All About Dietary Fat

By Laura Schoenfeld, RD

How much do you really know about dietary fat?

Most people have one of two viewpoints on fat consumption.

The most common belief in our society for many decades has been that dietary fat is bad for you. It’ll make you fat, clog your arteries, and send you into an early grave.

With the rise in popularity of low-carb diets, however, the pendulum has swung in the other direction. Many people now believe fat should be eaten abundantly, and that the more fat we eat the leaner and healthier we’ll be.

It’s no wonder there’s so much confusion!

What is actually true about dietary fat? Should we eat unlimited amounts of butter and spoon coconut oil into our coffee? Should we stick with fat-free dairy and lean chicken breasts? How much fat should we be eating to be healthy, fit, and free of chronic disease?

The Fat Basics

There are four major different types of fats, and they all impact our health in one way or another. Keep in mind that all fat-containing foods have a mix of these fats, but some have higher amounts than others.

Monounsaturated Fat

This type of fat is often referred to as healthy fat. “Monounsaturated” means that there is one double bond in the fatty acid chain, giving the oil some amount of flexibility and fluidity. Monounsaturated fats (MUFAs) are liquid at room temperature and tend to solidify in the refrigerator.

Monounsaturated fat is the least controversial of all the fats, and is likely protective against diseases such as heart disease, diabetes, hypertension, and even certain cancers. 1,2,3 A higher proportion of monounsaturated fat in our diet reduces the risk of insulin resistance and inflammation, and may even help keep us lean. 4,5,6

Most evidence to date supports the liberal use of monounsaturated fats without any need to restrict them in the diet.

This means most people can eat lots of this type of fat without concern for long term health risks.

Monounsaturated fats are found in lots of healthy whole foods. The most common sources of include olives and olive oil, avocado and avocado oil, and nuts such as almonds, macadamia nuts, and pistachios.

You may not realize, however, that many animal foods are high in MUFAs as well. Egg yolks are predominantly monounsaturated fat (two grams per yolk), and about half the fat found in pork and beef is monounsaturated.

Saturated Fat

Saturated fat has all single bonds in its fatty acid chain, making it more rigid and structured than the other types of fats. That’s why these fats are solid at room temperature.

Saturated fat is commonly called bad fat and has gotten a bad rap over the years thanks to poorly-executed research and industry influence over the past few decades. The truth is, there’s very little evidence that saturated fat in moderate amounts has any negative impact on our health.

Evidence published in 2017 shows that saturated fat intake is not associated with cardiovascular disease or stroke. 7 Other review papers have found similar results. 8

Plus, saturated fats play essential structural roles in the body, especially in the structure of cell membranes. Certain saturated fatty acids even show benefits for energy metabolism, immunity, intestinal health and metabolic health. 9

Even though the body can create all the saturated fat it needs, it’s possible that relying on this process (de novo lipogenesis) may deplete certain resources that affect the body’s optimal functioning.

Plus, many saturated fats found in animal foods also contain fat-soluble vitamins like vitamin A, D, and K2, all of which are crucial for good health. Avoiding saturated fats entirely makes it challenging to get adequate amounts of all three of those nutrients from our food.

Bottom line?

The majority of the population can consume saturated fat as a significant proportion of their fat intake and not experience an increase in chronic disease risk.

There is a small subset of the population who may benefit from a reduction in saturated fat intake. Certain genetic factors affect the way the body processes saturated fats, and for some people a higher saturated fat intake raises LDL cholesterol and may increase their weight. 10,11 It’s worth doing some genetic analysis if you’re seeing significant weight gain or very elevated LDL on a diet higher in saturated fat.

Foods higher in saturated fat include beef, lamb, pork, coconut, and dairy products like butter and cheese. Consuming these foods regularly is healthy for most people, and there’s no need to fear these foods in your diet.

The caveat here is that just because saturated fat isn’t likely to harm you in moderate quantities, it doesn’t mean that you should be adding tablespoons of extra fat to food and beverages. The evidence supports consuming saturated fat as part of a balanced diet containing a variety of fats and other nutrients. Eating tons of added, isolated saturated fats like coconut oil and butter to your food probably won’t benefit your waistline or your long-term chronic disease risk.

And as for the recent “coconut oil scare” in the headlines, much of this position by the AHA is based on outdated guidelines for saturated fat intake. Coconut oil is not a dangerous food, but it’s not a magic cure-all either. For a more in-depth look into the healthfulness of coconut oil, check out this informative podcast and this review article. Again, like other saturated fats, I’d suggest using them as part of a mixed diet and avoiding adding multiple spoonfuls of refined coconut oil to food and drinks.

Polyunsaturated Fat.

This is one of the more confusing and complicated fats. Polyunsaturated fats (PUFAs) contain two or more single bonds in their fatty acid chains, keeping them fluid even at cold temperatures.

The two most commonly discussed PUFAs are omega-6 and omega-3 fatty acids. Omega-6 fats are found primarily in nuts and seed oils and grain-fed animal fats. Omega-3s are found in fatty fish, certain nuts and seeds, grass-fed animal fats, and egg yolks.

These single bonds also make these fats more susceptible to oxidative damage when exposed to heat, light, or oxygen, which is why they smell rancid when they go bad.

When PUFAs get oxidized, they become inflammatory and toxic to the body. 12 This may be why a high consumption of PUFAs is associated with chronic diseases like cardiovascular disease, obesity, inflammatory bowel disease (IBD), rheumatoid arthritis, and Alzheimer's disease. 13

The research surrounding the healthfulness of consuming PUFAs is mixed, and even though omega-3 fats are all the rage right now, there’s some concern that overdoing these fats may do more harm than good. 14

Eating fatty fish, grass-fed meats, egg yolks, and moderate amounts of whole nuts and seeds is likely fine, but supplementing with high doses of omega-3 fats (e.g. fish oil) for a long time, or using PUFA-rich oils to cook with, may lead to increased inflammatory risk.

My recommendation to my clients is to avoid concentrated sources of PUFAs such as industrial seed oils (canola, corn, soy, margarine, etc.) and to not take high doses of fish oil for more than a couple months.

Foods that naturally contain PUFAs like fatty fish, poultry, and nuts and seeds can be eaten regularly but should be balanced with other foods containing primarily monounsaturated and saturated fats. Consuming grass-fed meats rather than grain-fed meats will further limit exposure to inflammatory industrial omega-6 fats.

Trans Fats

Trans fats generally refer to the artificial fats that are created by adding hydrogen atoms to a polyunsaturated fat, making these fats more solid and similar in consistency to saturated fats. While there are a few naturally occurring trans fats, most are created in a factory. Trans fats are less likely to spoil or go rancid, so foods made with it have a longer shelf life.

Unfortunately, these fats are well known to cause serious health issues when eaten regularly. They are known to raise LDL cholesterol and lower HDL cholesterol, and increase the risk of developing cardiovascular disease and type 2 diabetes. 6,7 There is no health benefit to these industrial trans fats, and they should be avoided as much as possible.

Trans fats are primarily found in shelf-stable baked goods, frozen processed foods, some margarines, and some fried foods. Common sources of trans fats include doughnuts, cookies, crackers, muffins, pies, and cakes.

Look for the words “partially hydrogenated” or “fully hydrogenated” in the ingredients list if the label does not disclose the trans fat content.

How dietary fat affects your body fat

Many people have polar opposite beliefs about the way that dietary fat affects body fat.

The “old school” belief is that eating fat is what makes you fat, and a low-fat diet is the best way to lose weight and keep it off. It was that belief that led to the popularity of the low-fat movement in the 80s and 90s.

These days, low-carb advocates argue that eating fat actually makes your body burn more fat, and that it’s actually carbs and sugar that lead to fat gain thanks to the rise in insulin that happens after you eat them.

The truth is that neither of these beliefs is correct.

You can gain body fat — or lose it — on a low-fat or low-carb diet. There’s no magic diet that leads to optimal body composition for everyone. If fat loss is your goal, ultimately the best diet is the one you can stick to and not cause hormonal disruption. (To learn more about how to lose body fat safely, read this!)

When I work with women who want to reduce body fat, I find that most do best on a diet that contains both carbs and fat in appropriate amounts to support general health, hormone production, good sleep, and satiety. Consuming too much or not enough fat usually negatively affects these factors, making it hard to stick to an extreme diet in the long term.

How much fat should you eat?

While there are no one-size-fits-all guidelines for fat consumption, there are some basic minimums that women need to hit for adequate fat intake.

According to the Food and Agriculture Organization of the United Nations, the absolute minimum any adult should eat is 15 percent of their calories from fat. For premenopausal women, this number jumps to 20 percent.

As an example, for a woman of childbearing age eating 2000 calories per day, this is about 45 grams of fat — the equivalent of about three tablespoons of oil.

From there, the amount of fat you need really depends on your health and fitness goals, overall calorie needs, and food preferences. Some of my clients don’t feel satisfied after a lower fat meal, while others struggle to digest a high-fat meal. There’s no perfect amount of fat to eat, and your intake may fluctuate day to day.

How do you know if you’re getting the right amount for you? Pay attention to the following signs and symptoms.

Too little fat in your diet can lead to:

  • Constant hunger shortly after eating
  • Dry skin and hair
  • Acne
  • Low sex hormones (estrogen, progesterone, testosterone)
  • Irregular periods/amenorrhea
  • Poor blood sugar control
  • Low mood, anxiety, or depression
  • Frequent sickness
  • Low body temperature
  • Premature aging
  • Unintentional weight loss or weight gain (depending on calorie intake)

Too much fat in your diet can lead to:

  • Unintentional weight gain
  • Stomach cramping
  • Loose stools or diarrhea
  • Constipation (when carbs are too low)
  • Inflammation (with too much PUFAs or trans fats)
  • Elevated cholesterol (in some people)

As you can see, the health concerns of inadequate fat intake are a little more concerning than excess fat intake, and don’t show up quite as fast. Most of my female clients do best on a diet that contains somewhere between 30 to 50 percent of calories from fat.

The take-home message is this: There’s no reason to fear dietary fat, particularly from whole foods. And there’s no magic to eating a very high fat diet either.

Eat the amount of fat that makes you feel your best, emphasizing the healthier whole-food fats like monounsaturated oils, saturated fats from coconut and pastured, grass-fed animals, and omega-3 fats from fatty fish, nuts and seeds. Use enough healthy fat to make your food taste good, and avoid deep-fried foods and oil-heavy restaurant dishes. Minimize your consumption of packaged and processed foods. Enjoy some butter on your veggies, avocado on your salad, and bacon and eggs at breakfast! Get the fatty tuna at the sushi restaurant (seriously, it’s the best.)

And remember: Don’t be afraid to experiment with different amounts of fat to figure out what works best for you and your goals.

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About the author:  Laura Schoenfeld, RD

Laura Schoenfeld is a registered dietitian trained in functional medical nutrition therapy. She helps her clients identify and implement diet and lifestyle changes that will allow them to live their healthiest, fittest, symptom-free life, without being consumed by thoughts of food and exercise. She loves hikes with her dog, beach trips, live music, and heavy weight training. Find her at


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