"He just grinned and said quietly, 'Barley sugars are the answer'. And it's been there from day one," said Mr McKinlay, 67, who has been flown to Auckland by World Vision for the 40th 40 Hour Famine this weekend.
"I think those who retail barley sugars have cause to thank Professor Scott for that advice."
Mr McKinlay directed the first two events before returning to teaching.
One reason the job with World Vision appealed was his experiences seeing poverty up close.
After school, he was a volunteer teacher in Western Samoa - "a bit different from safely middle-class Dunedin" - and years later he ran a school in Lima, Peru.
Mr McKinlay is now at the helm of his fifth school, Northern Southland College in Lumsden. The students there are, of course, taking part this weekend.
The 40 hour concept originally came from Canada, but was tweaked for New Zealand and Australia. The first New Zealand event raised about $250,000 - a total of around $72 million has now been given by Kiwis over the years.
The concept - involving a challenge and sponsorship from friends and family - has been widely imitated by other organisations, but was something new at the time.
Mr McKinlay said the event gave people a sense of making a difference to a problem that otherwise could seem too big to tackle.
"It's gone amazingly well. I think it's a brilliant idea because it gives people some notion of what it's like to go without food," Mr McKinlay said. "We don't understand that in this country ..."
The 40 Hour Famine added the idea that "other people could sponsor you to do it".
40th famine
• First New Zealand event started in 1975, directed by school teacher Trevor McKinlay.
• Concept proved hugely successful, and has been widely imitated by other charities since.
• A total of around $72 million has been raised through New Zealand 40 Hour Famines.
• The 40th event is running this weekend, with money raised going to Malawi in southeast Africa, which is in the middle of a severe food crisis.