The War on Saturated Fat: Vegetable Oil Industry, Twisted Science and Public Confusion
The role of fatty acids in health and disease are routinely oversimplified and disagreement persists in the academic study of the impact of various fatty acids so I will highlight some of the nuance.
Fats and oils (lipids) are the base of triglycerides, collections of molecules (fatty acids and glycerol) that are the main fats found in the blood. If the lipid is solid at ambient/room temperature, it’s referred to at a fat and if its liquid at ambient/room temperature it is referred to as an oil. Interestingly the region of origin affects the classification. For example, while coconut oil is solid at ambient temperature in much of the world it is liquid at ambient temperature in the tropics (Enig, 2000). Hence why it’s called coconut “oil”. Fats are further classified into short, medium and long chain lipids depending on the length of carbon chain backbone. Long chain as well as some medium chain fats must travel first though the lymphatic system while shorter chain fatty acids can travel directly to the liver via the hepatic portal vein (Enig, 2000). For this reason, some shorter chain fatty acids are being studied for therapeutic application in conditions where energy production could be altered such as neurodegenerative diseases, C.F.S., as well as epilepsy. The saturation of the lipid is dependent on the state of the carbon backbone. When all binding sites (carbon always has 4) are saturated with hydrogen this lipid is referred to as saturated. From a chemical standpoint the molecule is stable. When the carbon backbone has one double bond (one site is not fully saturated with hydrogen) this is called a monounsaturated lipid. Chemically it is considered moderately stable although less stable than saturated fat. When two or more sites on the carbon backbone are not fully saturated with hydrogen it’s a polyunsaturated fatty acid. This is the most unstable fatty acid molecule and is very reactive chemically. For this reason, polyunsaturated fats are very prone to oxidative reactions and rancidity (Katz, Friedman, & Lucan, 2015). This can be somewhat mitigated with the inclusion of vitamin E (Niki, 2013).
The role of fatty acids in health and disease are routinely oversimplified and disagreement persists in the academic study of the impact of various fatty acids so I will highlight some of the nuance.
Saturated Fat: Saturated fats include palmitic acid, stearic acid, myristic acid, and lauric acid. While often considered the “bad” type of fats the research remains murky on the exact effects of saturated fats. Fatty acids such as stearic acid may have a positive effect on cholesterol profile by lowering LDL (Mensink, 2005). Lauric acid is a fatty acid present in high quantities in mammalian breastmilk (including in humans). Lauric acid has antimicrobial properties, and some research suggests it raises HDL “good” cholesterol again creating a neutral to positive effect on cholesterol profile dependent on the individual.
Monounsaturated Fat: Monounsaturated fats include palmitoleic and oleic acid (the dominant fat in olive oil, avocado oil and even lard!) This is the fat that is most often associate with the concept of a mediterranean diet (Enig, 2000). Studies have shown that it improves cholesterol profiles by having a positive effect on HDL and neutral to positive effect on LDL (DiNicolantonio & O'Keefe, 2022). A metanalysis of over 50 studies additionally showed it improved markers of metabolic health including improved insulin sensitivity, improved HDL as well as improved blood pressure in participants (Kastorini et al., 2011). And unlike polyunsaturated fatty acids, it is relatively stable when heat is applied making it a better option for cooking than polyunsaturated oils.
Polyunsaturated Fats: While generally accepted as health promoting this is a great oversimplification and much nuance is often missing for context. Polyunsaturated fats include linolenic acid (omega-3) as well as linoleic acid (omega-6). These can be further categorized but in general they support the eicosanoid system of the body regulating inflammatory cascades. One must differentiate between small amounts of polyunsaturated fats naturally occurring in foods such as fish, nuts and seeds, eggs and even meats vs. the highly refined vegetable oils that are the backbone of the processed food industry. Additionally, while USDA guidelines recommend the liberal use of refined seed/vegetable oils there is much scientific debate regarding the healthfulness of these oils. For this reason, I will separate this into points of view considering both perspectives.
Pro vegetable oil position (polyunsaturated fats in refined form):
The diet heart hypothesis (the most notable accomplishment of Dr. Ancel Keys via the seven-country study) suggests that saturated fat is the primary driver of diet related LDL elevation (as opposed to familial hypercholesterolemia). Polyunsaturated fats tend to have a lowering effect on LDL cholesterol as opposed to some saturated fats which may elevate it. While there are a few peripheral arguments for the inclusion of high levels of polyunsaturated fats in the diet, it ultimately comes down to the impact on LDL cholesterol (Teicholz, 2014). This is the driving force behind the USDA guidelines to “reduce solid fats” and liberally include vegetable oils (U.S. Department of Agriculture & U.S. Department of Health and Human Services, 2015).
Anti vegetable oil position:
· Vegetable oils are a relatively new food substance in the human diet. As recent as in 1911 in America with the introduction of Crisco when scientists discovered they could stabilize vegetable oil by hydrogenation (Teicholz, 2014). While this partially hydrogenated version (trans fat) was banned in the U.S. after 2015 the un-hydrogenated versions are still ubiquitous in the processed food supply. And while hydrogenation is unhealthy some lipid chemists point out that these oils are very unstable when they are not hydrogenated (Enig, 2000). As we discussed previously polyunsaturated fats are chemically reactive and thus prone to free radical formation. Since the fats we consume ultimately build our cellular membranes when they are oversaturated with these polyunsaturated fats they are prone to lipid peroxidation (Katz, Friedman, & Lucan, 2015). This creates a cascade of oxidative damage that has a domino effect through surrounding cells.
· Our inflammatory response is governed by the eicosanoid system of the body. Omega-3 fats support the anti-inflammatory pathways while omega-6 fats tend to support the proinflammatory pathways. It’s estimated that hunter-gatherer societies had ratios close to 2:1 omega-6 to omega-3 our current intake of vegetable oil laden foods has increased our ratios to closer to 20:1 omega 6 to omega 3. Given our crises of chronic illness (many chronic diseases are thought to have inflammatory underpinnings including dementia, CVD, cancers, autoimmunity and diabetes mellitus) it may be erroneous to promote a diet so high in proinflammatory supporting omega-6 lipids.
· The primary reason these oils are considered health promoting is due to their lowering effects on LDL cholesterol. The original (and only) LONG term trials done of replacing more traditional fats in the diet with these polyunsaturated vegetable oils were done though the 1960s and 1970s. They include The Veterans Hospital Study, Minnesota Coronary Experiment as well as Sydney Heart Study. Collectively these studies are referred to as the CORE trials and many went on for years with the inclusion of over 86,000 participants in total. While these trials were imperfect, they were the only LONGTERM RCTs, occurring in hospital wards or nursing homes where diets were strictly controlled, and participants were often included for many years as opposed to current mechanistic research which usually takes place over a period of weeks not years (Teicholz, 2023). For ethical reasons these types of long-term interventions are no longer viable, but the CORE trials provide us with some very valuable insights. Why is this important? Because what we ultimately are trying to observe in nutritional science is the outcomes of hard markers like mortality rates. Plainly put we really don’t care what some random metabolic marker does over a six-week period. We ultimately want to know “Is this eating pattern going to shorter my life?” or “Is inclusion of this food going to protect me from heart disease?”. So, while these CORE trials were the initial justification of the extreme limitation put on U.S. recommendation for saturated fat intake (which ultimately led to the inclusion of vegetable oils in essentially all processed foods and sold as a “heart healthy” cooking alternative to more traditional fats), what does modern analysis suggest of these trials? Much reanalysis of these original trials has occurred in the last decade with very mixed results. Some suggest a modest improvement in CVD risk but as a 2020 Cochrane review points out, the benefit are very small. It states that “56 people need to reduce their saturated fat intake for four years for one person to avoid experiencing a CVD event” Additionally it points out that no reduction in all-cause mortality was observed or even that of coronary related death (Hooper et al., 2020). In simple language, while a slight reduction in cardiovascular events was seen this did NOT lead to a reduction in all-cause mortality or even from cardiac-related deaths.
Other metanalysis reevaluation of these original RCT’s used as justification of the 10% Saturated fat cap have found that while serum cholesterol levels were indeed reduced this did NOT lead to any meaningful impact on CVD risk and did not reduce all-cause mortality or CVD related death (Siri-Tarino et al., 2010).
Furthermore, a brand-new review of 20 RCTs concluded that beef has no meaningful impact of CVD risk at large (Sanders et al., 2024).
Maybe even more troubling is that some of the original RCTs done showed an increase in all cause mortality as well as in cancer deaths when traditional fats (higher in saturates) were replaced with polyunsaturated vegetable oils. It was of enough concern that the NIH held a series of workshops in the 1980s to address the issue of increased cancer rates observed in participants with higher vegetable oil intake. Ultimately the causal factor was not found, and the institute abandoned the effort choosing to focus on the rising rates of CVD deaths (Teicholz, 2014).
· The current view of CVD is increasingly nuanced with a focus on metabolic health vs a myopic, erroneous and reductionist view of distilling heart attack risk to LDL cholesterol alone. Even the prestigious American Heart Association no longer uses LDL as a risk factor in assessing one’s CVD risk as made evident in their PREVENT calculator. Rather markers such as HDL to triglyceride ratio, A1C, and fasting glucose are used to assess risk.
· Unintended consequences: When authorities began pushing for a reduction in fat (especially saturated fat) in the 1970s and 80s the calories had to be replaced with another macronutrient. Since protein is a metabolically laborious energy source for the body the natural contender was carbohydrates. This led to an excessively high carbohydrate diet (especially refined grains and sugars as pushed by the food industry). Many argue convincingly that the unintended consequence of this promotion led to the current epidemic of obesity, diabetes as well as other metabolic related conditions including CVD itself.
Given the many reasons stated above there is simply too much conflicting data to categorize unsaturated fat as “health promoting” and saturated fat as “disease promoting”.
The best dietary approach emphasizes a balance of unrefined carbohydrates, robust protein intake balanced out with a variety of fat sources from unprocessed foods. This would naturally include both unsaturated fats and saturated fats. Individual response regarding LDL production is highly bio-individual. Additional adjustments can be made to the individual’s fat intake based on their tendency to hyper-respond to saturated fat intake or not. If an individual sees substantial increase in LDL, they may sway some saturated fat sources for monounsaturated fats but continue to focus on adequate sources of fat-soluble vitamins and avoiding vegetable oils. Always keeping in mind that cholesterol ratios (HDL to Triglyceride), blood sugar parameters as well as inflammatory markers give a more accurate view of CVD risk than solely looking at LDL cholesterol.
References:
Enig, M. G. (2000). Know your fats: The complete primer for understanding the nutrition of fats, oils and cholesterol (10th printing). Bethesda Press.
Katz, D. L., Friedman, R. S. C., & Lucan, S. C. (2015). Nutrition in Clinical Practice: A Comprehensive, Evidence-Based Manual for the Practitioner (3rd ed.). Wolters Kluwer.
Niki, E. (2013). Role of vitamin E as a lipid-soluble peroxyl radical scavenger: In vitro and in vivo evidence. Free Radical Biology and Medicine, 66(3), 3-12. https://doi.org/10.1016/j.freeradbiomed.2013.03.022
Mensink, R. P. (2005). Effects of stearic acid on plasma lipid and lipoproteins in humans. Lipids, 40(12), 1201-1205. https://doi.org/10.1007/s11745-005-1486-x
DiNicolantonio, J. J., & O'Keefe, J. H. (2022). Monounsaturated Fat vs Saturated Fat: Effects on Cardio-Metabolic Health and Obesity. Missouri medicine, 119(1), 69–73.
Kastorini, C. M., Milionis, H. J., Esposito, K., et al. (2011). The effect of Mediterranean diet on metabolic syndrome and its components: A meta-analysis of 50 studies and 534,906 individuals. Journal of the American College of Cardiology, 57(11), 1299-1313. https://doi.org/10.1016/j.jacc.2010.09.073
Teicholz, N. (2014). The big fat surprise: Why meat, butter, and cheese belong in a healthy diet (1st ed.). Scribe Publications.
Teicholz, N. (2023). A short history of saturated fat: The making and unmaking of a scientific consensus. Current Opinion in Endocrinology, Diabetes, and Obesity, 30(1), 65-71. https://doi.org/10.1097/MED.0000000000000791
Hooper, L., Martin, N., Jimoh, O. F., Kirk, C., Foster, E., & Abdelhamid, A. S. (2020). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database of Systematic Reviews, 2020(8), CD011737. https://doi.org/10.1002/14651858.CD011737.pub3. Accessed 23 December 2024.
Siri-Tarino, P. W., Sun, Q., Hu, F. B., & Krauss, R. M. (2010). Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. The American Journal of Clinical Nutrition, 91(3), 535-546. https://doi.org/10.3945/ajcn.2009.27725
Sanders, L. M., Palacios, O. M., Wilcox, M. L., & Maki, K. C. (2024). Beef consumption and cardiovascular disease risk factors: A systematic review and meta-analysis of randomized controlled trials. Current Developments in Nutrition, 8(12), 104500. https://doi.org/10.1016/j.cdnut.2024.104500