DEAR DR. BLONZ: Is it possible that cold is an unappreciated fat-loss gimmick? A social media nutritionist used the example that one glass of ice water uses up about eight calories of energy as it warms to body temperature once consumed. Eight calories are not much -- about the amount in a half-cup of sliced cucumbers. But could this add up if cold foods were routinely consumed? What about taking cold showers? I realize that this all seems too good to be true, but I wanted your comment on his logic. -- T.O., San Diego
DEAR T.O.: This question gets aired periodically, and I am guessing it will make the rounds more frequently if it is now on social media; it fits right in the “too good to be true” category.
Calories get used to maintain body temperature within the range for its biochemical reactions. If a food consumed is cold, calories will be passively expended to bring it up to body temperature. We should also consider what happens if a food is warmer than body temperature. In that instance, the excess heat energy in the food would, in theory, spare a few of the body’s calories that would have been expended had the warm food not been eaten. Using the converse of that online nutritionist’s reasoning, this suggests that eating warmer food would inhibit the loss of weight.
While there is a logic here, it’s off by a thousandfold. Once understood, it becomes clear that the practical impact of food temperature on weight gain, or loss, is virtually nil.
We first need to appreciate that thermochemical calories are used in physics, whereas nutritional calories are used with foods and metabolism. A thermochemical calorie is the amount of energy needed to raise 1 gram of water 1 degree centigrade. A nutritional calorie, the one most people are familiar with, is 1,000 times a thermochemical calorie. (A nutritional calorie is defined as the amount of energy needed to raise 1 kilogram of water 1 degree centigrade.) In science textbooks and journals, nutritional calories are referred to as kilocalories (kcal) to avoid mix-ups. As per your online experience, the equating of these two has led to bogus conclusions.
For example, let’s start with eight ounces (227 grams) of refrigerator-temperature water at 41 F, or 5 C. Once consumed, body energy will bring that water up to body temperature, 98.6 F (37 C) -- an increase of 32 degrees centigrade (37 – 5 = 32). Multiplying 227 grams x 32 degrees gives us 7,263 thermochemical calories. We now need to express this as nutritional calories, which involves dividing by 1,000; this results in about 7.3 nutritional calories to warm the eight ounces of cold water. Assuming 3,500 nutritional calories in a pound of body fat, it would take about 30 gallons of cold water to use up the caloric equivalent of a pound of body fat.
Cold showers don’t offer much, either. When experiencing a cold shower, the body shunts blood away from the skin’s surface to avoid unnecessary heat loss. As with the cold water, there will be some loss of caloric energy, but it will, again, not be enough to make any significant contribution to the loss of body fat.
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