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Editor’s Note: This post was updated on August 23, 2018for accuracy and comprehensiveness. It was originally published on August 24, 2016.

Have you noticed the abundance of low-fat or fat-free options on the shelves? Do your friends refuse to eat a particular food because it has “just too much fat?” Despite popular opinion, national obesity rates have skyrocketed from approximately 15% to 35% since 1980.

Luckily, scientists now know that eating fat doesn’t make you fat; it is actually a vital macronutrient and energy source. Still, many people struggle with understanding “good” and “bad” fats. More importantly, with the increasing focus on macronutrient-based eating, how will dietary fat choices impact body composition?

Dietary Fats

There are four main types of dietary fat listed on food labels: saturated fats, trans fats, polyunsaturated fats, and monounsaturated fats. These are not to be confused with adipose tissue, the stored fat in your body. These four fats have different physiological effects once digested, some of which are beneficial and some of which may have negative impacts on health and should be limited.

A quick note: saturated vs. unsaturated fats

Fats are made up of chains of carbon atoms with a carboxyl (acid) group (COOH) at one end and a methyl groups (CH3) at the other end. Carbons are attached to each other and to hydrogen atoms – it’s the way the carbons are chained that differentiates saturated and unsaturated fats and impacts how our bodies process them. Unsaturated fats have one or more double bond(s) between carbon atoms, and foods rich in unsaturated fats tend to be liquid at room temperature (think: olive oil). On the other hand, saturated fats contain no double bonds and tend to be solid at room temperature.

Monounsaturated Fats

olive oil fat

Monounsaturated fat is one of the good guys. This type of fat makes up a substantial component of the oft-referred-to Mediterranean diet. Studies have shown the Mediterranean diet, when supplemented with monounsaturated fats like extra-virgin olive oil, may help prevent the incidence of adverse events related to cardiovascular disease.

A meta-analysis of 24 studies evaluating diets high in monounsaturated fats indicated a significant reduction in triglycerides, body weight, and systolic blood pressure in patients with type II diabetes. There was also a significant increase in HDL, the good cholesterol. Another study showed protective effects of dietary monounsaturated fatty acids in reducing risk factors associated with metabolic syndrome and cardiovascular disease.

So what does this mean for body composition?

There are currently no definitive correlations between monounsaturated fats and body composition. However, the studies mentioned above show monounsaturated fats have numerous health benefits. The reduction in triglycerides, body weight, and blood pressure can all lead to a reasonable assumption that monounsaturated fats have a positive effect on overall health by improving body composition and reducing cardiovascular risks.

So the next time you’re meal planning and looking at your macronutrient goals, be sure to include some heart-healthy fats in your shopping cart.

Sources of monounsaturated fats include:

  •        Olive, peanut, and canola oils
  •        Tree nuts, such as almonds, pecans, and hazelnuts
  •        Seeds, such as sesame and pumpkin seeds
  •        Avocados

Polyunsaturated Fats

Polyunsaturated fat, like Omega-3 and Omega-6, is commonly known as being beneficial. This category of dietary fats is home to essential fatty acids (fats your body needs but can’t make itself). Therefore, it must be eaten.

Unfortunately, not all polyunsaturated fats are created equal.

In a recent double-blind study, participants were instructed to maintain their regular level of exercise and diet while one group took safflower oil supplements, a source of Omega-6 fatty acids, and the other group supplemented with Omega-3 fish oil. The body composition of both groups was measured before and after a 6-week trial.

While neither group showed a change in body mass over the course of the experiment, the post-trial body composition assessment showed a small but significant increase in lean mass and a significant reduction in fat mass in participants supplementing with Omega-3 fish oil. These results were not echoed in the Omega-6 safflower oil group.

This investigation supports complementary data outlining the importance of a balanced intake of Omega-3 and Omega-6 fatty acids. Whereas our hunter/gatherer ancestors consumed a 1:1 ratio of Omega-3s and Omega-6s, our present ratio is estimated to be around 1:20.

The reasoning is simple: Omega-3s come from wild, unprocessed game sources (mainly fish) while Omega-6s are plant-based. Considering humans use plant-based oil just about every time we cook but no longer eat primarily grass-fed meats like we used to, the balance is skewed.

What does this mean for body composition?

First off, don’t let the natural appeal of oils heavy in Omega-6 fatty acids fool you into thinking that they’re automatically healthy because they come from plants. While Omega-6s have many important functions in the body (including skin and hair growth, maintaining bone density, and regulating metabolism), many of these oils seen on the store shelf are highly processed and have little to no nutritional value.

In excess, Omega-6s can cause inflammation and increase the risk of becoming obese. On the other hand, Omega-3s can counteract those effects, which is why a balanced ratio is of the utmost importance. In short, you need to balance your Omega-3 and Omega-6 intake.

Take a look at your current diet. Do you often use vegetable oil for cooking? Does your diet lack varied wild animal and plant sources? If so, make adjustments that include using less oil products for cooking and incorporating more fish and wild game into your meals. After making the necessary diet changes, consider taking a fish oil or algae oil supplement to further close the gap.

Sources of Omega-3 polyunsaturated fats include:

  •        Krill oil
  •        Fatty fish such as salmon and trout

Additional note: Flax (high in alpha-linolenic acid, or ALA) appears to have a more beneficial effect on cardiovascular risk, while fatty fish sources, which are high in eicosapentaenoic acid and docosahexaenoic acid (EPA and DHA, respectively), are incorporated into cell membranes in addition to providing heart-health benefits.

Sources of Omega-6 polyunsaturated fats include:

  •        Sunflower oil, corn, and soybean oil
  •        Walnuts
  •        Flax seeds

Trans Fats

Not all unsaturated fats are inherently “good.” Trans fats, or hydrogenated fats, are unsaturated fats that are processed (to create extra hydrogen bonds) so that they’ll behave like saturated fats. This process makes a product more shelf-stable and palatable.

Trans fats can lead to increased body fat and obesity, even in cases where there is little change in calorie intake. While saturated fats should be consumed in moderation from natural sources, trans fats are the super villain  and, should be limited at all costs. There are some exceptions to this rule (for example, conjugated linoleic acid, which is naturally produced in milk), but any man-made sources should be avoided.

Sources of trans fats include:

  •        Margarine
  •        Ice cream
  •        Frozen pizza
  •        Microwave popcorn
  •        Deep-fried foods

Saturated Fats

Here’s where things get a little tricky. Saturated fats have often been grouped with the villains of the dietary fat world when in reality they’re more of a misunderstood anti-hero. To clarify, naturally sourced, saturated fats can increase HDL cholesterol levels. Plus, diets high in dairy-based fats have been known to change body composition through fat loss, lean mass gain, and weight loss.

Unfortunately, most sources of saturated fats in the modern diet come from highly processed foods and baked goods, leading to the confusion over whether it’s good or bad. That being said, saturated fats should be limited, with greater precedence given to monounsaturated and polyunsaturated fats. For optimum body composition, make sure your limited amount of saturated fats aren’t coming from processed, shelf-stable sources and fatty cuts of meat.

Healthy sources of saturated fats include:

  •        Egg yolks
  •        Pasture-fed beef and poultry
  •        Coconut and coconut oil
  •        Minimally processed dairy products


Saturated vs. Unsaturated Fats in Body Composition

With so many different studies and advice on the different sources of dietary fat, it’s easy to get overwhelmed and confused. While dietary fat is an important macronutrient that should make up a substantial percentage of our diet, how does one break that down further to understand how certain types of dietary fats impact body composition?

A 2014 study conducted by Uppsala University in Sweden investigated that exact question.

Study participants were asked to maintain regular physical activity and a habitual diet while consuming an excess 750 calories per day via high-fat muffins. Half the participants’ muffins were made with sunflower oil, which is high in linoleic acid (a polyunsaturated fatty acid). The remaining participants’ muffins were made with palm oil, which is high in palmitic acid (a saturated fatty acid).

Both groups gained an average of 3.5 lbs in weight throughout the duration of the study. However, participants consuming saturated fat via palm oil gained more liver fat, visceral fat, and total body fat than those consuming polyunsaturated fat via sunflower oil. Participants eating sunflower oil gained nearly three times as much lean mass as those consuming palm oil.

The ratios of lean mass to fat tissue gained in the sunflower oil and palm oil groups were 1:1 and 1:4, respectively.

In short, this study adds credence to the recommendation that polyunsaturated fat should replace saturated fat in the diet whenever possible.

Key Takeaways

So which types of fat should you eat and how much? When reviewed together, these studies provide insights on eating fat and its correlation with weight gain, fat mass, lean mass and overall health. Ideally, trans fats should make up 0% of your diet. That part is easy to discern. This can be challenging due to the prevalence of trans fats in many processed consumer goods. Fortunately, since they’re mostly man-made, you will find little to no trans fats in unprocessed, whole foods.

Monounsaturated fats have numerous health benefits, including positive effects on body composition and cholesterol. These should make up a significant portion of fat you eat. Include more monounsaturated fats in your diet, start by adding small servings of nuts and seeds as snacks, and using beans or lentils as the main carbohydrate in a few meals per week.

Polyunsaturated fats also have numerous health benefits, including positive effects on body composition and cholesterol, even in situations of weight gain. These, too, should make up a significant portion of your daily dietary fat intake.

The caveat here is to ensure you find sources of polyunsaturated fats that are rich in Omega-3 and try to avoid excess sources of Omega-6 whenever possible. While polyunsaturated fats are proven good guys, they have a dark side in Omega-6s. Getting polyunsaturated fats from the wrong sources can have an adverse effect on body composition.

Rather than getting the majority of your polyunsaturated fat intake from oils, try to incorporate fatty fish, such as salmon or trout, as the main protein in a few of your meals each week. Though cooking oils like canola oil and sunflower oil are considered healthier options, moderation is key.

Finally, saturated fats should make up a minimal portion of your daily fat intake. This is also challenging due to the prevalence in processing, and shelf-stabilization methods by food producers. Again, focusing on a balanced diet of whole, minimally processed food sources—in essence, food without an ingredient list—will help limit the intake of saturated fats.

Remember, change takes time. You can begin by taking a look at your current fat intake and make substitutions as needed. If you’re still confused about the difference between dietary fat and body fat, check out the article Your Body and You: A Guide to Body Fat. And also, don’t forget that while balancing the types of fat in your diet are important, fat intake needs to be monitored in addition to overall caloric intake in order to meet your body composition goals.


Nikita Ross is a Precision Nutrition certified wellness coach and professional fitness writer. She believes that lifting both barbells and books is the key to self-improvement.

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