Because of a GBM's aggressive nature, the tumour is generally treated with radical chemotherapy and radiation which wasn't tolerated as well in older people, who would generally have palliative radiation instead to help settle the effects of the tumour.
Given GBM is diagnosed less frequently in younger patients (who would tolerate radical treatment better), it could take two to three years to recruit enough patients for the study.
Dr Jameson said the thinking behind the study was that cutting out carbohydrates puts metabolic stress on tumours.
He said studies in the United States in mice showed a keotgenic diet made little difference to how long the mice lived on average "but if you looked at mice who had a normal diet through radiation and those that had a no-carb diet through radiation there was a dramatic increase [in survival time]".
"The thinking is that tumour cells strongly prefer to use carbs, particularly refined carbs, glucose for fuel so if you deprive them and stress them out with a high-fat, high-protein diet and hit them with some other treatment at the same time they are much less able to resist the effects of radiation.
"Stressing out the tumour cells leaves them much more vulnerable; they haven't got the energy to try and repair the damage."
Dr Jameson said the study participants' results would be compared to medical records of people who've been treated for GBM over the past seven years.
There are three other similar studies underway around the world that are studying up to 40 patients each. Dr Jameson said some of those are using diet but some are using a powder, called KetoCal, that participants reconstitute. However, he said he felt putting patients on KetoCal wasn't an option as it was restrictive.
Dr Jameson said a ketogenic diet wasn't for everyone, and he tried it himself for seven weeks.
"I thought if our patients are going to have six and half weeks radiation with this diet I should try it. It was stressful. It's not just the tumour that gets stressed. If you're not the person who does most of the cooking it's very stressful for the cook."
He said the diet meant cutting out starchy vegetables and a lot of fruit, which was what he found "really tough".
It was also inclined to make people constipated. And multivitamin supplements would be given to patients to ensure they don't become deficient, given how many fruits and vegetables are ruled out.
Because of the study's small sampled size, Dr Jameson said it was likely that this study's findings may be pooled with three other studies that are underway around the world. Each of those studies aims to have about 40 participants.
"With small numbers the results can be all over the place, but if you pool them together then you have about 130, 140 patients," he said.
"If it does look promising then we'll need to do a randomised trial and you can't really control for that, so then the challenge becomes whether you give them bags of Ketocal or you do it with diet."
Dr Jameson said cancer patients and their families want to know what they can do that can make a difference.
"The whole thing about diets and cancer and going off sugar is out there. A lot of people do it anyway. This is the first time I've seen anything like the mouse studies that say [the diet] is a good idea but that it looks to be during treatment and not just diet by itself."
Anyone interested in finding out more or being recruited for the study can contact Dr Jameson on 839 8899 or email michael.jameson@waikatodhb.health.nz.
