Let's talk about FAT.
They're definitely a food group that i know confuses a lot of people, especially the types of fat and whether they have a positive or negative impact on your chances of losing weight.
Then there are some fats which you're told not to eat and others that you're told are the best thing since sliced bread, so what do you believe.
So let's clear things up for you with our definitive guide to fats!
First Of All, What Exactly Is Fat?
Structurally, fats are made from carbon, oxygen and hydrogen and vary in length of bonds depending on the type of fat.
Fats, unlike carbohydrates and proteins, are the most energy dense macro nutrient available to us because they provide a whopping 9 calories per gram, 5 more than carbs and fats which come in at 4 calories per gram.
There are three main types of fats that we obtain from the diet
- Saturated Fatty Acids
- Monounsaturated Fatty Acids
- Polyunsaturated Fatty Acids
There is also another type of fat present in the diet called a trans fat which is man made - more on this one later
Saturated fatty acids are found largely most animal products such as beef pork and lamb, alongside diary products like cream, cheese, butter, whole milk and most prepared foods like pastries, cakes and some ready meals.
Structurally, their carbon chain is saturated with hydrogen bonds with zero double bonds. This raises the melting point of saturated fatty acids compare to mono and poly unsaturated fatty acids which are broken down much easier.
So here is the part where maybe you're expecting me to tell you that saturated fatty acids are bad for you and the rest are good. Well, kind of and kind of not.
You see, for a long time it has been the view that saturated fats increase the bad (low densisty lipoproteins, LDL) cholesterol that in turn clogs your arteries and increases risk for heart attacks and strokes. Whilst too high a consumption of saturated fat does increase LDL cholesterol, surprisingly saturated fatty acids also increase the good cholesterol too, high density lipoproteins (HDL).
A meta analysis of the research conducted in 2010 by Siri-Tarino, P.W. et al (1) which included 347,747 participants with a 5-23 year follow up, found there was no significant link to conclude that saturated fatty acids were the primary course of cardiovascular disease (CVD) and coronary heart disease (CHD).
The Cochrane Database Systematic Review by Hooper et al (2015) included 15 randomized control trials with over 59,000 participants found no significant improvement of reducing saturated fat in the diet in relation to heart attacks, strokes and all cause deaths.
However, Hooper et al (2015) and Vessby et al (2001) did find that replacing saturated fatty acids with mono or n-3 polyunsaturated fatty acids did lead to improvements in cholesterol and insulin sensitivity due to the cardio protective nature of these types of fatty acids.
So whilst saturated fatty acids have historically been view as the 'bad' fat to be avoided at all costs, the literature doesn't support that view and actually, saturated fat can be included in a healthy diet.
Mono Unsaturated Fat
Mono unsaturated fatty acids are found in some animal meats, milk, nuts, avocados and olives alongside oils such as olive oil, sunflower oil, canola oil and nut oils.
The mono unsaturated fatty acid chain has one double carbon bond meaning that it has a lower melting point that saturated fats but a lower melting point than polyunsaturated fatty acids
There is plenty of evidence in the literature to show that mono unsaturated fatty acids can have a positive impact on all areas of health, especially when saturated fats and carbohydrates are replaced in the diet by mono unsaturated fatty acids whist maintaining energy balance or an energy deficit.
The presence of mono unsaturated fatty acids have been shown to reduce cholesterol levels, blood pressure, improve insulin sensitivity and inflammation, (3, 4, 5, 6, 7). Which in turn reduces the risk for heart disease and certain types of cancer (3, 4, 5, 6, 7).
Poly Unsaturated Fatty Acids
Structurally polyunsaturated fatty acid chain has more than one double bond and has the lowest melting point of all fatty acids.
Poly unsaturated fatty acids aren't like saturated fats or mono unsaturated fats in the respect that they and are considered essential and cannot be created by the body. These poly unsaturated fatty acids, Omega 3's and Omega 6's, must be provided by the diet to ensure the adequate levels needed.
Omega 3 fatty acids are found in fatty fish such as Salmon, Herring, Sardines, Mackerel and Trout.
Between to two polyunsaturated fatty acids, it is the Omega 3 fatty acid that is superstar and the benefits of this fatty acid on cognitive function and heart health are well documented in the literature. This is due to two types of acids found in Omega 3's; Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA).
van Gelder et al (2007) concluded that a moderate intake of EPA and DHA may postpone cognitive decline. Whereas, Yamagishi et al (2008) found an inverse relationship between fish and omega-3 intakes and cardiovascular mortality, especially heart failure, suggesting a protective effect against cardiovascular diseases.
Omega 6 fatty acids are found in safflower oil, grapeseed oil, soybean oil, flaxseed oil, sunflower oil, nuts, cereals, wholegrains as well as condiments such as salad dressings and mayonnaise.
Most people are consuming more than enough Omega 6 fatty acids in the diet, though an increase in Omega 3 fatty acids may be needed if you aren't eating fatty fish or supplementing with Omega 3 fish oils on a regular basis to optimise health.
It has been suggested that an imbalance in amount of Omega 6 fatty acids vs Omega 3 consumed may lead to increases in inflammatory markers associated with health decline (10, 11)
Here's where things take a little twist in our guide to fats.
Because there is another fat that we must be aware of, that potentially can have huge implications on our health and ability to lose weight and that is trans fats, in particular the man made versions.
Trans fats can actually be found naturally in some foods such as diary, beef and lamb.
But the hydrogenated trans fats are not found in foods naturally. These type of fats, through the hydrogenation process, have a chemical structure that has been altered to have hydrogen atoms on opposing sides of the carbon chain. The structure of unsaturated fats to create trans fat were altered to be used during the cooking process to extend the shelf life of foods.
Foods containing trans fats include cakes, pies, biscuits, crackers, shortening, most bakery products, margarine, most fast and deep fried foods, some frozen foods and some microwavable meals, vegetable oils.
Trans fats have been shown to significantly increase the bad cholesterol (LDL) without raising the good cholesterol (HDL) like most fatty acids do alongside impairing insulin sensitivity and blood sugar management as well as increasing markers of inflammation (12,13,14).
Because these fatty acids aren't found in foods naturally and have been chemically altered in a way that can impact physiological function and overall health, it would be a good idea to limit your intake of trans fats to the odd treat here and there.
Also, historically food manufacturers weren't required to list the presence of trans and hydrogenated fats on the food labels. Though thankfully, due to more awareness regarding their negative impact on health, some companies will display that their product is trans and hydrogenated fat free so i'd recommend checking the food labels of what you're eating to be sure.
Summing It All Up
Whilst there are clear differences between the type of fats we eat and also differences in the impact of these fats on our health, it is important to note that all types of these fats provide 9 calories per gram.
And because the body, in relation to fat storage, is able to store all these types of fats triglyceride within fat cells it is important to understand just how many calories you're actually eating from fat within your diet.
Naturally, based on what you've read so far in this article it would be remiss of me to not suggest ensuring that polyunsaturated fatty acids (in particular Omega 3 Fatty acids) and mono unsaturated fatty acids are higher than saturated fats due to their cardio protective nature and improvements on markers of health. It would also be remiss of me to not suggest keeping trans and hydrogenated fats to the bare minimum within your diets to preserve function and health.
From a caloric point of view, when setting a meal plan, my personal preference would be to recommend going no higher than 30% of your total calories from all types of fats to preserve a calorie deficit and allow you to see improvements in your body composition results.
Results like the ones below.
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1. Siri-Tarino, P.W. et al (2010). Meta-analysis of prospective cohort studies evaluating the associated of saturated fat with cardiovascular disease. American Journal Of Clinical Nutrition. Mar;91(3):535-46
2. Hooper, L. et al (2015). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Systematic Review. Jun 10;(6):CD011737
3. Garg, A. (1998) High-monounsaturated fat diets for patients with diabetes mellitus: a meta-analysis. American Journal Of Clinical Nutrition. 67 (3 Suppl):577S-582S.
4. Perez- Martinez, P. et al (2010). Dietary fat differentially influences regulatory endothelial function during the postprandial state in patients with metabolic syndrome: from the LIPGENE study. Atherosclerosis. April;209(2):533-8
5. Vessby, B. et al (2001). Substituting dietary saturated fat for monounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU study. Diabetologia. Mar;44(3):312-9
6. Appel, L. J. et al (2005). Effects of protein, monounsaturated fat and carbohydrate on blood pressure and serum lipids: results of the OmniHeart randomized trial. JAMA. Nov. 16;294(19):2455-64
7. Franceschi, S. et al (1996). Intake of macronutrients and risk of breast cancer. Lancet. May.18;347(9012):1351-6
8. van Gelder et al (2007). Fish consumption,n-3 fatty acids and subsequent 5-y cognitive decline in elderly men: The Zutphen Elderly Study. American Journal of Clinical Nutrition. Apr;85(4):1142-7
9. Yamagishi, K. et al (2008). Fish, omega-3 polyunsaturated fatty acids, and mortality from cardiovascular diseases in a nationwide community based cohort of Japanese men and women the JACC (Japan Collaborative Cohort Study for Evaluation of Cancer Risk) Study.
10. Tortosa-Caparros. E. et al (2017). Anti-inflammatory effects of omega 3 and omega 6 polyunsaturated fatty acids in cardiovascular disease and metabolic syndrome. Critical Reviews in Food Science. 2;57(16):3421-3429
11. Simopolous, A. P. (2008). The importance of the omega-6/omega-3 fatty acid ration in cardiovascular disease and other chronic diseases. Experimental Biology and Medicine. Jun;233(6):674-88
12. Hans, S. N. et al (2002). Effect of hydrogenated and saturated, relative to polyunsaturated, fat on immune and inflammatory responses of adults with moderate hypercholesterolemia. Journal of Lipid Research. Mar, 43(3):445-52
13. Hu, F. et al (2001). Diet, lifestyle and the risk of type 2 diabetus mellitus in Women. New England Journal of Medicine. 345:790-797
14. Mozaffarian, D. et al (2009). Health effects of trans-fatty acids: experimental and observational evidence. European Journal of Clinical Nutrition. 63,5-21