Shifting Views on Fat

By Dr. Mark Messina, PhD, MS, Director of Nutrition Science and Research, Soy Nutrition Institute (SNI) Global (June 21, 2022)


NOTE: This article is provided by SNI Global and U.S. Soy.


Dietary fat provides about one-third of our caloric intake.(1) But if Americans are confused about which type of, and how much, fat to consume, no one could blame them. As views about dietary fat evolve, even the scientific community debates this issue.


By the late 1950s there were already inklings that dietary fat type impacted health and coronary heart disease (CHD) risk.(2) As the findings from the Seven Countries Study by Angel Keys and colleagues gained in influence, recommendations to decrease saturated fat intake as a means of lowering CHD risk followed.(3) The first U.S. Dietary Guidelines, which have been issued every five years beginning in 1980, recommended reducing total fat and saturated fat intake – but the former was viewed primarily as a way of getting Americans to reduce the latter. By 2010, the Dietary Guidelines no longer included recommendations about total fat whereas to this day they continue to encourage reducing saturated fat intake.

The emphasis on saturated fat led consumers to ditch butter in favor of margarine. Unfortunately, margarine is created by partially hydrogenating unsaturated fatty acids, which leads to the creation of trans fatty acids. Trans fatty acids not only increase blood levels of LDL-cholesterol (bad cholesterol) but lower levels of good cholesterol (HDL-cholesterol), the combination of which markedly increases CHD risk.(4) In 2015, the Food and Drug Administration (FDA) ruled that artificial trans fats were unsafe to eat and gave food-makers three years to eliminate them entirely from the food supply.


Beginning in early 1990s, there was a surge of interest in olive oil, led in part by Harvard University researchers.(5,6) According to recent consumer surveys, Americans consistently rate olive oil as the healthiest of oils. Olive oil, which contains predominantly monounsaturated fat (oleic acid) is associated with the Mediterranean diet, which is typically rated as the healthiest diet. However, there is a lot more to the Mediterranean diet than olive oil. Furthermore, there is no single Mediterranean diet as 22 countries border the Mediterranean Sea.


After all of this back and forth on fats, where do things stand today? The American Heart Association (AHA) recommends using liquid plant oils rather than tropical oils (coconut, palm, and palm kernel), animal fats (e.g., butter and lard), and partially hydrogenated fats.(7) The AHA also notes that the cardioprotective effects of polyunsaturated fats are somewhat stronger than monounsaturated fats. In the U.S., the major polyunsaturated fat-containing oil, and the leading edible oil in the world, is soybean oil (commonly labeled as vegetable oil).(8) In 2017, soybean oil was awarded a health claim by the U.S. FDA. Suggestive language for use of the claim is “supportive but not conclusive scientific evidence suggests that eating about 1.5 tablespoons of soybean oil daily may reduce CHD risk.”(9) Another high polyunsaturated fat, corn oil, and two oils high in monounsaturated fat, olive oil and canola oil, also have health claims, although the language describing the strength of the evidence is strongest for soybean oil.(8)


Despite the consistent, decades-long advice, the recommendation to reduce saturated fat intake should be viewed through a somewhat nuanced lens. Relatively recent research suggests that because foods contain complex mixtures of nutrients, not all high-saturated-fat foods increase CHD risk.(10) Additionally, there is recognition that reducing the saturated fat content of the diet may not in and of itself be cardioprotective. Research has shown that when saturated fat is reduced by replacement with refined carbohydrate (cookies, crackers, white bread), CHD risk may actually increase. For the greatest benefit, saturated fat should be replaced with monounsaturated fat, and ideally, polyunsaturated fat.(11)


Views on the benefits of polyunsaturated have also been challenged. In the not-too-distant past, oils high in polyunsaturated fat (e.g., soybean oil) were criticized by some because the polyunsaturated fat they contain is of the omega-6 type.(12) Concerns were raised that this type of polyunsaturated fat, as opposed to the omega-3 type, causes inflammation. However, research shows this concern is unfounded and health agencies now emphasize the importance of consuming sufficient amounts of each type of fat, and not worrying about the ratio of the two.8 Soybean oil contains both types of fat and because of its widespread use in the U.S., it accounts for over 40 percent of our intake of both essential fatty acids, the omega-6 fat, linoleic acid, and the omega-3 fat, alpha-linolenic acid.(13)


Although most attention in connection with the health effects of dietary fat has been on CHD, in recent years there has been greater recognition that fat impacts more than just our heart. For example, intriguing research suggests that in comparison to polyunsaturated fat, saturated fat increases liver fat accumulation,(14) and may decrease insulin sensitivity.(15) Largely because of the obesity epidemic, the world is facing a markedly increased prevalence of liver disease, including fatty liver. Maintaining a normal body weight is the ultimate goal; however, for those who cannot achieve this goal reducing liver fat is helpful because over the years, fatty liver can turn into cirrhosis and even liver cancer.(16) Similarly, perhaps by choosing the beneficial type of fat, insulin sensitivity can be enhanced and diabetes can be prevented.


ABOUT THE AUTHOR:


Dr. Mark Messina is an internationally recognized expert on the health effects of soy. He has appeared on CNN and is regularly quoted by the media in publications including the New York Times, Newsweek, and USA Today. Dr. Messina has presented to both consumer and professional audiences in 44 countries on topics including soy and cancer risk, heart health, menopause, and men’s health. Dr. Messina is the co-author of The Simple Soybean and Your Health. His research has appeared in numerous professional journals including the American Journal of Clinical Nutrition, Journal of Nutrition, Lancet, and the Journal of the National Cancer Institute. Dr. Messina is a former program director in the Diet and Cancer Branch, National Cancer Institute, National Institutes of Health, where he initiated a multi-million dollar research program investigating the role of soy in cancer prevention. Dr. Messina is the director of nutrition science and research for Soy Nutrition Institute (SNI) Global.


ENDNOTES:


1. Austin GL, Ogden LG, Hill JO. Trends in carbohydrate, fat, and protein intakes and association with energy intake in normal-weight, overweight, and obese individuals: 1971-2006. Am J Clin Nutr 2011;93:836-43.

2. Page IH, Stare FJ, Corcoran AC, Pollack H, Wilkinson CF, Jr. Atherosclerosis and the fat content of the diet. Circulation 1957;16:163-78.

3. Pett KD, Willett WC, Vartiainen E, Katz DL. The Seven Countries Study. Eur Heart J 2017;38:3119-21.

4. Ginter E, Simko V. New data on harmful effects of trans-fatty acids. Bratisl Lek Listy 2016;117:251-3.

5. Sacks FM, Willett WW. More on chewing the fat. The good fat and the good cholesterol. N Engl J Med 1991;325:1740-2.

6. Willett WC, Sacks F, Trichopoulou A, Drescher G, Ferro-Luzzi A, Helsing E, Trichopoulos D. Mediterranean diet pyramid: a cultural model for healthy eating. Am J Clin Nutr 1995;61:1402S-6S.

7. Lichtenstein AH, Appel LJ, Vadiveloo M, Hu FB, Kris-Etherton PM, Rebholz CM, Sacks FM, Thorndike AN, Van Horn L, Wylie-Rosett J. 2021 Dietary guidance to improve cardiovascular health: A scientific statement from the American Heart Association. Circulation 2021;144:e472-e87.

8. Messina M, Shearer G, Petersen K. Soybean oil lowers circulating cholesterol levels and coronary heart disease risk, and has no effect on markers of inflammation and oxidation. Nutrition 2021;89:111343.

9. Qualified Health Claim Petition – Soybean Oil and Reduced Risk of Coronary Heart Disease (Docket No. FDA-2016-Q-0995). https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjFsfHlsojpAhVTCs0KHU6xBxgQFjAAegQIAxAB&url=https%3A%2F%2Fwww.fda.gov%2Fmedia%2F106649%2Fdownload&usg=AOvVaw1OacdW5qPEJwAz-_0yxdGz.

10. Mozaffarian D. Dairy foods, obesity, and metabolic health: The role of the food matrix compared with single nutrients. Adv Nutr 2019;10:917S-23S.

11. Li Y, Hruby A, Bernstein AM, Ley SH, Wang DD, Chiuve SE, Sampson L, Rexrode KM, Rimm EB, Willett WC, et al. Saturated fats compared with unsaturated fats and sources of carbohydrates in relation to risk of coronary heart disease: A prospective cohort study. J Am Coll Cardiol 2015;66:1538-48.

12. Simopoulos AP. The omega-6/omega-3 fatty acid ratio, genetic variation, and cardiovascular disease. Asia Pacific journal of clinical nutrition 2008;17 Suppl 1:131-4.

13. Blasbalg TL, Hibbeln JR, Ramsden CE, Majchrzak SF, Rawlings RR. Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century. Am J Clin Nutr 2011;93:950-62.

14. Luukkonen PK, Sadevirta S, Zhou Y, Kayser B, Ali A, Ahonen L, Lallukka S, Pelloux V, Gaggini M, Jian C, et al. Saturated fat is more metabolically harmful for the human liver than unsaturated fat or simple sugars. Diabetes Care 2018;41:1732-9.

15. Imamura F, Micha R, Wu JH, de Oliveira Otto MC, Otite FO, Abioye AI, Mozaffarian D. Effects of saturated fat, polyunsaturated fat, monounsaturated fat, and carbohydrate on glucose-insulin homeostasis: A systematic review and meta-analysis of randomised controlled feeding trials. PLoS Med 2016;13:e1002087.

16. Blanc V, Riordan JD, Soleymanjahi S, Nadeau JH, Nalbantoglu I, Xie Y, Molitor EA, Madison BB, Brunt EM, Mills JC, et al. Apobec1 complementation factor overexpression promotes hepatic steatosis, fibrosis, and hepatocellular cancer. J Clin Invest 2021;131.



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