The nursery assistant was clearly a lovely woman: kind and great with children. But as I watched her play with my two-year-old daughter, I felt a growing sense of unease.
She was only in her 20s, but she was already obese - morbidly so. She moved slowly and breathlessly, her face flushed.
Would she, I wondered, have the lightning reflexes needed to save an adventurous toddler from imminent danger?
And what sort of unhealthy habits would she teach my daughter, who would be eating her lunch and tea there each day?
Looking around, I noticed that she wasn't the only extremely overweight member of staff. I couldn't help worrying about the message this was sending to the children in their care: that being very fat is normal and - when children adopt role models so readily - even desirable.
My anxiety about this was the main reason I chose not to send my daughter to that nursery, despite its Ofsted rating of 'Good'. Instead, she goes to another, where the staff are all a healthy weight.
Is this snobbery or 'fatism'? I don't think so, but plenty will disagree with me.
This is the first time I have publicly admitted to feeling this way. Aware that the reaction would be anger and vilification, I censored myself. I told everyone I preferred the other nursery because it was smaller and friendlier. I knew I would be accused of discrimination, or 'fat-shaming', if I admitted the truth.
It's not politically correct to comment on anyone's size any more, and certainly not to say anything negative about obesity. Some even see the word "fat" as equivalent to a racial or homophobic slur.
Fat-positivity - also known as fat acceptance - has gone too far. Originally a response to discrimination against those who aren't slim enough to fit into society's beauty ideal, it's now an excuse for the severely obese to celebrate their bodies, the consequences be damned.
Activists say that 'fat is beautiful' and being obese isn't a problem. Anyone who points out it's not a good thing to be so overweight is condemned. Telling a woman she should think about losing weight for her health is, apparently, now "anti-feminist".
Take last week when I, perhaps foolishly, entered a Facebook discussion on obesity. A friend had shared a blog post by an overweight woman who was expecting a daughter. Worrying her child would also be overweight - a state she seemed to assume was not preventable - she talked about how she would bring up her child to deal with "fat antagonism" and help her grow into a "fat-positive person".
The response was a roar of approval: everyone agreed the woman's sentiments were marvellous, and wasn't it terrible that large women are made to feel ashamed of their bodies.
But I found it problematic - and said so. People should not be fat-shamed, but I had to point out that it was not inevitable the woman's daughter would become fat. Nobody is born obese.
And, more importantly, being overweight is not healthy, so, rather than teaching her daughter to accept it, she could teach her that it was something to be avoided if possible . . . and how.
While I didn't expect my comments to be very well-received, I didn't anticipate the hostile reception I got. I was sworn at and accused of being discriminatory and of "trolling". When I tried to defend my position, I was told I was upsetting people by making them feel bad about themselves.
Scientific evidence was denied - people said I was misquoting studies linking obesity to heart disease. I was asked to stop commenting. Shut up and go away.
My crime? Being a healthy weight. I was told the outsized don't want to be dictated to by slim people who can't understand what it's like to be fat - lumping me and everybody with a BMI under 25 together, as if we were all Kate Moss. But as I, and most people who aren't overweight, know only too well, staying a healthy weight isn't easy.
For me, it has been a lifelong struggle. The only reason I'm slim (I'm a size 10), and by no means skinny (I have a tummy and thighs that jiggle), is because I watch what I eat and exercise regularly.
Perhaps I feel so strongly about this because I'm a slim person with a fat person inside, wanting to burst out. My body clings on to every calorie it can. A doctor told me evolution had ensured I would survive a famine - not that useful for a 21st-century North London girl with a sedentary job.
So I have little sympathy for those who blame their genes or hormones for being fat. My grandmother was morbidly obese, and I have a hormonal condition - an underactive thyroid - which causes weight gain.
When my thyroid stopped working, I rapidly put on weight, going up to a size 14 and almost 11 st (I'm only 5 ft 3 in). I hated it: my thighs rubbed together and I had a muffin top. It took several years for medication to regulate my hormones and several more to lose the weight I'd gained.
It wasn't about dieting, it was about establishing a routine that would keep me slim for life: doing at least half-an-hour's exercise every day and never eating more than 1,500 calories. But I don't just want to stay slim for my health: I like being able to wear close-cut, fashionable clothes and feeling fit, especially now I have a toddler to run after.
Rolls of fat are not attractive - I shouldn't be scared to say that.
Research has proven that, in many ways, being obese is as unhealthy as smoking. It causes cancer, heart disease and diabetes and can impede fertility. Studies also disprove the notion one can be fat and fit. The heavier you are, the more likely you are to suffer from heart failure or stroke.
If that nursery assistant had been chain-smoking, everyone would have condemned her. But as a public health concern, the only real difference between smoking and obesity is that you can't passively get fat.
Although even that is open to question. For studies have shown your friends can have as much impact on your size as your genes. Your chances of becoming obese go up by a staggering 57 per cent if your best friend does. A friend in greed truly is a friend indeed.
It's not just because you're likely to spend time sharing fries or tubs of Haagen-Dazs. It's because it changes your perception of what is an acceptable weight. Obesity becomes the norm.
That, on a larger scale - pun intended - is what has happened to society. According to obesity statistics, 27 per cent of adults in England are obese and a further 36 per cent are overweight. So the majority of people are now fat: it's banal, not exceptional.
When size 16 is the average, it seems normal and desirable. It might be, for a woman who is 6 ft, who at size 16 probably won't be overweight. But a 5 ft woman almost certainly would be.
Vanity sizing means clothing sizes have increased along with women's girth, normalising larger bodies. While I may be a size 10 today, in the Fifties I would have been a size 14, which was then considered voluptuous.
When people talk about Marilyn Monroe being a curvy size 16, usually to make themselves feel better, they don't realise she would fit a 10-12 in today's clothes. Society is in a state of denial.
Whatever the apologists say - and the fat lobby has tried to blame the rising obesity problem on everything from the ubiquity of junk food to an airborne virus - in most cases, obese people are responsible for their own bulk.
There's a simple reason you put on weight: you expend fewer calories than you ingest. Many fat people say that they have a slow metabolism, but it's been shown the overweight often have faster metabolisms than slim people.
Once any underlying medical conditions have been dealt with, there is no reason the majority shouldn't be able to achieve a healthy weight.
Yes, some do have complex psychological or emotional issues that cause them to overeat. But is telling them it's fine to be obese really going to help them?
People can't help being tall or short, old or young. We can't help the colour of our skin, our cultural background or the place of our birth. We shouldn't criticise anyone for these things. Obesity isn't the same: people become fat.
I don't think that the disgust response to obesity is a social construct. I believe it's innate because we know unconsciously that it's a dangerous state.
Discrimination is never good. But neither is obesity. So let's stop celebrating it, and instead offer a bit of tough love.
This article was first published in the Daily Mail.