Bo Nash is 38. He lives in Arlington, Texas, where he’s a technology director for a textbook publisher. He has a wife and child. And he’s 5’10” and 245 lbs—which means he is classed as obese.
In an effort to lose weight, Nash uses an app to record the calories he consumes and a Fitbit band to track the energy he expends. These tools bring an apparent precision: Nash can quantify the calories in each cracker crunched and stair climbed. But when it comes to weight gain, he finds that not all calories are equal. How much weight he gains or loses seems to depend less on the total number of calories and more on where the calories come from and how he consumes them. The unit, he says, has a “nebulous quality to it."
Tara Haelle is also obese. She had her second son on St Patrick’s Day in 2014 and hasn’t been able to lose the 70 lbs she gained during pregnancy. Haelle is a freelance science journalist based in Illinois. She understands the science of weight loss, but like Nash, she doesn’t see it translate into practice. “It makes sense from a mathematical and scientific and even visceral level that what you put in and what you take out, measured in the discrete unit of the calorie, should balance,” says Haelle. “But it doesn’t seem to work that way.”(...)
The process of counting calories begins in an anonymous office block in Maryland. The building is home to the Beltsville Human Nutrition Research Center, a facility run by the US Department of Agriculture. When we visit, the kitchen staff are preparing dinner for people enrolled in a study. Plastic dinner trays are laid out with meatloaf, mashed potatoes, corn, brown bread, a chocolate-chip scone, vanilla yoghurt and a can of tomato juice. The staff weigh and bag each item, sometimes adding an extra two-centimeter sliver of bread to ensure a tray’s contents add up to the exact calorie requirements of each participant. “We actually get compliments about the food,” says David Baer, a supervisory research physiologist with the Department.
The work that Baer and colleagues do draws on centuries-old techniques. Nestle traces modern attempts to understand food and energy back to a French aristocrat and chemist named Antoine Lavoisier. In the early 1780s, Lavoisier developed a triple-walled metal canister large enough to house a guinea pig. Inside the walls was a layer of ice. Lavoisier knew how much energy was required to melt ice, so he could estimate the heat the animal emitted by measuring the amount of water that dripped from the canister. What Lavoisier didn’t realize—and never had time to find out; he was put to the guillotine during the Revolution—was that measuring the heat emitted by his guinea pigs was a way to estimate the amount of energy they had extracted from the food they were digesting.
Until recently, the scientists at Beltsville used what was essentially a scaled-up version of Lavoisier’s canister to estimate the energy used by humans: a small room in which a person could sleep, eat, excrete, and walk on a treadmill, while temperature sensors embedded in the walls measured the heat given off and thus the calories burned. (We now measure this energy in calories. Roughly speaking, one calorie is the heat required to raise the temperature of one kilogram of water by one degree Celsius.) Today, those ‘direct-heat’ calorimeters have largely been replaced by ‘indirect-heat’ systems, in which sensors measure oxygen intake and carbon dioxide exhalations. Scientists know how much energy is used during the metabolic processes that create the carbon dioxide we breathe out, so they can work backwards to deduce that, for example, a human who has exhaled 15 liters of carbon dioxide must have used 94 calories of energy.
The facility’s three indirect calorimeters are down the halls from the research kitchen. “They’re basically nothing more than walk-in coolers, modified to allow people to live in here,” physiologist William Rumpler explains as he shows us around. Inside each white room, a single bed is folded up against the wall, alongside a toilet, sink, a small desk and chair, and a short treadmill. A couple of airlocks allow food, urine, faeces and blood samples to be passed back and forth. Apart from these reminders of the room’s purpose, the vinyl-floored, fluorescent-lit units resemble a 1970s dorm room. Rumpler explains that subjects typically spend 24 to 48 hours inside the calorimeter, following a highly structured schedule. (...)
Measuring the calories in food itself relies on another modification of Lavoisier’s device. In 1848, an Irish chemist called Thomas Andrews realized that he could estimate calorie content by setting food on fire in a chamber and measuring the temperature change in the surrounding water. (Burning food is chemically similar to the ways in which our bodies break food down, despite being much faster and less controlled.) Versions of Andrews’s ‘bomb calorimeter’ are used to measure the calories in food today. At the Beltsville center, samples of the meatloaf, mashed potatoes and tomato juice have been incinerated in the lab’s bomb calorimeter. “We freeze-dry it, crush into a powder, and fire it,” says Baer.
Humans are not bomb calorimeters, of course, and we don’t extract every calorie from the food we eat. This problem was addressed at the end of the 19th century, in one of the more epic experiments in the history of nutrition science. Wilbur Atwater, a Department of Agriculture scientist, began by measuring the calories contained in more than 4,000 foods. Then he fed those foods to volunteers and collected their faeces, which he incinerated in a bomb calorimeter. After subtracting the energy measured in the faeces from that in the food, he arrived at the Atwater values, numbers that represent the available energy in each gram of protein, carbohydrate and fat. These century-old figures remain the basis for today’s standards. When Baer wants to know the calories per gram figure for that night’s meatloaf, he corrects the bomb calorimeter results using Atwater values.
Trouble begins
This entire enterprise, from the Beltsville facility to the numbers on the packets of the food we buy, creates an aura of scientific precision around the business of counting calories. That precision is illusory.
The trouble begins at source, with the lists compiled by Atwater and others. Companies are allowed to incinerate freeze-dried pellets of product in a bomb calorimeter to arrive at calorie counts, though most avoid that hassle, says Marion Nestle. Some use the data developed by Atwater in the late 1800s. But the Food and Drug Administration (FDA) also allows companies to use a modified set of values, published by the Department of Agriculture in 1955, that take into account our ability to digest different foods in different ways.
Atwater’s numbers say that Tara Haelle can extract 8.9 calories per gram of fat in a plate of her favorite Tex-Mex refried beans; the modified table shows that, thanks to the indigestibility of some of the plant fibers in legumes, she only gets 8.3 calories per gram. Depending on the calorie-measuring method that a company chooses—the FDA allows two more variations on the theme, for a total of five—a given serving of spaghetti can contain from 200 to 210 calories. These uncertainties can add up. Haelle and Bo Nash might deny themselves a snack or sweat out another few floors on the StairMaster to make sure they don’t go 100 calories over their daily limit. If the data in their calorie counts is wrong, they can go over regardless.
There’s also the issue of serving size. After visiting over 40 US chain restaurants, including Olive Garden, Outback Steakhouse and PF Chang’s China Bistro, Susan Roberts of Tufts University’s nutrition research center and colleagues discovered that a dish listed as having, say, 500 calories could contain 800 instead. The difference could easily have been caused, says Roberts, by local chefs heaping on extra french fries or pouring a dollop more sauce. It would be almost impossible for a calorie-counting dieter to accurately estimate their intake given this kind of variation.
Even if the calorie counts themselves were accurate, dieters like Haelle and Nash would have to contend with the significant variations between the total calories in the food and the amount our bodies extract. These variations, which scientists have only recently started to understand, go beyond the inaccuracies in the numbers on the back of food packaging. In fact, the new research calls into question the validity of nutrition science’s core belief that a calorie is a calorie.
Using the Beltsville facilities, for instance, Baer and his colleagues found that our bodies sometimes extract fewer calories than the number listed on the label. Participants in their studies absorbed around a third fewer calories from almonds than the modified Atwater values suggest. For walnuts, the difference was 21 per cent. This is good news for someone who is counting calories and likes to snack on almonds or walnuts: he or she is absorbing far fewer calories than expected. The difference, Baer suspects, is due to the nuts’ particular structure. “All the nutrients—the fat and the protein and things like that—they’re inside this plant cell wall.” Unless those walls are broken down—by processing, chewing or cooking—some of the calories remain off-limits to the body, and thus are excreted rather than absorbed.
by Cynthia Graber and Nicola Twilley, Ars Technica | Read more:
Image: Catherine Losing
In an effort to lose weight, Nash uses an app to record the calories he consumes and a Fitbit band to track the energy he expends. These tools bring an apparent precision: Nash can quantify the calories in each cracker crunched and stair climbed. But when it comes to weight gain, he finds that not all calories are equal. How much weight he gains or loses seems to depend less on the total number of calories and more on where the calories come from and how he consumes them. The unit, he says, has a “nebulous quality to it."
Tara Haelle is also obese. She had her second son on St Patrick’s Day in 2014 and hasn’t been able to lose the 70 lbs she gained during pregnancy. Haelle is a freelance science journalist based in Illinois. She understands the science of weight loss, but like Nash, she doesn’t see it translate into practice. “It makes sense from a mathematical and scientific and even visceral level that what you put in and what you take out, measured in the discrete unit of the calorie, should balance,” says Haelle. “But it doesn’t seem to work that way.”(...)The process of counting calories begins in an anonymous office block in Maryland. The building is home to the Beltsville Human Nutrition Research Center, a facility run by the US Department of Agriculture. When we visit, the kitchen staff are preparing dinner for people enrolled in a study. Plastic dinner trays are laid out with meatloaf, mashed potatoes, corn, brown bread, a chocolate-chip scone, vanilla yoghurt and a can of tomato juice. The staff weigh and bag each item, sometimes adding an extra two-centimeter sliver of bread to ensure a tray’s contents add up to the exact calorie requirements of each participant. “We actually get compliments about the food,” says David Baer, a supervisory research physiologist with the Department.
The work that Baer and colleagues do draws on centuries-old techniques. Nestle traces modern attempts to understand food and energy back to a French aristocrat and chemist named Antoine Lavoisier. In the early 1780s, Lavoisier developed a triple-walled metal canister large enough to house a guinea pig. Inside the walls was a layer of ice. Lavoisier knew how much energy was required to melt ice, so he could estimate the heat the animal emitted by measuring the amount of water that dripped from the canister. What Lavoisier didn’t realize—and never had time to find out; he was put to the guillotine during the Revolution—was that measuring the heat emitted by his guinea pigs was a way to estimate the amount of energy they had extracted from the food they were digesting.
Until recently, the scientists at Beltsville used what was essentially a scaled-up version of Lavoisier’s canister to estimate the energy used by humans: a small room in which a person could sleep, eat, excrete, and walk on a treadmill, while temperature sensors embedded in the walls measured the heat given off and thus the calories burned. (We now measure this energy in calories. Roughly speaking, one calorie is the heat required to raise the temperature of one kilogram of water by one degree Celsius.) Today, those ‘direct-heat’ calorimeters have largely been replaced by ‘indirect-heat’ systems, in which sensors measure oxygen intake and carbon dioxide exhalations. Scientists know how much energy is used during the metabolic processes that create the carbon dioxide we breathe out, so they can work backwards to deduce that, for example, a human who has exhaled 15 liters of carbon dioxide must have used 94 calories of energy.
The facility’s three indirect calorimeters are down the halls from the research kitchen. “They’re basically nothing more than walk-in coolers, modified to allow people to live in here,” physiologist William Rumpler explains as he shows us around. Inside each white room, a single bed is folded up against the wall, alongside a toilet, sink, a small desk and chair, and a short treadmill. A couple of airlocks allow food, urine, faeces and blood samples to be passed back and forth. Apart from these reminders of the room’s purpose, the vinyl-floored, fluorescent-lit units resemble a 1970s dorm room. Rumpler explains that subjects typically spend 24 to 48 hours inside the calorimeter, following a highly structured schedule. (...)
Measuring the calories in food itself relies on another modification of Lavoisier’s device. In 1848, an Irish chemist called Thomas Andrews realized that he could estimate calorie content by setting food on fire in a chamber and measuring the temperature change in the surrounding water. (Burning food is chemically similar to the ways in which our bodies break food down, despite being much faster and less controlled.) Versions of Andrews’s ‘bomb calorimeter’ are used to measure the calories in food today. At the Beltsville center, samples of the meatloaf, mashed potatoes and tomato juice have been incinerated in the lab’s bomb calorimeter. “We freeze-dry it, crush into a powder, and fire it,” says Baer.
Humans are not bomb calorimeters, of course, and we don’t extract every calorie from the food we eat. This problem was addressed at the end of the 19th century, in one of the more epic experiments in the history of nutrition science. Wilbur Atwater, a Department of Agriculture scientist, began by measuring the calories contained in more than 4,000 foods. Then he fed those foods to volunteers and collected their faeces, which he incinerated in a bomb calorimeter. After subtracting the energy measured in the faeces from that in the food, he arrived at the Atwater values, numbers that represent the available energy in each gram of protein, carbohydrate and fat. These century-old figures remain the basis for today’s standards. When Baer wants to know the calories per gram figure for that night’s meatloaf, he corrects the bomb calorimeter results using Atwater values.
Trouble begins
This entire enterprise, from the Beltsville facility to the numbers on the packets of the food we buy, creates an aura of scientific precision around the business of counting calories. That precision is illusory.
The trouble begins at source, with the lists compiled by Atwater and others. Companies are allowed to incinerate freeze-dried pellets of product in a bomb calorimeter to arrive at calorie counts, though most avoid that hassle, says Marion Nestle. Some use the data developed by Atwater in the late 1800s. But the Food and Drug Administration (FDA) also allows companies to use a modified set of values, published by the Department of Agriculture in 1955, that take into account our ability to digest different foods in different ways.
Atwater’s numbers say that Tara Haelle can extract 8.9 calories per gram of fat in a plate of her favorite Tex-Mex refried beans; the modified table shows that, thanks to the indigestibility of some of the plant fibers in legumes, she only gets 8.3 calories per gram. Depending on the calorie-measuring method that a company chooses—the FDA allows two more variations on the theme, for a total of five—a given serving of spaghetti can contain from 200 to 210 calories. These uncertainties can add up. Haelle and Bo Nash might deny themselves a snack or sweat out another few floors on the StairMaster to make sure they don’t go 100 calories over their daily limit. If the data in their calorie counts is wrong, they can go over regardless.
There’s also the issue of serving size. After visiting over 40 US chain restaurants, including Olive Garden, Outback Steakhouse and PF Chang’s China Bistro, Susan Roberts of Tufts University’s nutrition research center and colleagues discovered that a dish listed as having, say, 500 calories could contain 800 instead. The difference could easily have been caused, says Roberts, by local chefs heaping on extra french fries or pouring a dollop more sauce. It would be almost impossible for a calorie-counting dieter to accurately estimate their intake given this kind of variation.
Even if the calorie counts themselves were accurate, dieters like Haelle and Nash would have to contend with the significant variations between the total calories in the food and the amount our bodies extract. These variations, which scientists have only recently started to understand, go beyond the inaccuracies in the numbers on the back of food packaging. In fact, the new research calls into question the validity of nutrition science’s core belief that a calorie is a calorie.
Using the Beltsville facilities, for instance, Baer and his colleagues found that our bodies sometimes extract fewer calories than the number listed on the label. Participants in their studies absorbed around a third fewer calories from almonds than the modified Atwater values suggest. For walnuts, the difference was 21 per cent. This is good news for someone who is counting calories and likes to snack on almonds or walnuts: he or she is absorbing far fewer calories than expected. The difference, Baer suspects, is due to the nuts’ particular structure. “All the nutrients—the fat and the protein and things like that—they’re inside this plant cell wall.” Unless those walls are broken down—by processing, chewing or cooking—some of the calories remain off-limits to the body, and thus are excreted rather than absorbed.
Image: Catherine Losing
