Body Fat Explained

Body Fat Explained

By Dietitian, Lyndel Costain BSc RD

What is normal body fat?

Body fat - technically known as ‘adipose tissue’ - is made up fat cells or ‘adipocytes’.  Their chief role is to store energy in the form of fat, which we get from our diet. Body fat has many other life sustaining actions (see below). Like other tissues and organs, body fat is supplied with a network of blood vessels and nerves to enable it to work properly.

Where is normal body fat stored and distributed?

The key body fat storage depots are distributed directly under the skin (subcutaneous fat), deeper in the body around the stomach, kidneys and liver (visceral or abdominal fat), and in the breast. The size of these fat depots differs with age and between the sexes: typically women store more fat than men and have more subcutaneous rather than abdominal fat. In other words women are more likely to be pear-shaped than apple shaped.

Why do we need body fat distribution?

Body fat isn’t just a useless lump of stored fat. It cushions and protects vital organs such as the liver, kidneys and heart, and helps our body to stay at the right temperature. It produces hormones and many other chemical messengers that are important for fertility (we need a certain amount of fat on our hips and thighs to stay in tip-top reproductive shape), bone strength, immunity, regulation of sugar and fats in the blood, and appetite control. 

Is excess abdominal fat worse for our health?

Having too much body fat, particularly if it is distributed in the abdominal area, can upset how well the hormones and chemical messengers it naturally produces work. This means being apple-shaped puts us more at risk of health problems such as heart disease, high blood pressure, fatty liver, infertility, type 2 diabetes and certain types of cancer.

Do fat cells keep multiplying?

This has been debated for some time. A new study suggests that by the time we have reached adulthood, we have a set number of fat cells that no longer multiply but get bigger if we gain weight and smaller if we lose weight. 

Why do women change shape as they get older?

We can pretty much thank our hormones for that one.  After the hormonal changes of the menopause (oestrogen levels fall), fat distribution changes and women tend to store more fat in their abdomen and become more apple-shaped. Women may not necessarily gain weight on the scales but find some body fat ‘migrates’ up from hips to waist. This also means we are more susceptible to apple-shaped health risks - not good news.

To assess how healthy your waist measurement is:

Use a tape measure (it might be easier if you get someone to help you) and measure your waist ever so slightly above belly-button level. Men should make sure they don’t measure where their belt goes, which is typically below waistlines and bellies.


  • 32-35 inches (81-88cm) = ‘increasing health risk’ and further weight/waist increases should be avoided (or some lost)
  • 35 inches (88cm) or more = ‘high risk’ and  weight/waist loss advised.


  • 37-40 inches (94-102cm) = ‘increasing health risk’
  • 40 inches (102cm) or more = ‘high risk’.

How can we measure body fat?

The simplest way to assess if we have too much body fat for our health’s sake or not is to measure our waist (see above) and also our BMI (Body Mass Index).  If you want more specific detail, the amount or % of fat in the body can be approximately measured at home, by your doctor or at health clubs.

It can be useful when regular exercise is a key part of your approach to weight control. As well as seeing how the scales change, you can assess how the amount of fat in your body changes.

The most accurate way to measure body fat is with specialist (and expensive) equipment found in hospitals and research centres such as DEXA scans.  While not quite in the same league as DEXA, the simplest way to do it at home is to invest in some good stand on scales or hand held body fat monitors. Be sure to follow their directions for best results.

What is a healthy or ideal level of body fat?

Perhaps surprisingly there is no official guide for healthy levels of body fat. But the best known figures for adults (aged 20-60) are 21-34% body fat for women and 8-22% for men. Above or below these figures can reflect being overfat or underfat respectively.

What happens if we don’t have enough body fat?

We all need some body fat to be healthy. Having too little body fat increases the risk of brittle bones, loss of menstrual periods, infertility, dry skin, poor concentration, low mood, feeling cold, constant thoughts about food and low sex drive.

Can we change our body fat distribution?

Our basic body shape is inherited and can’t fundamentally be changed. So if you come from a long line of ‘pears’, then losing weight will mean you become a smaller, trimmer and healthier pear.  Vice versa if you gain weight.

When we lose weight we burn fat from fat stores all over our body. But studies suggest that abdominal fat stores are especially responsive to regular physical activity which gets your heart rate up e.g. walking, running, cycling, dancing, gardening, exercise classes.

For example a US study amongst obese, middle-aged women found that despite losing the same amount of weight, women who dieted and used the treadmill for 30 minutes or more, three times a week, reduced the size of their abdominal fat cells by 18%, compared to women who only dieted.

Adding in some regular resistance exercise such as weights may enhance the benefit too.
Note too that cigarette smoking, drinking too much alcohol and lack of physical activity are linked to laying down more abdominal fat. Studies also suggest a link between stress –and high blood levels of the stress hormone cortisol – and having more abdominal fat, even if not overweight.

Can you spot reduce ‘problem’ areas?

Body fat stores gain or lose fat in proportion to their size, so it’s not possible to spot reduce ‘problem areas’. Regular exercise may have an added benefit on abdominal fat – but this doesn’t mean that it will make unwanted bellies disappear.  Targeted toning exercise such as sit-ups and weights can improve muscle tone and shape but won’t simply get rid of fat in the targeted areas. 

What is the best way to reduce body fat?

When we consume fewer calories (from food and drink) than we burn (via metabolism and exercise) to get the energy we need to keep functioning properly we tap into our body fat to use their stored energy – and lose weight. However whenever we lose weight, as well as body fat, we also lose some lean tissue (mostly as muscle). While we can’t stop this happening, we can optimise the amount of fat we lose relative to muscle by being as active as we can.

For example, one roundup of studies found that when inactive women lost around 10kg (1.5 stone) over 3 months then approximately 22% of the weight lost was lean tissue if they dieted only, compared to 17% if they lost weight by combining diet and exercise. 

In short, the best way to lose body fat is by combining a healthy, reduced calorie diet with regular exercise. Drinking sensibly, not smoking and finding ways to manage stress may also help to keep abdominal fat at a healthier level.

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