Healthspan July 11, 2018

From what we’re seeing, it’s become pretty clear: fats are very much ‘in’ right now.  According to the latest dietary trend research, more and more people are considering high-fat, low-carb diets. But are high-fat foods healthy or harmful, and should you be eating more of them? 

There’s no question that fat is an essential macronutrient; indeed, too little fat can lead to some a lack of some micronutrients, such as vitamin E and zinc.1

However, what’s debated is how much fat per day is ideal? And how much of it should account for your overall daily calorie intake to reap the most benefit? The only way to know is to at the science behind a high-fat diet approach and see if we can draw some conclusions.

What is a high-fat diet?

A high-fat diet is a diet that sources the majority of its calories from fat. Percentages can vary from 45-75% of calories, and even up to 90% in some ketogenic diets.2 In terms of calories, a diet is divided between the three macronutrients: protein, fat, and carbohydrates. So, if you increase fat, you will generally reduce one, or both, of the other macronutrients.

For instance, carbohydrates are reduced with most high-fat diet programmes. These are referred to as ‘high-fat, low-carbohydrate’ diets.

A higher fat intake is a key component of many popular diet trends right now, including paleo, primal, and ketogenic. Each of these has a different take on which foods to eat and exclude, as well as having a different goal. What they do all agree upon, however, is that fat is an essential part of any healthy diet.

What does the body use fat for?

Fat is an essential nutrient for the body, though some types are more essential than others. Some of the ways that fat works in your body include:

  • Absorption of fat-soluble nutrients
  • Creation of hormones
  • Structure of cell membranes
  • A major energy source
  • Blood clotting
  • Wound healing
  • Inflammation3

What are the different types of fat?

There are four main types of fat that we consume as part of a human diet. Some are considered ‘healthy’ fats, whilst some are associated with illness and present a disease risk.

Polyunsaturated fat is found in many different foods. Polyunsaturated fat is where the fatty acids omega-3, omega-6 and omega-9 are found. High omega-3 foods are considered healthy, but some experts consider high omega-6 sources to be unhealthy if not balanced appropriately.4 Fats that are polyunsaturated are usually liquid at room temperature.

Monounsaturated fats are found in plant foods such as avocado and olive oil. It is considered a healthy fat source.5 Monounsaturated fats tend to be liquid or semi-solid at room temperature. As an example, avocado is an excellent source of monounsaturated fat, but the fat is very soft when ripe.

Saturated fat is found in animal-based foods including meat, but also in coconut products. Saturated fat is highly debated, with some experts arguing it’s unhealthy, whilst others are saying there’s no evidence that it causes disease.6 At room temperature, saturated fats are solid – think of the fatty layer on a piece of meat or a block of butter.

Finally, trans-fat is found in trace amounts in some natural foods. But the majority of trans-fat is created artificially and found in processed foods such as margarine. It may come as no surprise then, that trans-fat is considered the worst type of fat. 7 It is solid at room temperature. In fact, one of the reasons why manufacturers create trans-fat is to solidify an unsaturated fat such as olive oil.

Most foods are a combination of different fat types. But they are usually classified based on which type of fat makes up the majority; this is despite them being composed of all three fat types.

Which foods are high in fat?

There are many foods that are considered high in fat. Some of the fat sources that come from natural and whole food sources include:

  • Nuts and nut butters
  • Seeds and seed butters
  • Avocado
  • Olive oil
  • Coconut oil
  • Avocado oil
  • Butter
  • Cream and sour cream
  • Cheese
  • Fatty cuts of meat
  • Oily fish
  • Egg yolks
  • Coconut cream and milk
  • Nut and seed-based flours

There are also more processed foods that are high in fat. Chips, crisps, baked goods, deep-fried foods and processed foods are generally sources of saturated and/or trans-fats.

The benefits of eating high-fat foods

It’s clear that fat is a nutrient that plays a vital role in the body. But there are other benefits that may occur when you increase your intake of high-fat foods.

Fat is required to absorb fat-soluble nutrients such as vitamins A, D, E and K from foods.8 It can also increase the absorption of some beneficial antioxidants.9 These nutrients are involved in many mechanisms, from wound healing, boosting immunities, to maintaining healthy vision.

Some higher fat diets, such as the Keto diet, instruct you to cut back on carbohydrates. This may mean a reduction in added sugars, which comes with a host of health benefits.10 When following a higher-fat diet, you may have steadier energy throughout the day due to balanced blood sugar levels. This diet approach is also associated with a reduction in triglycerides, a known risk factor for heart disease.11, 12

High-fat foods such as fatty fish and avocados are generally healthy choices. Fatty fish is an excellent source of omega-3 fatty acid, which acts as an anti-inflammatory compound. Avocados are a source of monounsaturated fat; both present quality health benefits, protecting against prevalent conditions like heart disease.13, 14

Additionally, many people are turning to higher-fat diets as a means of weight loss. Some research also supports high-fat, low-carbohydrate diets as one way to successfully lose weight.15, 16 However, some medical practitioners are still sceptical of the diet’s long-term benefits.

The downside of eating high-fat foods

One major drawback is the energy density of fat. High-fat foods contain more calories per gram than other foods. This means that it can be easy to over-consume high-fat foods and exceed your calorie needs — especially if you haven’t lowered your carbohydrate intake, too. If portions are not controlled, a high-fat diet can lead to weight gain.

There are a lot of unhealthy fat options out there. Processed foods and products such as margarine are sources of trans-fats, which can be harmful to your health, for instance by increasing risk of coronary heart disease.17, 18

Quantity can also be a factor for some people. They may experience digestive issues such as diarrhoea and bloating when they consume high-fat foods. This could be due to malabsorption or other digestive issues. High-fat foods are also low in fibre, so if care is not taken, a high-fat diet can be deficient in fibre. This can lead to digestive symptoms and may increase the risk of certain diseases.19

A high-fat, low-carbohydrate diet may not suit everyone. Some groups that may experience ill effects on high fat include women who are pregnant or breastfeeding and athletes.20 It can also be difficult to follow in combination with a vegetarian or vegan diet, as many staples of a plant-based diet are higher in carbohydrates.

Is a high-fat diet healthy?

High-fat foods can be beneficial, or they can be harmful. This depends on the type of fats consumed and the person who is eating them, due to the genes you’ve inherited. If you do choose to increase the fats in your diet, focus on the wholefood options such as nuts, seeds, and avocados, and begin cooking with olive oil. Remember that fats are very energy-dense. If you add extra fat into your diet, you may need to reduce other foods to maintain an energy balance.

If you'd like to read more about the effect of various diets on your health, as well as find more information on how you can promote good gut health, then head over to our Gut Health advice centre.


References
1. Meksawan, K., Pendergast, D. R., Leddy, J. J., et al. (2004).Effect of low and high fat diets on nutrient intakes and selected cardiovascular risk factors in sedentary men and women. Journal of the American College of Nutrition, 23(02).
2. Freeman, J.M., Kossoff, E.H. and Hartman, A.L., 2007. The ketogenic diet: one decade later. Pediatrics, 119(3), pp.535-543.
3. Harvard Medical School (2018). The truth about fats: the good, the bad, and the in-between. [online] Harvard Health.
4. Simopoulos, A.P., 2002. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomedicine & pharmacotherapy, 56(8), pp.365-379.
5. Wang, D.D., Li, Y., Chiuve, S.E., Stampfer, M.J., Manson, J.E., Rimm, E.B., Willett, W.C. and Hu, F.B., 2016. Association of specific dietary fats with total and cause-specific mortality. JAMA internal medicine, 176(8), pp.1134-1145.
6. Weinberg, S.L., 2004. The diet–heart hypothesis: a critique. Journal of the American College of Cardiology, 43(5), pp.731-733.
7. Mozaffarian, D., Aro, A. and Willett, W.C., 2009. Health effects of trans-fatty acids: experimental and observational evidence. European journal of clinical nutrition, 63(S2), p.S5.
8. National Academy of Sciences (1989). Fat-Soluble Vitamins. [online] Ncbi.nlm.nih.gov.
9. Brown, M.J., Ferruzzi, M.G., Nguyen, M.L., Cooper, D.A., Eldridge, A.L., Schwartz, S.J. and White, W.S., 2004. Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings as measured with electrochemical detection. The American journal of clinical nutrition, 80(2), pp.396-403.
10. World Health Organization, 2015. Guideline: sugars intake for adults and children. World Health Organization.
11. Boden, G., Sargrad, K., Homko, C., Mozzoli, M. and Stein, T.P., 2005. Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2 diabetes. Annals of internal medicine, 142(6), pp.403-411.
12. Phinney, S.D., Bistrian, B.R., Wolfe, R.R. and Blackburn, G.L., 1983. The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation. Metabolism, 32(8), pp.757-768.
13. Wang, L., Bordi, P.L., Fleming, J.A., Hill, A.M. and Kris‐Etherton, P.M., 2015. Effect of a moderate fat diet with and without avocados on lipoprotein particle number, size and subclasses in overweight and obese adults: a randomized, controlled trial. Journal of the American Heart Association, 4(1), p.e001355.
14. Daviglus, M., Sheeshka, J. and Murkin, E., 2002. Health benefits from eating fish. Comments on Toxicology, 8(4-6), pp.345-374.
15. Bueno, N.B., de Melo, I.S.V., de Oliveira, S.L. and da Rocha Ataide, T., 2013. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. British Journal of Nutrition, 110(7), pp.1178-1187.
16. Sackner-Bernstein, J., Kanter, D. and Kaul, S., 2015. Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis. PLoS One, 10(10), p.e0139817.
17. Weinberg, S.L., 2004. The diet–heart hypothesis: a critique. Journal of the American College of Cardiology, 43(5), pp.731-733.
18. De Souza, R. J., Mente, A., Maroleanu, A., et al. (2015). Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ, 351. [Online].
19. Yang, Y., Zhao, L.G., Wu, Q.J., Ma, X. and Xiang, Y.B., 2015. Association between dietary fiber and lower risk of all-cause mortality: a meta-analysis of cohort studies. American journal of epidemiology, 181(2), pp.83-91.
20. Phinney, S.D., 2004. Ketogenic diets and physical performance. Nutrition & metabolism, 1(1), p.2.
21. Qi, L. (2014). Gene-diet interaction and weight loss. Current Opinion in Lipidology, 25(01).
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