Depends on what they're saying.
If they're chastising you or telling you to lose weight when you're not overweight, that's not okay.
If they're simply giving you general advice about healthier choices then you're being incredibly judgemental and unkind. How do you know they don't follow that advice? Perhaps they eat lots of healthy foods, but in too large amounts. Perhaps they eat lots of healthy foods but don't move enough (for a variety of reasons). Perhaps they used to be a lot bigger but are losing weight now by following their own advice. Perhaps they're struggling a lot with their mental health or dealing with a huge amount of other stuff and healthy eating has taken a back seat for a bit.
The fact of the matter is that health professionals are qualified to make recommendations. But they don't have to follow it themselves, nor do recommendations cure/prevent every ill or account for people's complex lives that can make it extremely hard for some people to lose weight and maintain that weight loss.
Equally, does every dermatologist wear SPF 50 every day? Would you judge them if they had spots? And if you spotted a dietician in the supermarket with a trolley full of crisps and cakes would up think they were being inappropriate? What if you went to see an orthopaedic surgeon and they had a limp? None of these things are absolutely optimal in some respects, but no person is 100pc of the time.
The nurses are human beings and are, as such, flawed. If the advice is evidence-based and if it's delivered in an appropriate way for you then just let them do their job. They're paid to think about your health; you're not paid to think about theirs.