"Why I cheated on Sam Wood."

Dear Sam Wood,

First up, I want to say I’m sorry.

I never meant to hurt you.

I had high hopes for our relationship. Really, I did.

I thought we would be great together, a match made in heaven: you, a spunky young fitness dude who could tell me what to eat and how to exercise; me, a girl who sometimes undoes the top button of her jeans when she sits down.

When I signed up for your 28 Day program, I pledged that I would be loyal to you forever. In sickness and in health. For richer or for poorer.

At that point, I was already looking back on the “old Zoe” with disdain.

“Old Zoe” ate cake for breakfast. “Old Zoe” thought Doritos, guacamole and wine was a healthy dinner.

“Old Zoe” sometimes got breathless walking up the stairs and tried to laugh it off in front of her coworkers while her lungs lit themselves on fire and exploded. “Old Zoe”, I decided, was dead to me.

The weekend before the program began, I told my friends to forget what I looked like. It's possible the words "I'm going to be so thin and glowing with health next time you see me that you won't even recognise me and might be intimidated" passed my lips. But I can't confirm.

It would be sad, I pondered, that I wouldn't be able to fit into any of my clothes anymore, but I guess it would be a good excuse to buy an entire new wardrobe in a size eight.

Or size six. Did they make size four in Australia?

Who knew how fit and thin I would become? Would I have to order from a specialist clothing store for superfit Instagram models? I wouldn't mind, I supposed, so long as the delivery time wasn't too long.

Yes - I saw the potential problems and I faced right up to them.

Sam, when I looked into your eyes staring back at me from my computer that first Monday morning, I really thought this would be the start of our new life together.

It lasted about 45 minutes.

That first day, I caved and ate chocolate fondue for morning tea, which was weird, because even I do not normally eat chocolate fondue on an average weekday morning.

I guess it was partially the fact that I couldn't move my legs, having never done more than five squats in a row before.

I jumped back on the bandwagon with a delicious egg salad for lunch and fell right back off again by eating the rest of a tub of caramel ice-cream on the pretence of "cleaning out the freezer".

(Sam, I know you said to clean out the freezer before we started the program. Again, I am sorry. I am not great at taking instructions).

The next few days passed in a blur of illicit eating. I knew it was wrong, but it felt so right! There were no limits to my hunger!

Each morning, I did my workout, and then the cravings began. As I chewed my tofu, I thought about my next secret meal: a sneaky afternoon burrito? A block of Cadbury Oreo chocolate? A wheel of cheese? Hot chips? A small village?

Every night, I caved. Sometimes, I caved before the night. Sometimes I caved before midday. Once - and I am so, so very sorry Sam - I had a Danish for breakfast.

Each morning, I pledged to re-commit. To strengthen my relationship with Sam. There were so many people in the private Facebook group doing such great things! They were all becoming thin and fantastic, and I was eating a packet of Wagon Wheels!

Yesterday, I got off the bus after work and walked straight into Coles. I bought two bags of Doritos, two avocados, two lemons and two bottles of wine. My boyfriend had cooked Sam Wood's dinner (vegetarian ratatouille), but I ate guacamole and wine and passed out on the couch in a delicious food coma.

Watch Zoe struggle through a workout with Madonna's personal trainer.

Sam... I think this is the end of us.

I know this is a cliche, but in this case it's true: It actually isn't you. It's me.

The 28 Day program is really great. I love the exercises.

I will - and this is a big deal for me - continue to do them, despite the sometimes-not-being-able-to-walk-afterwards thing. It clearly works for a huge range of people, and you're an excellent motivator.

But this is the thing, Sam, and I hope we can still be friends: I'm not ready to commit yet.

There's so much food to explore! So many flavours of Messina to try! Cadbury keeps reinventing itself with chocolate-y gimmicks, and I just couldn't live with myself if I didn't try them all!

(FYI: Strawberry Oreo is a winner, Vegemite is a non-starter).

I appreciate you giving us a go. I really do. Maybe one day I'll be ready, but for today, there are some cupcakes calling my name.

"Old Zoe," they shout. "Join us!"

And I do.

Sorry (but sort of not sorry), Sam Wood.