Greggs, fuel of the north. The steak to my bake. The sausage to my roll. The chargrilled chicken to my oval bite. The hero of the high street, filling the gaping maws of the masses and putting a sausage roll in the hands of any man, woman and child with 85p to their name. I grew up in a small Yorkshire town that still doesn't have a Nando's, but – for as long as I can remember – has had not one but two Greggs, very, very close to one another. Just the way it should be.

Suffice to say, I like Greggs a lot, so on paper the "challenge" of eating there exclusively for a week – an idea that came to me after the chain launched its new diet plan, "Minimise Me" – is potentially as good as it's ever going to get. Some have suggested I might ruin Greggs for myself by eating too much of it. Bullshit. The only foreseeable hiccup is that since no one has ever let me b2b that many sausage rolls, I can't bank on the response of my insides.

The weight-loss thing is a secondary concern. I've never stuck to a diet in my life, unless you class "eating nothing but frozen pizzas for my three years at uni" as a diet, which I'm pretty sure you don't. But for the record, my weight at the start of the week is 12st 8lbs.

So here I am, your pound shop Morgan Spurlock, ready to beige out for a solid seven days.

DAY ONE

The first thing I arrogantly overlooked when deciding to only eat Greggs for a week was that I would have to actually visit Greggs. Central London actually has a fledgling Greggs delivery service, but heartbreakingly I'm outside the delivery area both at home and work. So that's that.

I was out last night but I feel fine, until I impulsively order a cold slice of pepperoni pizza for breakfast, which immediately induces a grim eating-last-night's-leftovers feeling. I sit in a nearby park nursing a Greggs coffee, which is better than it has any right to be, and enjoy my pizza-induced hangover breakfast surrounded by pigeons. Not a great start, but I'm not sure I can hold Greggs entirely accountable for this.

The second thing I arrogantly overlooked when deciding to eat Greggs for every meal for a week is that Greggs' "Minimise Me" diet was a carefully controlled experiment put together by a professional dietician, while my interpretation of the diet is very much "Let's see how many steak bakes I can eat before I die."

With this in mind I load up on sausage rolls for lunch and steak bakes for tea (that's "dinner" if you're from the south) because there's no way I'm walking back to Greggs for each meal. It means that most meals I'm eating this week are both a few hours old and cold, but when it comes to Greggs that's pretty much par for the course.

I draw the line at buying stuff for the following day, because I'm not an animal.

DAY TWO

Arguably the best thing about Greggs is the staff. They're an army of salt-of-the-earth dinner ladies who have been poached from their jobs slopping out school lunches, into the fast-paced pasty rat-race. Every transaction is a showcase for their warm smiles, thick arms and solid gold hearts. And they're all called Pauline.

This morning I'm in luck, as Pauline has decided to give me an extra sausage in my sandwich. I'm not sure why I'm being gifted a bonus meat stick, but I'm not complaining. I'm also probably going to be put on some sort of barista blacklist for saying this, but: Greggs' coffee is wonderful and shits all over Starbucks, Pret and anywhere else that apparently burns their beans and milk on purpose.

For lunch I eat a Chargrill Chicken Oval Bite (a non-pasty staple of the Greggs menu), then, for tea, while the whole world seems to be having torturously incredible-smelling barbecues, I'm on a steak bake that I've jazzed up with Sriracha. Two days in and I'm already polishing turds. Well, not turds. Steak bakes. Which I love.

DAY THREE

I've had to re-route my journey to work, setting off an hour early to get to a Greggs. On the plus side, I'm up early, I'm walking more and I'm having breakfast consistently for the first time in about 15 years. Admittedly, one breakfast was pizza, but I feel like I've already pulled off a lifestyle change worthy of a book deal and a Goop profile. Today, I'm celebrating the new me with a continental almond croissant.

Speaking of which: I once worked with an Italian guy who went out to lunch and came back really excited because he had, and I quote, "Found this really incredible boulangerie" (that's European for "bakery"), which we should all check out. After a little probing, the boulangerie turned out to be a little known bakery by the name of "Greggs". Proof that you all need to put your snobby pretensions aside and enjoy the place for what it is: a world quality purveyor of baked goods.

I also ate a chicken and bacon baguette (surprisingly better than Pret) and a couple of sausage rolls for tea. Mildly depressing, yet otherwise unremarkable.

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DAY FOUR

While we're on about sausage rolls, a guy I met in a pub a few years ago who claimed to work in the Greggs factory told me that one of the key ingredients in Greggs' sausage rolls is potato peelings. He revealed this information as if I was going to be horrified and on the phone to Wikileaks within the hour. In fact, the revelation – which, according to the ingredients laid out on the Greggs website, is completely untrue – had the opposite effect on me. I don't know about you, but when I purchase a lukewarm rod of pulped animal for less than a quid, I kind of presume there are going to be worse things than potato peelings in there.

Anyway, for breakfast I eat an apricot and yoghurt bun, which was like eating a scouring pad with a glob of yoghurt in it. Lunch is a write-off too. A Coconut, lime and chilli chicken salad – Greggs does salad now – that comes with a tub of sauce. The sauce is really sickly and essentially inedible, so it's a good job I discover this after dumping the whole lot all over my leaves.

Maybe this is how you lose weight on the Greggs diet? By just not eating anything?

Having ruined most of my salad I'm forced to crack into my tea pasty early, but that means I'm now left Greggs-less for the evening. Half expecting to wake up shivering like I'm late for a fix, it's time to head back to the bakery.

DAY FIVE

I'm not in the mood for risk taking today. Almond croissant. Safe. Tuna Crunch baguette. Can't go wrong. Greggs' own brand crisps. Not as bleak as they sound. Greggs' own brand lemon and lime-flavoured water. I mean, it's water – you can't go wrong. A bun with a plastic monster ring on it. Did you get jewellery with your pudding?

Greggs, we're back on talking terms. Let's forget the salad debacle and move on.

DAY SIX

Breakfast is a two sausage and bean melt. As the name suggests, there are two sausages involved here. They run down either side as a sort of structural support to hold the beans in. A master class in engineering. As the name also suggests, it's all melted together in a congealed blur of cheese and beans. The best.

Sadly, the same can't be said for the katsu chicken bake I pick up for lunch; once you've smashed through the almost impenetrable outer shell, there's just a sad dollop of nauseating curried chicken waiting for you. It's like eating a curried tortoise.

I haven't got enough of my lunch break to make the trek back to Greggs, so unless I eat my tea now – which I'm not going to do because I already learned that lesson – I'm going to have to just deal with it. Six days in and I'm over it. Fuck knows how the people who did a month of eating Greggs for the official Minimise Me diet managed.

DAY SEVEN

With my relationship with Greggs starting to take a nosedive, it's time to celebrate the final day with a blowout. The best thing about buying loads of stuff is that at least there's room for error. My dry-as-a-desert pain au chocolat goes in the bin after one bite. The calzone bake is actually alright, even if it finishes its sad life by dumping sauce out of its back-end all over my desk.

Greggs' ginger beer is decent, the mature cheddar crisps are passable and there are two Belgian buns that I bought because I thought they looked like boobs and that's kind of the level that we're operating on right now. A couple more sausage rolls for good measure because they haven't killed me yet. Consider it a lap of honour; a glorious home run by the boys in blue and orange.

And with that, we're done. Twenty-one meals later, a week of pastry-wrapped highs and lows, all in the name of getting paid. At this point I'm meant to have some kind of revelation. 'Holy shit, I lost seven stone in seven days!' Or 'I am now Britain's fattest man!' Except none of that happened. I'm literally the exact same weight as I was before: 12st 8lbs. I didn't dramatically shit my pants and I don't have unexplainable heart pain.

Sure, Greggs, we need some time apart. But ultimately, I love you.