This article was written by Registered Nutritionist and Dietetically Speaking intern Sophie Gastman and reviewed by Registered Dietitian Maeve Hanan.

Although body fat has a negative reputation, thanks to diet culture, it plays a number of vital roles when it comes to our health.

Body Fat 101

Fat, also known more scientifically as adipose tissue, has many important functions in the body beyond just contributing to our body shape such as energy storage, temperature regulation and hormone function to name a few.

First, let’s break down what fat actually is. 

Adipose tissue is stored all over our body and it can be found just underneath the skin or surrounding our internal organs. 

The fat underneath the skin that you can visibly see or physically pinch is called subcutaneous fat, whereas the fat packed around our organs is termed visceral fat (1). 

The only way to find out how much visceral fat you store is from an MRI or a CT scan, but waist circumference can also be used as an indicator (please note: we don’t recommend checking your waist circumference if you are recovering from disordered eating or working on improving your body image) (2). 

Breaking it down further, adipose tissue is made up of different types of fat cells – two of them being white and brown cells. White fat makes up the majority of fat in adults and is used for energy storage.

Brown fat on the other hand, is used for expending energy and heat production (3). This type of fat helps newborns regulate their body temperature and it is believed that the amount of brown fat decreases with age (4). 

Body Fat and Energy Storage 

The excess energy from the food we eat gets stored in adipocytes (fat cells). Whilst this may sound like a bad thing if you’ve been subject to the brainwashing effects of diet culture, without this ability to store energy as fat, it’s unlikely humans would have survived this long.

Being able to release energy from fat stores is a way our bodies have adapted to survive, for example, in periods of food insecurity or long-term illness. 

You may be wondering why we can’t rely on the energy we store from carbohydrates instead, which is stored in the form of glycogen. The main reason for this is that the amount of glycogen our body can store is limited, whereas our fat storage capacity is virtually infinite. This is because glycogen is a lot bulkier than fat as each gram of glycogen is stored with at least 3g water (5).

Fat, on the other hand, can pack tightly together without water so more energy can be stored in less space. In addition to this, fat is much more energy-dense, providing more than double the amount of energy per gram than carbohydrates (9 kcal vs. 4 kcal). 

Temperature Regulation and Organ Protection

Another major role of body fat is temperature regulation and insulation. The subcutaneous layer of fat forms an insulating barrier around the body, protecting the body from extreme temperatures by regulating heat loss (6).

This subcutaneous layer is also what protects and cushions our body from hard surfaces.

The role of visceral fat is to protect vital organs, such as the heart and liver. 

Whilst our white fat cells work to insulate, brown fat cells can actually create heat and help the body maintain its temperature by oxidising fatty acids within the cell (7).

As mentioned before, it was originally thought that only babies had brown fat and that we lose it as we age, however, researchers have now discovered that adults have small amounts of brown fat too, mainly around the shoulders and the neck (8). 

Body Fat and Hormone Regulation

A less commonly known function of body fat is that it plays a really important role in hormone regulation.

Our adipose tissue contains a number of cells that not only secrete certain hormones and proteins, but can also respond to signals from other hormones.

This means that adipose tissue is a key player in regulating a variety of processes including, energy metabolism, immune function and neuroendocrine function (9). 

For example, adipose tissue secretes the hormone leptin (the satiety or fullness hormone), which signals to the brain about body fat stores and regulates appetite. So when fat levels are too low this can lead to feeling hungry a lot of the time. 

Fat tissue also secretes a hormone called interleukin-6 (IL-6), which is involved in regulating fats and glucose in the body (10). 

On top of this, adipose tissue is an important site for metabolising and secreting sex steroids, making it necessary for optimal reproductive health (11).

So having too little body fat can reduce levels of sex hormones, such as oestrogen in women.

Studies have shown that a female must have at least 17% body fat before menstruation can occur and at least 22% body fat to maintain regular menstrual cycles after the age of 18 (12). The level of body fat needed for female fertility can also vary between different people. For example, 26 – 28% body fat has been seen to promote regular ovulatory cycles (12). 

Low levels of oestrogen can also lead to other health issues such as weakened bones, low muscle mass and worsened heart health (13, 14).  

Storage of Fat-Soluble Vitamins

Fat-soluble vitamins (A, D, E & K), which are important for a variety of functions including eye health, protecting cells from damage and helping wounds heal, are absorbed during digestion. After this, any fat-soluble vitamins that aren’t needed are stored in adipose tissue for later use.

The role of adipose tissue in the storage of these vitamins means we don’t need to consume large amounts of these vitamins on a daily basis as they are not excreted out of our system in bodily fluids the same way water-soluble vitamins are. 

So How Much Body Fat Do We Need? 

Men and women require different amounts of body fat, with women normally needing higher levels than men. This is related to differences in body composition and the demands of pregnancy, breast tissue and other hormonal requirements such as menstruation. 

The minimum body fat percentage for men is said to be around 4-6%, whereas for women it’s between 9-15% (15, 16). However, a healthy range for men is estimated as being between 12-20% and between 20-30% for women; although this can vary based on age and between different individuals (17). 

As you can see from reading this article, if body fat levels fall too low this can lead to a number if health issues such as:

• Low energy
• Feeling cold
• Hormone imbalances
• Issues related to low oestrogen levels in women such as worsened bone and heart health
• Constant hunger
• Fertility issues
• Vitamin deficiencies

Although body fat is often seen as a bad thing by diet culture, it plays a number of vital roles for our health.

If you are concerned that your body fat may be too low, don’t hesitate to seek support from qualified health professionals, including a dietitian.  Click here for information about the one to one service from Dietetically Speaking.

References

1. Mittal, B., 2019. Subcutaneous adipose tissue & visceral adipose tissue. Indian Journal of Medical Research, 149(5), p.571.
2. Ross, R., Neeland, I., Yamashita, S., Shai, I., Seidell, J., Magni, P., Santos, R., Arsenault, B., Cuevas, A., Hu, F., Griffin, B., Zambon, A., Barter, P., Fruchart, J., Eckel, R., Matsuzawa, Y. and Després, J., 2020. Waist circumference as a vital sign in clinical practice: a Consensus Statement from the IAS and ICCR Working Group on Visceral Obesity. Nature Reviews Endocrinology, 16(3), pp.177-189. 
3. El Hadi, H., Di Vincenzo, A., Vettor, R. and Rossato, M., 2019. Food Ingredients Involved in White-to-Brown Adipose Tissue Conversion and in Calorie Burning. Frontiers in Physiology, 9.
4. Virtanen, K., Lidell, M., Orava, J., Heglind, M., Westergren, R., Niemi, T., Taittonen, M., Laine, J., Savisto, N., Enerbäck, S. and Nuutila, P., 2009. Functional Brown Adipose Tissue in Healthy Adults. New England Journal of Medicine, 360(15), pp.1518-1525.
5. Fernández-Elías, V., Ortega, J., Nelson, R. and Mora-Rodriguez, R., 2015. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology, 115(9), pp.1919-1926.
6. Gregory, E., 1989. Thermoregulatory aspects of adipose tissue. Clinics in Dermatology, 7(4), pp.78-92.
7. Betz, M. and Enerbäck, S., 2017. Targeting thermogenesis in brown fat and muscle to treat obesity and metabolic disease. Nature Reviews Endocrinology, 14(2), pp.77-87.
8. Yoneshiro, T., Aita, S., Matsushita, M., Kameya, T., Nakada, K., Kawai, Y. and Saito, M., 2011. Brown Adipose Tissue, Whole-Body Energy Expenditure, and Thermogenesis in Healthy Adult Men. Obesity, 19(1), pp.13-16.
9. Kershaw, E. and Flier, J., 2004. Adipose Tissue as an Endocrine Organ. The Journal of Clinical Endocrinology & Metabolism, 89(6), pp.2548-2556.
10. Coelho, M., Oliveira, T. and Fernandes, R., 2013. Biochemistry of adipose tissue: an endocrine organ. Archives of Medical Science, 2, pp.191-200.
11. Bélanger, C., Luu-The, V., Dupont, P. and Tchernof, A., 2002. Adipose Tissue Intracrinology: Potential Importance of Local Androgen/Estrogen Metabolism in the Regulation of Adiposity. Hormone and Metabolic Research, 34(11/12), pp.737-745.
12. Frisch, R., 1987. Body fat, menarche, fitness and fertility. Human Reproduction, 2(6), pp.521-533.
13. Gordon, C.M. and Nelson, L.M., 2003. Amenorrhea and bone health in adolescents and young women. Current Opinion in Obstetrics and Gynecology, 15(5), pp.377-384.
14. Iorga, A., Cunningham, C.M., Moazeni, S., Ruffenach, G., Umar, S. and Eghbali, M., 2017. The protective role of estrogen and estrogen receptors in cardiovascular disease and the controversial use of estrogen therapy. Biology of sex differences, 8(1), pp.1-16.
15. Friedl, K., Moore, R., Martinez-Lopez, L., Vogel, J., Askew, E., Marchitelli, L., Hoyt, R. and Gordon, C., 1994. Lower limit of body fat in healthy active men. Journal of Applied Physiology, 77(2), pp.933-940.
16. Norgan, N., 1997. The beneficial effects of body fat and adipose tissue in humans*. International Journal of Obesity, 21(9), pp.738-746.
17. Abernathy, R. and Black, D., 1996. Healthy body weights: an alternative perspective. The American Journal of Clinical Nutrition, 63(3), pp.448S-451S.