Some experts say high fat foods are associated with cardiovascular diseases, clogged arteries, and weight gain. Others claim fat needs to be incorporated into a healthy diet because it plays an essential role in weight loss and maintaining stable blood sugar levels. With numerous terms (saturated fat, trans fat, monounsaturated fat, polyunsaturated fat, omega-3, omega-6, omega-9) constantly being thrown around and countless contradictory health claims, it's no wonder why fat is a confusing topic.
So, I am here to clear some (hopefully all) of this confusion up. This post will provide a fundamental understanding of dietary fats, and the role each type of fat plays in our well-being and long-term health.
The Basics:
Fat is one of three essential macronutrients (the other two being protein and carbohydrates).The acceptable macronutrient distribution range (AMDR) for total fat intake is 20-35% of energy intake, or total calories consumed (1). Each gram of fat, no matter the type of fat, contains 9 calories.
Saturated vs Unsaturated Fat…
SATURATED FATS
What are saturated fats?
Saturated fats are solid at room temperature and are predominantly found in animal products, such as milk, butter, cream, cheese, fatty meats, baked goods, like muffins or cakes, fried foods, as well as coconut oil.
How do Saturated fats affect my health?
A preponderance of research illustrates a strong positive link between overconsumption of saturated fats and high levels of LDL cholesterol, a major risk factor for coronary heart disease (2). High intake of saturated fat also reduces optimal functionality of liver receptors, potentially contributing to hyperlipidemia, a condition involving abnormally high levels of cholesterol (hypercholesterolemia) and triglyceridies (hypertriglyceridemia) in your blood (3). This dysregulation of serum lipid concentrations increases risk of heart attacks, strokes, transient ischaemic attacks, and atherosclerosis, which is the constriction of arterial walls due to plaque build up. Moreover, two independent cross-sectional studies found a strong relationship between the fatty acid composition of muscle tissue (the main insulin sensitive tissue) and insulin sensitivity. In other words, high saturated fat intake relative to other forms of fat decreases insulin sensitivity and is, therefore, a predictor of type 2 diabetes (4).
Should I eliminate Saturated fat?
There is absolutely no need to completely eliminate saturated fat. In fact, I don't even think that is possible, as many sources of unsaturated fats, like olive oil, simultaneously contain saturated fat. Plus, there is nothing wrong with having a delicious cheese pizza, well cooked steak, or fresh goat cheese in your salad. Rather, you should be cognizant of your overall saturated fat intake and make a deliberate effort to swap saturated fats with mono or polyunsaturated fats (discussed later on). The American Heart Association recommends that 5- 6% of total calories be derived from saturated fat (5). For example, if you consume a 2,000 calorie diet, try your best to stick to about 13 grams (=120 Kcal) of saturated fat per day.
UNSATURATED FATS
What are unsaturated fats?
Unsaturated fats are liquid at room temperature and are mainly found in foods derived from plants, such as vegetable oils, nuts, and seeds. There are 2 main categories of of unsaturated fatty acids.
trans unsaturated fats (natural and artificial trans fats)
cis unsaturated fats (monounsaturated and polyunsaturated fats)
1. Trans Unsaturated Fatty acids (TUFA)
These fats have a notorious reputation, and not a good one at that. But what are trans fats? And must they be so feared?
1a) Artificial Trans Fats
Artificial trans fats are the result of a chemical process known as hydrogenation, where hydrogen is added to liquid oil- an unsaturated fat, converting it into a solid, enabling it to adopt properties similar to that of saturated fats, such as longer shelf life. Unfortunately, hydrogenation strips fat of its benefits, ultimately increasing levels of and LDL (“bad”) cholesterol, while lowering levels of HDL (“good”) cholesterol. As a result, artificial trans fats raise your risk of developing a stroke, heart disease and type II Diabetes (6). Research also indicates that trans fat may lead to weight gain and abdominal fat accumulation, regardless of calorie intake. In fact, a six year study revealed that monkeys fed on a trans fat diet gained 7.2% of their body weight, while monkeys consuming a monounsaturated fat diet gained only 1.8% (7). No, we are not monkeys, but the basis remains true: industrialized trans fats can be detrimental to our health. These several severe health risks associated with trans fat consumption motivated the U.S. Food and Drug Administration (FDA) to ban manufactures from adding partially hydrogenated oils/trans fats to foods. Nonethless, products such as cookies, pies, crackers and pastries, may still be secretly ridden with industrialized trans fats, so keep your eye out for them!
How do I spot trans fats?
First, look at the nutrient label and ensure there are 0g of trans fats. Second, look out for partially hydrogenated oils on the ingredient list, as 0g on a label does not necessarily mean trans fats aren't sneakily hiding in your food.
1b) Naturally-occurring trans fat/ Ruminant Trans fatty acids (R-TFA)
Naturally-occurring trans fats are produced within the gut of ruminant animals, such as cattle, sheep and goats. These fats do not appear to have the same health-damaging effects as industrialized trans fats. In fact, Flora Wang, a researcher in University of Alberta, found that a diet high in trans vaccenic acid (VA), a naturally occurring trans fat that constitutes more than 50% of R-TFA) (8), can apparently reduce risk factors associated with heart disease, diabetes and obesity (9). VA's properties can be attributed to its ability to minimize the production of chylomicrons: fat and cholesterol particles linked to metabolic disorders (9). A 2014 systematic review and meta-regression of clinical trials also suggests that ruminant trans fats suggests that an average intake (~4.2% of daily energy intake) of R-TFA does not appear to exacerbate cardiovascular risk factors (10). Despite these promising findings, more investigation as to what levels of R-TFA are safe and for which population/life-stage groups, is required.
2. Cis Unsaturated Fatty acids
2a) monounsaturated fatty acids (MUFA)
Monounsaturated fats are found in foods such as avocados, peanut butter, almonds, cashews, hazelnuts, pumpkin seeds and olives, as well as plant based oils such as canola, olive, safflower and avocado oil. Multiple studies show that monounsaturated fats are associated with a number of health benefits such as weight loss and a reduced risk of heart disease (11). One study also found that monounsaturated fats are associated with decreased blood pressure in those diagnosed with type II Diabetes (12). In addition, a diet high in monounsaturated fats can reduce triglyceride levels in the blood by 19% and lower cholesterol by 22% in patients with diabetes (13). The most common MUFA in the diet is oleic acid (Omega- 9), which can be produced naturally by the body, and is also found in food like olive oil. A study conducted by the Northwestern University Feinberg School of Medicine in Chicago revealed that oleic acid blocks the action of HER-2/neu, a cancer-causing oncogene found in about 30% of breast cancer patients (14). Basically, oleic acid can help prevent breast cancer, so make sure to drizzle that olive oil onto your salads!
2b) Polyunsaturated fatty acids
Polyunsaturated fats include omega-3 and omega-6 fatty acids. These fats are essential because they are not produced by the body and therefore, we need to obtain them from our diet. Omega-3 fats are found in foods like salmon, flaxseed, eggs and walnuts. They play an important role in the function of human cell membranes, improving heart health and aiding in weight loss. The are 3 forms of omega-3 fats:
Eicosapentaenoic acid (EPA):
Docosahexaenoic acid (DHA)
Alpha-linolenic acid (ALA)
EPA is anti-inflammatory, meaning it reduces inflammation and promotes healing, DHA comprises roughly 8% of our brain’s weight and plays a significant role in the formation and development of our brain, while ALA is used to prevent atherosclerosis and even treat rheumatoid arthritis (15). The World Health Organization recommends that healthy adults consume a minimum of 250–500mg combined EPA and DHA each day. The recommended dietary allowance (RDA) for alpha-linolenic acid is 1.6 grams per day for men and 1.1 grams per day for women (1).
Omega-6 fatty acids are found in nuts and seeds, meat, poultry, as well as, in corn, safflower and sunflower oil. There are four types of omega-6 fats:
Linoleic acid (LA)
Arachidonic acid (AA)
Gamma linoleic acid (GLA)
Conjugated Linoleic acid (CLA)
The main type of omega-6 fats is linoleic acid, its pro-inflammatory properties aiding in the proper function of skin, nerve, immune and reproductive systems (16). However, Western diets are often high in omega-6 and deficient in omega-3 fats, promoting the pathogenesis of diseases, such as, cardiovascular disease, cancer, and inflammatory and autoimmune disease (17). In other words, omega-6 fatty acids are extremely important, but excessive amounts (relative to omega-3) concurrently cause bodily chaos. The recommended ratio of omega-6 to omega-3 is 4:1 (17). You do not necessarily need to cut back on your omega-6 intake (although awareness of intake is important), but ensure you are consuming more foods higher omega-3!
In Summary...
There are 2 over-arching categories of fats: unsaturated and saturated
Saturated fats raise LDL cholesterol, causing plaque build up in arteries (atherosclerosis) which increases risk of heart attacks and strokes. SF also reduces insulin sensitivity, a risk factor for Type II Diabetes.
Unsaturated fats are divided into trans and cis unsaturated fats.
Trans fats can occur naturally in animals, or artificially, by means of hydrogenation. Natural trans fats do not appear to cause adverse health effects, while industrial TF are strongly linked to weight gain, stroke, heart disease and diabetes.
cis unsaturated fats include monounsaturated and polyunsaturated fats. Monounsaturated fats, including omega-9 fats. Polyunsatruated fats include omega-3 fats (Eicosapentaenoic acid, Docosahexaenoic acid, Alpha-linolenic acid) and omega 6 fats (Linoleic acid, Arachidonic acid, Gamma linoleic acid, Conjugated Linoleic acid)
omega-9 fats are non-essential. They improve insulin sensitivity and reduce risk of breast cancer.
omega-3 fats must be obtained from the diet and are anti-inflammatory, lower risk of heart disease as well as, arthritis, and constitute significant components of the human body, such as, the brain.
omega-6 fats must also be obtained from the diet and are pro-inflammatory. Consuming a proper ratio of omega-6 to omega-3 is beneficial to health.
Fat is our FRIEND! We need fat to keep us full and to help with many of our internal bodily processes. As long as the majority of our fats come from healthy unsaturated sources while a smaller portion of our energy intake comes from other foods such as burgers, pizzas or pies - you are golden! Remember that the main factor which determines your health and well-being is the BALANCE of foods within your diet.
References
Institute of Medicine. 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. https://doi.org/10.17226/10490
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://www.heartuk.org.uk/low-cholesterol-foods/saturated-fat
Risérus, U., Willett, W. C., & Hu, F. B. (2009). Dietary fats and prevention of type 2 diabetes. Progress in lipid research, 48(1), 44-51.
https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/saturated-fats
Dhaka, V., Gulia, N., Ahlawat, K. S., & Khatkar, B. S. (2011). Trans fats-sources, health risks and alternative approach - A review. Journal of food science and technology, 48(5), 534–541. https://doi.org/10.1007/s13197-010-0225-8
Kavanagh K, Jones KL, Sawyer J, Kelley K, Carr JJ, Wagner JD, Rudel LL. Trans fat diet induces abdominal obesity and changes in insulin sensitivity in monkeys. Obes Res. 2007;15:1675–1684. doi: 10.1038/oby.2007.200.
Kuhnt, K., Degen, C., & Jahreis, G. (2016). Evaluation of the impact of ruminant trans fatty acids on human health: important aspects to consider. Critical reviews in food science and nutrition, 56(12), 1964-1980.
University of Alberta. (2008, April 5). Natural Trans Fats Have Health Benefits, New Study Shows. ScienceDaily. Retrieved May 10, 2021 from www.sciencedaily.com/releases/2008/04/080402152140.htm
Gayet-Boyer C, Tenenhaus-Aziza F, Prunet C, Marmonier C, Malpuech-Brugère C, Lamarche B, Chardigny JM. Is there a linear relationship between the dose of ruminant trans-fatty acids and cardiovascular risk markers in healthy subjects: results from a systematic review and meta-regression of randomised clinical trials. Br J Nutr. 2014 Dec 28;112(12):1914-22. doi: 10.1017/S0007114514002578. Epub 2014 Oct 27. PMID: 25345440; PMCID: PMC4301193.
Kaippert, V. C., dos Santos Lopes, M., de Carvalho, P. D., & Rosado, E. L. (2015). Effects of unsaturated fatty acids on weight loss, body composition and obesity related biomarkers. Diabetology & Metabolic Syndrome, 7(Suppl 1), A139. https://doi.org/ 10.1186/1758-5996-7-S1-A139
Qian, F., Korat, A. A., Malik, V., & Hu, F. B. (2016). Metabolic Effects of Monounsaturated Fatty Acid-Enriched Diets Compared With Carbohydrate or Polyunsaturated Fatty Acid-Enriched Diets in Patients With Type 2 Diabetes: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Diabetes care, 39(8), 1448–1457. https://doi.org/10.2337/dc16-0513
A Garg, High-monounsaturated-fat diets for patients with diabetes mellitus: a meta-analysis, The American Journal of Clinical Nutrition, Volume 67, Issue 3, March 1998, Pages 577S– 582S, https://doi.org/10.1093/ajcn/67.3.577S
Win, D. T. (2005). Oleic acid-The anti-breast cancer component in olive oil. Au JT, 9(9), 75-78.
Fleming, J. A., & Kris-Etherton, P. M. (2014). The evidence for α-linolenic acid and cardiovascular disease benefits: Comparisons with eicosapentaenoic acid and docosahexaenoic acid. Advances in Nutrition, 5(6), 863S-876S.
Kim, J. H., kim, yoo H., & Kim, Y. J. (2016). Conjugated Linoleic Acid: Potential Health Benefits as a Functional Food Ingredient. He Annual Review of Food Science and Technology. doi: 10.1146/annurev-food-041715-033028