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Fat lies and thin truths - is this how Joe Public understands the health implications of fat in his diet?

Eggs and a tape mesaure

11 Sep 2015

You will commonly hear the statement 'You are what you eat'. It is perhaps, therefore, not surprising that most of the population are under the false impression that dietary consumption of fats, particularly animal fats, will lead to accumulation of fat on their bodies and in their arteries with the obvious negative effects on their cardiovascular health. Fats are an essential part of the diet and provide much more than just energy. Metabolites derived from fats are critical for the smooth operation of our bodies.

Government bodies around the world have urged us to reduce our fat intake, and particularly our saturated fat intake, but the incidences of obesity, type 2 diabetes and metabolic syndrome have continued to rise inexorably. One important contribution to this has been the development of 'Low fat' or 'No fat' ranges of processed foods which in fact have a higher calorific content than their full fat alternatives. They also have a high content of refined sugars. Ironically, it is fructose, rather than dietary fat, that is the human body’s fuel of choice to build its visceral adipose deposits!

Trans fats were developed to preserve and harden natural, unsaturated oils and fats such as fish and vegetable oils using a process called hydrogenation. The problem is that fat molecules were created that do not occur naturally; hence it not surprising that our bodies have difficulty in coping with them. We now have strong scientific evidence of the association of trans fats intake with cardiovascular disease and other serious diseases.

Until recently, epidemiological data on health outcomes in regard to fat intake lumped trans fats and saturated fats together. This has led to the demonization of many natural, animal fat based foods, particularly processed dairy and meat products. Whilst some individual saturated fatty acids can be shown to reduce the flexibility of major blood vessels following consumption compared with most unsaturated fatty acids, it must be remembered we do not consume pure forms of single fatty acids and that cardiovascular health can only be determined by using a big basket of scientific measurements (biomarkers). Over the last few years, there have been a steady stream of academic papers challenging the conventional wisdom that saturated fat intake was bad for your cardiovascular health. This work has been very well summarised in a very recent meta-analysis in the British Medical Journal by De Souza et al. (1). The key findings of this study reveal that trans fats, but NOT saturated fats, are significantly associated with all-cause mortality. Interestingly, ruminant/dairy trans-palmitoleic acid was found to be inversely associated with type 2 diabetes.

Manufacturers of industrial food fats have almost entirely ceased production of hydrogenated, artificial trans fats. However, as the demand for high melting, hard textured fats is still high, they use an alternative process of fat modification called chemical or enzymatic inter-esterification. As with the process of hydrogenation, this type of esterification creates fats that are not found in nature. As such, there must be some concerns regarding the long term health consequences of using this process, even though to date it has a clean bill of health.

Replacement on a like for like calorie basis of refined carbohydrates with lipids appears to be beneficial to heart health, particularly if those lipids are unsaturated. The global agri-business giants, supported by government health advice, have thus been keen to champion greatly increased intakes of vegetable oils containing polyunsatured fatty acids (PUFAs), particularly soya, corn, sunflower, cotton seed and rape seed oils. The result has been a many fold increase of intake of PUFAs over the last hundred years. Some commentators says this has been a major factor in the reduction of heart disease, but it is more likely this has been due to a wide range of other factors such as reductions in smoking, infections and stress, and increase in pharmacological interventions.

In fact, excess PUFA intake may be deleterious to health because it can upset the natural lipid balance in our bodies. Most vegetable oils are rich in omega 6 fatty acids. A high intake can upset the balance of omega 6 fatty acids and omega 3 fatty acids in our cells, particularly our cell membranes. It is the long-chain omega 3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), derived only from marine oils, that are the source of many metabolites that are essential for health maintenance. EPA and DHA help prevent inflammation, the key factor in so many diseases. DHA is present in all the key organs of the body, particularly the brain, nervous system, heart and testes! DHA ensures the flexibility and plasticity of cell walls - which in turn allow chemical and electronic inter-cell communication. The consumption of oily fish, the main source of marine omega 3 fatty acids in the diet, continues to fall. In the UK, the average intake of EPA and DHA is around 200 mg/day, which sounds quite reasonable when the European Food Safety Authority (EFSA) recommends an intake of 250 mg for maintenance of basic heart, brain and eye health. However, this figure is misleading when you consider that the median intake is much closer to just 30mg a day. This is because a small minority of the population enjoy a regular intake of oily fish with concomitant sky high EPA/DHA levels in their blood whilst the great majority eat little or no oily fish. In certain circumstances, the body can make its own EPA and DHA (as can be seen in some vegans and vegetarians), but this only happens if the intake of omega 6 fatty acids is extremely low. Again, the balance of fatty acids is really important here!

Fat is an important and enjoyable part of our diet. It provides flavour and texture to foods. It is a carrier of the essential fat-soluble vitamins A, D, E and K. Yes, fat is a major source of calories, but it is so much more. Isn’t it time you looked a bit more carefully at this macronutrient?

The SCI Lipids group is holding a 2 day conference on current controversies with regards to dietary lipid intake entitled: “Lipids and Health: Risk, Reward and Revelation” at the SCI HQ in Belgravia, London.

Reference:

De Souza, R. J., Mente, A., Maroleanu, A., Cozma, A. I., Ha, V., Kishibe, T., Anand, S. S. (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, h3978. http://doi.org/10.1136/bmj.h3978

Dr Rob Winwood,
SCI Lipids Committee

Disclosure of interest: The author is an employee of DSM Nutritional Products and chair of the scientific committee of trade organisation GOED. He also enjoys a full English breakfast when he can! The opinions expressed in this article are entirely his own.

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