19 April 2021

Dietary Fat: What is it?

For many years dietary fat received a bad rep in the media, despite it being an essential macronutrient that plays an important role in hormone synthesis and nutrient absorption. However in recent times we have seen a huge change in this opinion, which has coincided with the rise of low-carbohydrate, high-fat (LCHF) and ketogenic diets. So, let's investigate this a little further. 

What is dietary fat, and what is its role within the body?

Dietary fat, protein, and carbohydrate are the 3 main macronutrients. Macro means large; macronutrients are nutrients which are required in large amounts and play an essential role within our body. As well as being an energy source, they facilitate nutrient absorption, hormone production, and cell growth. There are a number of different types of dietary fat which we will discuss later; some are positively associated with health outcomes while others are negatively associated.

Understanding the molecular structure

A dietary fat is a type of lipid (a molecule which does not mix in well in water) and can be referred to as either a triglyceride or triacylglycerol in reference to the molecule’s chemical makeup. Triglycerides are made up of three (this is where the prefix comes from, ‘tri’ = ‘three’) hydrocarbon tails (hydrogen and carbon molecules attached together in a linear structure) and a glycerol head. The length and type of bonds in these hydrocarbon tails is what creates the different types of dietary fat. 

What are the different types of dietary fat?

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Saturated fats:


This type of fat only has single bonds in the hydrocarbon tails, which means that the molecules can stack very closely together. Remember, saturated fats are solid at room temperature. Generally speaking, saturated fats are found in animal products (like red meat and full-fat dairy products). These should be avoided due to a positive association with increased low-density lipoproteins (LDL), which is associated with an increased risk of heart disease and hypertension. 

I may be hearing a “Woah, slow down” from some of you nutrition whizzes out there. In the last decade there has been a lot of very strong evidence published about medium-chain triglycerides (MCT). Basically an MCT is a saturated fat, but the hydrocarbon chain is much shorter than those found in animal products. This makes MCTs behave more like an unsaturated fat, and they potentially possess some very intriguing benefits, such as a thermogenic effect, antibacterial effect, and positive effect on neurological function. These shorter MCTs are found in plant-based products like coconut oil. But, before you start looking online for MCT products, remember the research is still very young, and the potential benefits may have been over-hyped.

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Monounsaturated fats:


Have one double bond in the carbon tail (remember ‘mono’ means ‘one’). Foods which contain monounsaturated fats are usually liquid at room temperature but turn to solids when chilled. Foods high in monounsaturated fats are things like: nuts, avocado, olive oil, peanut butter. These types of fats are considered good for your health, with a well documented positive effect on cholesterol levels and reduction in risk of heart disease.

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Polyunsaturated fats:


Have more than one double bond in the carbon tail (remember, ‘poly’ means ‘many’). This type of fat can be further divided into omega-3 and omega-6 fats. The difference here is the placement of the double bonds. It is recommended to consume foods high in polyunsaturated fats. Foods high in omega-3 fats are oily fish, chia seeds, and flaxseeds. These foods have a positive effect on brain and eye health along with a protective effect on heart health. Foods high in omega-6 fats are eggs, sesame seeds, and wholegrain breads. These foods are essential for the synthesis of hormones. 

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Trans fats:


Refer to unsaturated fats with a double bond going in the opposite direction to mono- and poly-unsaturated fats. This type of fat does occur naturally in the food supply, but this is very rare! The majority of trans fat in the food supply is the result of the partial hydrogenation of oil during processing, therefore it is found in highly processed packaged foods. The hydrogenation of oil is done to increase the shelf life of products but also has a range of undesirable effects on human health. Luckily for New Zealanders trans fat is not a huge issue due to legislation surrounding food production, but remember to read the food labels if you visit the States.

How does all of this information fit into the scope of practice as a Personal Trainer?

As a personal trainer, you will find clients come to you seeking advice surrounding eating. Using this information, we can advise clients to focus on foods high in mono- and poly-unsaturated fats and limit consumption of foods high in saturated fats. In a practical sense, this would be done through promoting lean protein sources, nuts, seeds, oily fish, specific oils, and fruits and vegetables along with recommending a decrease in highly processed and refined foods.

However,  it is important to remember your scope of practice. Personal trainers can provide general guidelines for healthy eating but if a client comes seeking specific dietary advice then outsource to a qualified health professional, such as a nutritionist or dietitian. 

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