by Jennifer Nelson, M.S., R.D. and Katherine Zeratsky, R.D.
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Mayo Clinic nutritionistsJennifer Nelson, M.S., R.D. and Katherine Zeratsky, R.D. |
This week's topic is calories. It seems that predicting the number of
calories you need to cut — or to burn — to lose weight is being
questioned. Furthermore, the number of calories thought to be in foods
may or may not be what's actually in the food. Let's look a bit deeper.
Calories and weight loss
The traditional calorie calculation goes like this: 1 pound of
body fat equals 3,500 calories. So if you decrease your intake — or burn
— 500 calories a day, you should lose 1 pound a week (500 x 7 = 3,500).
Although this equation works mathematically, researchers are noticing
that it doesn't seem to work as well in the messier real world.
Nutrition experts agree that many factors — in addition to calories —
affect the rate of weight loss. These include your genetics, your
metabolic rate, what your body is losing (fat, muscle or water), how
your body adjusts to fewer calories and more exercise, and even how much
sleep you get. All these factors can alter the prediction of weight
loss. And that makes it difficult to predict how fast you or anyone else
will lose weight.
Calories in food
Also being questioned is the century-old Atwater method for
calculating the number of calories found in foods according to their
carbohydrate protein and fat contents. It's long been thought that if
you know the grams of carbohydrate, protein and fat in a food you can
get a fairly good estimate of the total calories in that food. So, for
example, 1 gram of carbohydrate has 4 calories and 1 gram of fat has 9
calories — knowing how many grams of each are in the food, you can
estimate the total calories.
However, food and nutrition experts are having to rethink this
assumption. It appears that the Atwater method overestimates the number
of calories in a food or mixed diet by as much as 25 percent compared to
more precise measurements that mimic what a person may actually digest,
absorb and metabolize. If that's the case — and that hasn't been proven
yet — it may mean that food labels and tables listing calorie content
of foods might be off.
These questions fascinate nutrition experts, who welcome reexamination
of old assumptions. But what does it mean if you're trying to educate
people about losing weight? What does it mean when your attempt to lose
weight isn't as easy or speedy as you'd like? Be reassured that the
age-old recommendation to "eat less and exercise more" is still in
effect. Steady, life-long commitment remains important.
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