The thyroid issue is a good example - because I think it does go under reported a lot of the time.
The dog recently was diagnosied with hypothyroidism. TBH it had gotten pretty bad in him before I saw a vet, so convinced was I that he just needed to move more and eat less. But however much I cut back on food for him, he never lost so much 100g.
So he went back to the vet for a third time and I insisted on a blood test which revealed low thyroid hormone.
So he was given thyroid hormone replacement.
6 weeks later and despite him now eating twice as much food as he was before, the weight is literally falling off him.
Which makes me think...
a) hormones have a massive influence on whether or not you lose weight, the dog was being chronically underfed (almost 50% of the recommended calorie intake for his age and size) and it wasn't making the slightest bit of difference to his weight which was way too high
b) how often does a relatively 'mild' case of something like hypothyroidism in humans just never get diagnosed. How many people walk around thinking their tiredness is just 'normal' tiredness when really they have low thyroid hormone levels?