"I know from people I met in hospital who had also received treatment elsewhere in Scotland, it does not have to be this bad."
Ms Johnstone spent the best part of three months at the Beatson West of Scotland Cancer centre last year and kicked off a campaign for better meals by collecting statements about the food from fellow patients.
She said dinners often looked like they were meant to, but did not smell or taste familiar. "There were a huge number of meals that were refused," she said, explaining she lost more than a stone in hospital - despite the anti-sickness drugs that kept nausea from chemotherapy at bay.
Following her column on the issue in The Herald last year, David Maguire, a Glasgow restaurateur, got in touch. He was also worried about the quality of food he saw when visiting his sister Ruth, who had suffered a serious motorbike accident, at the Southern General.
Now Mr Maguire, whose dining establishments included Glasgow's Stazione and Lux, has visited the two super kitchens which supply hospitals in NHS Greater Glasgow and Clyde with patient meals and looked into the reheating process which takes place near the wards. Mr Maguire said: "People say hospital food is anaemic, bland and mushy. What I am trying to answer technically is, why?"
He has obtained recipes that show some meals, such as chilli con carne or beef and mushroom casserole, resemble cookery. Others, such as sausage in onion gravy, require the combining of ingredients that have been processed elsewhere. Only mushrooms are chopped in-house.
According to Mr Maguire, the super kitchens operate five days a week from 9am to 5pm.
He said: "Everything is done at a pace to fit these hours."
He said he was told there was no bank of freezers for storing a large supply of food, despite staff requests. In the hospitals, he believes there are too few staff available to enhance the food even by putting things that cook quickly in the oven at different times.
In some hospitals the food is plated on the wards. At the Beatson, food is plated up centrally and covered. Mr Maguire said the covers he saw had no holes to prevent condensation. According to his findings, by the time Ms Johnstone got a cheese omelette it had travelled frozen from the manufacturer to a super kitchen, been switched to a different container, reheated for 90 minutes and then plated and left under a cover where moisture builds.
"That is why it is inedible," said Mr Maguire. "There are basic procedural things at every stage that compromise the food. You could take the same raw materials and a chef could turn it into edible stuff."
NHS GGC said freshly peeling and chopping carrots was a "manually intensive approach" that "would simply not be cost-effective when catering on a scale such as ours". The board added: "Pre-diced vegetables are widely purchased in quality food retail outlets by discerning home cooks every day."
NHS GGC stress they listen to feedback, citing changing their supplier of mashed potato as an example. Their statement added: "Another improvement also sees a senior nurse on every ward overseeing each meal time with a designated meal-time coordinator ensuring patients get the meal they ordered and that it is at the correct temperature.
"Our meals are served by staff trained in food service allowing our nurses to concentrate on providing assistance to those patients who need help with eating and drinking at the bedside."