The primary role of fat is to store energy, however, it is needed in the body for a wide variety of other purposes such as cushioning and protecting the internal organs, shock absorption for the bones, providing insulation, regulating body temperature, as well as maintaining healthy skin and hair. The body simply cannot function properly without body fat, however, if we accumulate too much body fat, it can have a negative effect on the body. Excess body fat leads to obesity and this can cause many other health issues such as Type 2 diabetes and cardiovascular disease.
Why Do We Get Fat?
From an evolutionary perspective, storing fat gave humans an advantage because we could survive through times when food was scarce. When food was plentiful, we’d eat what we could and store any excess energy as fat. When food was scarce, we’d have the fat reserves to provide fuel. It was a case of feast and famine. These days, evolution doesn’t seem to have caught up with modern civilization, where generally speaking, food is plentiful. Getting fat these days is the result of several factors including, eating too much food, lack of exercise and also genetics to a degree. For most people, getting fat is a simple equation. Too many calories coming in and not enough going out. In other words, caloric intake exceeds caloric output. The energy equation is not balanced.
Fat as an Energy Source
Fat or more specifically, white fat in humans is composed primarily of lipids. About 85 to 90% of fat is lipids. These lipids are stored triglycerides which are the main constituents of body fat in humans. One pound of fat is 454 grams and if 90% of this is made up of lipids, we have around 400 grams of stored triglycerides. One gram of fat provides 9 calories so 400 grams provides 3,600 calories of stored energy. Our body can use fat stores as fuel and 3,500 calories of fat provides enough fuel for a 150 pound person to walk 35 miles. One pound of fat to walk 35 miles! That is a pretty good fuel source.
The Obesity Epidemic
Increasing fat stores beyond a certain point is clearly not a strategy for good health, regardless of how good a fuel source it is. This served a purpose many thousands of years ago as humans were evolving, but these days, it just means that millions of people are constantly going on diets to lose the extra pounds. Obesity is one of the biggest public health challenges of the 21st century which affects more than 500 million people worldwide and contributing to cardiovascular disease, type 2 diabetes and metabolic syndrome. Recent studies have suggested that adipose (fat) tissue obesity induces an inflammatory state that plays a pivotal role in the development of the metabolic syndrome.
This type of fat is composed of a single lipid droplet and has far less mitochondria and blood vessels, thus resulting in its lighter white or yellow appearance. White fat is the predominant form of fat in the body and has many purposes. It provides the largest energy reserve in the body. It’s a thermal insulator and cushion for our internal organs, and cushions us from the external environment. Basically, when you fall on your behind, you’ve got some cushioning to soften the blow! It is also major endocrine organ, producing one form of estrogen as well as leptin, a hormone that helps regulate appetite and hunger. It’s also got receptors for insulin, growth hormone, adrenaline, and cortisol (the stress hormone). So, all those fat cells are busy doing something and not just sat there. But if we consume too many calories and don’t expend enough calories, we get fat and beyond a certain point, it becomes unhealthy as the risks of chronic disease increase.
This fat is composed of several small lipid (fat) droplets and a large number of iron-containing mitochondria (the cell’s power-plant for burning energy). The iron, along with lots of tiny blood vessels, gives this fat its brownish appearance. Until relatively recently, it was thought there was little if any brown fat in humans that had any biological value. Research in 2009 changed this view as scientists identified and characterized the presence of brown fat in adult humans with studies that showed major depots of metabolically active fat in the cervical–supraclavicular region which is the front of the neck. There has been more recent discoveries of brown fat in adults around such vital areas as the heart, brain, and spinal cord. Further studies indicated that adult brown fat in humans responds to stimulation by the sympathetic nervous system and likely participates in both cold-induced and diet-induced thermogenesis. Essentially, the purpose of brown fat is to burn calories in order to generate heat. This stands to reason when we consider that brown fat is found around the key internal organs.
Researchers at UC Berkeley found that exposure to cold temperatures increases levels of a newly discovered protein called transcription factor Zfp516. This protein is critical for the formation of brown fat. The UC Berkeley team discovered that the Zfp516 protein activates uncoupling protein 1 (UCP1), found only in the mitochondria of brown fat and involved in the generation of heat. It was also found that with extended exposure to chilly air, transcription factor Zfp516, also helps the more abundant white fat in our bodies, become more similar to brown fat in its ability to burn energy. If we could get white fat to act more like brown fat, then this could be harnessed as a therapy for weight loss and for Type 2 diabetes.
This is the type of fat that gathers around the abdominal organs and is sometimes referred to as 'active fat' because research has shown that this type of fat plays a distinctive and potentially dangerous role affecting how our hormones function. Researchers have found that visceral fat secretes a protein called retinol-binding protein 4 (RBP4) which has been shown to increase resistance to insulin. This condition can lead to glucose intolerance and type 2 diabetes. We all have a certain amount of visceral fat, however, when it becomes excessive, the risk of cardiovascular disease and type 2 diabetes increases. Why do we store visceral fat? Research has shown that stress has a significant effect on where fat is stored in the body and that the stress hormone, cortisol, significantly increases the storage of visceral fat.
Most of the remaining non-visceral fat is found just below the skin in a region called the hypodermis. Generally, subcutaneous fat is not associated with the classic obesity-related pathologies, such as heart disease, cancer, and stroke, however, emerging research is showing that subcutaneous fat cells around the belly can be just as harmful as visceral fat cells. Like all other fat organs, subcutaneous fat is an active part of the endocrine system, secreting the hormones leptin and resistin.
Body Mass Index
Body Mass Index or BMI has been used for many years as an indication of whether a person is the right weight for their height. However, it is a flawed method because it does not take into account body fat and how it is distributed around the body. In addition, it does not tell us anything about our fat composition or the health risks. So why is it so widely used? Simply because it is easy to calculate based on only a couple of parameters; height and weight. However, if you are an athletic person and weigh more because you have more muscle, the BMI calculation could categorise you as obese! There are better ways to get an understanding of your body fat levels.
More Effective Ways to Measure Body Fat
Having an effective method for measuring is important as it gives us an indication of how much fat we are carrying and also provides the starting point for a weight loss program. Weight loss is really the wrong term here as we don’t want to just lose weight, we want lose a specific amount of body fat and keep hold of muscle. All too often, fad diets and crash diets will result in large amount of weight loss but is it really healthy weight loss? Not if you are losing a lot of muscle tissue with it.
Charting our body fat over a period time gives us a tangible way to monitor progress and when we see progress, we feel more motivated. This helps us to keep on the program, even when it is getting tough.
Fig. 1. Recommended fat levels
The recommended fat level tables above are from the American Council on Exercise and derived from World Health Organisation data. From this, we can see that for a male between the age of 30 and 40, a low body fat percentage would be between 11 and 13%. For a woman between 30 and 40, a low body fat percentage would be between 18 and 21%. Lets bear in mind that if you are very active in sports or an athlete, then your body fat levels may well be less than 10%. In the next article, we'll take a look at the various ways to measure body fat levels.
Sports & fitness nutritionist, researcher and author on a mission to improve the human condition. Focusing on evidence-based and outcome-based nutrition, training, mindset & environment