Can you lose weight by keeping the thermostat turned down?

Dear Cecil:

We've heard that when you're cold, your basal metabolism kicks into high gear and your body burns up calories faster. Does this mean you can lose weight by keeping the thermostat turned down? Also, is there a "good" time of day for stoking up on more munchies? In other words, is there a point during the day when your metabolism is really cranking and the calories from an extra dessert will just go up the flue rather than around your waist?

Cecil replies:

If half the ingenuity the Teeming Millions waste on trying to avoid dieting and exercise could be devoted to something constructive, we’d cure cancer in a week. Let me start by laying down the two basic axioms of fat science. Axiom 1: There is no good way to lose weight that does not involve eating less or exercising more. Axiom 2: If the choice is between eating less and exercising more, choose the latter.

Now for the specifics. You do burn up calories faster when it’s cold, although after a while your body adapts and the effect is reduced. Not that it matters much. Unless you exercise at the same time, you’re not going to be burning the right calories. When your metabolism is in “rest” mode, you burn mostly glucose, the simple sugar that’s found in your blood. Your fat cells remain untouched, and you don’t lose any weight. But when you engage in sustained, strenuous (i.e., aerobic) exercise, your system shifts gears and you start metabolizing body fat. This typically occurs about 15 or 20 minutes into your workout, when you experience the familiar phenomenon known as “hitting your stride.” Suddenly, things seem easier. That’s because fat is a more efficient fuel — it provides 18 times more energy than glucose. Working out in the cold (within safe limits, of course) will burn even more fat, although curiously enough so will working out in the heat — your body uses up a lot of calories trying to keep you cool, too. Once fat metabolism gets started, it takes at least an hour, and maybe as long as four or five hours, before your body switches back to “rest” mode. So you can safely eat a big meal after working out and be confident you’ll burn it off pretty fast.

Which brings us to question two. Your metabolic rate does fluctuate during the day, peaking out around midday. Studies indicate that a load of calories taken at night will result in more weight gain than the same amount taken in the morning. So if you must make a pig of yourself, do it before noon. Morning is also the best time to exercise if you want to lose weight. One study indicated that two-thirds of the calories you burn up in the morning come from fat, whereas less than half come from fat in the afternoon.

A couple other interesting factettes: Whatever you do, don’t try to lose weight by simply knocking off eating altogether. If you do, your bod simply shifts into “starvation” mode. Your metabolism slows down in order to conserve your energy supply and you work off fat very slowly. Also, the act of eating itself kicks up your metabolic rate 5 to 30 percent. This has led some nutritionists to suggest that you ought to eat lots of little meals during the day rather than one or two big ones. Knowing human nature as he does, however, Cecil fears the Teeming Millions will regard this as license to munch out all day on Snickers bars, which needless to say is not the idea. Try Cecil’s Experimental Do or Diet instead. 7 AM: Fruit on high-fiber cereal with low-fat milk. Gets the blood sugar up, increases mental alertness. 10:30 AM: Half an hour of vigorous exercise, e.g., running, cycling, swimming, handball, etc. 11 AM: The big meal of the day. Preferably it shouldn’t be that big, but if you must pork out, now is the time to do it. Include fish several times a week. 3 PM: Optional snack, such as fruit, veggies (raw carrots especially recommended), trail mix. For a change, try popcorn (lightly salted, no butter), a good fiber source. 7 PM: Light supper. Cecil prefers salad with French bread and candles. 8 PM: Vigorous lovemaking with the party(s) of your choice. Good for the disposition, and burns off ugly fat too. Three months from now: Report your results to Cecil, especially if this whole thing works. You’ll have the satisfaction of contributing to the betterment of mankind, and I’ll get the Nobel prize.

Send questions to Cecil via cecil@straightdope.com.

Comment on this Column