They get a bad rap, but we all need fats in our diet for our bodies to function optimally. On top of providing a concentrated source of energy, fats also help absorb nutrients and support cell growth. Although certain types of fat are essential in our diet, many low-fat diet fads have demonized all fats. In contrast, many high-fat diet fads suggest that any and all fats are good. The truth is that a healthy diet can vary widely in terms of its fat content. And the effect fat has on our health depends on the type of fat we consume and the food source it comes from. Let’s discuss this in further detail.

The longstanding recommendation is that a healthy, balanced diet should get about 20-35% of its calories from fat. This amount can be appropriate, but we also see many healthy, long-living populations consume less than this. For example, on the island of Okinawa, Japan, a traditional diet based on sweet potatoes, rice, tofu and vegetables provided only about 10% of calories from fat. We also see healthy populations that consume slightly more than the standard range. Many long-living Mediterranean populations consume upwards of 40% of calories from fat, with most of it coming from olives, olive oil and nuts.

It is important to note that calorie intake in these healthy populations typically matched energy expenditure, helping them maintain a healthy body weight. This suggests that as long as calorie intake is appropriate, the percent of fat in the diet can vary from 10-40%. With that being said, the type of fat, and the food source it comes from, is what can significantly impact our health.

There are four main types of fat: trans, saturated, polyunsaturated and monounsaturated fat. Let’s break these down by their impact on our health and common food sources in the diet.

TRANS FAT (AKA HYDROGENATED OR PARTIALLY HYDROGENATED OIL)

Health impact: Trans fats are the worst type of fat we can consume. Their intake is strongly associated with an increased risk of cardiovascular disease and inflammation. They also appear to promote obesity and type-2 diabetes. ₁ 

Food sources: Trans fats occur naturally in small amounts in meat and dairy products. They are frequently added to commercially prepared cakes, cookies, pies, donuts and biscuits. They may also be found in fast food, deep-fried foods, margarines, frozen pizzas and other processed junk food.

SATURATED FAT

Health impact: Reducing the amount of saturated fat in our diet, or replacing it with healthier fat sources, is consistently associated with lower rates of cardiovascular disease, cancer, respiratory disease mortality and all-cause mortality. ₂₋₆

Food sources: Saturated fat is largely found in beef, lamb, pork, poultry skin, butter, ice cream, lard, high-fat dairy, coconut and palm oil. Although there is some controversy over whether plant sources, like coconut and palm oil, are healthier compared to animal sources, the research shows that these still increase LDL (bad) cholesterol, which is strongly associated with cardiovascular disease. ₇₋₁₀

POLYUNSATURATED FATS

Health impact: There are two main types of polyunsaturated fats: omega-6 and omega-3. Both are essential in our diet, however excessive consumption of omega-6 fat—from foods fried in vegetable oil—is not ideal. Despite this, people tend to be healthier when they consume polyunsaturated fats instead of saturated or trans fat. ₅

Food sources: Good sources of omega-3 fat include oily fish (salmon, mackerel, sardines), walnuts, flaxseed, chia seeds, hemp seeds and soy products. Good sources of omega-6 fat include vegetable oils, nuts and seeds. Although fish and vegetable oils can be a good source of these fats, we’re better off getting them from whole plant-based foods, such as nuts and seeds, because nuts and seeds not only provide these essential fats, but also contain fiber, antioxidants, vitamins and minerals.

MONOUNSATURATED FATS

Health impact: Choosing plant-based monounsaturated fats over saturated or trans fat is associated with lower rates of cardiovascular disease, cancer and all-cause mortality. ₂

Food sources: Olives, olive oil, peanuts, avocados, nuts and seeds are all good sources of monounsaturated fat. As with polyunsaturated fat, we are better off getting these fats from whole foods over oils because all the fiber and nutrients are retained.

THE BOTTOM LINE

The debate about how much or which types of fat we should consume is often dominated by those making extreme claims or by those shouting the loudest. But if we look at the research, we consistently see that a healthy diet can be lower or moderate in terms of its fat content. We also see that choosing more fat from plant sources and less from animal sources is consistently associated with better health. In general, we want to get most of our fat from a variety of nuts, seeds, avocados and olives; consume smaller amounts of low-saturated fat oils; and avoid animal products and junk food that contains saturated and/or trans fat. Doing this will ensure an adequate intake of health-promoting fat, while limiting or avoiding the types of fat that undermine our health.

References:

1. Harvard School of Public Health: Shining the Spotlight on Trans Fats.

2. Zhuang, Pan et al. “Dietary Fats in Relation to Total and Cause-Specific Mortality in a Prospective Cohort of 521 120 Individuals With 16 Years of Follow-Up.” Circulation research 124,5 (2019): 757-768. doi:10.1161/CIRCRESAHA.118.314038

3. Ricci, Cristian et al. “Type of dietary fat intakes in relation to all-cause and cause-specific mortality in US adults: an iso-energetic substitution analysis from the American National Health and Nutrition Examination Survey linked to the US mortality registry.” The British journal of nutrition 119,4 (2018): 456-463. doi:10.1017/S0007114517003889

4. Sacks, Frank M et al. “Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association.” Circulation 136,3 (2017): e1-e23. doi:10.1161/CIR.0000000000000510

5. Mozaffarian, Dariush et al. “Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials.” PLoS medicine 7,3 e1000252. 23 Mar. 2010, doi:10.1371/journal.pmed.1000252

6. Briggs, Michelle A et al. “Saturated Fatty Acids and Cardiovascular Disease: Replacements for Saturated Fat to Reduce Cardiovascular Risk.” Healthcare (Basel, Switzerland) 5,2 29. 21 Jun. 2017, doi:10.3390/healthcare5020029

7. Ye Sun, Nithya Neelakantan, Yi Wu, Rashmi Lote-Oke, An Pan, Rob M van Dam, Palm Oil Consumption Increases LDL Cholesterol Compared with Vegetable Oils Low in Saturated Fat in a Meta-Analysis of Clinical Trials,The Journal of Nutrition, Volume 145, Issue 7, July 2015, Pages 1549–1558, https://doi.org/10.3945/jn.115.210575

8. Laurence Eyres, Michael F. Eyres, Alexandra Chisholm, Rachel C. Brown, Coconut oil consumption and cardiovascular risk factors in humans,Nutrition Reviews, Volume 74, Issue 4, April 2016, Pages 267–280, https://doi.org/10.1093/nutrit/nuw002

9. Neelakantan, Nithya et al. “The Effect of Coconut Oil Consumption on Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Clinical Trials.” Circulation 141,10 (2020): 803-814. doi:10.1161/CIRCULATIONAHA.119.043052

10. Fernández-Friera, Leticia et al. “Normal LDL-Cholesterol Levels Are Associated With Subclinical Atherosclerosis in the Absence of Risk Factors.” Journal of the American College of Cardiology 70,24 (2017): 2979-2991. doi:10.1016/j.jacc.2017.10.024