Atwater Food Energy Value System

The Atwater system of ascertaining energy values in foods was developed by Wilbur Olin Atwater, a college chemistry professor, around the end of the nineteenth century. Atwater knew that food contained three main substances the body uses for energy: protein, fat, and carbohydrate. Using a simple laboratory device called a bomb calorimeter, he recorded how much heat was released when typical proteins, fats, and carbohydrates were completely burned. He found that there was not a lot of variation among the different types of each item. For example, all proteins tended to produce a little more than four kilocalories of heat per gram (kcal/gram).

After that, Atwater needed to know two more things. First was how much of the major macronutrients-protein, fat, and carbohydrate-a food contains. Fat was easy, because unlike protein and carbohydrates, fat dissolves in ether (a liquid used to dissolve other substances). So Atwater chopped foods finely, shook them up with ether, and weighed how much material was dissolved in the ether. That gave him a food’s fat content (or, more strictly, lipid content: lipids include both fats, which are solid at room temperature, and oils which are liquid). The same method is used today. Protein was harder to index because no test identifies proteins in general. However, Atwater knew that about 16 percent of the weight of an average protein was nitrogen. So he found a way to measure the amount of nitrogen, which gave him the concentration of protein.

Carbohydrates were the hardest. There was no test then, nor is there now, for identifying the concentration of carbohydrates in general. But Atwater knew the main organic matter in foods was the three big items, protein, fat, and carbohydrate. He also knew how to calculate the total amount of organic matter. He simply burned the food completely, leaving only the mineral ash that did not burn and was therefore the inorganic part. Knowing how much organic matter the food contained and how much fat and protein it held, he obtained the amount of carbohydrate by subtraction: the weight of the carbohydrate was what was left when the weights of the fat, protein, and mineral ash had been subtracted from the total weight of the original food item.

Atwater was thus able to estimate the amount of protein, lipid, and carbohydrate in his food. The second piece of information he needed was how much of the food a person eats is digested, as opposed to being passed through the body unused. This required him to analyze the feces (waste matter) of people who were eating precisely measured diets, which he duly did. He was then able to estimate, for each of the three nutrients, how much of what was eaten was also digested. Once again he found that there was little variation within the categories of protein, fat, and carbohydrate, so he assumed the variation could be ignored.

The chemist now had what he wanted. He knew how much energy each of the three big types of macronutrient contained, how much of each macronutrient was present in the food, and how much of it was used in the body. Ignoring variation within each type of macronutrient he proposed the convention that still dominates the food industry and government standards. By taking into account the proportion of the food that he found was not digested, which was rarely more than 10 percent, he claimed that on average proteins and carbohydrates each yield four kcal/gram, while lipids yield nine kcal/gram. These are known as Atwater’s general factors.

This simple and convenient system forms the basis of the Atwater convention and is essentially what the United States Department of Agriculture’s National Nutrient Database and McCance and Widdowson’s The Composition of Foods use to produce their tables of nutrient composition. But nutritionists have long recognized important limitations in the Atwater convention, so it has been modified in various ways, such as by making the general factors more specific in 1955 when the Atwater specific-factor system was introduced to take advantage of a half century of nutritional biochemistry research. For example, the energy value of different types of protein is known to vary: egg protein produces 4.36 kcal/gram, whereas brown rice protein produces 3.41 kcal/gram. An exhaustive list of such variants has been compiled.

 

 

1

The Atwater system of ascertaining energy values in foods was developed by Wilbur Olin Atwater, a college chemistry professor, around the end of the nineteenth century. Atwater knew that food contained three main substances the body uses for energy: protein, fat, and carbohydrate. Using a simple laboratory device called a bomb calorimeter, he recorded how much heat was released when typical proteins, fats, and carbohydrates were completely burned. He found that there was not a lot of variation among the different types of each item. For example, all proteins tended to produce a little more than four kilocalories of heat per gram (kcal/gram).

The word “ascertaining” in the passage is closest in meaning to

Adescribing

Bdetermining

Cmaintaining

Dmaximizing

 

2

After that, Atwater needed to know two more things. First was how much of the major macronutrients-protein, fat, and carbohydrate-a food contains. Fat was easy, because unlike protein and carbohydrates, fat dissolves in ether (a liquid used to dissolve other substances). So Atwater chopped foods finely, shook them up with ether, and weighed how much material was dissolved in the ether. That gave him a food’s fat content (or, more strictly, lipid content: lipids include both fats, which are solid at room temperature, and oils which are liquid). The same method is used today. Protein was harder to index because no test identifies proteins in general. However, Atwater knew that about 16 percent of the weight of an average protein was nitrogen. So he found a way to measure the amount of nitrogen, which gave him the concentration of protein.

According to paragraph 2, why is it easy to find out a food’s lipid content?

ALipids remain when fats are removed from the oils found in a food.

BLipids melt easily and can be removed from the food by heating it above room temperature.

CLipids are the part of the food that remains after the proteins have been dissolved in ether.

DLipids are the only part of the food that dissolves in ether.

 

3

Carbohydrates were the hardest. There was no test then, nor is there now, for identifying the concentration of carbohydrates in general. But Atwater knew the main organic matter in foods was the three big items, protein, fat, and carbohydrate. He also knew how to calculate the total amount of organic matter. He simply burned the food completely, leaving only the mineral ash that did not burn and was therefore the inorganic part. Knowing how much organic matter the food contained and how much fat and protein it held, he obtained the amount of carbohydrate by subtraction: the weight of the carbohydrate was what was left when the weights of the fat, protein, and mineral ash had been subtracted from the total weight of the original food item.

Which of the following can be inferred from paragraph 3 about carbohydrates?

ACarbohydrates weigh more than proteins and fats.

BThe concentration of carbohydrates is similar in different foods.

CCarbohydrates are made of inorganic matter.

DCarbohydrates can be burned off completely.

 

4

Carbohydrates were the hardest. There was no test then, nor is there now, for identifying the concentration of carbohydrates in general. But Atwater knew the main organic matter in foods was the three big items, protein, fat, and carbohydrate. He also knew how to calculate the total amount of organic matter. He simply burned the food completely, leaving only the mineral ash that did not burn and was therefore the inorganic part. Knowing how much organic matter the food contained and how much fat and protein it held, he obtained the amount of carbohydrate by subtraction: the weight of the carbohydrate was what was left when the weights of the fat, protein, and mineral ash had been subtracted from the total weight of the original food item.

According to paragraph 3, why did Atwater burn the food completely?

ABecause the weight of the remaining ash would be equal to the weight of the carbohydrates in the food

BBecause the characteristics of the remaining ash would show the relative amounts of the protein, fat, and carbohydrates in the food

CBecause knowing the weight of the remaining ash would make it possible to estimate the total weight of the macronutrients in the food

DBecause the remaining ash could be tested for its carbohydrate composition, whereas the unburned food could not

 

5

Atwater was thus able to estimate the amount of protein, lipid, and carbohydrate in his food. The second piece of information he needed was how much of the food a person eats is digested, as opposed to being passed through the body unused. This required him to analyze the feces (waste matter) of people who were eating precisely measured diets, which he duly did. He was then able to estimate, for each of the three nutrients, how much of what was eaten was also digested. Once again he found that there was little variation within the categories of protein, fat, and carbohydrate, so he assumed the variation could be ignored.

According to paragraph 4, why did Atwater analyze the feces of people who were eating precisely measured diets?

ATo measure the lipids, carbohydrates, and proteins that were eaten but were not digested

BTo determine the effects of different types of food on digestive health

CTo demonstrate the benefits of a strictly controlled diet

DTo develop guidelines for the amounts of macronutrients people should eat

 

6

The chemist now had what he wanted. He knew how much energy each of the three big types of macronutrient contained, how much of each macronutrient was present in the food, and how much of it was used in the body. Ignoring variation within each type of macronutrient he proposed the convention that still dominates the food industry and government standards. By taking into account the proportion of the food that he found was not digested, which was rarely more than 10 percent, he claimed that on average proteins and carbohydrates each yield four kcal/gram, while lipids yield nine kcal/gram. These are known as Atwater’s general factors.

According to paragraph 5, each of the following was one of Atwater’s findings EXCEPT:

AProteins are digested at a slower rate than lipids.

BTypically, about 10 percent of the food is not digested.

CProteins and carbohydrates produce about the same amount of energy.

DLipids produce more energy than the same amount of protein.

 

7

This simple and convenient system forms the basis of the Atwater convention and is essentially what the United States Department of Agriculture’s National Nutrient Database and McCance and Widdowson’s The Composition of Foods use to produce their tables of nutrient composition. But nutritionists have long recognized important limitations in the Atwater convention, so it has been modified in various ways, such as by making the general factors more specific in 1955 when the Atwater specific-factor system was introduced to take advantage of a half century of nutritional biochemistry research. For example, the energy value of different types of protein is known to vary: egg protein produces 4.36 kcal/gram, whereas brown rice protein produces 3.41 kcal/gram. An exhaustive list of such variants has been compiled.

Why does the author provide the information that “egg protein produces 4.36 kcal/gram, whereas brown rice protein produces 3.41 kcal/gram”?

ATo explain why eggs are a better source of protein than brown rice

BTo show an example of variations that Atwater predicted and were later confirmed by more recent research

CTo argue that different types of protein have only small differences in energy values

DTo help show why Atwater’s general factors needed to be modified to be more specific

 

8

This simple and convenient system forms the basis of the Atwater convention and is essentially what the United States Department of Agriculture’s National Nutrient Database and McCance and Widdowson’s The Composition of Foods use to produce their tables of nutrient composition. But nutritionists have long recognized important limitations in the Atwater convention, so it has been modified in various ways, such as by making the general factors more specific in 1955 when the Atwater specific-factor system was introduced to take advantage of a half century of nutritional biochemistry research. For example, the energy value of different types of protein is known to vary: egg protein produces 4.36 kcal/gram, whereas brown rice protein produces 3.41 kcal/gram. An exhaustive list of such variants has been compiled.

The word “compiled” in the passage is closest in meaning to

Acollected

Bproposed

Creviewed

Daccepted

 

9

Look at the four squaresthat indicate where the following sentence could be added to the passage

His aim was to ensure that poor people could use their limited resources to get adequately nourished.

Where would the sentence best fit？Click on a square  sentence to the passage.

10

In the late 1800s, Atwater devised a system for estimating the energy values of foods that still provides the basis for the nutritional table in use today.

AAtwater measured how much energy a gram of each of the three major macronutrients produced, then devised methods for estimating how much of each macronutrient different foods contained

BConsidering the amount of food that passes through the body undigested, Atwater found that, on average, proteins, lipids, and carbohydrates are digested at the same rate.

CAtwater’s original system ignored energy differences among different types of protein, fats, and carbohydrates, but this limitation has been corrected by more recent biochemistry research.

DTo estimate the energy people actually get from a food, Atwater conducted experiments to find out how much of each of the major nutrients in food that is eaten is actually digested.

EAtwater devised a rough test for distinguishing the major nutrients from the inorganic part of a food by means of burning the food completely, but a more accurate method is available today.

FAtwater introduced his specific-factor system in order to compete with McCance and Widdowson’s rival system and win the approval of the United States Department of Agriculture.

 

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