A SmugTwit has just had its email read out on Radio 5 Live. It was boasting that its waist has remained the same size (30 inches, iirc) for many years and includes the SmugTwit ritual claim that this is because of "Moderation in all things."
SmugTwits often attribute their slimness to various virtues - not being greedy/lazy/etc. Most of them, if they were honest, would admit that actually they can, and do, eat whatever they like and as much of it as they like, without gaining any weight, but they enjoy feeling superior to overweight/obese people and attributing excess weight to greed and/or laziness.
Slim people are slim because they have strong, healthy blood vessels and are not sensitive to salt. Their slimness has nothing to do with their moral fibre, nor, indeed, "moderation in all things"...(o:
How to lose weight
How to lose weight