Why Weight? Obesity is a trajectory from healthy – measure and act’

22 August 2019

Kindly provided by Dr Harriette Carr (pictured left), Ministry of Health 

The traditional approach to obesity in primary care has been to determine if someone’s body mass index (BMI) is over 30kg/m2. If it is, we encourage them to lose weight through behaviour change strategies, food and activity. If that fails, pharmaceutical or surgical approaches are considered.

We know it is very hard for people to lose weight and maintain this weight loss for a range of reasons. There’s also the stigma that people with obesity experience.

The Clinical Guidelines for Weight Management in New Zealand Adults recommend regular monitoring of height, weight and BMI to enable early identification of weight change rather than waiting until a person is obese to offer advice.

People do not become obese overnight – weight gain is typically a gradual process that continues throughout life. If weight gain is gradual, why wait till someone is obese? There is the opportunity to move towards a prevention approach to obesity within primary care. 

Professor Wendy Brown, The University of Queensland, presented data from a 16 year study of young Australian women (Australian Longitudinal Study of Women’s Health) at Australia’s National Obesity Summit earlier this year. Her research highlights the gradual change in weight over time, and relative consistency of change. 

Of 4,881 women with a healthy BMI at baseline (1996: 18-23 year olds), after 16 years (2012: 34-39 year olds) 11 percent had developed obesity, 29 percent were overweight (but not obese), and 59 percent had maintained a healthy weight. Figure 1 shows the growth trajectory based on their 2012 weight.

Figure 1: weight change over time 

Figure 2: Rate of weight change 

Figure 2 illustrates the average annual weight change (kg/year) for the women in the study; women who maintained a healthy weight over the 16 year period had an average annual weight gain of less than 0.5kg/year, while those who developed obesity had an average annual weight gain of over 1kg/year. 

Through regular/opportunistic weighing and recording of height/weight/BMI (and waist circumference if appropriate) of all patients regardless of their current weight status, trends should start to emerge on an individual’s weight gain. Plotting this data on a graph enables it to be used as a communication tool and to help predict what someone’s weight might be in 10 years time if they continue as they are now. Weight change can also be an indicator for a range of other health conditions, mental wellbeing, stress, drug treatments, and a response to major life events.
By using this approach, the message changes from telling someone that they are obese and recommending weight loss, to working with them to make small life changes so they maintain their current weight.

Graph references

1 - Ministry of Health 2017. Clinical Guidelines for Weight Management in New Zealand Adults Adults. Ministry of Health. Wellington. www.health.govt.nz/publication/clinical-guidelines-weight-management-new-zealand-adults

2 - https://www.health.gov.au/internet/main/publishing.nsf/Content/DE86DA1B3530640BCA258397000F2379/$File/Presentation%20-%20Wendy%20Brown.pdf