WELLNESS
07/21/2015 01:24 pm ET Updated Jul 21, 2015

Here’s The Best Online Calorie Calculator, According To Science

But it still might not work for you.
Want to lose weight, but don't know where to start? A free online calorie calculator -- the Body Weight Planner -- is now available to the public after several years as a research tool for scientists at the National Institutes of Health.  
 
There are plenty of free tools online to help you count calories in diet and exercise, but this one is noteworthy because its algorithms were validated in several controlled weight loss studies in human beings, notes a press release, and because it takes into account a person's slowing metabolism. 
 
Kevin Hall, a scientist at the NIH's National Institute of Diabetes and Digestive and Kidney Diseases, created the tool. He demonstrated how the calculator works using his own weight loss goals as an example: 
 
 
Hall, a 44-year-old man who wants to lose 20 pounds off his 5’10, 180-pound frame, is going to have to eat about 2,300 calories per day, provided he sticks to his resolution to walk his dog in the mornings three times a week. Once he reaches his goal weight, he’s going to have to maintain that weight loss by keeping up his dog-walking activity level and eating about 2,600 calories a day.
 
The NIH bills the planner as a cutting-edge tool that will empower people to take their health into their own hands, but research on the success of such calculators and trackers is mixed, according to Dr. Zhaoping Li, director at the Center for Human Nutrition at UCLA's David Geffen School of Medicine. She praised the federal government for its official nod toward the utility of trackers and calculators, but, she noted, human beings themselves are not “simple machines” who operate on a calories in, calories out basis.
 
That's not news to anyone who has ever tried to lose weight. A depressing study out of London last week estimated an obese man’s chances of reaching a normal body weight at 1 in 210, while the chances were slightly better for women at 1 in 124. For the severely obese, those numbers were even more frightening, and only about 8 percent of obese men and 10 percent of obese women were able to lose five percent of their body weights, a modest but medically significant amount. Most of those who did achieve this weight loss regained it within five years. 
 
Calculators can't provide prescriptions for weight loss or protections against regain -- they are merely standardized guidelines. The problem is that not all metabolisms, circumstances and eating habits are standardized. 
 
“If a professional athlete walked at 3 miles per hour speed for a half hour, they’d burn [calories] totally differently than someone even at the same weight," Li explained.
 
The professional athlete-office worker comparison is  facetious, but the truth is that many factors are at play when it comes to how people consume and burn calories. Environment matters, for example. Everything from work stress to family dynamics to whether or not your neighborhood is walkable can influence exercise levels and dietary habits.
 
And emerging research shows that gut bacteria affects a person's ability to absorb calories, said Li. For instance, food may be absorbed as three calories in a lean person and seven calories in an obese person, she explained, simply because of differences in how gut bacteria breaks down the meal.
 
In other words? Don't expect this calculator to give you a full game plan. Instead, Li recommends a multidisciplinary approach, including buy-ins from family members and doctors. And you'll need to examine the environmental influences of your diet and exercise routine if you want to make a meaningful change.
 
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