I AM wary of security guards who work in the retail sector. I understand that they do an important job and do not begrudge them their big walkie-talkies, but I had a nightmare once about being falsely accused of lifting a packet of Pacers (pre-striped) from Fine-Fare and still carry the emotional scars.

Consequently, when I leave a shop and realise I am going to walk past a security guard, I hold on to my receipt for dear life. If, for whatever reason, I don’t have a receipt, I “walk naturally,” an exaggeratedly loping gait adopted by gangsta rappers and drunks.

So I was perturbed when I was stopped by a security guard on my way IN to a convenience store. “Excuse me,” he said.

I panicked. I nearly said: “They didn’t give me a receipt.”

But then I realised I didn’t have any groceries on me. Maybe I looked shifty. Maybe they were being proactive, like the police in Minority Report, and had identified me as a potential shoplifter thanks to my “natural walk.”

“Yes?” I lamely offered.

“Can you settle an argument?”

I doubt it, I thought. I usually cause them. “Go on.”

“He reckons . . . ” – he indicated an embarrassed- looking young man filling the chiller section – “. . . you can turn fat into muscle. You can’t, can you?”

I’ll admit I wasn’t expecting this. Of course you can’t turn fat into muscle, you just can’t. It’s like changing marble into cheese. But, in the confusion of the moment, I couldn’t remember why.

“No, you can’t.”

“And why not?”

I looked around, hoping that Magnus Pyke or Dr Miriam Stoppard might walk in.

“They’re just different.” That should do it, I thought. It didn’t. They were still looking at me.

“They’ve got a different cellular structure.” I was pleased with that. I remembered the term “cellular structure” from Superman The Movie. That was definitely a science term.

I felt sorry for the chiller man, who up to this point had lived his life with the sure knowledge that you could turn fat directly into muscle in some sort of weird alchemical experiment. Now I was tearing his certainties apart.

It reminded me of a former colleague from my reporting days. He was the office junior, so we would give him onerous tasks such as making cups of tea and doing vox pops (ie, standing in the howling wind and rain with a notebook and camera while asking those punters too slow or distracted to avoid oneself what they think of the finer points of education policy/soup/etc.)

He came back one winter morning shivering violently. It had been a cold day and the passing pensioners uncommonly nimble. “Get that boy a cup of tea,” said the normally flint-hearted editor.

“Oh, no, it’s all right. I’ve got this,” said Junior, his lips blue and the first hint of frost-bite about his fingertips. It was an ice-cold can of Coke, so cold steam was curled around it.

“You need a hot drink.”

“No, you know how when you’re hot you’re supposed to have a hot drink to cool you down?”

We nodded. We’d all heard that old wives’ tale.

“Well, I’m cold, so I’m having a really cold drink to warm me up.”

Apparently, he’d done that since he was a child, despite the evidence which must have built up over the years. It’s a wonder he hadn’t become an ice-based super-villain.

I snapped back into the moment. The guard and the chiller man were still looking at me. I think by that point they were finding me wanting.

“Look, they’re just different. It’s like saying you can change marble into cheese.”

A moment of silence.

“See, I told you,” said the security guard and the chiller man turned away, defeated by the power of my argument.

I went and bought my ironically-cold Coke, then “walked naturally” out of the shop past the security guard. He was looking the other way.