How can I keep off weight once I have lost it?

It is really difficult to do it by yourself. In one study of more than 1,000 women, those who regained the least weight had kept in regular touch with their mentors by phone or face-to-face. For the women who did return to their original weights, their greatest difficulty was carrying on with exercise. Once you have lost the weight, you need to keep in close touch with whoever helped you to do so - for years afterwards, even.

It's obvious that when parents are always arguing and stressed, their children may suffer from anxiety, too. But a friend says she read that they can also become physically ill, with fevers and infections. Is there any evidence for this?

Surprisingly, there is. University of Rochester (New York) academic Mary Caserta followed the parents of 169 children for more than three years. The children of the parents with the most emotional stress had significantly more physical illnesses, mainly infections, than those in calmer households. This was shown even in the children's immune white-cell counts: they were higher, showing more immune system activity and confirming the extra infection load. Why this should be is unknown, but Caserta's findings naturally kicked off a flood of research into which types of parental stress most affect children. So if you are arguing a lot or are over-anxious, please hide it from your children.

· Do you have a question for Dr Smith? Email doctordoctor@theguardian.com