By Dr. Neerja L. Bisht, MD

Fats are essentially a form of lipids, which is a generic term given to compounds mainly found in tissues of plants and animals. Fats are the primary energy depots used for long-term energy requirements during periods of extensive exercise or during periods of inadequate food and energy intake. The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO), in their overall goal to support health and nutritional well-being of individuals and populations stated “dietary fats include all the lipids in plant and animal tissues that are eaten as food.”¹ Lipids have been defined as substances that repel water but can dissolve in fat solvents, and along with carbohydrates and proteins form part of living cells and are essential for normal body functions.

Fatty acids constitute the main components of these lipid entities and are required in human nutrition as a source of energy and for metabolic and structural activities. Fatty acids are not much used for energy production than carbohydrates, and are stored in the adipose (fat) tissue. This becomes relevant when persons consume high-fat diets with high calorie content leading to obesity. The most common dietary fatty acids have been subdivided into three broad classes:¹

• Saturated fatty acids (SFAs): Typical food sources include dairy fat, coconut, peanut, and palm oils
• Monounsaturated fatty acids (MUFAs): typical sources include most vegetable oils, olive oil, sunflower oil, safflower oil, mustard oil, rapeseed oil, and marine oils.
• Polyunsaturated fatty acids (PUFAs): The most important families, for human health and nutrition, are the n-6 and n-3 families. Typical sources for the omega (n)-6 PUFA include most vegetable oils, animal oils, animal fat, liver, fish, and evening primrose and blackcurrant oils. Typical sources for the omega (n)-3 PUFA include flaxseed, canola, soya bean, and fish (especially oily fish-salmon, herring, anchovy, smelt and mackerel) oils.

Many studies have established that SFAs have an adverse effect on blood cholesterol levels and recommendations have been made to replace SFAs with PUFAs or MUFAs in diets for optimal health.² The food industry has products that have been altered by groundbreaking animal feeding technologies to substitute MUFAs from SFAs in dairy products such as margarines. At this point, it is also important to note that studies have now indicated that low-fat products can raise sugar levels so persons with diabetes, or those keeping a check on their sugar and carbohydrate intake levels, may have to read the nutrition labels more carefully and possibly avoid such products.

Definite beneficial effects have been associated with the omega-3 PUFAs, namely eicosapentaenoic and docosahexaenoic acids (EPA and DHA). Considered as essential fatty acids (EFAs), these are present in fish-based diets and if not taken in adequate amounts can lead to:

• Risk of heart disease
• Hypertension
• Inflammatory and immune disorders: ulcerative colitis, Crohn’s disease, rheumatoid arthritis
• Depression
• Neurological dysfunction

Increasingly, many dairy and other food products such as eggs and meats are enhanced with EPA and DHA though innovative animal feeding technologies, so that an optimum amount is available in the body upon consumption of these products. In addition, supplemental oils and capsules provide an alternative route to taking recommended amounts of EPA and DHA.

On the other hand, diets high in n-6 PUFAs, a feature of many western diets, contributes adversely to health and lead to:³

• Decreased bleeding times
• Atherosclerosis (hardening of blood vessels)
• Type 2 diabetes
• Heart attack
• High cholesterol levels
• Obesity

Other EFAs include linoleic, linolenic, and arachidonic acids, collectively termed vitamin F. These PUFAs cannot ordinarily be synthesized in the body. Lack of dietary n-6 polyunsaturated fatty acids is characterized by rough and scaly skin, dermatitis, Linoleic acid is necessary for the synthesis of the n-6 series of PUFAs and prostaglandins. Prostaglandins are hormone-like substances, have various effects on smooth muscle and inflammatory processes and can play a role in cardiovascular disease⁴ and even cancer⁵. Safflower, sunflower and corn oils are high in linoleic acid, as are as are other vegetable oils, nuts, and seeds. Alpha linolenic acid is the precursor of the bioactive omega-3 PUFAs, EPA and DHA and soya bean, flaxseed, canola, as well as pumpkin and walnut are the best food sources. Due to the effects of these EFAs on the human body, a diet that has an optimal intakes of the n-6 : n-3 ratio of 1–4 has been recommended.⁶ It is the imbalance in this ratio in dietary patterns that adversely affects health that has been highlighted in the preceding paragraphs. Consuming higher quantities of n-3 PUFAs can reverse high n-6:n-3 ratios. A recent study⁷ conducted on a small group of normal healthy volunteers found that the oral supplementation with 1.6 g/d of EPA and 1.2 g/d of DHA at the end of 4 weeks was associated with higher blood concentrations of n-3 PUFAs and lower n-6:n-3 ratios.

Then, what are trans fatty acids?

Trans fatty acids (TFAs) became a subject of interest when it was observed that foods high in TFAs led to coronary heart disease. TFAs are found in butter, oils, and spreads that are commonly used in diets all across the globe. Typical food sources include biscuits, pies, many red meats, and deep fried fast foods. Although the food industry has taken notice and altered the amount of TFAs, persons consuming a diet rich in TFAs run a risk for increase in blood cholesterol levels ultimately leading to heart disease.

WHO/FAO recommendations of fats and fatty acids intakes

The following recommendations for adults have been based on scientific evidence. For optimal health, overall dietary patterns, energy intakes, age groups, BMI (body mass index) and lifestyle must also be taken into consideration.¹

Minimum total fat intakes for adults (energy from fat (i.e. %E fat)

• 15%E to ensure adequate consumption of total energy, essential fatty acids, and fat soluble vitamins for most individuals.
• 20%E for women of reproductive age and adults with BMI <18.5, especially in developing countries in which dietary fat may be important to achieve adequate energy intake in malnourished populations.

Maximum total fat intakes for adults

• 30–35%E for most individuals.

SFA

• SFA should be replaced with PUFA (n-3 and n-6) in the diet and the total intake of SFA not to exceed 10%E.

MUFA

• MUFA is calculated by difference,(refer to the values given above and below)

i.e. MUFA = Total fat intake (%E )– SFA (E%) – PUFA (E%) – TFA (%E)

PUFA

• Acceptable range for total PUFA (n-6 and n-3 fatty acids) can range between 6 and 11%E. The adequate intake to prevent deficiency is 2.5–3.5%E
• Recommended range for PUFA is 6–11%E
• EPA + DHA consumption is set at 2 g/day
• Estimated average requirement for linoleic acid is 2%E and an adequate intake of 2–3% E
• Arachidonic acid is not essential for a healthy adult whose habitual diet provides linoleic acid > 2.5%E

Trans fats

• Current recommendation of a mean population intake of TFA of less than 1%E

Based on the above reference values, dietary reference values that are easy to understand have been translated to dietary reference intakes, or DRIs. DRIs are now the standard for assessing clinical deficiencies of vitamins, minerals, protein, and energy (calories) and the development of chronic diseases. The use of DRI also includes substances in foods, such as fats and fatty acids. Different populations may present with a slightly altered DRI because of a different dietary pattern and requirement. However, there is convincing evidence that even the slightest intake of SFAs leads to high cholesterol levels, obesity and heart disease. Hence no RDI exists for SFAs.

The Food and Nutrition board from the Institute of Medicine (IOM) provided information for Americans and Canadians on the interpretation and uses of DRI.⁸ The report detailed the following recommended dietary allowances (RDA) and adequate intake (AI) and tolerable upper intake level (UL) for optimal health, an increase of which could potentially cause adverse health outcomes in adults:

• Total fat: No AI, RDA, or UL because of insufficient data to determine a defined level of fat intake at which risk of inadequacy or prevention of chronic disease occurs, however fat is a major source of energy for the body and an Acceptable Macronutrient Distribution Range (AMDR), has been estimated at 20 to 35 percent of energy
• SFAs and Trans fats: No AI, RDA, or UL because of insufficient data to determine a defined level of fat intake at which risk of inadequacy or prevention of coronary heart disease. A diet as low as possible in SFAs is recommended
• Omega (n)-6 PUFA (linoleic acid): The AI is 17 g/d for young men and 12 g/d for young women
• Omega (n)-3PUFA (α-linolenic acid: The AI is 1.6 and 1.1 g/d for men and women

In conclusion, fats are a major source of fuel energy for the body and aid in the absorption of fat-soluble vitamins. Consumption of fat and fatty acids are important maintaining optimal health as long as they are available to the body in adequate amounts.

References

1. Fats and fatty acids in human nutrition. Report of an expert consultation. FAO Food and Nutrition paper. 91.2010. (pdf).
2. Williams C. Dietary fatty acids and human health. Annales de zootechnie, 2000, 49 (3), pp.165-180. <10.1051/animres:2000116>. <hal-00889890>
3. Simopoulos AP. Essential fatty acids in health and chronic disease. Am J Clin Nutr. 1999 Sep;70(3 Suppl):560S-569S.
4. Ricciotti and Fitzgerald. Prostaglandins and inflammation. Arterioscler Thromb Vasc Biol. 2011 May; 31(5): 986–1000. doi: 10.1161/ATVBAHA.110.207449
5. Wang and Dubois. Pro-inflammatory prostaglandins and progression of colorectal cancer. Cancer Lett. 2008 Aug 28; 267(2): 197–203.
6. E. Patterson, R. Wall, G. F. Fitzgerald, R. P. Ross, and C. Stanton, “Health Implications of High Dietary Omega-6 Polyunsaturated Fatty Acids,” Journal of Nutrition and Metabolism, vol. 2012, Article ID 539426, 16 pages, 2012. doi:10.1155/2012/539426.
7. McDaniel J, Ickes E, Holloman C. Beneficial n-3 polyunsaturated fatty acid levels and n6:n3 ratios after 4-week EPA + DHA supplementation associated with reduced CRP: A pilot study in healthy young adults. Modern Research in Inflammation 2013; (2):59-68. http://dx.doi.org/10.4236/mri.2013.24008.