Lisa Day was diagnosed with type 1 diabetes when she was 14.
It meant her body didn't produce insulin so to stay alive she had to inject it daily as well as take extra care with the food she ate.
She died on 12 September 2015 after years of suffering with diabulimia.
The term, which isn't yet medically recognised, refers to diabetic people who deliberately take too little insulin in order to lose weight.
Lisa's older sister Katie Edwards has been looking through the diary her sister wrote just after she was diagnosed.
Lisa started writing the diary just after she was diagnosed with type 1 diabetes in September 2001.
Boxing Day 2001
"I feel really fat. I want to lose weight. Think I'm about 9 stone."
New Years Day 2002
"I have to do my injections in a mo. I am going to ring Sam tonight so that I can meet with him tomorrow. I've just made myself sick twice."
Flicking through the pages, Katie describes Lisa: "She was my younger sister. She was fun, but serious at times. She had a lot of friends. She loved life but you could tell that there was something deep down that was troubling her.
"She always had a bit of a sad shadow following her around."
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13 February 2002
"Non-uniform day. I feel so FAT. Everyone looked great today but me. I threw up my food today. I have to quickly do my art homework."
"I am so pleased and I feel great. Haven't eaten chocolate in four days and I've lost half a stone. Mike texted me last night and everything is good. Must learn not to go red.
"I weigh 55.8 kg.
"I think I am bulimic."
Katie says she didn't realise how bad things were. She and her mum only recently found the diary.
"I'm not sure which came first, diabetes or eating problems," Katie tells Newsbeat, as she looks through photos of her sister.
"But I know that before Lisa was a diabetic she was completely happy, would eat what she wanted and wasn't funny about food at all.
"When she was diagnosed as diabetic she was told to keep diaries and write down what she was eating and what her sugar levels were."
"I keep having to make myself sick otherwise I feel guilty about what I've eaten."
"I feel so fat. I hate myself. I start working at the pet shop tomorrow. Disco at FC tomorrow, going with Holly."
"I had a really bad hypo at lunch. I was sitting with Mike and his girlfriend. I don't think he thinks I'm fit any more."
Almost everyone with type 1 diabetes will have a "hypo" at some stage. Hypos (hypoglycaemia or low blood glucose) happen when your blood glucose level drops too low.
In people who don't have diabetes, the right amount of insulin is usually produced at the right time so their blood glucose level doesn't go too high or too low.
But in people with type 1 diabetes, the balance of insulin, food and physical activity sometimes isn't right and blood glucose levels drop too low.
"I went to dance today and the gym. I haven't made myself sick for ages! Saw Mike again today. V boring day."
At this point Lisa wasn't aware of diabulimia.
"Over Lisa's time as a diabetic it changed," Katie tells Newsbeat. "They [diabetics] have to look really hard at what they eat when diagnosed.
"I think Lisa looked at it too hard. It was to the point where when she ate food she wouldn't have any sauce, any butter, no nothing on it.
"Sometimes she would just have half a jacket potato or she would just have fish not cooked in oil, no nothing, and she would lose a hell of a lot of weight."
"I remember once Mum gave her an ice cream and she was so proud that she'd eaten this but she was so ill because her stomach rejected it as she hadn't been eating enough."
"I hate being diabetic. I can't eat when I want (like not having to eat in the evening) cos I don't want to put on extra weight."
Katie remembers how Lisa changed her eating habits as time went on.
"She was clever to start with - not eating a lot - but when she got the pump and things - she realised if she didn't take her insulin she would lose weight anyway - if she didn't take her insulin she could eat all the foods she wasn't supposed to."
An insulin pump is a battery-operated device that provides regular insulin throughout the day via a tiny, flexible tube (cannula), inserted under the skin. It can give someone with type 1 diabetes more flexibility.
"I've been doing stomach exercises and bum exercises and going to the gym like every day, I can't do any more or I'll die from exhaustion, but maybe that's a good thing as I'm so fat.
"I'd better go and burn some of my dinner off like doing star jumps or something, please let me die."
At this stage, in 2002, Lisa's family didn't realise just how bad things were getting.
"The diabetic is in charge of their care, they know how much insulin is needed and it's up to them to look after themselves," Katie tells Newsbeat.
"Me and my family, we assumed she knew what she's doing. There was nothing we could do and if she said she's done something... she's basically had her life in her own hands."
"I went swimming today and did about six lengths. Boring. I've been hiding skimmed milk in my room so I don't get as much fat from semi-skimmed!"
"Didn't go to school today. I've now been writing a diary for a year.
"So in the past year I've become bulimic - but I'm getting better. Yeh.
"But I've lost 1 and a half stone. I now weigh 7 and a half stone."
"Went back to school today. Lesley and Phoebe had a fight. I threw up some pasta, I ate too much. I don't want to lose any more weight before I go to the hospital in two weeks."
"One month until Christmas! I really want to go to hospital on Thursday so I can eat lunch without feeling guilty, but I'm a bit scared about my weight. I felt really bad on Sat coz I didn't eat round Holz."
"Joe and Tom texted me. I've been told they think I'm well fit. GREAT my weight loss is paying off."
Katie talks about her sister's love of "baking cakes and cooking curries" adding that she just "ate it because she didn't take her insulin".
"As time went on she realised she could run her blood sugars high, not take insulin, eat what she wanted and lose weight anyway.
"She wasn't knocking back desserts, coke and sweets but when it came to food she'd literally eat what she wanted."
With that it brought on awful side-effects and, Katie says, "problems with her stomach, problems with her feet".
"She's just generally getting worse and worse and you can tell, there's a picture here - see how pink her cheeks are - that's one of the signs of it.
"Whenever you saw Lisa, if her cheeks were that colour you knew she wasn't taking her insulin."
Lisa also developed serious stomach pains.
"She had this stomach condition where she was eating food but her stomach wasn't processing it and it was coming out the same the other side and she was getting terrible pains - and in and out of hospital between January and April last year.
"They said it was damage she had done through her misuse of insulin and it really got her down."
This was one of Lisa's last entries in this diary.
23 June 2004
"I feel as if I'm going to succeed, hit my red dress again and lose one to one and a half stone by September."
Lisa's mum still has the red dress that her daughter obsessed over.
"Lisa said a million times, 'That's my target dress,' which is pretty sad. I don't even think it's a proper size eight and she was gagging to get back into it. There's no way I could get in that."
In the years after this diary, Katie says Lisa was in and out of hospital and "even when she was smiling you could tell there was something else going on".
"Looking back now since she's died I've realised everything she had to do and how hard it must've been for her.
"I was aware she had to take insulin," says Katie. "But I didn't know how involved she had to be, and with this diabulimia thing I didn't realise about other people having it and that's only really come to light since she's died.
"I just think it's really sad. If Lisa had help 10 years ago maybe she'd still be here because she'd be looking after herself."
The UK's first ever diabetes and eating disorder service has launched at King's College in London.
The charity, DWED (Diabetics With Eating Disorders) has been campaigning to have omitting insulin to lose weight officially recognised as a mental illness.
A new set of guidelines for the treatment of eating disorders, which includes how best to treat those who also have diabetes, is expected to be released by the National Institute of Health and Care Excellence (Nice) in early 2017.
On Monday it will be a year since Lisa died.
"I don't want to sit here all day and be crying all day and upset 'cause it was the most awful week of my life," says an emotional Katie.
"I just want to turn it into something more positive and a bit more cheerful but we will remember her in some way, yes."
There's more information on diabetes at BBC Advice.
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