I used to blame one of the following reasons for all the extra calories I consumed between Thanksgiving and New Years:

1. Because we're surrounded by people we love, and most of them are trying to get us to eat just one more helping, one more treat.

2. Or because holidays with the family tend to bring up all sorts of emotions (many of them stressful), so emotional eating kicks in - even if we're really good at eating right every other day of the year.

3. Or because we really don't want to avoid the pumpkin pie and turkey stuffing and candied yams - they're our favorites, but they aren't on the table any other time of the year. What the heck - we can indulge just this once, and it won't hurt all that much.

Then comes the day after Thanksgiving, or the week after Christmas, and we truly regret those extra helpings.

We remember those bits of chocolate fudge, the special holiday cookies, and yes, those candied yams, and we really wish we hadn't eaten them, because now they show up as an extra five or ten pounds that we have to work so hard to lose.

This week I discovered that there may be another reason why holidays with the family wreak havoc with our diets. I found it in a book on child development.

Judith Rich Harris started a firestorm of controversy among child psychologists, teachers, and parent groups when she wrote "The Nurture Assumption: Why Children Turn Out the Way They Do." Ms. Harris found some startling evidence that some of our most cherished assumptions about childhood may be wrong.

The most controversial theory, and the main argument in her book, is that parents have less influence over our children's future happiness and success than we think they do. Children mold themselves, according to Ms. Harris, according to the norms and expectations of their peer groups, not their parents.

But parents aren't totally off the hook.

She also said that kids of almost any age act in different ways when they're at home and when they're away from home - and that doesn't change when we grow up. We have different personalities and ways of acting and interacting with family than we do with our business associates, our friends, and with strangers.

According to her, the most successful corporate CEO becomes a kid again when he goes home to Mom.

It's this "multiple personality" idea that made me think of those holiday dinners that add so many inches to our adult waistlines. According to the author, we may be bright, independent, successful people out in the "real world." But take us home again and we relate to our parents and our siblings (and grandma and grandma, too), in much the same way we did when we were kids.

And nothing brings back those family emotions and behaviors as intensely as large family events where we all gather around the dinner table. We might be able to say "no thanks" when a fellow employee offers us a chocolate at work, but it takes real will power to say "no" to Aunt Betsy's homemade fudge, even if we don't particularly like her fudge.

Most families eat responsibly, or try to, every day of the year except at those special family dinners. But when we go to all that work to fill the table with all that food, it becomes natural to eat as much of it as we can.

Since memories have powerful effects on our moods, we don't even need to go home in order to slip back into "holiday eating mode". Just use an old family recipe for holiday cookies, or put the turkey and all it's trimmings on the table, and we discover that "today really isn't a good day for counting points," or "it just wouldn't be Thanksgiving if I didn't have an extra helping of mashed potatoes." We forget the will power and eat the way we're "supposed to" for the holidays.

Is this "multiple personality" theory just an interesting idea, or will it help us stay on our diet during the holidays?

I actually think it might help. Sometimes, knowledge really is power.

Slipping back into old patterns of behavior may be "natural," but it isn't totally beyond our control if we know it's happening. It's the unconscious behaviors that are so difficult to control - bring the reasons for them out in the open, and we can be our strong, successful selves again.

And we don't have to avoid the big family meals entirely - we just need to occasionally remember, while we're there, that we are actually grownups now and we don't have to take the extra helping if we don't want to.

It really won't hurt our aging mother's feelings if we don't fill our plates with Turkey and trimmings at least twice, and then go back for thirds an hour after leaving the table - or if it does, it really isn't our fault.

And if we really can't help ourselves, and end up five or ten pounds heavier by the end of the holidays, we can always count on the New Year's resolutions to get us back on track.