Possibly just the way the stars are aligning but we have recently experienced a number of sits where the home owners thought it would be a good idea to put their beloved chubby pet on a diet just as the sit starts.
I’m guessing the thinking behind this is that Fido may “ease “ into the new regime think these newbie humans just don’t know the rules 
. Regardless it adds another level of challenge to the sit that we really don’t need.
Thank you for you attention
It’s hard when it’s new food they aren’t keen on.
We’ve also had hosts that have wanted us to walk their dogs more than they do, so they could lose weight.
With one, it was amazing what a difference just 1 week of consistent short walks did. The hosts left a very lazy dog who loved mooching around his garden, and they returned to a dog that got hugely excited at the sight of the leader 
@HappyDeb We had that experience last summer. The HO took us on a very slow walk with the dog -off lead- and allowed him to dictate the turning point… He was rather overweight and lazy. We, ourselves, love our brisk morning walks with a dog so decided that rythym wasn’t going work for us! So we put the dog on his lead and he walked much faster than offlead with the occasional encouraging pull! We also increased the distance he walked. It took him a few days to get used to it and then he was fine! With the food we were told how much in grams but the HO herself just used her hand and guessed it. When I actually measured the handfuls it was more than the grams so I measured it acurately, meaning he got less food. He didn’t notice the change.
Anyway…After nearly 4 weeks of increased exercise and a little less food he was becoming slimmer & fitter and looked great! We wondered how the owner would react…..
but she didn’t even notice!!! 
So the poor dog is probably fat and lazy again.. 
Fully agree! There is one thing if this is needed due to a recent vet visit and the change may be urgent due to some medical issues like allergies or inflammation.
But if not, this just creates additional anxiety for the pets.
I can also see how this can be an “easy way out” for hosts that are to permissive when it comes to feeding routine and treats. So they won’t be seen by the pet as the “bad guys”.
Also with cats, if you don’t feed them as expected, they are able not to even let you sleep, be it during the night or super early morning… just trying to get their way.
We have done several sits with pets on weight loss diets . It’s very hard to resist those mournful eyes of the “starving “ pets . The most stressful sit was a cat , who was only fed once a day and her food had to be weighed out precisely and so she was “hungry “ all the time . She was a lovely cat but she meowed so very loudly every time you went in the kitchen because she was certain we were starving her !!!
After one such sit we received a text - took xx to the vet she has lost xxkgs ..
At first I thought it was a complaint but it was followed up with “I am so pleased she is her target weight now”
In retrospect, I’m sure I was ‘used’ on one sit to attempt to break the dog’s habit of waking up at 4am and demanding attention, in the form of barking at ever-increasing volume and intensity, none of which was mentioned in the hastily scribbled welcome guide that I received upon arrival. Apparently he was allowed upstairs, but only after 6.30/7.00am.
The sit was for three weeks, and the first couple of weeks were a battle of wills during which I religiously ignored the early morning wake up calls as instructed, (whilst screaming silently into a pillow). By week three, I was broken. Feeling far less charitable and rather mug-like, I decided that the owners could train their own blinking dog when they returned. ‘Fido’ enjoyed some lazy mornings curled up on the carpet at the side of my bed, and I learned some valuable lessons for future sits.
Ha, we’ve experienced this multiple times. And understatement of pet calorie intake (e.g. not mention pet eating human food). And overestimation of typical pet exercise. All three situations cause pet calorie deficit.
As we’ve gained housesitting experience we’ve asked more rigorous questions and applied great pet care experience. We’re not trained as vets or pet diet specialists. If in doubt, we revert to common sense in maintaining reasonable pet care.