Dietary Studies Include Many Factors
Many of the dietary studies for monounsaturated fats used olive oil as a source of oleic acid. This does not distinguish between omega-9 fatty acids (like oleic acid) or other monounsaturated fatty acids (like omega-3 or omega-6). Other compounds present in olive oil and other monounsaturated fatty acids in the diets also have positive health effects.
Determining which components contribute the most to those effects can be difficult without tightly controlled studies, especially when diets were self-reported by participants .
Men and Women Respond Differently
Population (epidemiological) studies often did not distinguish between men and women, and many intervention studies had exclusively male participants. In cases where data for men and women were analyzed separately, the effects on blood cholesterol levels were often smaller in women than in men .
Safety and Negative Effects
Oleic acid is generally safe and well-tolerated in the amounts normally present in foods. However, excess levels may be associated with certain health risks.
Omega-9 concentrations (expressed as a percent of the overall cell membrane) in red blood cells of 3,000 patients were correlated with the risk of dying after 10 years. The relationship was nonlinear (U-shaped), indicating that both low and high levels of omega-9 could increase the risk of heart failure and death .
Mice fed an exclusively omega-9 diet developed deficiencies in essential fatty acids (linoleic and alpha-linolenic acids) .
Converting one’s diet exclusively to any single fat source can be detrimental.
In mice, increased dietary intake of omega-9 fatty acids (like oleic acid) has been linked to poor reproductive outcomes, including smaller litters of pups and shorter gestation periods. This is likely due to changes in steroid hormone synthesis during gestation .
When mothers consumed high oleic acid diets during pregnancy, lowered sperm count and motility were observed in male offspring due to increased DNA damage (fragmentation and oxidative stress) in mice .
As mentioned, olive oil is the best and most extensively studied source of oleic acid.
Other vegetable oils (coconut, safflower, etc.) also contain oleic acid, but in smaller quantities.