Having and keeping a healthy body weight is recognised in both the Australian Dietary Guidelines and the Eating and Activity Guidelines for New Zealand as crucial for good health and wellbeing.

The Body Mass Index or BMI is used to estimate your best weight for health. It is calculated by  dividing your weight (kg) by height in meters squared.

The BMI ranges:

18.5 or less = underweight
18.5 - 24.99 = healthy weight
25 - 29.99 = overweight
30 or more = obese

Current evidence suggests people with a BMI of less than 18.5 or higher than 25 are more likely to die prematurely of a health-related issue than those with a BMI within the defined healthy weight range.

BMI is not a perfect measure. It cannot differentiate between muscle mass and body fat. It would therefore overestimate the body fat content of body builders and high performance sports people. It would also underestimate body fat in the elderly or people with a physical disability. 

Obesity trends 

Overweight and obesity in Australia and New Zealand have increased over time.

• 31.3% of Australian adults and 8.1% children were obese in 2017/18
• 30.9% of New Zealand adults and 11.3% children were obese in 2018/19

Overweight and obesity have increased from 63.4% in 2014/15 to 67% in 2017/18, in Australia. There was a large increase for those aged 18-24 years in this time. 

In New Zealand, adult obesity increased since 2011/12 but not by a significant amount. Similarly for children, there has been no major change in this time. 

Causes of obesity

Obesity increases the risk of many chronic conditions and diseases including insulin resistance, diabetes, high blood pressure, heart disease, stroke, some cancers, gout and sleep apnoea.

Obesity is complex and there can be many causes. These include eating more kilojoules than your body uses, inactivity, genetics, conveniences linked to modern living, and socio-economic factors. 

For many, too much energy or kilojoules consumed from any source, including sugars, contributes to weight gain.

For sugars and obesity, the research continues to show no direct causal relationship, outside of the contribution to energy intake. Reducing sugar intake is shown to lead to weight loss (or a reduction in weight gain), if there is overall less energy consumed in the diet. 

'The data suggest that the change in body fatness that occurs with modifying intake of sugars results from an alteration in energy balance rather than a physiological or metabolic consequence of monosaccharides or disaccharides.' Te Morenga et al 2013

Researchers have looked at obesity trends next to sugars intake over time. Over a 30 year period in Australia they found that added sugars and sugars in soft drinks has gone down, at the same time that obesity has increased. This suggests that something more than energy from sugars is at play.   

Attention is now turning to all foods and drinks that contribute too much energy to the diet. Cutting down on all sources of excess kilojoules (or energy) reflects an evidence based and sensible approach to avoid weight gain, in addition to getting enough physical activity.

' ...it may be time to rethink the approach of focusing on a single energy source in the diet when tackling childhood obesity.' Wong & Louie 2018

Learn more in our fact sheet on sugars and body weight here

REFERENCES

• Ministry of Health. Obesity Statistics.
• Australian Bureau of Statistics.  4364.0.55.001 - Australian Health Survey: First Results, 2011-12
• Te Morenga L, Mallard S & Mann J. (2012). Dietary sugars and body weight: systematic review and meta-analyses of randomised controlled trials and cohort studies. BMJ, 345:e7492
• Khan TA & Sievenpiper JL. (2016). Controversies about sugars: results from systematic reviews and meta-analyses on obesity, cardiometabolic disease and diabetes. European Journal of Nutrition, 55(Suppl 2):S25–S43
• Barclay AW & Brand-Miller J. (2011). The Australian Obesity Paradox: A substantial decline in sugars intake over the same time frame that overweight and obesity have increased. Nutrients, 3(4):491-504
• Brand-Miller J & Barclay AW. (2017). Declining consumption of added sugars and sugar-sweetened beverages in Australia: a challenge for obesity prevention. Am J Clin Nutr, 105(4):854-863.
• Wong THT & Louie JCY. (2018). The direct and indirect effect associations of usual free sugar intake on BMI z-scores of Australian children and adolescents. Eur J Clin Nutr, 72:1058–1060
• Choo VL, Ha V & Sievenpiper JL. (2015). Sugars and Obesity: Is it the Sugars or the Calories? Nutrition Bulletin, 40(2):88-96