"It is definitely a shock to the system," says the Sydney-based PR. "You have a fleeting moment of denial where you think 'Is that me?', and then once reality sets in, you feel sad and depressed because you realise this is what you now look like and it's how others must see you and what you have done to yourself, as a result of lack of exercise and irresponsible diet."

Lana's story reflects a common experience - it is getting harder for many of us to tell what size we really are and studies show that we are increasingly in denial about our weight, with serious repercussions for our health.

"Weight misperception is common among both overweight and normal weight women of reproductive-age," says associate professor Mahbubur Rahman from the University of Texas Medical Branch in the US who conducted research to see how accurately women could perceive their own body weight. The study found that one in four overweight and obese women wrongly thought they were a normal weight, making them vulnerable to cardiovascular and other obesity-related diseases.

Further evidence about the failure to notice our expanding waistlines was highlighted by a Bupa report last year, which revealed that only one-third of Australians consider themselves overweight while their body mass index showed that six out of 10 are overweight or obese.

Australian Stefanie Allen, 39, says she too only became aware of her large weight gain after looking at photos. "I had this double chin and comparing them with past photos I noticed I didn't even look like the same person any more. My clothes didn't fit and I was buying two sizes larger than ever before, yet I just pretended it wasn't happening. I avoided clothes shopping. The realisation has been horrible. I feel sick when I think about it but I still can't motivate myself."

So why are so many of us in fat denial? Experts believe there may be more to denying the reality of piling on the kilos than just embarrassment.

"People are increasingly in denial about being overweight in part because more and more people are overweight and they now see that as normal," says Dr Robin Willcourt, director of anti-ageing clinic, Epigenx Integrated Medicine, in Victoria.

"For women the idea of being fat can be so unacceptable that they block out any sense that they are overweight and then frequently become grossly obese. Denial is overt but a subconscious response is also at work in shaping one's image of oneself."

"Because most people are overweight these days, it becomes easier to underestimate your weight," agrees exercise scientist and author, Rob Greco. "If an overweight girl stands amongst a group of skinny girls, then she will likely see herself as overweight. However, if an overweight girl stands amongst a group of overweight girls, then she likely see herself as being of a 'normal' weight." This goes a long way towards explaining why many of us often underestimate our body size, he says.

In The New York Times, Tara Parker-Pope writes that scientists are only now beginning to understand the complicated process in which the brain (in particular, the posterior parietal cortex) integrates signals from all the senses to form our body images. "Because our bodies change over time, the brain must constantly adjust its perception. Scientists believe that this internal calibration system can sometimes go haywire, notably for sufferers of anorexia, bulimia and body dysmorphic disorder, and possibly for obese people too."

So, she adds, while "researchers admit that some denial may have to do with personal embarrassment, the consistency of the findings suggests that neural processing and psychology probably both play a role".

Greco acknowledges there are many difficulties in admitting to being overweight. "Many of us who have a weight problem very often deny that we do so. I mean let's face it, being overweight can really be hard to manage, especially when it makes you feel out of control and especially when you don't know how to fix it.

"Admitting that you are fat means that you are accepting that you are not in control of your life - something which most of us don't like to admit. Especially when you live in a world that warrants control in career, relationships, children, finances, your body and everything in between. Not being in control is very damaging to your ego, reputation and how you define your self-worth. It can lead to emotional eating, self-esteem issues, panic attacks, anxiety and even depression. Obviously not everyone is in denial about their weight. There are some people who know they are overweight and are just too tired or stressed or unmotivated to do anything about it."

- If you think you might be in denial, Greco suggests asking yourself:

- Do I have a body weight that falls within a healthy body mass index range?

- Does my body reflect who I really am?

- Do I honour and respect my body the way I should?

- Does my body support everything I want to do with my life?