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The decrease in muscle mass with ageing, however, is not inevitable, as people who perform regular weight training typically retain most of their muscle mass and ability to lift weights. Thus, decreased muscle mass with ageing for most people occurs because they are not challenging their skeletal muscles regularly. The good news is that interval sprinting exercise can significantly increase muscle mass.

As we age, blood hormone levels can decrease because of reduced secretion by the body’s endocrine glands. The receptors on the body’s cells can become insensitive too and don’t respond to hormones effecttively. For women, the largest hormonal change concerns decreased oestrogen when menopause occurs, whereas for men, the largest hormonal change typically involves reduced testosterone.

Alcohol

Alcohol contains 7 calories per gram which is more than the 5 calories contained in a gram of carbohydrate and protein and just under the 9 calories per gram contained in fat. Thus, consuming 2–3 average-sized alcoholic drinks a day adds up to over 500 calories. In a week, over 3500 extra calories would be consumed. Since 1 calorie equals 9 grams of fat, that means having 3 drinks every day of the week adds almost 400g of fat to your diet. According to studies in this area, the majority of these calories appear to be deposited as belly fat. It has also been shown that consuming alcohol makes people hungry.

However, a small amount of daily beer or wine, containing 14 grams of ethanol for women and about 28 grams for men, is beneficial for health. An average drink – a regular-sized glass of beer or wine – contains about 14 grams of ethanol. Studies have shown that women who drink about 1 drink a day and men who consume 2 drinks a day have a lower incidence of diabetes, stroke and heart disease.
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Ethnicity

Surprising differences emerge when belly fat accumulation is compared between different ethnicities. A study conducted by Louisiana State University researchers found similar results to a number of other studies that have shown that African-American women possessed less belly fat compared to Caucasian women.
10
A research study of African-American and Caucasian men involving universities from Canada and the USA showed similar results.
11
An article published in the
International Journal of Obesity
also indicated that Japanese-American men had greater amounts of belly fat than Caucasian men.
12

However, the strongest relationship between negative health and accumulation of belly fat seems to occur in people of South Asian descent. Research conducted at the State University of New York found high amounts of belly fat in Indian migrants, although they were not obese.
13
A study by Canadian researchers in 2011 found that people of South Asian descent accumulated dangerous belly fat on and in their internal organs when they put on total body fat. Adding belly fat to and inside organs like the liver and kidneys is more likely to lead to coronary artery disease and type 2 diabetes. In contrast, people of Caucasian descent added fat to their waistline rather than deep inside their bellies.
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These researchers also found that people who originated from India, even though they possessed a similar BMI to Caucasians, had significantly more belly fat. They also had more cardiovascular disease risk factors, such as metabolic syndrome and high cholesterol levels. The researchers suggested that, compared to people of Caucasian descent, those with South Asian heritage had less room underneath their skin to store fat (subcutaneous fat), therefore their excess fat was stored in fat compartments deep in the belly.

Overall, the increase in belly fat appears to be particularly troublesome in people of South Asian descent, as they seem to suffer more health problems, such as atherosclerosis and type 2 diabetes, when they develop belly fat. This is why the BMI cut-off for health problems by being overweight sometimes differs by ethnicities (see Table 1).

Why small increases in belly fat in people of Asian descent bring about greater cardiovascular problems than in non-Asians is unclear. Why people with South Asian heritage are getting fatter, however, is likely due to a change in lifestyle. People of Asian compared to European ethnicity have typically possessed far less body and belly obesity, an outcome of their plant-based diets and physically active lifestyle. However, developing countries such as India and China are now adopting Westernised lifestyles that involve consuming much more processed food and performing far less physical activity. The outcome is that countries that used to have very low levels of obesity and type 2 diabetes now have the fastest growth rates of these diseases. Given that developing countries are rapidly adopting Westernised lifestyles and that many Asians who emigrate eat Western foods and do not exercise, it is very important for individuals of Asian ethnicity to prevent an increase in belly fat by eating healthy foods and exercising regularly.

Smoking

Typically, smokers weigh less than non-smokers, as smoking may reduce appetite and also elevate metabolic rate, which induces fat burning. There is evidence, however, to show that cigarette smoking increases belly fat accumulation: a large, population-based study in the UK found that men and women who smoked possessed increased belly fat.
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How smoking increases belly fat is unclear, but shortly after a smoker finishes a cigarette, blood cortisol levels can increase for up to 30 minutes. We know that cortisol can increase belly fat accumulation due to its effect on blood sugar and insulin levels. Smokers also exercise far less than non-smokers, which is also likely to contribute to increased belly fat accumulation.

The impact of belly fat on health

As mentioned, belly fat emits a number of chemicals that can negatively affect health. Belly fat cells secrete chemicals called cytokines, which make the liver inflamed. They also bombard the liver with free fatty acids, which are converted to triglyceride and cholesterol and end up in the bloodstream. This cycle can cause type 2 diabetes and lead to atherosclerosis and cardiovascular disease.

Increased belly fat has been associated with a number of medical conditions, including:

• cardiovascular disease
  
• type 2 diabetes
  
• hypertension
  
• elevated blood cholesterol
  
• increased blood sugar
  
• dementia
  
• asthma
  
• colorectal cancer
  
• breast cancer
  
• bowel cancer
  
• pancreatic cancer
  
• endometriosis
  
• gallbladder problems
  
• sleep apnoea
  

For example, in Chinese adults, a bigger waist circumference – an indicator of belly fat – predicted development of hypertension, regardless of whether a person was normal weight or overweight.
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Another study found that older people with more belly fat had worse memories and were less verbally fluent.
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Interestingly, researchers from Spain tracked 3235 adult men and women for 2 years and found that waist circumference predicted disability. People with the largest waist circumference had 2.2 times more risk of mobility disability and 4.8 times more agility disability compared to adults with lower waist circumference.
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And a study in Europe involving nearly half a million women found that excessive belly fat, estimated by waist-to-hip ratio, was related to elevated colorectal cancer risk.
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Possessing elevated levels of body and belly fat increases general cancer risk, and people with large waistlines are at higher risk for bowel, breast and pancreatic cancer development and, in postmenopausal women, for cancer of the womb lining. Studies have also shown that in both young and older Japanese-American men, belly fat obesity predicted heart attack and hypertension development. Belly fat accumulation has also been associated with gallstones and Alzheimer’s disease.

How to measure your body and belly fat

Measuring body fat accurately is difficult. To measure body fat, medical professionals and researchers use methods that include magnetic resonance imaging (MRI), dual energy X-ray absorptiometry (DEXA), computed tomography, underwater weighing, skin-folds, Bod Pod (a volume-measuring technique) and bioelectrical impedance (opposition to the flow of an electrical current through the body). Unfortunately, most of these methods are expensive, and DEXA and computed tomography involve ionising radiation. These assessments all have their strengths and weaknesses but all incur a cost. Low-cost indirect measures, such as body mass index (BMI), provide an approximate estimate of body fat.

BMI

BMI is calculated by dividing a person’s body weight in kilograms by their height in metres squared. BMI has been used to identify individuals whose weight increases their risk for heart disease and diabetes. People with BMIs of 25.0 to 29.9kg per square metre (kg/m
2
) are considered overweight, and those with BMIs of 30kg/m
2
are considered obese. However, BMI can be misleading because it does not consider muscle mass, so very muscular or tall individuals can have a BMI of over 30kg/m
2
but actually can be very lean. To calculate your BMI, go to www.health.gov.au/internet/healthyactive/publishing.nsf/Content/your-bmi, or use the formula below.

How to calculate your BMI

Divide your weight in kilograms by your height squared in metres. A male weighing 85 kilograms with a height of 1.8 metres, for example, would first multiply 1.8 metres by 1.8 metres to get 3.24 metres, then divide 85 kilograms by 3.24 metres to arrive at a BMI of 26 (that is, 26kg/m
2
).

As can be seen in Table 1 (below), a BMI of greater than 25 is considered overweight, whereas a BMI of 30 and over is obese. BMI values are independent of age for adults, and although BMI is the same for both genders, it varies according to ethnicity. The World Health Organisation convened the Expert Consultation on BMI in Asian populations in 2002 and concluded that the number of Asians with a high risk of type 2 diabetes and cardiovascular disease was substantially more at BMIs lower than the existing WHO cut-off point for overweight, 25kg/m
2
. The BMI cut-off point for increased moderate health risk ranged from 22 to 25 in different Asian populations, and ranged from 26 to 31 for high health risk. In Japan and China a BMI of greater than 23 is now considered overweight and an increased health risk.

Table 1. Criteria for body mass index (BMI) in adults (BMI = weight ÷ height squared).

Adapted from The International Classification of Adult Underweight, Overweight and Obesity according to BMI.
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Bioelectrical impedance devices

Bioelectrical impedance analysis devices are relatively cheap but tend to underestimate body fat. Although their results are affected by the amount of water found in bodily tissues, if used regularly under standardised conditions – once a week, fasting in the morning – they will give a reasonable estimate of body fat change. Optimal body fat levels have been suggested to be around 10–20% in men and 20–25% in women.

A new bioelectrical impedance device for measuring belly or visceral fat has recently been developed by Tanita and is called the Viscan AB 140. Comparisons between this device and estimates of central fat carried out by DEXA have shown that their values are very similar (they correlate about r =0.95). However, comparisons between gold-standard estimates of belly fat such as MRI and computed tomography do not appear to have been carried out.

Table 2. International Diabetes Federation criteria for ethnic or country-specific values for waist circumference.

Adapted from Alberti, Zimmet and Shaw.
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Waist circumference

Waist circumference is an easy measure to obtain and is strongly related to belly fat assessed by clinical methods. Thus, having a large waist circumference usually means you have a significant amount of belly fat. Measure your waist circumference immediately above your navel with the tape being level with the top of your right hip bone. The tape measure should not be pulled too tight and you should take shallow breaths. Having someone else take the measure reduces error, and it is best if 2 measurements are taken and the average value recorded. Optimal waist circumferences for men and women of Asian and European descent are indicated in Table 2 (above), but if you are very large or tall these values may be inaccurate. Waist circumference greater than these values is associated with increased cardiovascular and metabolic health problems.