02/06/2012 12:05 pm ET | Updated Apr 07, 2012

Biggest Nutrition Traps, Part 3: Mean vs. Extremes

In the final installment of this three-part series on the most common mistakes even health-conscious people make with their diets, I want to talk about focusing on the average (or mean) rather than the extremes in your diet.

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The Thanksgiving Trap

A couple of weeks before Thanksgiving, a writer called to interview me for a piece she was doing. The average Thanksgiving dinner is said to contain 3,000 calories. Her story was on ways to burn 3,000 calories over the course of the Thanksgiving-day weekend, ostensibly neutralizing the effect of the big meal.

It was a cute idea (and here's a link to the piece), but it's a perfect example of how we tend to overestimate the impact of our most extreme behavior and underestimate the importance of our typical behavior. Obviously, a single day of overindulging is not going to make you fat, any more than a single hyper-active weekend is going to keep you slim. How much you eat and exercise on all the rest of the days of the year is what's really going to determine your size and shape.

The Sin and Repent Cycle

We seem to be wired to pay more attention to the exception rather than the norm. If we've been really "bad," our impulse is to make up for it by being really "good" for a day or two. But in reality, it's not our worst days or our best days that tell the story. It's not the day that our team wins the Super Bowl and we celebrate by polishing off an entire tray of nachos. Nor is it the next day, when we do penance by eating nothing but cabbage broth. It's all the days in between.

Think of it like a grade point average. Getting an A is great. So is going an entire week without French fries. But a single A has a relatively minor impact on a solid C average. And a single French-fry-less week doesn't do too much to offset the effects of eating French fries the other 51 weeks of the year. Your grade point average would be higher if you focused on getting all Bs -- even if you never got a single A. And you'd be better off nutritionally if you cut your French fries consumption in half over the course of the entire year than if you cut them out entirely for a single week.

Focus on the Mean, Not the Extreme

In other words, small positive changes that become a permanent part of your routine have a much bigger impact than big dramatic gestures that last only a few days. So don't waste too much energy fretting over a particularly bad choice you may have made -- and don't exhaust your willpower on an extreme but short-term correction. Focus instead on improving your nutritional grade point average by making your typical day a little healthier. For some suggestions on small changes that make a big difference, see "Weight Loss Doesn't Have to be a Losing Battle."

Much of what you hear about weight loss is a myth. Find out the truth in Monica Reinagel's new book "How to Win at Losing: 10 Diet Myths That Keep You From Succeeding."

For more by Monica Reinagel, MS, LDN, CNS, click here.

For more on diet and nutrition, click here.