Why Do We Need Fats in Our Diet?

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We recently explored the importance of body fat. This article by Registered Nutritionist Sophie Gastman (reviewed by Registered Dietitian Maeve Hanan) will explore the importance of consuming fat in our diet.

Where Do We Find Fats In Our Diet?

Fats are found in a number of different foods. And the two main types of dietary fats are saturated and unsaturated fat. 

Saturated fats are found in: 

  • The visible fat on red meat
  • Butter
  • Cheese
  • Coconut oil
  • Palm oil
  • Products made with 

Unsaturated fats can be broken down into two further important groups: monounsaturated fats and polyunsaturated fats.

The polyunsaturated fats omega-3 and omega-6 are known as ‘essential fatty acids’ as the body can’t create these so they need to be consumed in the diet.

Monounsaturated fats can be found in:

  • Olive oil
  • Rapeseed oil
  • Avocado
  • Nuts and nut butters
  • Seeds
  • Tahini

Sources of omega-3 include:

  • Salmon
  • Sardines
  • Trout
  • Mackerel
  • Herring
  • Kippers
  • Crab
  • Seaweed
  • Soya-based foods e.g. soybean oil, tofu and tempeh
  • Rapeseed oil
  • Walnuts
  • Flaxseeds
  • Chia seeds

Sources of omega-6 include:

  • Sunflower oil
  • Safflower oil
  • Soybean oil
  • Corn oil
  • Sesame oil
  • Walnut oil
  • Products that have been made using the above oils e.g. spreads, mayonnaise, fried foods

All of these types of fat play important roles in our body, but many people in Western countries would benefit from eating more unsaturated fat as compared with saturated fat. This is due to the numerous benefits of unsaturated fats, such as improved heart health and lower inflammation levels (1). 

Fats Are A Good Source of Energy

Whilst carbohydrates may be the main energy source for our bodies, dietary fats are the most energy-efficient form of food.

Per 1 gram of fat they supply the body with 9 calories, which is more than double what is supplied by proteins and carbohydrates.

As touched on in our previous article on the importance of body fat, fats are used for a longer term energy storage compared to carbohydrates. Whilst carbohydrates are readily utilised by the body as a preferred form of energy, fats stored in adipose tissue have to first be broken down into free fatty acids and glycogen before being turned into glucose via the gluconeogenesis pathway.

This is an evolutionary mechanism we developed to cope through long periods of starvation, but it also comes in handy these days for example in endurance activities when our glycogen stores can easily become depleted. 

Absorption/Bioavailability of Fat-Soluble Vitamins

Despite having a bad rep, the fat we eat in our diet (before it gets stored away as energy in adipose tissue) is involved in a variety of important processes.

Without any fats in our diet, we would struggle to optimally absorb some of the fat-soluble vitamins, and more specifically, the carotenoids (that can act as antioxidants in our body) which are present in many vegetables (2). 

This is because many of these vitamins are found in plants and are normally contained within fibrous cell walls, making them difficult for us to absorb. However, the addition of dietary fats to a meal can help to promote their release from the plant matrix.

One small study found that the bioavailability of lycopene (found in tomatoes), is normally quite low but when consumed with fat the bioavailability increases from 6 g to 28 g (3). Bioavailability is the amount of a substance which enters the circulation when introduced into the body and so is able to have an active effect.

In addition to improving bioavailability, some dietary fats are great sources of these fat-soluble vitamins, which would be hard to obtain on a low-fat diet. For example, nuts, seeds and avocados are a great source of vitamin E, and animal foods like eggs, fatty fish and liver are a great source of vitamin A. 

Fats Are Needed For Certain Hormones

Fats also play a structural role for many important substances in the body, including hormones.

This means that inadequate dietary fat intake can have an effect on things like our fertility.

For example, studies have shown that higher intakes of PUFAs (poly-unsaturated fatty acids), particularly omega-3’s, are beneficial for enhancing female fertility (4).

It has also been noted that linoleic acid (an omega-6 PUFA), increases the release of luteinising hormone from pituitary cells, which regulates the function of the testes in men and ovaries in women (5). This is why consuming a very low-fat diet can affect both male and female fertility. For women, in particular, this can contribute to issues like hypothalamic amenorrhea*, which is a big sign of hormone imbalance (6). 

*Hypothalamic amenorrhea is the loss of a natural period as a response to stress placed on part of the brain called the hypothalamus, which connects the brain to the endocrine system. Common risk factors include: not consuming enough to fuel exercise, excess exercise, low body fat levels and high stress levels.  

Essential Fatty Acids

Most of the fats we require can be synthesised in the body, however, there are types of essential fats that the body cannot make and must be obtained from food. These are called omega-3 and omega-6 fatty acids.

Despite only making up a small proportion of our diets, these fats are needed to form cell membranes and therefore affect the function of the cell.

For example, some cell membranes, such as the retinal photoreceptors (aka the part of the eye that responds to light) are particularly enriched in omega-3’s, making up about 30% of all of the fatty acids in the membrane (7).

Brain cells and other tissues in the nervous system also contain a high level of fat, in fact, the human brain is around 60% fat (8). 

Omega-3 fatty acids are found in foods like fish, vegetable oils, nuts, and flax seeds and their benefits aren’t just limited to cell function and eye health. They can also be anti-inflammatory, promote brain health, especially in children, and may even play a role in treating depression and anxiety (9-11). 

Most of us get plenty of omega-6 fats in our diets from vegetable oils, such as sunflower oil. Omega-6 fats have been shown to lower LDL cholesterol (the ‘bad’ kind) and boost HDL cholesterol (the ‘protective’ kind) (12). But many people would benefit from adding more omega-3 fats into their diet. 

Satiety and Taste 

You may have wondered why fatty foods taste so delicious and moreish. The first reason is that fats have the ability to dissolve and concentrate flavour and odour chemicals, prolonging the release of flavours in our mouths and therefore making the food taste better (13).  

Secondly, fatty foods often have a great mouthfeel (14). For example, think about when chocolate melts on your tongue, smoothly coating it – most people would agree this is a pleasant sensation. Now think of fat-free cheese or yoghurt and it’s hard to imagine the same kind of mouthfeel. 

In the world of healthy eating, we often forget that eating what tastes good to us is also a vital component of a peaceful relationship with food. Whilst eating for optimal health is important, food is nourishment in a lot of different ways and part of healthy eating is allowing yourself to enjoy the taste and sensory experience of food as well. 

Research has also demonstrated that fat can be more satiating than other macronutrients as it slows gastric emptying. A study from 1999 found that when high-fat and low-fat soups of equal volume and energy content were ingested, the high-fat soup suppressed hunger and induced fullness, slowing gastric emptying more than the low-fat soup. It was also better at reducing intake at the test meal which was given two hours later (15).This means that adding a source of fat to your meal can actually help you feel satisfied with your meal, and will keep you fuller for longer. 

Summary

Although fats aren’t as vilified as they were in the 80s, there is still some fear and uncertainty lingering around including them in our diets. It’s important to remember how vital their role is in providing us with energy, aiding the absorption of vitamins, regulating hormones and most importantly, making food taste good.   

References

  1. Clifton, P. and Keogh, J., 2017. A systematic review of the effect of dietary saturated and polyunsaturated fat on heart disease. Nutrition, Metabolism and Cardiovascular Diseases, 27(12), pp.1060-1080.
  2. Dimitrov, N., Meyer, C., Ullrey, D., Chenoweth, W., Michelakis, A., Malone, W., Boone, C. and Fink, G., 1988. Bioavailability of beta-carotene in humans. The American Journal of Clinical Nutrition, 48(2), pp.298-304.
  3. Brown, M., Ferruzzi, M., Nguyen, M., Cooper, D., Eldridge, A., Schwartz, S. and White, W., 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.
  4. Gaskins, Audrey J.; Chavarro, Jorge E. (2017). Diet and Fertility: A Review. American Journal of Obstetrics and Gynecology. 
  5. Barb CR, Kraeling RR, Rampacek GB. 1995. Glucose and free fatty acid modulation of growth hormone and luteinizing hormone secretion by cultured porcine pituitary cells. J Anim Sci 73:1416–1423.
  6. Shufelt CL, Torbati T, Dutra E. Hypothalamic Amenorrhea and the Long-Term Health Consequences. Semin Reprod Med. 2017;35(3):256-262. doi:10.1055/s-0037-1603581
  7. Bazan, H. E., Bazan, N. G., Feeney-Burns, L., & Berman, E. R. (1990). Lipids in human lipofuscin-enriched subcellular fractions of two age populations. Comparison with rod outer segments and neural retina. Investigative ophthalmology & visual science, 31(8), 1433–1443.
  8. Chang, C. Y., Ke, D. S., & Chen, J. Y. (2009). Essential fatty acids and human brain. Acta neurologica Taiwanica, 18(4), 231–241.
  9. Kiecolt-Glaser, J., Belury, M., Andridge, R., Malarkey, W. and Glaser, R., 2011. Omega-3 supplementation lowers inflammation and anxiety in medical students: A randomized controlled trial. Brain, Behavior, and Immunity, 25(8), pp.1725-1734.
  10. Helland, I., Smith, L., Saarem, K., Saugstad, O. and Drevon, C., 2003. Maternal Supplementation With Very-Long-Chain n-3 Fatty Acids During Pregnancy and Lactation Augments Children’s IQ at 4 Years of Age. Pediatrics, 111(1), pp.e39-e44.
  11. Kiecolt-Glaser, J., Belury, M., Andridge, R., Malarkey, W. and Glaser, R., 2011. Omega-3 supplementation lowers inflammation and anxiety in medical students: A randomized controlled trial. Brain, Behavior, and Immunity, 25(8), pp.1725-1734.
  12. Demetz, E., Schroll, A., Auer, K., Heim, C., Patsch, J., Eller, P., Theurl, M., Theurl, I., Theurl, M., Seifert, M., Lener, D., Stanzl, U., Haschka, D., Asshoff, M., Dichtl, S., Nairz, M., Huber, E., Stadlinger, M., Moschen, A., Li, X., Pallweber, P., Scharnagl, H., Stojakovic, T., März, W., Kleber, M., Garlaschelli, K., Uboldi, P., Catapano, A., Stellaard, F., Rudling, M., Kuba, K., Imai, Y., Arita, M., Schuetz, J., Pramstaller, P., Tietge, U., Trauner, M., Norata, G., Claudel, T., Hicks, A., Weiss, G. and Tancevski, I., 2014. The Arachidonic Acid Metabolome Serves as a Conserved Regulator of Cholesterol Metabolism. Cell Metabolism, 20(5), pp.787-798.
  13. Montmayeur, J. and Le Coutre, J., 2010. Fat Detection: Taste, Texture, and Post Ingestive Effects (Frontiers in neuroscience). CRC Press, Chapter 11. 
  14. Kindleysides, S., Beck, K., Walsh, D., Henderson, L., Jayasinghe, S., Golding, M. and Breier, B., 2017. Fat Sensation: Fatty Acid Taste and Olfaction Sensitivity and the Link with Disinhibited Eating Behaviour. Nutrients, 9(8), p.879.
  15. Cecil, J., Francis, J. and Read, N., 1999. Comparison of the Effects of a High-Fat and High-Carbohydrate Soup Delivered Orally and Intragastrically on Gastric Emptying, Appetite, and Eating Behaviour. Physiology & Behavior, 67(2), pp.299-306.

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