He's only just returned from a holiday touring Brittany on a tandem with his long-term girlfriend Fenella, so when James Morton zips nimbly on his bike to our meeting place at a park in the west end of Glasgow - bashfully accepting friendly smiles from strangers en route - he's looking fit and chilled.

But not for long.

Settling down to enjoy a piece of his favourite cake (shop-bought for our photograph), he stops to remember the number of public appearances and demonstrations he's scheduled to do over the next few weeks before returning to university. There's bread-making demos at the Belladrum music festival, the Edinburgh Fringe, Dundee Flower Festival, BBC Good Food Show and the Wigtown Book Festival, and a judging gig for Borders Biscuits. Plus a constant stream of media interviews.

Give him the merest crumb of sympathy, though, and he gives you the brush-off.

"I feel very privileged because my life has totally changed since I appeared on the Great British Bake-Off, and it has made me a whole lot busier," declares the only Scot of the three finalists in the last series of the BBC show, which attracted more than seven million viewers. Then 21, he was also the youngest (notably all were men, more of which later). "It's very rewarding and it's given me opportunities I wouldn't otherwise have had."

Morton, the son of Shetland-based BBC radio broadcaster Tom, says he'd have been unable to publish his first book at age 22 without his newly acquired TV profile. Due to launch later this week, it's all about his pet pastime: baking bread.

"After GBBO we were called in and asked if we'd like to write a book. I put together a proposal for a guide to breadmaking because I felt there wasn't a book about that on the market that address the home baker. And I didn't want to go down the path of putting out yet another book about baking cakes." He met with his publisher last October, started writing in November and completed his 60,000-word commission within a month.

The most difficult recipe in the book is for panettone, and his favourite is for yum-yums. "Greggs' yum-yums are awesome," he says, smacking his lips, "but they're better when you make them yourself. So are doughnuts. In fact, anything deep-fried. I tried making cronuts the others day; basically they're deep-fried croissant dough. They were good, but then I deep-fried some ready-made croissants from Tesco, and there was no difference."

All this is prevarication. What I find pertinent are Morton's withering comments about the rising number of people who don't eat bread as they believe they have an intolerance to gluten, a natural protein derived from wheat. Morton believes the symptoms some people experience after eating bread - bloating, cramping and flatulence among them - is nothing to do with gluten, and he wants to make a stand against the "scaremongering and lobbying" by companies producing "unnecessary" health foods to combat it.

"It's ridiculous!" he exclaims. "For many immoral and frankly silly reasons, a gluten-free diet is now a health trend. A quarter of North Americans follow a gluten-free diet and that's 25% more than there should be.

"A few people can't eat gluten. The former affects 1% of us in the UK, the latter is rarer. We're talking about definitely less than two per cent of people who should not eat gluten.

"Otherwise, there is no evidence to suggest gluten is causing your problems. Adopting a gluten-free diet is a massive, severely life-restricting undertaking yet there have been no placebo controlled trials into stomach upsets that aren't caeliac related.

"Cutting out bread might make people feel better, so they think gluten was the culprit. I don't doubt there's a possibility the bread is actually causing these symptoms. Just take a look at the unnecessary chemicals on the ingredients label of a supermarket loaf." He rhymes off a list that - apart from the essential flour, water and salt - includes yeast, flour proteins, salt, vinegar, dextrose, fructose, soya flour, rehydrogenated vegetable fat, E472e emulsifier, and E300 flour treatment agent.

These additives, he says, are nothing compared to how most big-brand breads are made. "Most shop-bought breads are underbaked to the point that if you squeeze the inside of them they will turn back into dough. Starch is very difficult to ingest. I can hazard a guess at the bloating that would result from eating a few slices of raw bread dough."

More than 80% of commercially made bread in the UK is based on the Chorleywood Bread Process (CBP), which uses lower-protein wheat, additives and high-speed mixing to cut the need for fermentation.

Home-made bread can be "very good for you indeed", says Morton, who first learned how to bake from his maternal grandmother on Shetland. "You can make bread that lasts for weeks without any preservatives with just flour, salt and water. It takes longer to make it properly; that's why commercial bakers use the CBP process, so they can produce bread as quickly as is humanly possible.

"I also find making bread an enlightening, almost meditative process. Kneading takes you away from your busy life. I bake when I need to get away from things."

Despite all these pleasant distractions, he is determined to pursue his medical career - he says the two disciplines are not unrelated. He's about to enter his fourth year of Medicine at Glasgow University and has two foundation years ahead of him before he qualifies. Then he will specialise. He says he hasn't a clue about which area to focus on - unlike Fenella, who is in the same year as him and plans to go into Geriatrics. The pair recently moved in together: the advance on his book helped him buy his first flat in the west end. They live next to their old rented flat, where Morton's brother Magnus still lives. He has a half-brother Dave Nelson, the songwriter-guitarist for Paulo Nutini, and a younger sister Martha, who is also studying Medicine at Aberdeen University.

His mother is a GP in Shetland and his other half-brother Sandy is in A&E at a hospital in Derry, Northern Ireland. Is he attracted to A&E, where there's a shortage of doctors?

"There's always a rush from medics to get onto the A&E run-through course, but after they see what goes on, they get dispirited and the drop-out rate is phenomenal," he says.

One of the main reason he's obsessed with breadmaking is its overlap with science. "There's a huge amount of chemistry and microbiology involved in bread, especially in sourdough," he enthuses. "I'm fascinated by yeast but the best thing is bacteria, which co-exists with yeast in the sourdough starter." He talks of yeasts munching on starch, breaking down sugars, the multiplication of carbon dioxide and bubble creation. He admits to a burning desire to write another bread book, one that would go into more details of the alchemy. "You can go very science-y and very deep into the processes and feeding schedules and sourdough starters and you can do interesting things with a bacteria and different types of grain. It would explore all that and come up with my own formula."

Given Scotland's climate is not conducive to growing bread-quality wheat, he agrees there's potential in using heritage grains from his homeland of Shetland, such as beremeal and barley. However he would prefer if Scotland grew more rye, his favourite grain. Another idea would be a book about home-brewing, again no stranger to the wonders of alchemy. He likes to make his own beer and one of his best friends is Owen Sheerins, a fellow medic from Kilmarnock who is currently the British champion home-brewer.

First, he's keen to see how his first book performs.

l Brilliant Bread by James Morton is published on August 29 by Ebury, priced £20.