[zug_zug]

> that many of those with the lowest intake of treats were on a diet due to bad health

I haven't read this study, but any study that isn't complete garbage normally would examine the to groups across all variables (age, gender, weight, health, etc) and deliberately control for any systematic differences between groups.

[tuukkah]

You can never control for all variables when humans are involved. (You can only control for variables that your data contains.)

EDIT: From the article: "[There's a] need for future research to incorporate more accurate measures, such as urinary sodium excretion, to more precisely assess the impact of sodium intake as a potential confounding factor."