Expert Roundtable: AHA Update on Dietary Fat Intake and CVD Risk

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Lowering the intake of saturated fat and replacing it with polyunsaturated fats will lower incidence of CVD.
Lowering the intake of saturated fat and replacing it with polyunsaturated fats will lower incidence of CVD.

Although the American Heart Association (AHA) recommended replacing saturated fat with unsaturated fat for cardiovascular disease (CVD) prevention in 1961, the message shifted to reducing total fat and replacing it with carbohydrates in the 1980s and 1990s.1,2 This led to an increased intake of refined starches and sugars. Obesity rates jumped from 10% in the early 1980s to nearly 40% in 2014, and rates of type 2 diabetes doubled.1-3

"Epidemiological studies and clinical trials have shown that reducing total fat is not effective in preventing [CVD] because when people cut back on total fat, they replace it with carbohydrates," according to Frank B. Hu, MD, PhD, professor and chair in the Department of Nutrition at the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, and coauthor of a recent review on the topic.1 As a result, the 2015-2020 Dietary Guidelines for Americans recommend replacing saturated and trans fats with unsaturated fats from vegetable oils, nuts and seeds, and oily fish.4

In June 2017, the AHA released a presidential advisory highlighting results of randomized controlled trials showing that replacement of saturated fats with polyunsaturated fats reduced CVD risk by almost 30%, as well as similar findings from additional studies.5,6 The authors concluded that "lowering intake of saturated fat and replacing it with unsaturated fats, especially polyunsaturated fats, will lower the incidence of CVD."

To learn more about these updates and glean suggestions for helping patients make the recommended dietary changes, Cardiology Advisor asked several experts to weigh in: Dr Hu; Erin D. Michos, MD, MHS, FACC, FAHA, associate professor of medicine and epidemiology and associate director of preventive cardiology at Johns Hopkins School of Medicine in Baltimore, Maryland; and Andrew M. Freeman, MD, FACC, FACP, associate professor and director of cardiovascular prevention and wellness at National Jewish Health in Denver, Colorado.

Cardiology Advisor: What are the proposed mechanisms by which lower intake of saturated fats and higher intake of unsaturated fats may lower CVD risk?

Dr Hu: Compared with unsaturated fats, saturated fat intake increases total and LDL [low-density lipoprotein] cholesterol levels, a major risk factor for CVD. Saturated fat has also been shown to increase insulin resistance, chronic inflammation, and clotting factors, which have all been associated with elevated CVD risk.21

Dr Michos: Saturated fats raise LDL cholesterol, a major fuel of atherosclerosis. Replacing saturated fats with polyunsaturated and monounsaturated fats appears to reduce LDL concentrations. In addition, polyunsaturated fats may have other potentially beneficial mechanisms for reducing CVD risk, such as reducing platelet reactivity and thrombosis risk.

Cardiology Advisor: What are some ways physicians can encourage and support patients in shifting toward these kinds of dietary choices?

Dr Freeman: Many physicians have limited, if any, nutritional training. They should further their nutrition knowledge through online or live coursework and reading about nutrition, and be able to apply this in day-to-day practice. Quick questions about exercise habits and what the patient ate last night for dinner should be asked at every visit. Engaging the extended care team, including dietary and nutrition services, is suggested. "Walking the walk" in terms of eating a predominantly low-fat, plant-based diet can set the example for many patients. Finally, advocating for additional nutrition and lifestyle education during medical school training and beyond is strongly suggested.

Dr Hu: It is important to focus on healthy food choices and healthy dietary patterns. Use liquid vegetable oils such as olive oil, canola oil, and soybean oil for cooking instead of butter, lard, and palm oil. Consume a diet rich in plant-based foods such as fruits, vegetables, whole grains, nuts and seeds, and legumes, and limit consumption of red and processed meats and sugar-sweetened foods and beverages. 

Dr Michos: My simple message is to eat [fewer] animals and eat more plants! Vegetables should be the main course and animal protein the side dish. I also advise patients to eat more real foods and minimize processed, packaged foods. I think patients are simply overwhelmed with mixed and confusing messages about what constitutes a healthy diet. I like to think of dietary patterns rather than specific foods. I encourage patients to shift toward DASH-type [Dietary Approaches to Stop Hypertension] and Mediterranean-style diets, which are more plant-based. Approaches should be individualized to each patient based on their current eating habits, [CVD] risk factors, and willingness to make change.

I strongly recommend that patients read food labels and understand serving sizes, and track their food intake to increase awareness of how much saturated fat and total calories they consume; there are many easy-to-use [mobile phone] apps [for this purpose]. I may gently point out specific examples based on their food log and suggest replacement choices, and I get their feedback on whether they think those changes are feasible. I also let patients make their own suggestions of what they can change: the clinician should facilitate, not dictate, the discussion.

Cardiology Advisor: What are potential challenges for patients in adopting a healthier dietary pattern?

Dr Hu: There is a lot of confusion about saturated fat, with some studies suggesting it is not harmful, as previously believed. However, in these studies, saturated fat was compared with refined carbs, and both are unhealthy in terms of CVD risk. However, when compared [with] unsaturated fats or whole grains, higher consumption of saturated fat is a significant risk factor for CVD. Therefore, dietary recommendations should emphasize that saturated fat should be replaced by unsaturated fats and healthy carbohydrates such as whole grains.

Dr Freeman: There is widespread misinformation available [to patients] on the Internet about the potential benefits of a high-fat diet. In some of the high-fat diets, it is true that weight loss and lipids may improve, but often this is transient, and the deleterious effects of a high-fat diet often outweigh the weight loss benefit.

Dr Michos: It can be difficult to overhaul a whole lifetime of food patterns, especially when dietary food patterns are embedded in social traditions and cultural norms. Sometimes it just takes baby steps: address 1 goal at each visit, for gradual but relentless forward progress. Replace 1 food now, and next visit, make the next change, and so forth.

References

  1. Wang DD, Hu FB. Dietary fat and risk of cardiovascular disease: recent controversies and advances. Ann Rev Nutr. 2017;37:423-446.
  2. Flegal KM, Carroll MD, Kuczmarski RJ, Johnson CL. Overweight and obesity in the United States: prevalence and trends, 1960-1994. Int J Obes Relat Metab Disord. 1998;22(1):39-47.
  3. Flegal KM, Kruszon-Moran D, Carroll MD, Fryar CD, Ogden CL. Trends in obesity among adults in the United States, 2005 to 2014. JAMA. 2016;315(21):2284-2291.
  4. US Department of Health and Human Services, US Department of Agriculture. Dietary guidelines for Americans: 2015-2020. 8th ed. Washington, DC: 2015. http://health.gov/dietaryguidelines/2015/guidelines. Accessed August 29, 2017.
  5. Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary fats and cardiovascular disease: a presidential advisory from the American Heart Association [published online June 15, 2017]. Circulation. doi: 10.1161/CIR.0000000000000510
  6. Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev. 2015;(6)CD011737.
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