Fat comes in many forms. From what is inside of us, to the fat we eat, it has the conflicting image of both an essential macronutrient, and a hinderance to the body’s health. For the most part though, the latter view has seen fat develop an image problem, and as something to avoid at all costs. Yet fat does serve a significant purpose, and knowing what this constitutes can help provide a more balanced view.
In simple terms, fat can be divided into what we ingest, dietary fat, and body fat, the fat that is stored within us. Both dietary and bodily fat come in many forms, and each has a role to play.
Good and bad roles of fat
In its bodily form, fat is a concentrated source of energy, used as a back up for when carbohydrates are not available. It is one of three macronutrients needed by the body for growth, energy provision and other bodily functions. The other two are carbohydrates and protein, yet these each contain only 4 calories per gram, compared to 9 calories per gram in fat.
Body fat, is known by the scientific term ‘lipid’. As an insulator of the body, ‘adipose tissue’ stores these lipids, which help to maintain core body temperature. The adipose tissue serves another function, to produce protein hormones, that have an influence on energy metabolism. This function may prove to be part of a strategy in the treatment of metabolic diseases such as obesity and type 2 diabetes.
Body fat also surrounds and protects vital organs such as the heart, from sudden movements or external forces. It is now common knowledge however that once these fats are stored in excess, the likelihood of illness increases, such as heart disease or inflammation of osteoarthritis . Therefore to keep fat at a level that provides just what the body needs, careful consideration of fat sources external to the body, is essential.
Fat in its dietary form is an essential part of any diet, providing aroma and texture, but also helping to metabolise certain nutrients. For example fat soluble vitamins A, E, K and D are better absorbed when consumed with fat. So the nutrients in a salad can be better absorbed by the body, when consumed with the monounsaturated fat of olive oil.
Fat also helps us feel satisfied after a meal for longer, because it takes longer to digest than carbohydrates or protein. It also makes baked food more tender, and helps heat transfer in cooking. The trick however is knowing where and what types of fat are in food, the correct quantity of each to consume and which ones will benefit the body most.
Sources of fat in food
Fats in food are built of many different fatty acids, but can be divided more simply into predominately saturated or unsaturated fats. These can be further divided into four categories of fats, from the healthier monounsaturated and polyunsaturated containing omega-3 and omega-6 fatty acids, through to less healthy saturated fats and unhealthy trans fats. To illustrate this spectrum of fats, food oils are a great example, as they are something consumed every day. Note that all food oils contain these polyunsaturated, monounsaturated, and saturated fatty acids, but in varying amounts, as seen in the chart below.
At the healthy end of this fatty acid spectrum are monounsaturated fats, with extra virgin olive oil and good quality canola oil having a high content. The polyunsaturated group is made up of omega-3 and omega-6 fatty acids, that can be sourced in healthy amounts from walnut oil and fish oil.
Somewhere in-between these healthier fats and the one to avoid, is saturated fat, with greater proportions found in oils such as palm and coconut. Simply put, animal fats, like lard and butter, are saturated fats which remain solid at room temperature, rather than a liquid like unsaturated plant based oils. The health qualities of these saturated oils are currently being debated, as small amounts can have the benefit of providing a range of quality nutrients.
Finally trans fats are the one to avoid. In small amounts they occur naturally in dairy and meat products, but for the most part this type is manufactured by adding hydrogen to unsaturated fats. This process increases the shelf life of the oil, as well the amount of times it can be reused before breaking down. It also turns the oil from a liquid into a solid for easier transportation, which is cheaper than using animal fat for the same purpose.
This is good news for food producers, but not so for the end user as these fats raise bad (LDL) cholesterol levels and lower good (HDL) cholesterol levels. Pies, cakes, biscuits, chips, margarine and fast or fried food, are the usual suspects when identifying trans fats in food.
The World Health Organisation recommends that trans fats make up no more than 1% of a person’s diet, saturated fat less than 10%, and that ideally they are both replaced with unsaturated fats, with total fats intake being less than 30% of a persons total energy intake.
It is also worth noting that regardless of whether food that is consumed is made up of carbohydrates, protein or fat, whatever is not used by the body, will be stored by the body as fat. So someone who wishes to increase their muscle mass for example, can each as much protein as they like, but ultimately the body can only utilise so much and any excess calories will stored for another day.
Fats within the body
From a dietary perspective we can make many decisions about what fats to eat. The body however treats fat molecules as just another nutrient. Once digested by the gut, they are absorbed via the small intestine and made soluble so as to travel via the bloodstream. These are then taken up by muscles and other parts of the body for fuel, with any excess stored within the body’s adipose tissue for later use.
There are two main types of storage of adipose tissue, ‘visceral’ that surrounds the internal organs and ‘subcutaneous’ that is beneath the skin. So subcutaneous fat is what we can grab or pinch, and in excess can lead to health issues including cardiovascular disease, Type 2 diabetes, musculoskeletal conditions and some cancers. Visceral fat in contrast in stored deep in the body, so even if someone is thin, poor health and diet may mean that they are carrying this fat in excess. High amounts of visceral fat can lead to high blood pressure and high blood sugar levels, which in turn increases the risk of heart disease, stroke and diabetes.
There are two main types of body fat, brown and white. Brown generates body heat through burning calories, while white stores energy. All fats cells contain a nucleus, fat droplets and mitochondria. These mitochondria play a key role in energy metabolism, with white cells only having a few, and a greater amount are in found in beige fat, with even more in brown.
This increased ability of energy metabolism in brown fat allows it to burn calories, and as result it has been of great interest for future treatment of obesity and diabetes. There is also a current focus on beige fat, where ‘brown like’ fat cells develop in white fat due to various activators, such as exercise. Once again this type of fat has the potential to help with weight management, as beige fat stores the energy that would otherwise be stored just as white fat.
Brown fat is more abundant in babies so as to keep them warm, but is reduced within the first few years once they gain the ability to shiver to generate heat. Some brown fat is still retained in the neck, shoulders and throughout the torso after this point, with its thermal qualities being activated by cold temperature.
Whereas brown fat burns calories in order to generate heat, white fat stores calories. White fat cells store this energy as a single, large fat droplet, providing its thermal insulation properties. The transition of these fat cells from white, to beige and then to brown, sees a single fat droplet change to many smaller ones, more specialised for burning in the production of heat.
Yet whatever colour fat cells are, the total number within the body remains the same throughout one’s adult life. So losing or gaining weight affects the amount of fat stored within these cells, rather than the number of cells. What constitutes a ‘healthy’ amount of body fat is roughly 20% for men and 25% for women, yet it is expected that everyone’s fat percentage will increase with age.
Taking stock of body fat
Distribution of fat varies from one person to another. In general women collect fat through the buttocks and thighs, whist in men it is around the abdomen, and there are many ways in which to measure its total percentage within the body.
Measuring a skin fold is one that is commonly used. This method although fairly accurate, is best conducted with multiple readings over a period of time by someone skilled and experienced in taking such measurements. Once read, these measurements can be compared to a chart that takes into account the age and gender when estimating the body fat percentage. It is also important that the same fat fold site is used every time and that the emphasis is on the change in reading, rather than the accuracy of the readings themselves.
For those requiring the most accurate reading of body fat, a Dual Energy X-ray Absorptiometry or DEXA scan is the gold standard. Although expensive and less accessible compared to body calliper measurements, the scan uses low dose x-rays to identify the distribution of body fat and divide the body into total body mineral, fat tissue mass and lean mass.
Bathroom scales now have a common feature known as Bioelectric Impedance Analysis or BIA which uses the opposition of electrical current through the body to measure both body fat percentage and fat free body mass. As muscle has a higher water content compared to fat, their levels of conductive resistance vary and so the analysis can be calculated in conjunction with a persons height and weight. The level of a persons hydration can vary the results of these readouts, and the accuracy of this technology is argued, especially in relation to devices where the signal is sent from only one source such as foot scales or hand held devices.
Beyond these methods there is a simple, inexpensive and less invasive way in which to estimate body fat. It involves measuring the circumference of the waist, and then comparing this measurement to either the circumference of the hips of to a persons overall height. These ‘waist-to-hip’ and ‘waist-to height’ ratios also have merit in that they can flag the potential of developing heart disease.
For males, the World Health Organisation (WHO) suggests having less than a 0.9 waist-to-hip ratio and for women a slightly lower ratio of 0.85. So if a man had a waist of 86cm his hips should measure under 77.5cm whereas a woman should be under 73cm, for them both to have a healthy ratio. As for the waist to height ratio, 0.5 is healthy, in other words the waist circumference is half one’s height.
So long as the tape measure used is placed in the correct location for readings, this data will provide a useful estimation as to whether the body is carrying excess fat. To find the point from which to take a waist circumference, take the mid point between the lowest rib and the Iliac crest – which is the top most part or ‘wing’ of the pelvis. Measurements should be taken so that the tape is snug but not pressing into the waist, and is measured at the point of expiration, when the diaphragm is in its neutral position.
Of course it is one thing to know how much body the fat is carrying, but quite another when it comes to getting it to budge.
Burning body fat
For some time now there has been discussion of a ‘fat burring zone’, suggesting that the level of intensity of a workout will determine whether fat calories or glycogen calories are burned. This is based on how the body uses energy during exercise, as energy can be taken either from fat or glycogen stores. Fat is the long term storage for the body, whereas glycogen is a readily available form of glucose, stored as carbohydrates in the muscles and liver.
Other sources talk of cutting carbohydrates to prompt the body into a state of ‘ketosis’. This is where the body, deprived of an energy source such as the glucose from carbohydrates, starts converting fat stores into ketones to use as fuel for cells. Although a normal metabolic process, the ‘ketogenic’ diet sees the process of ketosis encouraged through the eating of a healthy amount of fats and protein, whilst keeping carbohydrates to a minimum. Seen by some as a form of starvation, the argument is that there is nothing to fear as long as the calorie intake is sufficient and that what is consumed is nutrient dense, in other words plenty of healthy food.
Taken further, the methods used to burn body fat can even encompass the properties of the foods we eat. Tomato juice and turmeric are said to reduce inflammation and consequently effect fat cells. Tamarind, via its supposed influence on serotonin levels, is offered as an appetite suppressant, with this hunger dampening qualities also being attributed to chia seeds and the king of vegetables, kale. Kale is also said to be good for clearing toxins from the body that would otherwise make it harder for the body to shed fat. Avocado and brazil nuts are promoted as boosting the body’s metabolism, with black coffee rating a mention for stimulating adrenaline.
Weight is something that a lot of us battle with, yet the truth about keeping fat under control can be found in this simple mantra for healthy living;
Eat whole fresh food. Not too much. Mostly plants.