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‘The rate of weight loss had no impact on long-term weight management’

Katrina Purcell discovered that long-term weight loss was not affected by how rapidly a person shed the kilos in the first place.

Interview by Cally Sheng
 

‘I have always wanted to be a dietitian, ever since high school. I wanted to know how to eat healthily because I was into sport and I wanted to be fit.  

I started cycling when I was 13 and finished when I was 21. I won second place in the 2002 National Track Cycling Championships held in Sydney.

My partner at that time, Ryan Bayley, won two gold medals as a track cyclist in the 2004 Summer Olympics. He loved to eat junk food and he was proud to maintain his unusual diet to bike gold.

‘We think people are obese because they are lazy. They are not.’

Being a professional cyclist means you have to be lean. In spite of Ryan, it is believed by athletes that you get more power if you are more “ripped”. That’s what led me to study about weight loss and weight regain. I wanted to uncover the factors that affect the management of weight.

People are told that you’re more likely to succeed if you gradually lose weight as your body needs time to adapt. By contrast, it’s easier to put all your weight back on if you lose weight rapidly.

Australian dietary guidelines normally recommend patients who are seeking weight loss treatment, and clinicians who provide such treatment, to bear in mind that a slower weight loss approach is superior to a faster one.

However, there’s no evidence to prove this. My study found that rapid weight loss is actually more effective than gradual weight loss.  

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My research was carried out in Australia. My colleagues and I selected 200 obese people. They were randomized and assigned to one of two groups, a rapid weight loss group and a gradual weight loss group. 

The first group used a commercially available, very low calorie diet for 12 weeks according to manufacturer’s prescription.

The second group used a low calorie diet for 36 weeks based on recommendations in the Australian Guide to Healthy Eating.

Only those who had achieved a target of 12.5 per cent weight loss got to the next stage, which was a weight maintenance phase for 144 weeks. This was one of the longest follow-up studies done so far.

My research found three key findings. First, the rate of weight loss had no impact on long-term weight management. People in both groups regained exactly the same amount of weight (71 per cent) in the end.

‘My study shows that a person’s weight will return to its old level even after three years of maintaining a lower body weight.’ My study shows that a person’s weight will return to its old level even after three years of maintaining a lower body weight. This is because your hunger hormones increase and your satiety hormones decrease when you lose weight.

This finding has implications for dietitians making efforts to help their patients overcome obesity. We need medications to help suppress hunger after weight loss to stop weight regain.

The problem of current pharmaceutical research is that it only focuses on one hormone or two hormones. An efficient pharmacotherapy, nevertheless, is akin to a cocktail. You have to take all the hormones into account.

Second, the study shows that the speed of initial weight loss will not hinder ultimate weight loss success. A greater number of people dropped out in the gradual weight loss group than in the rapid weight loss group mainly because they could not stick to their dietary program requirements.

During the weight loss phase, fewer participants in the gradual weight loss group achieved their target (12.5 per cent weight loss) than in the rapid weight loss group.

The reason why weight loss over a short period of time worked was because it was rewarding. People want to see an instant outcome when conducting behaviour change. When they did it slowly, their determination diminished over the course of the study. 

‘In my view, there is no need to treat people who are just obese as if they have an underlying medical condition.’

These findings are not consistent with present dietary guidelines, which recommend gradual — over rapid — weight loss. I think my work points to the need for the guidelines to be reviewed.

Thirdly, my research shows that obesity is under strong genetic control. Genetics define our body weight.

This is important since it changes the way we think about obesity. We think people are obese because they are lazy. They are not.

Many patients worked really hard and most did lose a significant amount of weight, but they eventually regained the same amount of weight. Although it is possible for people to maintain a low amount of weight, they feel hungry all the time.

Few studies suggest that if you lose weight and put back on your weight, you are going to be worse off than maintaining your weight from the beginning. What I want to do next is to see whether or not weight loss is actually a bad thing.

In my view, there is no need to treat people who are just obese as if they have an underlying medical condition.

After all, what is the point of losing weight if we are going to regain all that weight, especially when it can be detrimental to your health? ’

Katrina Purcell’s thesis is titled: “The effect of rate of weight loss on long-term weight management: a randomised controlled trial.”

My PhD is an irregular series in which The Citizen speaks with recent Melbourne University PhD graduates. 

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THE CITIZEN is a publication of the Centre for Advancing Journalism. It has several aims. Foremost, it is a teaching tool that showcases the work of the students in the University of Melbourne’s Master of Journalism and Master of International Journalism programs, giving them real-world experience in working for publication and to deadline. Find out more →

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