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7 Myths About Dietary Fats You Should Stop Believing Right Now

Serena Marie, RD


Fat is an essential part of our diets. But it's also largely misunderstood.


This article provides some useful information on why it makes absolutely no sense to regard 'dietary fat' as a single substance - i.e. why labelling a food or diet simply as 'high fat' (or 'low fat') is meaningless with respect to its likely effects on health and disease.

Both the type and quality of fat we eat is what matters. And generally speaking, modern, western-type diets rich in industrially processed foods contain an unhealthy balance of fats, while traditional human diets - made up of whole or minimally processed foods - provide a healthier balance of fats.

What the article does not make clear is the 'polyunsaturated fats' (PUFA), which broadly come in two kinds - omega-3 or omega-6 - are dietary essentials, just like vitamins and essential minerals. We need them for life, but cannot make them, so they must come from the foods we eat. 

We need both these kinds of essential fats, but we also need them in the right balance.  And this is even more important for brain health than it is for body health - because the brain is 60% fat, and it really does matter what kind.

Like most media articles, this one also disappointingly fails to make any distinction between between the short-chain omega-3 and omega-6 fats - which plant and seed oils can provide - and the long-chain omega-3 and omega-6, which are found pre-formed only in animal-derived foods. 

This distinction is critical, because it is the long-chain omega-3 and omega-6 (known as LC-PUFA) that are biologically essential. And while some conversion of short to long-chain fats is usually possible, this process is inefficient and unreliable in humans. 

In particular, conversion within the body cannot provide enough of the long chain omega-3 DHA - found naturally in fish and seafood - and essential for healthy brain development and function.

So while it's true that both salmon and flax or chia seeds may 'contain omega-3', only the fish will provide the type of omega-3 you need.

  • For more on the multiple benefits of omega-3 polyunsaturated fats see here.
  • See here for information on the toxicity of trans fats.
  • More on saturated fats here.
  • and for articles on the ketogenic diet, see here.

14 August 2019 -


From the fat-phobic 1990s to today's keto-crazed culture, it's clear that the obsession with dietary fat permeates generation after generation of dieters.

But whether you love it or hate it, dietary fat plays an important role in keeping your body healthy and strong. In fact, it influences everything from your metabolism to your immunity and even plays a role in inflammation and vitamin absorption, according to the Academy of Nutrition and Dietetic's most recent position paper on the topic, published in 2014.

Bottom line? Fat is an essential part of our diets. But it's also largely misunderstood. Here, we'll bust seven common myths about the macronutrient that just aren't true.

Myth 1: All Fats Are Created Equal

All types of dietary fat contain 9 calories per gram, but each kind affects the body differently, according to the 2015-2020 Dietary Guidelines for Americans.

(1) Saturated Fats: Saturated fats, which are commonly found in coconut oil and animal meat, are often solid at room temperature. These have the potential to raise cholesterol, so they should be eaten in moderation.

(2) Trans Fats: Trans fatty acids are actually man-made substances used to improve the shelf-life of processed foods. In 2015, the U.S. Food & Drug Administration (FDA) ruled that trans fats are not safe for human consumption given their effect on increasing "bad" cholesterol and decreasing "good" cholesterol. In 2018, trans fats were banned in the U.S., but international travelers should be wary of processed foods containing "partially hydrogenated" oils, as this is another term for trans fat.

(3) Monounsaturated Fats: These fats are generally liquid at room temperature and considered to be heart-healthy, per the American Heart Association. Common sources of monounsaturated fat include olive and avocado oil, avocados, almonds and nut butters.

(4) Polyunsaturated Fats: By far the most confusing of the fatty acids, these liquid fats are categorized either as "omega 3" or "omega 6." Omega-6 sources of fat include vegetable oil and soybean oil, which are abundant in the standard American diet, while omega-3 sources are less common, found in fatty fish like salmon, flax seeds and chia seeds. Both are important to your body, but too much omega-6 in your diet may contribute to inflammation.


Myth 2: Saturated Fat Is Bad for You

Saturated fat was formerly thought to cause heart disease, which led to an influx of "fat-free," high-carbohydrate products on grocery store shelves. But more recent research has started to dig deeper into this thinking.

A meta-analysis of more than 300,000 people published in the American Journal of Clinical Nutritionin March 2010, for example, concluded that there's no evidence to link dietary saturated fat to heart disease risk. However, replacing some of these fats with polyunsaturated fats can help lower your risk of heart disease, according to a July 2017 advisory published in the American Heart Association's journal Circulation.

So remember: Everything in moderation. Instead of avoiding saturated fats altogether, simply exercise portion control when choosing fatty cuts of meat, cheese or butter, and make sure you're getting a mix of other healthy fats in your diet.

Myth 3: All Fatty Foods Raise Your Cholesterol

Dietary fat's effect on cholesterol varies depending on the type of fat.

Remember here that LDL cholesterol is "bad" cholesterol, while HDL is "good" cholesterol.

  • Saturated fat increases LDL but also increases HDL, lending it a neutral effect on blood cholesterol when eaten in moderation.
  • Trans fat increases LDL and decreases HDL, which is why the FDA banned it in 2018.
  • Monounsaturated fat decreases LDL and increases HDL.
  • Polyunsaturated fat decreases LDL and increases HDL.

Myth 4: Vegetable Oil Is the Healthiest Oil

While vegetable, canola and soybean oils contain a good amount of heart-healthy monounsaturated fat, the manufacturing process that produces them leaves much to be desired. These oils are refined, bleached and deodorized (RBD), meaning they're treated with solvents and subjected to intense heat, which can strip away nutrients.

While the RBD process is accepted as safe, I suggest avoiding highly-processed RBD oils and reaching instead for cold-extracted or cold-pressed olive or avocado oil. Avocado oil, especially, is also rich in monounsaturated fat and safe for cooking at higher temperatures.

Myth 5: If You Want to Lose Weight, You Should Stop Eating Fat

In a large clinical trial of 609 overweight adults published in the February 2018 issue of the Journal of American Medical Association, researchers found no significant difference in weight loss between those who followed a low-fat diet and those who restricted carbs.

In other words, finding an eating pattern that works best for your personal dietary preferences and lifestyle is optimal when trying to lose weight. And remember that it all comes down to more calories out than in, whether you're eating a low- or high-fat diet.

However, dietary fat may make adhering to a low-calorie diet easier by increasing your metabolism and sense of fullness. Also, medium-chain triglycerides, found in palm oil and coconut oil, may increase fat burning and support weight loss when added to the diet, per a February 2015 meta-analysis in the Journal of the Academy of Nutrition and Dietetics.

Myth 6: Margarine Is Healthier Than Butter

Margarine was once touted as a healthy alternative to saturated fat-laden butter, by instead providing calories from trans fatty acids. However, in 2018 the FDA banned the use of trans fat in the United States' food supply. So margarine is now made primarily from omega-6 polyunsaturated fats.

Sounds healthy, then, right? But butter may still be the better option.

According to a study in the April 2017 issue of Foods, grass-fed butter provides saturated fat but also high amounts of alpha-linolenic acid, an omega-3 polyunsaturated fat that helps reduce inflammation in the body. And a growing body of research suggests that replacing omega-6 fats with omega-3s may reduce the production of pro-inflammatory factors in the body.

Myth 7: All Fat Is Good on the Keto Diet

The ketogenic diet encourages followers to get a whopping 70 percent of their daily calories from fat. While reducing your carbohydrate intake may support weight loss, eating a very high-fat diet rich in pro-inflammatory foods may contribute to blood clots, heart disease and high blood pressure.

A November 2018 review in Open Heart suggests that it's ideal to consume more foods rich in omega-3 fatty acids. So ideally, a keto diet would be based around foods rich in omega-3 and monounsaturated fats from grass-fed meats and dairy, fatty fish, nuts and seeds, avocados and olive oil.

Even if you find success losing weight on a ketogenic diet, eating a diet rich in high-quality fats will ensure that your heart stays healthy as well.