A weight loss doctor emailed me in response to my column two weeks ago entitled "The Mystery of Metabolism". In that article, I had written that 3,500 calories is equal to one pound of fat. This is a commonly accepted figure that can be found in almost all nutrition, health, and fitness books.
He wrote, "It actually takes approximately 4,000 calories to deposit or burn one pound of fat and not 3,500 only. Here are the actual computations. Given: 1,000 grams = 2.2 pounds, and 1 gram of fat = 9 calories. Then: 1 pound of fat x 1,000 grams / 2.2 pounds = 454 grams of fat, and 454 grams x 9 calories / 1 gram = 4,086 calories."
There is a big difference between 3,500 calories and 4,086 calories. What is the correct figure?
The doctor's computation is logical and correct because one gram of fat is equal to nine calories but 3,500 calories is also correct because of other factors. Here is the explanation from Dr. Patrick Bird of the University of Florida's College of Health and Human Performance
"When we burn fat, or other nutrients, heat is produced, which is measured in calories. Each gram of fat generates 9 calories, and 454 grams equals one pound. But a pound of fat is not all fat. It's about 10% water. All of our body tissues--fat, muscle, bone, skin--contain some water. And water has zero calories.
"In addition, not all the nutrients we eat are completely absorbed from the digestive tract to meet metabolic needs. In the case of fat, roughly 5% is eliminated in the feces. This 10% water content and 5% non-absorbed fat accounts for the 15% difference between the calculated 4086 calories and the actual 3500 calories in a pound of fat."
The doctor's email got me to thinking about how people are always talking about calories but many don't really know what a calorie is, where it comes from, how it is measured, etc. So here are some calorific facts.
What is a Calorie?
A calorie is unit of heat. According to physicist Paul Doherty, a calorie is the heat flow needed to raise the temperature of one gram of water by one degree Celsius (1.8 degrees Fahrenheit).
A calorie in physics is different from a calorie in nutrition. Doherty explains that one food calorie (which should technically be spelled with a capital C) is 1,000 times bigger than one physicist's calorie (spelled with a small c). In other words, a food calorie is actually a kilocalorie (Kcal). It is the amount of heat needed to raise the temperature of one kilogram of water by one degree Celcius. Sometimes, the physics calorie is called a small calorie while the food calorie is called a big or large calorie. Whew! No wonder one website starts its definition of calories with an ice-breaker question: How many calories do you burn just trying to understand what a calorie is?
So now you know that a cup of rice has 220,000 physics calories or in food terms, 220 Calories or 220 kilocalories. Since it is difficult for the general public to deal with all those zeros, the term "calorie" spelled with a small c is usually used when referring to food or exercise. In a nutrition label, it will appear as "cals" or "Kcal". So there is no further confusion, for the rest of this article, the word "calorie" refers to a food calorie, Calorie or kilocalorie.
If you buy European or Australian food products, you may have noticed the word "joules" or "kilojoules". A joule is the metric system's equivalent of a calorie. One food calorie is equivalent to 4,184 joules. In his article, "Counting Calories", Doherty notes, "In the United States, advertisers can claim a can of diet soda has "less than one calorie." In Australia the equivalent statement just doesn't sound as impressive: "less than 5000 joules." On the other hand, candy advertisements in Australia can say that you'll "get a megajoule jolt from our candy bar!"
Here's more food or calories for thought. According to Julia Layton of the "How Stuff Works" website, we tend to associate calories with food, but they apply to anything containing energy. For example, four liters of gasoline contains about 31 million calories. She says, "You could drive a car 35 kilometers on the calories in 217 Big Macs".
Where do Calories Come From?
Physiologist Len Kravitz answers this question for us: "It is actually plants that create the primary molecules in food that contain the energy quantified as calories. Green plants create these molecules from carbon dioxide and water by capturing energy from the sun in a process called photosynthesis."
Plants use this energy from the sun to create carbohydrates, which plants then use to create fats and proteins. Animals and humans absorb these nutrients when they eat plants or when they eat other animals. The same applies for fish in the ocean. The bottom line according to Kravitz is that "the primary source of all calories is carbohydrates created by plants from carbon dioxide and water by capturing the energy of the sun". In short, calories come from the sun. I think it's fascinating to realize that the fat stored in your abdomen or hips originally came from outer space.
How are Calories Measured in Food?
Doherty explains: "To measure the calorie content of food accurately, scientists use a bomb. A bomb calorimeter to be precise. The food sample to be measured is dried and ground into a powder. Then it is placed into the bomb calorimeter, a strong metal container surrounded by a water bath. The metal container is pumped full of pure oxygen at 30 atmospheres pressure and the food is ignited. The resulting energy released is fast and violent; just like a bomb. The steel container holds in the explosion. The calorimeter turns the energy stored in the food sample into heat flow. The temperature increase of the water and metal of the calorimeter reveals how many calories the food contained." Now you know what food scientists do in their laboratories - they blow up food.
From these experiments, scientists know that one gram of fat contains 9 calories, one gram of protein or carbohydrate contains four calories, and one gram of pure alcohol contains seven calories.
These figures are rounded off for ease in calculation. Fat actually has 9.3 calories while protein and carbohydrate have 4.2 calories per gram. Also, according to Dr. Bird, the amount of heat generated from fat differs a little for various foods depending on fatty acid content. For example, there are 9.5 calories in one gram of fat in meat and 9.25 calories for dairy products.
How are Calories Burned During Exercise Measured?
It's quite easy to grab hold of a chart showing how many calories are burned during various types of exercise. The information is available over the Internet, in nutrition manuals, and in fitness books. The groundwork for the research behind this information dates all the way back to the 1890's.
By measuring the heat produced by the body during exercise, scientists are able to determine the equivalent in calories. This method is called "direct calorimetry".
Another method involves measuring the amount of oxygen used and the amount of carbon dioxide produced during exercise. This is an example of "indirect calorimetry". The exerciser breathes through a mouthpiece or is placed in a special room called a metabolic chamber where ventilation is tightly controlled.
Scientists have found out that the burning of carbohydrates during exercise is equivalent to 5.05 calories for every one liter of oxygen consumed. For fat it, is 4.73 calories per one liter of oxygen. They also found out that there is a greater production of carbon dioxide when carbohydrates are burned compared to when fat is burned. So, scientists can accurately determine how many calories come from carbohydrates and how many come from fat during a single session of exercise. In fitness textbooks, the figures are rounded off to 5 calories per one liter of oxygen.
Scientists have also discovered that while resting (sitting quietly while reading a book or watching TV), the average person burns one calorie per kilogram of body weight per hour. In terms of oxygen, it is 3.5 milliliters of oxygen per kilogram of body weight per minute. This is what is known as your resting metabolic rate or RMR. If you burn more calories than the average person, you are considered to have a fast metabolism and if you burn less, then you have a slower than normal metabolism. This is also the definition of one MET or one metabolic equivalent.
When you read a book or an article that says that jogging burns 8 METS, it simply means that jogging burns eight times more calories than when you are resting. So if you weigh 120 pounds, you are burning 54.5 calories per hour while resting and 436 calories per hour of jogging.
Any activity that burns 3 to 6 METS is considered to be of moderate intensity while an activity that burns more than 6 METS is considered to be a vigorous or high intensity activity. METS are usually used to determine the intensity when you take a treadmill stress test.
Most cardio machines (treadmill, bike, elliptical trainer, and rower) base their calorie burning formulas on a reference person who usually weighs 130 or 150 pounds. Unless you weigh exactly that much, the number being displayed on the console is slightly inaccurate. Here's how to make it more accurate.
Find out from the gym staff what the cardio machines calculations are based on. Let's assume its 130 pounds. Divide the number of calories burned by 130 pounds. Multiply the answer by your weight in pounds.
For example, the treadmill's display console says you burned 300 calories. Divide 300 calories by 130 pounds. The answer is 2.30 calories per pound. Multiply that by 120 pounds (your weight). The answer is 277 calories.
Then, if you are feeling bad because that's all the calories you burned for one hour of walking, console yourself with the fact that you burned 277,000 physics calories.