Eating more than two eggs a day could give Mark Edwards irreversible brain damage due to a rare condition.
The 35-year-old is among one in 10,000 people in the UK born with Phenylketonuria (PKU), a condition where the body is unable to break down amino acid phenylalanine from protein, which build up in the blood and brain.
It means that people with the condition are unable to live off of a normal diet and even if the recommended guidelines are exceeded, it could lead to serious consequences.
Mark, of Llanegryn, in Gwynedd , said it is something he has comes to terms with having to live without meat, cheese, poultry, eggs and milk, unless they are low-protein alternatives.
He said: "I was diagnosed with the condition from birth and all babies are tested for it. I was put on a low-protein diet from birth.
"It was virtually unheard of in those days and my mum told me I was in my baby chair crying for food but she didn't know what I'd be able to eat.
"Back then there was no internet, Facebook or Twitter so you were on your own and had no one to speak to."
Mark, who works for food manufacturers Brighter Foods, has to attend regular check ups to make sure his protein levels are safe and he has monthly blood tests.
He said: "If I'm over what I'm supposed to have, I start to feel irritable and that's when I know my levels are too high so I cut back down on things.
"If I ignore it and carrying on eating protein I have anxiety and depression and if I carried on again I would get irreversible brain damage."
The NHS says without treatment, PKU can damage the brain and nervous system, which can lead to learning difficulties.
At present, Mark's recommended daily allowance for protein is 6g or 0.2oz's a day, but the daily level recommended for each PKU sufferer differs.
He said: "I have always been aware that I've had this condition since I was really young and what the outcome would be if I ate normally.
"It's easier growing up having to have a specialised diet rather than having to go back on it but I actually love the smell of bacon, that's the one thing I wouldn't mind trying but it doesn't bother me. I am matter of fact about it."
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Despite not being able to eat much protein in his diet, Mark said he is one if the fittest people in his workplace and he is currently training for the Manchester 10k which he has completed four times.
He is involved in a campaign to make the drug Kuvan - the only medication used to treat PKU - available on the NHS and to ask drug company BioMarin to make if affordable to patients.
The cost for 140 Kuvan currently stands at £4,000, a sum Mark says is too expensive for most people, but the benefits would be significant with Mark being able to up his protein intake to 15g or 0.5ozs a day.
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Last week he and members of campaign group NSKPU met with politicians in Westminster, including supporter and Plaid Cymru's Westminster leader Liz Saville-Roberts, and handed in a petition of 17,000 signatures.
He said: "It would make such a difference to my life."
A spokesperson from BioMarin said: "The burden and severity of PKU as a disease in the UK is not recognised by NICE or the NHS.
"BioMarin has made an offer to the NHS which is very competitive compared to other markets but it has not been accepted."
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