There's an upside to the cold weather that has hit much of the country over the past few weeks. Exercise in the cold can help you burn more calories -- at least according to the January issue of the Harvard Health Letter. Here's an explanation:

"There are two types of fat in the human body: white fat and brown fat. Brown fat is the heat-producing, calorie-burning fat that babies need to regulate their body temperatures. Most of it disappears with age, but adults retain some brown fat. Dutch researchers reported findings last year that showed that moderately cool temperatures of 61° F activated brown fat in 23 of 24 study volunteers. This is a good thing because brown fat burns calories more efficiently than white fat, and so may help control weight. When we get chilled this winter, we may take some consolation that at least we're firing up those brown fat cells.

"In some countries, the use of cold temperatures for medical purposes is taken quite seriously. Several years ago, Finnish researchers reported the results of a study of 10 women who, for three months, took cold-water plunges (20 seconds in water just above freezing) and submitted to whole-body cryotherapy sessions. Blood tests showed a two- to threefold jump in norepinephrine levels minutes after cold exposure. Norepinephrine is a chemical in the nervous system that wears many hats, including a possible role in pain suppression."