Eating at night has long been associated with weight gain. Years ago, nutrition pioneer Adele Davis gave her well-known advice to “eat breakfast like a king, lunch like a prince and dinner like a pauper.” Yet the conventional wisdom today is that a calorie is a calorie, regardless of when you eat it, and that what causes weight gain is simply eating more calories than you burn. Nutrition experts call this the calorie in/ calorie out theory of weight control. According to the U.S. Department of Agriculture’s Weight Control Information Network web site, “it does not matter what time of day you eat. It is what and how much you eat and how much physical activity you do during the whole day that determines whether you gain, lose, or maintain your weight.” CONTINUE READING BELOW A study in the journal Obesity added to the confusion by suggesting that there may be more to nighttime eating than just overeating calories. Northwestern University researchers found that eating at night led to twice as much weight gain -- even when total calories consumed were the same. But this research was done on mice, not humans, and the reason for the weight gain is unknown. And a single mouse study should not cause us to toss out the wealth of evidence supporting the calorie in/calorie out theory. Still, there are good reasons to be cautious about eating at night. Diet books, dietitians, and even Oprah recommend not eating after dinner (other than a small, calorie controlled snack) because it’s just so easy to overdo it.