A med & grad student who used to work the line in LA, NYC, SF and Napa talking about the science of cooking and cooking with science. Harold McGee's On Food And Cooking - The Science and Lore of the Kitchen never satisfied my kitchen curiosity and more than one Chef grew exasperated with my asking "Why?" I'll try to stay on topic, but you may see a kvetch or two about the school & hospital.
My posts are presented as opinion and commentary and do not represent the views of LabSpaces Productions, LLC, my employer, or my educational institution.
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Food labeling is complicated. And confusing. For one thing, there is a lot of information on there, from calorie count to ingredients to calories per gram of fat. You almost need a science degree to start to understand it. Serving size, for example, isn’t helpful. On a bag of Doritos you’ll see that the serving size is 1oz (28g), and that there are about 9 servings in a bag. Now I have a kitchen scale. I advocate the use of a kitchen scale in cooking. But I, for one, am not going to pull out the scale when I want some chips to watch the Niners in week 2 of the NFL Playoffs. I don’t sit at home on a Saturday after the Costco run measuring out individual servings of pistachios and chips and peanuts and pretzels. I have other things to do. And yes, the new labels do approximate how many Doritos make up a serving, about 12, but I’m still not going to sit there and count out 12 chips per person per serving. Friends and family will think I finally fell off the deep end and have me committed.
But one of the big puzzles about the nutritional information is how it is calculated. Calories can be done quickly. Throw the items into a bomb calorimeter and burn them. Measure the increase in temperature and calculate the kJ of energy. Then convert those kJ to kcal. 4.184kJ = 1 kcal. Why kilo-calories? Because 1 food calorie (Cal) is equal to 1,000 calories (cal). Now there’s a diet plan. Convert all junk food Calories to calories. That 1 serving of Doritos will have 150,000 calories. The completely clueless as to the difference between Calories and calories would think twice and maybe not eat the chips.
Unfortunately, the bomb calorimeter isn’t very accurate for determining the number of food calories something has. The burning of an item is a lot more efficient than our bodies. If our bodies were that efficient at burning food, our feces would be a lot smaller. Instead, a process called the Atwater system is used. The Atwater system attempts to take into account urinary, fecal, secretion and gaseous losses of food energy. It’s also disputed a lot. But there are no real alternatives to the Atwater system. With the Atwater system the number of food calories is determined by adding up assigned values – 4kcal/g of protein and carbohydrates, 7kcal/g of alcohol, 9kcal/g of fat. These values were determined by first burning in a bomb calorimeter and averaging those values, Atwater called these “Gross Energy Values” (GE). He then multiplied GEs by “Digestibility Coefficients,” which were determined by mixing up large quantities of foods and serving them. Then measuring the amount of nitrogen and undigested proteins, fats and carbohydrates in urine and feces. I don’t know if he determined these from a table or human experimentation. If someone else does, please feel free to let me know. And if it was human experimentation, I feel really sorry for whatever grad student had to go collect Mr. Jones’ poop to sift through for chemical analysis and burning.
But this only tells you how many Calories a given food has. How do they know how much sugar or vitamin A or molybdenum is in there? That information is typically determined with the help of a digester. You put a sample of the food in the digester, and the machine breaks up the food into pieces (or liquid or mush) for analysis. That product is then taken and run through a series of chemical tests to determine concentrations of nutrients.
So that means each new product gets run through a series of chemical and physical tests to determine food labeling, right? Well, no. That can get expensive. Really expensive. All of the information determined from the Atwater system and the digester actually goes into a standard table. A company can have its own standard table or use the USDA’s, or whatever local equivalent government agency to the USDA. These tables are only good for certain things. Those Doritos may have gone through the digester and analysis, but a Double Double from In-N-Out probably did not. Instead, the nutritional information for the Double Double is instead calculated from the tables. There’s an entry for cooked patties, for the tomatoes, the lettuce, etc. So if you want the exact number of food calories in that Double Double, you're out of luck. That data doesn't exist.
And because it’s all standardized information, there is no variation for different growers or ranchers. To the USDA a peach grown at BigAgro Factory Farm is no different than a peach at Frog Hollow Farms. Which is interesting, since the Frog Hollow Farm, and similar local (for me) purveyors, make a better tasting product. Which makes me wonder about the accuracy of those standardized tables. If I see different peaks in GC-IR in running samples casually, doesn’t that mean there are differences in content? And if there are differences in content, just how accurate are those averaged values the USDA gives?
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I have always wondered if those numbers were straight off of a calorimeter or if they were adjusted for digestion etc. Thanks :)
So the digested values are lower than those from the calorimeter? Also, wouldn't cooking affect the calorie content ? And finally, wouldn't different carbohydrates be digested to different degrees?
Yes. Digested values are lower than from the calorimeter.
Cooking does affect calorie content, there are values for both cooked and raw foods on the USDA tables. If I were making red sauce and wanted to know the nutritional content, I'd have to add up the cooked values for the garlic, onion, tomatoes, basil and oil. It's really monotonous and some of the people who do the nutritional information for small restaurants have binders with the information.
The digestibility coefficients are supposed to take into account incomplete digestion of nutrients. To what degree? I never found a concrete answer. Which is why the Atwater system is disputed. But no one has proposed a better model.
One thing I find interesting (please read that as "infuriating") is the fact that serving size can change depending on the container. A serving of Doritos in one style bag isn't a serving in another style bag.
I noticed this with Coca-Cola first. A serving size in a standard can is 12 oz. In a bottle, it's 8 oz. So if you gave a 12 oz can, that's one serving of Cola. Double it and put it in a bottle? That's not 2, but THREE servings.
In keeping with your example of Doritos, Frito Lay makes a bag they call "Big Grab". It is also one serving, but of 75 grams, rather than 28 grams serving size for the standard bag you find at the grocery store. That's nearly 3 times the size, yet both are "one serving".
If someone tells me they want "one serving" each of Doritos and Coke, which do I go by? Do they want 8 or 12 oz? 28 or 75 grams?
Serving size is also on a table at the FDA. It is determined by averaging the amount of food a panel of testers eat. So something like the Doritos a bunch of people eat and track what they eat. Once they're done, the values are averaged. With liquids, the default serving size for anything non-alcoholic is 8oz. Goes back to the whole 8oz = 1 glass thing. I'm not sure where that started, though. I can do a bit of digging.
With convenience packages, it's a matter of "value for money." One of the first instances of this is Coke vs Pepsi. The original Coca-Cola bottle was 6.5oz. The original Pepsi was 8oz. Both sold for five cents in the US. During the great depression, Pepsi went up to 12oz bottles, and kept the price at five cents. So people who bought pepsi were getting twice as much product for the same price. Same concept today. If you look at the pricing of packages, if you get the larger size it seems like only a bit of change more for a lot more product. And it became convenient for packages that were designed to be consumed in one sitting to just re-work the nutrition label so that the single consumption package was one serving.