By Matt Fitzgerald | For Active.com
Counting calories is a simple concept. Throughout the day you rely on food labels and online resources to determine the number of calories contained in each food and beverage you consume. At the end of the day you add it all up and, voila, you know exactly how many total calories you took in.
But what is simple in principle is almost impossible in practice. A few factors combine to make it almost unobtainable to accurately measure your daily calorie intake. One component has to do with the difference between how calorie counts are determined in the laboratory and how calories are extracted from food in your body. To determine the calorie content of foods, scientists incinerate them inside a device called, appropriately enough, a calorimeter. This device incinerates all types of foods equally well.
Your body is different. It extracts calories more easily from cooked foods, soft foods and low-fiber foods than it does from raw foods, harder foods and high-fiber foods. So, for example, if you eat 100 calories of steamed white rice, your body will absorb more calories than it would from 100 calories of raw lettuce.
Apart from this issue of calorie extraction, the calorie information you see on food packaging and on restaurant menus is seldom 100 percent accurate in the first place. A 2011 study by researchers at Tufts University found that only 7 percent out of 269 items on restaurant menus contained calorie counts that were within 10 calories of advertised totals.
Things get even more dicey when you try to count calories in home-prepared meals and snacks. Even experts admit that their estimates are little more than wild guesses. “I have a Ph.D. in nutrition, and I can’t tell if my dinner is 500 or 800 calories just by looking at the plate,” said Jean Mayer, lead author of the study mentioned above, in an interview for U.S. News & World Report.