The general consensus is that gaining an excessive amount of body fat is bad for our health. But have you ever stopped to think why? What is it about adipose tissue, or body fat, that makes it so harmful to our health?

Let’s take a closer look.

What adipose tissue really is

What comes to mind when you think about adipose tissue?

The image that springs to the fore for me is a dense mass of fat. That blob of orange-yellow fat you see in weight-loss adverts, to be precise. It makes me a little nauseous just thinking about it.

But is adipose tissue just fat?

It may surprise you to learn that it’s not. After all, we don’t just have fat mass stored beneath our skin – that’s not really how fat storage in our bodies works.

Adipose tissue is a connective tissue, composed primarily of cells called adipocytes. In simple terms, adipocytes are tiny storage units for fat that swell up when full. When the body needs energy, these cells release the stored fat, shrinking back down and helping fuel our daily activities.

Adipose tissue isn’t just a body fat store, though. It’s a highly active endocrine organ, which releases hormones and communicates with other organs and the rest of the body. The hormones it releases include leptin, which you may know as the fullness hormone (Kershaw & Flier, 2004).

When we gain body fat, the amount of leptin produced by our adipose tissue also increases. This travels around in our bloodstream, and when it reaches the brain, it signals that we’re full and indicates that we should stop eating.

The adipose tissue we’re discussing here is white adipose tissue, and it’s the most common type of adipose tissue in humans. I won’t spend much time discussing it here, but it is worth noting there is another type of adipose tissue, called brown adipose tissue. You may have heard this referred to as baby fat.

It is called brown adipose tissue because it contains organelles like mitochondria and is highly vascularised (meaning it has a dense network of blood vessels), giving it its darker colour. This brown adipose tissue is used by newborn mammals to produce heat and maintain body temperature, and it is gradually lost with age.

Brown adipose tissue is not our main focus here. When we discuss body fat and health, we are generally referring to white adipose tissue, so I will stick to that moving forward.

So, we’ve established that it is white adipose tissue that we store in our bodies when we consume more energy through food than we expend. But why do we store it, and what is it used for?

Briefly, in the days when humans were hunter-gatherers, food was scarce. When it was available, they feasted, gorged, and stored the energy they did not immediately need for later use when they were forced to remain fasted (O’Dea, 1991; Heitmann et al., 2012).
We still have the same genes that cause us to feast when food is available, and store the excess energy from food we eat in our adipose tissue. However, now that food is no longer scarce but readily available on every street corner, we are susceptible to overeating. As a result, we gain body fat.

Now that we understand what adipose tissue is and its role in our body, let’s explore why too much of it (especially in certain places) can be harmful.

Why is excess fat harmful?

A little body fat is needed. It helps insulate us against the cold and provides cushioning to internal organs. However, too much can be harmful. Why is that?

As previously mentioned, adipose tissue is an active endocrine organ. It releases hormones and cytokines (small proteins that act as chemical messengers to communicate with organs around the body) as well as alters macrophage (a type of white blood cell) function and increases the number of macrophages, contributing to systemic low-grade inflammation in the body (Saltiel & Olefsky, 2017).

Effectively, this means our immune system is in overdrive, resulting in a level of inflammation around the body that is higher than optimal. This systemic inflammation may lead to insulin resistance in our muscles and liver, which can lead to type II diabetes (Saltiel & Olefsky, 2017).

Insulin resistance in adipocytes mean adipose tissue can also release fatty acids which exacerbate inflammation. These can be deposited in the liver, resulting in fatty liver disease, or they may also build up a plaque in blood vessels, potentially leading to heart disease and/or stroke (outlined in King, 2022).

The sheer weight of excess body fat can also exert mechanical stress on the body. It may contribute to osteoarthritis, cause compression of kidney vessels (renal compression), leading to kidney disease, and compress airways during sleep, leading to reduced oxygenation and potentially sleep apnoea (all outlined in King, 2022).

So, we’ve established that an excessively high body fat percentage is harmful for a myriad of reasons. But would it surprise you to learn that where adipose tissue is stored in your body also has a major impact on your health?

You see, the amount of body fat you carry may not be as important to your health as where that body fat is stored.

The importance of adipose tissue distribution: visceral vs subcutaneous fat

There are two main ways that excess body fat may be stored: as visceral fat, or as subcutaneous fat.

Visceral fat, or intra-abdominal adipose tissue, is stored around the organs (e.g., kidneys, heart, liver, skeletal muscle) and may, in fact, penetrate them. Fatty tissue infiltration, for example, is often observed in the skeletal muscle and liver of obese (and elderly) individuals.

Subcutaneous fat, on the other hand, is stored beneath the skin, more superficially (closer to the surface) in the body. This means less adipose tissue is found around the internal organs.

Perhaps you’ve already guessed, but visceral adipose tissue is more dangerous than subcutaneous adipose tissue, and has been linked to other health conditions like diabetes, heart disease, and cancer. Therefore, where adipose tissue is stored has a significant impact on metabolic health, with metabolic health generally being better in those with low intra-abdominal adipose tissue (King, 2022).

You might also be interested to know that just having a low BMI does not mean that you have low intra-abdominal fat. Unfortunately, where we predominantly store our fat is largely dependent on our genes, meaning we cannot actually control or change it much.
It may be that we have a healthy BMI but store much of our adipose tissue viscerally, and therefore have poorer metabolic health.

Equally, and perhaps surprisingly, if you have a high BMI but your genes dictate that most of your adipose tissue is stored subcutaneously, you may, in fact, have lower volumes of intra-abdominal adipose tissue, and actually have comparatively good metabolic health! This is commonly referred to as metabolically healthy obesity.

This is just one of a multitude of drawbacks of using BMI as a measure of health and why we should not rely on it alone. That’s a discussion for another day, though.

While subcutaneous adipose tissue may not pose as much risk as visceral adipose tissue (Frank et al., 2019), this does not mean that storing a lot of fat subcutaneously is all fine and dandy for the body. On the contrary, it may still lead to obesity and metabolic issues.

In fact, King (2022) substantively states the following:

The phenomenon of metabolically healthy obesity is a widely debated issue and may have implications for healthcare resource prioritisation. It is important to note, however, that only 10–34% of obese individuals are classed as metabolically healthy (Muñoz-Garach et al., 2016). Moreover, longitudinal data suggests that in such individuals, the appearance of obesity-related health problems may be delayed, rather than prevented entirely (Hamer et al., 2015).

So, what does this mean for you? How can you tell whether you tend to store more adipose tissue viscerally or subcutaneously?

Adipose tissue distribution actually depends on a number of factors.

What factors contribute to adiposity and body fat distribution?

I briefly mentioned that where we store fat in our bodies is highly dependent on genetics. After all, some people’s genes dictate that they store more fat in their abdomens, while others’ dictate it should be stored in the hip, glute, and thigh regions.
But what else has the potential to influence adipose tissue distribution around the body?

• Sex hormones.
  – Testosterone. This promotes fat storage in the abdomen by directing fat storage away from the gluteal region, which is why men tend to store fat more viscerally (Frank et al., 2019).
  – Oestrogen. This promotes fat storage in the hips and thighs, which is why women tend to store more fat in these areas (Frank et al., 2019).
• Age. It has been found that visceral adipose tissue increases with age, even at the same waist circumference. This means, for example, that an older man with the same waist circumference as a younger man is likely to have more visceral adipose tissue than the younger man (Kuk et al., 2005).
• Overall adiposity. Perhaps quite intuitively, if we store more fat, we will likely have more visceral adipose tissue. Therefore, being obese, for example, means we likely (although not certainly) have higher intra-abdominal adipose tissue than someone who is at a healthy body weight.

OK, so you probably have a better idea of what’s likely to cause us to store more fat viscerally. But do you yourself have a high volume of intra-abdominal adipose tissue, or do you store your fat more subcutaneously?

How can we assess our own adipose tissue distribution?

It’s all well and good knowing what body fat distribution depends on. But if BMI cannot give us an indication of where our adipose tissue is distributed, what measures can?

• Waist-to-hip ratio. This is the ratio of your waist circumference to your hip circumference. A higher ratio indicates a higher risk of cardiometabolic diseases. The optimal ratio varies depending on ethnicity, but in general, it should be less than 0.8–0.85 for women and less than 0.9–0.95 for men (Qiao & Nyamdorj, 2009).
• Waist-to-height ratio. This is a more recent indicator that compares waist circumference to height. It is meant to be a simple, easy-to-remember metric, where your waist circumference should be less than half your height, meaning the ratio should be less than 0.5 (Gibson & Ashwell, 2020).

Are there any other, more precise methods of measuring total body fat and its distribution?

Indeed there are, although they tend to be more costly!

These include MRI (magnetic resonance imaging) and DXA (dual-energy X-ray absorptiometry) scanning, which are able to provide internal images of the body and hence, a good understanding of one’s body composition, how much adipose tissue one is carrying and where it is distributed.

Total body fat percentage can also be estimated using BIA (bioelectrical impedance analysis) scales, which can certainly be much cheaper than DXA or MRI, but equally are less accurate and cannot give a good indication of where adipose tissue is distributed around the body.

Now that you’ve found out whether or not you’re likely to be storing more fat viscerally, what can you do about it? If the factors that contribute to adipose tissue distribution are mostly out of your control, is that it? Are you simply at greater risk of developing a chronic disease?

Not necessarily. In particular, not if you’re not obese.

While we cannot selectively lose weight in certain areas, losing some body fat will inadvertently help us reduce visceral adipose tissue. This can have immense benefits on our health and reduce our risk of developing cardiometabolic diseases.

A healthy, balanced diet (perhaps the Mediterranean diet) and staying active are recommended to improve body composition (Muñoz-Garach et al., 2016).

The American College of Sports Medicine (ACSM) recommends that we do 150-250 minutes of moderate-intensity exercise per week to maintain our body weight and prevent weight gain (Donnelly et al., 2009). If our goal is to lose weight, the recommendation is at least 150 minutes of exercise for modest weight loss (2-3 kg), and between 225 and 420 minutes of exercise every week for a 5-7.5 kg weight loss (Donnelly et al., 2009).

Other options, such as surgery, may be available for individuals who are obese and find it extremely challenging to lose weight (Muñoz-Garach et al., 2016). However, that is beyond the scope of this blog post, and I would recommend speaking to your GP if you feel that you fall into this category.

 

Conclusion

Adipose tissue distribution is extremely important because where we store our body fat has a significant impact on our health. Visceral adipose tissue stored around the internal organs in the abdomen increases our risk of developing cardiometabolic diseases and is generally worse for our health than subcutaneous adipose tissue, which is stored beneath our skin.

Where we store fat is determined by a number of factors, many of which cannot be altered. However, if we stay active and maintain a healthy, balanced diet, we can keep our total body fat at a healthy level and reduce our risk of disease and mortality.

Exercise is a great way to support our endeavour to keep our body fat, and especially our visceral adipose tissue, at a healthy level. Starting today, with small, consistent changes, you can make a real difference in managing your body fat and lowering your risk of serious health conditions. It’s never too late to start taking control of your health!

 

Disclaimer: As a sports science graduate, I am not medically qualified to give advice and would recommend speaking to a doctor or healthcare professional if you are struggling with your body weight and experiencing obesity. If you are not currently physically active, please speak to a healthcare professional before starting exercise. Equally, if you are considering changing your exercise regimen, please consult your doctor. This blog post is merely meant to serve as an educational and leisurely read, offering some guidance on how much exercise the literature and ACSM guidelines recommend.

References

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Frank, A. P., de Souza Santos, R., Palmer, B. F., & Clegg, D. J. (2018). Determinants of body fat distribution in humans may provide insight about obesity-related health risks. Journal of Lipid Research, 60(10), 1710–1719. https://doi.org/10.1194/jlr.r086975

Gibson, S., & Ashwell, M. (2020). A simple cut-off for waist-to-height ratio (0·5) can act as an indicator for cardiometabolic risk: recent data from adults in the Health Survey for England. British Journal of Nutrition, 123(6), 681–690. https://doi.org/10.1017/S0007114519003301

Hamer, M., Bell, J. A., Sabia, S., Batty, G. D., & Kivimäki, M. (2015). Stability of metabolically healthy obesity over 8 years: the English Longitudinal Study of Ageing. European Journal of Endocrinology, 173(5), 703–708. https://doi.org/10.1530/eje-15-0449

Heitmann, B. L., Westerterp, K. R., Loos, R. J. F., Sørensen, T. I. A., O’Dea, K., McLean, P., Jensen, T. K., Eisenmann, J., Speakman, J. R., Simpson, S. J., Reed, D. R., & Westerterp-Plantenga, M. S. (2012). Obesity: lessons from evolution and the environment. Obesity Reviews, 13(10), 910–922. https://doi.org/10.1111/j.1467-789x.2012.01007.x

Kershaw, E. E., & Flier, J. S. (2004). Adipose tissue as an endocrine organ. The Journal of Clinical Endocrinology and Metabolism, 89(6), 2548–2556. https://doi.org/10.1210/jc.2004-0395

Kuk, J. L., Lee, S., Heymsfield, S. B., & Ross, R. (2005). Waist circumference and abdominal adipose tissue distribution: influence of age and sex. The American Journal of Clinical Nutrition, 81(6), 1330–1334. https://doi.org/10.1093/ajcn/81.6.1330

Muñoz-Garach, A., Cornejo-Pareja, I., & Tinahones, F. (2016). Does Metabolically Healthy Obesity Exist? Nutrients, 8(6), 320. https://doi.org/10.3390/nu8060320

O’Dea, K. (1991). Traditional diet and food preferences of Australian Aboriginal hunter-gatherers. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 334(1270), 233–241. https://doi.org/10.1098/rstb.1991.0112

Qiao, Q., & Nyamdorj, R. (2009). The optimal cutoff values and their performance of waist circumference and waist-to-hip ratio for diagnosing type II diabetes. European Journal of Clinical Nutrition, 64(1), 23–29. https://doi.org/10.1038/ejcn.2009.92

Saltiel, A. R., & Olefsky, J. M. (2017). Inflammatory mechanisms linking obesity and metabolic disease. Journal of Clinical Investigation, 127(1), 1–4. https://doi.org/10.1172/jci92035