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The Prediabetes Nutritionist


Dietary Fat: Functions, Requirements and Healthy Sources

Fat is likely the most feared macronutrient.

How many times have you avoided eating an avocado, adding oil to your dressings or cooking with butter or coconut oil for fear of weight gain or heart disease?

Trust me, you’re not alone!

With guidelines insisting that we avoid fat like the plague, it’s no wonder many of us constantly seek high-sugar foods to fill the void – a far worse option if you ask me.

Fat is not the bad guy.

It’s an essential component of your diet that plays a critical role in your wellbeing. This blog post can’t correct the plethora of misinformation surrounding fat, but it lays the foundation.

This article explains fat and its types, functions, how much we need, and healthy sources.

Let’s delve in!

What is fat?

Fat or fatty acids are diverse compounds made up of carbon, hydrogen, and oxygen atoms. Structurally, they appear as a long chain of carbons bonded together and flanked by hydrogen atoms.

At one end of the fat molecule (the alpha end) is an acid group. And at the other end (the omega end) is a methyl group. Depending on their chemical structure, they can be saturated, unsaturated or trans fats.

Saturated and unsaturated fat

Saturated means that all the carbon atoms in the fat molecule have no room to accept more hydrogen atoms. These fats are usually solid at room temperature and typically present in animal products, e.g., beef, chicken, and dairy. But they are also present in select plant foods like coconut and palm oils.

Saturated fats are unlikely to go rancid because of their chemical structure.

Unsaturated means that one or more of the carbon atoms in the fat molecule has room to accept more hydrogen atoms.

If only one carbon atom in the fat molecule can accept hydrogen atoms, it is called a monounsaturated fat. However, if more than one carbon atom in the fat molecule can accept hydrogen atoms, it is a polyunsaturated fat.

Unsaturated fats are usually liquid at room temperature and are typically present in vegetable oils, e.g., avocado, olive, corn, safflower and rapeseed oils. But they are also present in fish as polyunsaturated fats and in animal products, albeit in lower quantities.

Unsaturated fats are likely to oxidise and go rancid because of their chemical structure.

Trans fats are actually a type of unsaturated fatty acid. But, their chemical structures make them semi-solid at room temperature.

Trans fats such as conjugated linoleic acid occur naturally in ruminant animals like cows and sheep and appear in foods such as beef, milk, and butter. However, most trans fats are produced commercially.

Manufacturers make trans fats by adding hydrogen atoms to vegetable oils. This process transforms the liquid oils into solid fats, making them less likely to go rancid and increasing the shelf-life of the end product.

Polyunsaturated fat

Why do you need fat?

1 | Energy: Just like carbohydrates and protein, dietary fats supply energy. They are a denser energy source, providing nine calories per gram, compared with four calories per gram from protein or carbohydrates.

Your body uses a combination of carbohydrates and fats to fuel endurance exercises, but muscles rely on carbohydrates for short, intense exercise.

As the duration of exercise increases, your body relies more on fats than carbohydrates for energy. And about 50% of the energy your body uses at rest and light exercise comes from fat.

When you eat excess calories, you store them as fat in your fat tissues. Your capacity to store fat is limitless.

Each adipose cell can increase about 50 times in weight, and if the amount of fat to store exceeds the cell’s capacity, your body will create more fat cells to store fat.

2 | Structural component: Fats (phospholipids) are an important part of your cell membranes. Phospholipids participate in digestion, acting as emulsifiers. They also act as protective coverings for nerve cells.

3 | Vitamin absorption and transport: Fat is a solvent for vitamins A, D, E and K. It carries these vitamins to the small intestine, where they are absorbed. People who absorb fat poorly, such as those with cystic fibrosis, are at risk for deficiencies of the fat-soluble vitamins.

If you eat a very low-fat diet, you may be unable to efficiently absorb and utilise these vitamins, putting you at risk of deficiencies and chronic diseases.

4 | Insulation: The layer of fat just below the skin keeps you warm. Fat surrounding your organs, particularly your kidney, protects them.  

5 | Regulating body processes: Fats are necessary to make hormones, including oestrogen, testosterone, and the active form of vitamin D. The essential omega-3 fats decrease blood clotting and inflammation.

How much fat should you eat?

Obesity is a risk factor for many chronic diseases rife in society nowadays, particularly heart disease and type 2 diabetes. And weight control is one way to minimise the risk of these diseases.

After Ancel Key’s (flawed) seven-country study in the 70s, showing a link between fat intake and heart disease, UK and US dietary guidelines began promoting low-fat diets.

No recommended daily allowance for total fat intake exists for adults. However, UK and US guidelines recommend total fat intake should be no more than 35% of total daily calories, equating to 78g for those who consume 2000kcal daily.

And because of the supposed link between saturated fat and heart disease, UK (and US) guidelines controversially recommend that saturated fats constitute 10% (maximum) of your daily calories

A thorough discussion of the nuances surrounding this recommendation is beyond the scope of this blog post. I will address it in a future post but note that current research suggests the total fat and saturated fat recommendations are flawed.

Because it is a dense source of calories, many people try to limit fat intake to manage body weight. However, excess calories from any macronutrient, whether fat, carbohydrate or protein, will contribute to weight gain.

If you need to lose weight, your overall calorie intake is more important than the specific ratio of carbohydrates, fats, and protein in your diet. Moreover, a high-fat diet on its own does not cause or increase your risk of heart disease.

Instead, it’s the overall composition and quality of your diet (plus family history and other lifestyle factors) that determines your risk of heart disease.

Simply choosing low-fat versions of pastries, cookies and cakes won’t improve diet quality. You’ll likely end up eating more refined sugar and salt since food manufacturers use them to compensate for the mouthfeel and texture that fat provides.

A high sugar or carbohydrate diet may increase your triglyceride levels and lower your high-density lipoprotein (HDL) cholesterol levels, which is harmful to heart health.

What are the best and healthiest sources of fat?

The best and healthiest sources of fat are whole, unprocessed plant and animal foods. All plant and animal foods contain fat, some more (and better) than others.

Nuts (e.g. walnuts, cashews, almonds, macadamia), seeds (chia, flaxseeds, sunflower, sesame, pumpkin), olives, avocado, soya beans and coconut are good sources of whole fats.

Apart from providing fats, these foods provide fibre and other micronutrients that are beneficial to your health. However, plant fats are rich in pro-inflammatory omega-6 fats, so it is vital to eat enough anti-inflammatory omega-3 fats.

Fish is an excellent source of polyunsaturated omega-3 fats, particularly the elongated EPA and DHA types. Oily fish, particularly salmon, mackerel, sardines and herring, are excellent sources of omega-3 fats. You should aim to eat them at least three times per week.

Red meat, eggs, dairy and poultry, are sources of fat, albeit saturated fat. Although you should focus on monounsaturated and polyunsaturated fats, eating saturated fat in moderate quantities is not harmful to your health.

Your cells and tissues need saturated fat to function correctly. For example, saturated fats are a component of your nerve cell membranes and signalling proteins.

healthy sources of fat |

Tips for incorporating fats healthfully into your diet

1 | Emphasise fish, particularly oily fish such as salmon and mackerel, because they are rich in anti-inflammatory omega-3 fats. Eat fish at least twice a week to enjoy its benefits.

2 | Choose lean meat (beef, veal, pork) and skinless poultry. Loin and round cuts of meat have less total fat (and saturated fats). Trim visible fat from meat and poultry and remove the skin from poultry. Lean meat isn’t fat-free; it simply has less fat.

3 | Avoid margarine, pastries, cakes and processed foods as they are sources of trans and saturated fats. Many studies show that trans fats are harmful to heart health.

4 | Avoid deep-frying and frying in general. Instead, bake, boil, broil, steam or stir-fry foods. Heating oils to high temperatures cause them to oxidise and produce harmful compounds. Excess fat from deep frying can also increase the calorie density of meals and may put you in a calorie surplus, leading to weight gain and increasing your risk of metabolic health conditions.

5 | Eat whole fats instead of processed fats. E.g., eat coconuts instead of coconut oil, olives instead of olive oil and walnuts instead of walnut oil. Oils are protected from oxidation in the whole food, and the whole food contains other beneficial nutrients that are lost through processing.

6 | Learn to read the ingredient list on packaged processed foods before you purchase them. Avoid buying products that contain trans fats and those that are rich in refined sugars and saturated fats. A product with 5% or less total and saturated fat is low, and those with 20% or more total and saturated fats is high.

7 | Add flavour to your meals with herbs and spices instead of high-fat dips, spreads and sauces.

The bottom line is that fat is an integral part of your diet that contributes to your wellbeing.

On its own, it isn’t the cause of obesity, heart disease and other metabolic diseases. Instead, metabolic diseases and obesity are the results of excess calorie intake from unbalanced, unhealthy diets.

Include fats healthily by prioritising unsaturated fatty acids, particularly those from oily fish, nuts and seeds. Eat fats from meats, poultry, eggs and other animal foods in moderate quantities, choosing lean cuts as often as possible.

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  2. Keys, A. (1970) Coronary heart disease in seven countries. Circulation, 41, 1186-1195.
  3. Lardinois, C.K. (2020) Time for a new approach to reducing cardiovascular disease: Is limitation on saturated fat and meat consumption still justified? The American Journal of Medicine,
  4. Gershuni, V.M. (2018) Saturated fat: part of a healthy diet. Current Nutrition Reports., 7(3), 85-96.
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  6. Willet, W.C. (2002) Dietary fat plays a major role in obesity: no. Obesity Reviews, 3(2), 59-68.
  7. Nettleton, J.A., Brouwer, I.A., Geleijnse, J.M., and Hornstra, G. (2017) Saturated fat consumption and risk of coronary heart disease and ischemic stroke: A science update. Annals of Nutrition & Metabolism, 70(1), 26-33.
  8. Galli, C., and Calder, P.C. (2009) Effects of fat and fatty acid intake on inflammatory and immune responses: A critical review. Annals of Nutrition & Metabolism, 55, 123-139.
  9. Calder, P.C. (2015) Functional roles of fatty acids and their effects on human health. Journal of Parenteral and Enteral Nutrition, doi:10.1177/0148607115595980.
  10. Nettleton, J.A., Brouwer, I.A., Mensink, R.P., Diekman, C., and Hornstra, G. (2018) Fats in foods: current evidence for dietary advice. Annals of Nutrition & Metabolism, 72:248-254.
  11. Liu, Y., Poon, S., Seeman, E., Hare, D.L., Bui, M., Luliano, S. (2019) Fat from dairy foods and ‘meat’ consumed within recommended levels is associated with favourable serum cholesterol levels in institutionalised older adults. Journal of Nutritional Science, 21(8), e10.
  12. Fat and politics – Nina Teicholz on how the Seven Countries Study influenced dietary policy. Available from: Accessed: 29 March 2021.


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The Comments

  • Pamela
    April 12, 2021

    This information was really helpful because most diets call for no fat at all.

    • Somi Igbene PhD ANutr
      > Pamela
      April 13, 2021

      Hi Pamela!

      I’m so glad you found this article helpful. This is the exact reason why ‘diets’ are useless and harmful. Learning to eat a healthy, balanced diet that personalised to your unique needs and preferences is the way to go 🙂

      Thanks so much for reading.