In food and nutrition “fat” or “fats” have various meanings:
- Fat is a food nutrient.
- Fats is a food group.
- Fat is a component in the blood.
- Fat is a description of body size.
- Fat is a body tissue.
Confusingly, some writers mix these terminologies up. Even more confusingly, these various meanings of fat can be described by different words and in various ways.
“Fat“ is a macro-nutrient in foods. The macro-nutrients are protein, carbohydrate, fat and (in adults) alcohol. Once digested and absorbed, macro-nutrients provide energy (kilojoules/ calories) to the body for use in various bodily processes. Fat has other functions in the body including cell membrane structure and transport of fat-soluble vitamins. Fats in food can be referred to as “lipids” where lipids are organic substances insoluble in water and soluble in organic solvents. Technically though, food-fats are a sub-class of lipids known as triglycerides. Triglycerides have a glycerol backbone with three fatty acids attached. The fatty acids can be saturated, monounsaturated or polyunsaturated. Food lipids include triglycerides, phospholipids and cholesterol. (1)
“Fats” as a food group includes solid fats (butter/ margarine) and liquid oils. This food group contain foods that are comprised almost entirely of fat (the macro-nutrient) with only tiny amounts of protein or carbohydrate (or none), and hardly any vitamins or minerals unless fortified. They are not whole-foods but rather extracted fats from whole foods; such as butter from milk, or olive oil from olives. They are generally not eaten as foods on their own but rather added to foods or used in cooking.
In the 1970s/ 1980s fats was one of the five food groups in Australia. Back then the five food groups were bread and cereals; vegetables and fruit; meat and alternatives; milk & milk products; and fats (butter or table margarine) (2). In the 1990s the five food groups had a major change and became bread & cereals; fruit group; vegetables, legumes; meat, fish, poultry, eggs, nuts, legumes; and (v) milk, yoghurt, cheese. At that time, it was considered nutrients in fats such as Vitamin A could be obtained from other foods, and fats as a separate food group was unnecessary (3).
The most recent (2013) Australian Dietary Guidelines do not include fats as a nutritious food group. However, it considers foods with mainly unsaturated fats (spreads, oils, nuts, seeds, nut butters, avocado) may have ‘health benefits’ (4). The Dietary Guidelines for Americans similarly do not consider fats as a food group but includes monounsaturated and polyunsaturated oils (canola, corn, olive, peanut, safflower, soybean, sunflower) or whole-foods high in these fatty acids (nuts, seeds, seafood, olives, avocados) can form part of a healthy eating pattern (5). Thus, these more recent guidelines group some fatty whole-foods with liquid oils and do not simply group extracted fats.
Both these guidelines, as do many around the world, recommend dietary patterns lower in saturated fat.
“Blood fats” are generally referred to as “blood lipids”. They move along in the aqueous environment of the blood attached to proteins as “lipoproteins”. It is postulated some lipoproteins may increase risk and others protect against risk of diseases such as heart disease and Type 2 diabetes. The various lipoproteins doctors test for are described here.
“Fat” as a description for body size is considered offensive and stigmatizing. I agree and therefore will not discuss it further in this post.
“Fat” is a name for body tissue. There are three main types. Essential fat is required in small amounts in the bone marrow, vital organs, muscles and nervous system; as well as structural components of cell membranes. Storage fat (known as adipose tissue) generally accumulates sub-subcutaneously (under the skin). Ectopic fat accumulates in cells of non-adipose tissue that normally only have small amounts of fat. Accumulation occurs viscerally (around the abdomen) and also may deposit in or around vital organs including muscles, liver, pancreas, and the heart. This distinction in body fat accumulation is critical as abdominal fat and ectopic fat are considered risk factors for non-communicable diseases such as type 2 diabetes. Sub-cutaneous fat does not bear the same risk. In fact the definition of “obesity“ by the World Health Organisation is when body fat has accumulated to the extent of having an adverse effect on health. Although body-weight is used as a guide on a population basis (6); for an individual, body-fat distribution is an important consideration. Some people of lower body weight can be at risk of disease (and therefore technically ‘obese’) if they have a tendency to accumulate fat around the abdomen or ectopically. A good guide is waist circumference. Recommendations for Australian adults can be found here.
A more complex aspect is how food-fats relate to blood-fats … or body-fat … or disease risk … and why was there been a change in food-group categorization where fats fell out of favour and have now come back (albeit in recommendations for oils, fatty fish and nuts)? Most importantly, what consideration do these have for an an individual? I will address these questions in a future post.
Disclaimer: Nothing in this article or on this website should be taken as medical or dietary advice. Anyone reading any information provided within should seek advice from their own medical practitioner for any issue, disease, illness or health-related problem they may have. Always seek your own advice from a medical practitioner or dietitian before changing your own diet.
(1) E Whitney, S R Rolfes, T Crowe, D Cameron-Smith, A Walsh. Understanding Nutrition. Australia and New Zealand Edition. 2nd Edition. Cengate Learning. 2014.
(2) Food For Health. National Food Authority. Commonwealth of Australia. 1991
(3) The Australian Guide to Healthy Eating. Background information for nutrition educators. Commonwealth of Australia. September 1998.
(4) National Health and Medical Research Council. Eat For Health: Australian Dietary Guidelines Summary. Canberra: National Health and Medical Research Council, 2013.
(5) Dietary Guidelines for Americans 2015-2020, 8th edition. US Department of Health and Human Services and US Department of Agriculture. December 2015.Available at https://health.gov/dietaryguidelines/2015/resources/2015-2020_Dietary_Guidelines.pdf
(6) Defining Adult Overweight and Obesity. Centers for Disease Control and Prevention. June 16, 2016. Retrieved 21 November, 2018.