“In past decades, dietary guidance has almost universally advocated reducing the intake of total and saturated fat, with the emphasis shifting more recently from total fat to the replacement of saturated fat with polyunsaturated fats and the elimination of trans fat. These recommendations and the link between fat consumption and the risk of cardiovascular disease have been among the most vexed issues in public health: are dietary fats “villains,” are they benign, or are they even “heroes” that could help us consume better overall diets and promote health?”
This quote from a 2018 analysis on diet and heart health in the medical journal, The BMJ, sums up the challenge of making recommendations for dietary fat intake. You may reason that if some fats are healthier than other fats, why not eliminate all “bad” fats and consume as much healthy fat as desired? Remember, everything in moderation. As we review the established guidelines for daily fat intake, we’ll explain the importance of balancing fat consumption with proper fat sources.
Heart disease is the leading cause of death in the United States, claiming the lives of nearly 650,000 Americans in 2017. Deaths from stroke, which shares many of the same risk factors, accounts for an additional 150,000 fatalities each year. The burden of cardiovascular disease makes it critical to address dietary and lifestyle choices that can decrease risk factors for these diseases. According to the American Heart Association, the following risk factors for heart disease are modifiable, meaning they can be managed or changed by the individual:
- high blood pressure
- high blood cholesterol
- tobacco use
- poor diet
- physical inactivity
- overweight or obesity
In light of these risk factors, there are many dietary strategies related to fat intake that can reduce the risk of heart disease. The amount and type of fat that a person eats can have a profound effect on the way their body metabolizes fat and cholesterol.
If left unchecked, improper dietary fat consumption can lead down a path to severe health problems. An elevated level of lipids—including triglycerides and cholesterol—in the blood is called hyperlipidemia. Many diseases and health conditions are associated with high blood lipid levels, including:
- Cardiovascular disease
- Heart attack
- Congestive heart failure
Because of the association between dietary fat consumption and hyperlipidemia, health experts have developed recommendations for fat intake to help guide food choices. The acceptable macronutrient distribution range (AMDR) from the Dietary Reference Intake Committee and recommendations for adult fat consumption from the Dietary Guidelines for Americans are as follows:
- Fat calories should be limited to 20-35 percent of total calories, with most fats coming from polyunsaturated and monounsaturated fats, such as those found in fish, nuts, and vegetable oils.
- Consume fewer than 10 percent of calories from saturated fats. Some studies suggest that lowering the saturated fat content to less than 7 percent can further reduce the risk of heart disease, but other studies contradict this recommendation.
- Keep the consumption of trans fats (any food label that reads partially hydrogenated oil) as low as possible. (As manufactured trans fats are being phased out of the U.S. food supply, Americans don’t have to worry as much about identifying and avoiding trans fats. However, they’re still used in other parts of the world.)
- Choose more lean and low-fat products when selecting meat, poultry, milk, and dairy products.
Being conscious of the need to reduce blood cholesterol levels to improve health often means limiting the consumption of saturated fats. Multiple studies have shown an association between the saturated fats found in some meat, whole-fat dairy products, butter, and tropical oils (coconut and palm oils) and higher LDL cholesterol levels. However, while saturated fats have a historical reputation for being unhealthy, more recent research has suggested that the link between saturated fat and heart disease may not be as clear cut as we once thought.
The BMJ’s analysis on dietary fat and heart health explains the complicated relationship as such:
“Synergism and interactions between different components of foods together with the degree of processing and preparation or cooking methods lead to a ‘food matrix’ effect which is not captured by considering single nutrients. Different types of food that are high in saturated fats are likely to have different effects on health. For example, dairy products and processed meats, both high in saturated fats, are differentially associated with many health outcomes in prospective epidemiological studies, often in opposite directions. One explanation for this divergence is that despite their similar fat content, other components of these two food groups are associated with different health effects. For example, dairy products contain minerals such as calcium and magnesium and have probiotic features if fermented, whereas processed red meat has a high salt and preservative content.
To produce public health guidelines on which foods to eat or avoid to reduce the risk of chronic disease is complicated because dietary fats are typically mixtures of different types of fatty acids. Animal fats, for instance, are the main sources of saturated fats in many modern diets, but some animal fats are higher in monounsaturated fats than saturated fats, and polyunsaturated fats in vegetable oils will typically contain both omega-3 and omega-6 fatty acids in different concentrations. Hence, conclusions about the health effects of saturated and polyunsaturated fatty acids are unlikely to consistently translate to the health effects of the fats, oils, and foods in which those fatty acids are present.”
In an article from Tufts University Health & Nutrition Letter, Links Between Saturated Fat, Blood Cholesterol & Heart Disease Prove Complex, researcher Ronald M. Krauss, MD, said, “there is insufficient evidence from prospective epidemiological studies to conclude that dietary saturated fat is associated with an increased risk of cardiovascular disease (CVD).” Researchers state that reducing saturated fat intake may not clearly decrease CVD risk in part because people tend to replace saturated fat with processed carbohydrates. Recent studies have attempted to tease out different approaches to lowering saturated fat in the diet, showing that the types of foods used to replace saturated fat affect the risk of heart disease.
- If saturated fat in the diet is replaced with unsaturated fats, risk for heart disease decreases.
- If saturated fat in the diet is replaced with refined carbohydrates, risk for heart disease increases.
The 2015 DGA report described the evidence as follows:
“Strong and consistent evidence shows that replacing saturated fats with unsaturated fats, especially polyunsaturated fats, is associated with reduced blood levels of total cholesterol and of low-density lipoprotein-cholesterol (LDL-cholesterol). Additionally, strong and consistent evidence shows that replacing saturated fats with polyunsaturated fats is associated with a reduced risk of CVD events (heart attacks) and CVD-related deaths.
Some evidence has shown that replacing saturated fats with plant sources of monounsaturated fats, such as olive oil and nuts, may be associated with a reduced risk of CVD. However, the evidence base for monounsaturated fats is not as strong as the evidence base for replacement with polyunsaturated fats. Evidence has also shown that replacing saturated fats with carbohydrates reduces blood levels of total and LDL-cholesterol, but increases blood levels of triglycerides and reduces high-density lipoprotein-cholesterol (HDL-cholesterol). Replacing total fat or saturated fats with carbohydrates is not associated with reduced risk of CVD. Additional research is needed to determine whether this relationship is consistent across categories of carbohydrates (e.g., whole versus refined grains; intrinsic versus added sugars), as they may have different associations with various health outcomes. Therefore, saturated fats in the diet should be replaced with polyunsaturated and monounsaturated fats.”
Dr. Krauss summed up the recommendations as such: “An overall eating pattern that emphasizes whole grains rather than refined carbs such as white flour, along with foods high in polyunsaturated fats, such as fish, seeds, nuts and vegetable oils, is of more value for reducing coronary heart disease risk than simply aiming to further reduce saturated fat.”
Figure 5.29. Examples of heart healthy meals, including fish, nuts, seeds, whole grains, and unsaturated fats
Dietary cholesterol also has a small impact on overall blood cholesterol levels, but not as much as some people may think. For most people, decreasing dietary cholesterol intake has little impact on blood cholesterol, because their bodies respond by reducing synthesis of cholesterol in favor of using the cholesterol obtained from food. Genetic factors may also influence the way a person’s body responds to changes in cholesterol intake. The 2015 U.S. Dietary Guidelines for Americans (DGA) suggest limiting saturated fats, thereby indirectly limiting dietary cholesterol since foods that are high in cholesterol tend to also be high in saturated fats. (Eggs and fish are notable exceptions; both are high in cholesterol but low in saturated fats.)
The 2015 DGA dropped the previous recommendation (from the 2010 DGA) to limit the consumption of dietary cholesterol to 300 mg per day, but with a caveat: “This change does not suggest that dietary cholesterol is no longer important to consider when building healthy eating patterns. As recommended by the Institute of Medicine, individuals should eat as little dietary cholesterol as possible while consuming a healthy eating pattern.”
- Focus on whole food sources of dietary fat, because they come packaged with vitamins, minerals, phytochemicals, and sometimes fiber and protein.
- Remember that saturated fats are found in large amounts in foods of animal origin. They should be limited within the diet.
- Some highly processed foods, such as stick margarines, cookies, pastries, crackers, fried foods, and snack foods are sources of saturated fat (and historically, trans fats) that can elevate your cholesterol levels, so use them sparingly.
- Fatty fish like salmon, tuna, and halibut are heart-healthy due to their high levels of omega-3 fatty acids, which can reduce inflammation and lower cholesterol levels. The American Heart Association recommends consuming fish—especially fatty fish—twice per week.
- Nuts and seeds contain high levels of unsaturated fatty acids that aid in lowering LDL when they replace saturated fat in the diet.
- Most plant-based oils (except tropical oils like palm and coconut oils) are good sources of polyunsaturated and monounsaturated fats and may help to lower LDL. Substitute oils for solid fats when possible.
- Choose whole-grain and high-fiber foods. Reduced risk for cardiovascular disease has been associated with diets that are high in whole grains and fiber. Fiber also slows down cholesterol absorption. The AHA recommends that at least half of daily grain intake come from whole grains.
- Soluble fiber reduces cholesterol absorption in the bloodstream. Plant-based foods rich in soluble fiber include oatmeal, oat bran, legumes, apples, pears, citrus fruits, barley, and prunes.
- Check out additional information on What is the Best Oil for Cooking?
In addition to dietary changes, don’t forget the value of physical activity. Physical inactivity increases the risk of heart disease. Physical exercise can help manage or prevent high blood pressure and high blood cholesterol. Regular activity raises HDL while also decreasing triglycerides and plaque buildup in the arteries. And activity consistently burns calories, which can help with weight loss or maintaining a healthy weight.
VIDEO: “Fats – Biochemistry,” by Osmosis, YouTube (February 14, 2018), 12 minutes. This video gives an overview of some of the topics discussed in this unit, including the different types of fatty acids and their impact on health, and digestion and absorption of triglycerides.
- Lindshield, B. L. Kansas State University Human Nutrition (FNDH 400) Flexbook. goo.gl/vOAnR, CC BY-NC-SA 4.0
- University of Hawai‘i at Mānoa Food Science and Human Nutrition Program, “Digestion and Absorption of Lipids,” CC BY-NC 4.0
- Forouhi, N. G., Krauss, R. M., Taubes, G., & Willett, W. (2018). Dietary fat and cardiometabolic health: evidence, controversies, and consensus for guidance. Bmj, 361, k2139.
- Links Between Saturated Fat, Blood Cholesterol & Heart Disease Prove Complex – Tufts University Health & Nutrition Letter Article. (2010, May). Retrieved from https://www.nutritionletter.tufts.edu/issues/6_5/current-articles/Links-Between-Saturated-Fat-Blood-Cholesterol-Heart-Disease-Prove-Complex_592-1.html.
- Dietary Guidelines for Americans 2015–2020 8th Edition. (n.d.). Retrieved from https://health.gov/dietaryguidelines/2015/guidelines/
- “Traditional stethoscope with a red heart” by Marco Verch is licensed under CC BY 2.0
- “Pile of Donuts” by Anna Sullivan is in the Public Domain, CC0
- Figure 5.29. “Healthy Meal” by Louis Hansel is in the Public Domain, CC0; Healthy Brunch Photo by “Healthy Brunch” by Jannis Brandt is in the Public Domain, CC0; “Concept Diet” by Marco Verch is licensed under CC BY 2.0.
- “Heart-Shaped Bowl” by Jamie Street is in the Public Domain, CC0