They suffer from many health issues that pugs are prone to, including breathing, spine and leg problems all of which are exacerbated when a pug is overweight.
The best way to check if your pug is the right weight, rather than its actual weight is by its Body Condition Score (BCS), where a BCS of 5 out of 9 is ideal. Probably slimmer than most people realise.

Pugs can live up to 15 years or more, and most will have health issues along the way, plus the breed is particularly prone to weight gain. Therefore the correct amount and quality of food, as well as regular exercise, is an important formula to keeping them fit and healthy.
It is important that you do not overfeed your pug as an overweight pug will find it difficult to sustain any form of exercise. They love their food, and unfortunately many of us are guilty of overindulging our beloved (and demanding) pugs by giving them extra treats and titbits from our food. Sadly, this means we could be killing them with kindness.
Obesity in dogs is classed as a welfare issue by DEFRA under their welfare legislation.
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For further Pug Health issues articles, please go to the following webpages:
Pug Health & Wellbeing | The Pug Dog Welfare & Rescue Association
&
Seasonal Hazards for Pugs | The Pug Dog Welfare & Rescue Association