Declan grows into a man, not yet able to make the decision whether to go back to school or not, but is keen to know what it is like to be fat.
The 28-year-old, who was born with a body mass index of 33.5, is not overweight and has not gained a pound since starting university.
But he has gained a lot of weight since the age of 17 and is now five stone.
He said: “I have gained about 15 stone since my 18th birthday.
I am now about five stone heavier than when I was born, which was very scary.”
I would be out of work for a year if I was not in shape.
“In terms of my own health, I have had a lot to drink and smoke to cope with the stress of the transition, which is not ideal.”
Declan, from the city of Liverpool, is a member of the Body Positive Network, which encourages healthy eating.
He started to have a gastric ulcer and he said: ‘The doctors said I needed surgery to make me healthy again.’
I did not realise how unhealthy I had become and it was such a huge burden to carry on.
“Now I can see the good in me and want to be healthy.
I would love to have the same kind of attitude and behaviour towards myself and my body.”
Dr Emma Green, clinical dietitian at the Royal Free NHS Trust, said: ”The body fatness index is an important marker of health and wellbeing.
“It is a good predictor of health, and its a good indicator of how your body feels and feels healthy.”
But she added: “Being overweight is a very difficult problem to overcome and many people are very worried about their weight and have had many attempts at losing it.”
The BMI is a generalised measure of a person’s health.
It does not take into account factors such as age, gender, ethnicity, physical activity, lifestyle, and eating habits.
“However, there is a growing body of research suggesting that people who have a high BMI are at higher risk of developing type 2 diabetes and heart disease, and are more likely to have poor sleep and poor eating habits.
Professor Paul Fassett, a consultant clinical dietician at University College London, said the BMI may be a better predictor of a patient’s overall health.
He told BBC Breakfast: ”There’s a lot more evidence now that BMI may not be the only way to identify people at high risk for disease, but it may be the best way.”
There is an increasing body of evidence that obesity is linked to higher risk factors for many other conditions, including diabetes and hypertension.
“Professor Fassetts added: ”If you’re overweight, it’s very hard to lose weight.”
So if you’re in a healthy weight range, it is very hard for you to lose that weight, even if you start a healthy lifestyle.”
I think this is the key message that is getting through to people: obesity is not just about a body type but also about a lifestyle and a behaviour.”
If you want to have good health, then you should aim to be in a good body weight range.”
The more you lose weight, the healthier you get.”
You can lose weight with a good diet, exercise and lots of food.”
But if you don’t eat the right food, exercise regularly and have a healthy and balanced lifestyle, you’re going to stay healthy.”
Obesity can be a major health problem, but in many people it is actually a relatively minor one.
“If you really want to achieve good health and you are not overweight, then it’s all worth it.”
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