To determine if your Siamese cat is at a healthy weight, you can use the Body Condition Score (BCS) system. This system rates your cat’s body condition on a scale of 1 to 9, with 1 being very thin and 9 being very overweight.

To perform a BCS assessment on your Siamese cat, follow these steps:

1. Stand above your cat and look down at it. You should be able to see a visible waistline behind the ribs and the abdomen should tuck up slightly.
2. Feel your cat’s ribs. You should be able to feel the ribs without pressing too hard, but they should not be visible.
3. Look at your cat from the side. The chest should be visible from the side, but the abdomen should not be sagging.
4. If your cat scores a 3 on the BCS scale, it is at a healthy weight. If it scores lower than 3, it may be underweight and you should consult with your veterinarian. If it scores higher than 3, it may be overweight and you may need to adjust its diet and exercise routine.

It is important to note that every cat is different, and the BCS system is only a general guide. If you have concerns about your cat’s weight, it is always best to consult with your veterinarian.