All dietary fats and oils are a combination of polyunsaturated (PUFAs), monounsaturated (MUFAs), and saturated fatty acids (SFAs). Each are distinguished by their chemical composition and they each affect the body, and health, in different ways.
PUFAs are fatty acids with more than one double bond in their chemical structure. The first double bond in omega-6 (n-6) fatty acids occurs between the sixth and seventh carbon atom from the methyl end of the chemical structure. In omega-3 (n-3) fatty acids, the first double bond occurs between the third and fourth carbon atom. PUFAs are usually liquid at room temperature. Two PUFAs, the n-6 fatty acid linoleic acid (LA) and the n-3 fatty acid alpha-linolenic acid (ALA), are essential fatty acids, meaning humans must obtain them from diet.1 Two n-3 fatty acids, DHA and EPA, are synthesized from ALA at low rates and are considers conditionally essential, meaning the human body can’t produce enough to supply the body’s requirements and should be obtained from diet.1 Popular oils that are high in PUFAs are: soybean oil, corn oil, and sunflower oil. n-6 fatty acids are found in large quantities in industrial seed oils while n-3 fatty acids are found in flaxseed oil, flaxseeds, chia seeds, and cold water fatty fish, as well as supplements. Despite the recommendations of the USDA dietary guidelines and health agencies like the American Heart Association, evidence is growing that replacing natural fats with solvent extracted industrial seed oils rich in PUFAs and high in n-6 fatty acids is detrimental to human health. PUFAs are susceptible to lipid oxidation during processing, storage, and heating, which leads to rancidity and the production of toxic compounds, including aldehydes and hydroperoxides.2 The greater the degree of unsaturated fatty acid composition, the greater the oxidation of the oils when exposed to processing, heat, metals, and light.2 Heat especially accelerates the oxidation process of PUFAs, including heat from cooking. Primary and secondary products of lipid oxidation increase oxidative stress within the human body.3 Increased oxidative stress increases systemic inflammation. Chronic systemic inflammation leads to disease states, including heart disease, autoimmune diseases, asthma, arthritis, insulin resistance, and some types of cancer.4 In general, n-6 fatty acids also play a role in increasing inflammation responses and blood clotting, while n-3 fatty acids are involved in anti-inflammatory responses and blood thinning.4 Western diets currently have an average 15:1 ratios of n-6 fatty acids to n-3 fatty acids, with some people consuming has high as 40:1 ratio, further increasing chronic disease rates.5 Increasing n-3 fatty acids while decreasing n-6 fatty acids to a more natural ratios of 4:1 or 2:1, not even the optimal 1:1 ratio, offers benefits at both preventing and treating diseases.5,6
MUFAs are fatty acids with one double bond in their chemical structure. They’re usually liquid at room temperature. Popular fats that are high in MUFAs are: olive oil, avocado oil, lard, bacon fat, high oleic safflower oil, canola oil, almond oil, and macadamia nut oil and the foods these oils are derived from. Be aware that some popular high MUFA oils like canola oil and high oleic safflower oil are often solvent extracted industrial oils, rather than expeller or cold pressed natural oils. MUFAs are much more resistant to lipid oxidation than PUFAs, even after heated.7 Oleic acid, especially olive oil, has numerous health benefits, including reducing the oxidation of serum LDL-C, improving blood pressure, reducing insulin resistance, and protecting against obesity.8,9 Increasing MUFAs improves health outcomes for many of the risks associated with metabolic syndrome and heart disease.9
SFAs are fatty acids without double bonds in their chemical structure. This makes them solid at room temperature and highly resistant to lipid oxidation, though it is still possible since all fats and oils contain a combination of PUFAs, MUFAs, and SFAs. Fats and oils with high SFA content are ideal for cooking and deep frying, though no fats or oils should be used more than once for frying. Popular high SFAs are: butter, ghee, full fat dairy, beef tallow, coconut oil, and palm oil. Contrary to conventional nutritional advice, saturated fats are not a major cause of heart disease. Evidence is growing that SFAs do not contribute to heart disease or metabolic diseases and are either neutral or protective against them. Data from the largest blinded randomized control dietary study in US history done during the sixties and seventies was recovered and re-evaluated recently.10n-6 PUFAs linoleic acid decreased serum cholesterol, but had no effect on heart disease risk while significantly increasing the risk of premature death.10 This was one of the first studies to show that lowering cholesterol is a poor surrogate endpoint for reducing heart disease risk and it increases all cause mortality, but it was buried due to results that contradicted prevailing thought.10 A recent large multi-country cohort study found no evidence of increased cardiovascular disease with high SFA intake and an inverse relationship between all cause mortality and high fat diets.11 There was also an inverse relationship between high SFA consumption and stroke.11 A diet rich in SFAs increases the particle size of LDL-C while also increasing the amount of HDL-C.12 Large, buoyant LDL-C are not associated with plaque in the arteries or increased risk of heart disease, unlike small, dense LDL-C and oxidized LDL-C.12 Another reason conventional nutrition advice recommends decreasing foods with high SFAs is an assumption that the higher calorie content of fatty acids (9 calories/gram) compared to carbohydrates (4 calories/gram) increases risk for obesity and metabolic disease. This has also proven false. A number of studies show that full fat dairy products are protective against metabolic disease, diabetes, and obesity, whereas low fat dairy products aren’t.13,14 Meta-analysis of weight loss diets showed that low carbohydrate, high fat diets resulted in greater long term weight loss than low fat diets, as well as improvements in blood pressure and HDL-C.15
There’s little to fear about dietary saturated fatty acids, and I recommend everyone consume fats that are as close to their natural state as possible over solvent extracted seed oils. This includes rendered animal fats (lard, tallow, duck fat), dairy fats (butter, cream, ghee), cold pressed fruit oils (avocado, coconut, olive), and cold pressed seed and nut oils (almond, macadamia, walnut, flax) as well as whole foods containing these fats like beef, lamb, pork, eggs, whole milk, cheese, avocados, olives, coconut, nuts, seeds, salmon, tuna, mackerel, and sardines. SFA and MUFAs, as well as whole food sources of DHA and EPA, are healthier options than PUFAs. The chart below gives a comparison of the fatty acid make-up of popular cooking fats.
1. “Essential Fatty Acids.” Linus Pauling Institute. Oregon State University. Written 2003. Updated 2014. http://lpi.oregonstate.edu/mic/other-nutrients/essential-fatty-acids
2. Halvorsen, BL and Blomhoff, R. “Determination of lipid oxidation products in vegetable oils and marine omega-3 supplements.” Food Nutr Res. 2011; 55. doi: 10.3402/fnr.v55i0.5792.
3. Sottero, B, Rossin, D, Poli, G, Biasi, F. “Lipid oxidation products in the pathogenesis of inflammation-related gut diseases.” Curr Med Chem. 2017. doi: 10.2174/0929867324666170619104105.
4. Hunter, P. “The inflammation theory of disease: The growing realization that chronic inflammation is crucial in many diseases opens new avenues for treatment.” EMBO Rep. 2012; 13(11): 968–970. doi: 10.1038/embor.2012.142
5. Simopoulos, AP. “The importance of the ratio of omega-6/omega-3 essential fatty acids.” Biomed Pharmacother. 2002; 56(8): 365-379. doi: 10.1016/S0753-3322(02)00253-6
6. Lands, B. “Consequences of Essential Fatty Acids.” Nutrients. 2012; 4(9): 1338–1357. doi: 10.3390/nu4091338
7. Casal, S, Malheiro, R, Sendas, A, Oliveira, BP, Pereira, JA. “Olive oil stability under deep-frying conditions.” Food Chem Toxicol. 2010; 48(10): 2972-2979. doi: 10.1016/j.fct.2010.07.036.
8. Kratz, M, Cullen, P, Kannenberg, F, et al. “Effects of dietary fatty acids on the composition and oxidizability of low-density lipoprotein.” EJCN. 2002; 56(1): 72-81.
9. Gillingham, LG, Harris-Janz, S, Jones, PJ. “Dietary monounsaturated fatty acids are protective against metabolic syndrome and cardiovascular disease risk factors.” Lipids. 2011; 46(3): 209-228. doi: 10.1007/s11745-010-3524-y.
10. Ramsden CE, Zamora D, Majchrzak-Hong S, Keturah R, Faurot KR, Broste SK, et al. “Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73).” BMJ. 2016; 353 doi: 10.1136/bmj.i1246
11. Dehghan, M, Mente, A, Zhang, X, et al. “Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study.” The Lancet. 2017. doi: 10.1016/S0140-6736(17)32252-3
12. St-Pierre, AC, Cantin, B, Dagenais, GR, et al. “Low-Density Lipoprotein Subfractions and the Long-Term Risk of Ischemic Heart Disease in Men: 13-Year Follow-Up Data From the Québec Cardiovascular Study.” Arterioscler Thromb Vasc Biol. 2005; 25: 553-559. doi: 10.1161/01.ATV.0000154144.73236.f4
13. Drehmer, M, Pereira, MA, Schmidt, MI, et al. “Total and Full-Fat, but Not Low-Fat, Dairy Product Intakes are Inversely Associated with Metabolic Syndrome in Adults.” J Nutr. 2016; 146(1): 81-89. doi: 10.3945/jn.115.220699
14. Crichton, GE, Alkerwi, A. “Whole-fat dairy food intake is inversely associated with obesity prevalence: findings from the Observation of Cardiovascular Risk Factors in Luxembourg study.” Nutr Res. 2014; 34(11): 936-943. doi: 10.1016/j.nutres.2014.07.014
15. Bueno NB1, de Melo IS, de Oliveira SL, da Rocha Ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr. 2013; 110: 1178-87. doi: 10.1017/S0007114513000548.
16. Wikimedia Common. Chart: Comparison of Dietary Fats.png