Calculation of the Composition and Energy Content of a Given DietExercise 1

1.1 Food composition and nutrient requirements are dull subjects, full of figures which are so difficult to remember. You might be relieved to know that you need not remember any figures—they are readily available in easily accessible publications.

1.2 What you need to do is to use the figures to solve some everyday problems. If you solve such problems often enough, the figures which you use most frequently will eventually become a part of your awareness without your having made any effort to remember them. Whether you will be actually offering dietary advice on an everyday basis is not important; what is important at this stage is that you should gain acquaintance with some exercises of the type presented here. The acquaintance would be valuable to you in your future work as a doctor.

1.3 If you happen to run a small clinic, you might have to do many such exercises for your diabetic or obese patients.

1.4 If you join a big organization you may have a dietitian available to help you, but you can make good use of her expertise only if you are well acquainted with the subject yourself. Further, wheneverthe dietitian runs into some difficulty, she may turn to you for guidance. Then if you cannot solve the problem, you would cut a sorry figure.

1.5 That sort of predicament is an occupational hazard for doctors. There would be lots of things that you may have never been taught, or you have forgotten through prolonged disuse. But whenever anyone in the hospital has any problem, you, as the leader of the health care team, will be approached for guidance. Therefore, although you may choose to be master of only one, it will pay you in the long run if you are also the Jack of all. If you succeed in learning anything even remotely related to the medical profession, one day you will thank your stars for it.

1.6 This exercise will tell you how to calculate the composition and energy content of a given diet; that is, if you know what you or your patient eats, you should be able to tell how much protein or fat it contains, and how many Calories it provides. This information is basic for scientific evaluation of the diet.

1.7 The calculation involves four basic steps. First, list every item of the diet. It is customary to evaluate a day's intake at a time. Hence, write down every item of the diet consumed during the day.

1.8 Second, break up each item into its major ingredients. The tables on food composition generally list only the ingredients. Hence find out the ingredients of each item consumed, and the weight of each ingredient that went into the portion consumed.

1.9 Third, find the composition and energy content of every ingredient used. The bible for this information is Nutritive Value of Indian Foods published by the National Institute of Nutrition, an ICMR institute in Hyderabad. Published tables will give you the composition and energy content per 100 g of the edible portion of a food. From this information, you can easily calculate the corresponding values for any weight of the food.

1.10 Fourth, calculate the individual nutrient content of the quantities of ingredients actually consumed. Now you simply have to add up the individual nutrient content of the ingredients to get the total intake of these nutrients.

1.11 To recapitulate, the four steps are: First, list every item. Second, break the items into their ingredients. Third, find the nutritive value of each ingredient from the published tables. And finally, add up the individual values to get the nutrient composition and energy content of all the items listed.8

1.12 Let us apply this knowledge to determine the nutrient composition and energy content of just one meal.

1.3 The first step, as we have learnt, is to list every item.

The meal consists of two chapaties, one helping of rice, and one serving each of dal, vegetable and curd.

1.14 The next step is to break these items into ingredients.

Each chapati has 25 g wheat and 2 g cooking medium, which is a vegetable oil. One helping of rice consists of 50 g rice cooked in 5 g of the medium. The serving of dal has 50 g of the dry dal which has been cooked using 2 g of the cooking medium. The vegetable has equal quantities of potato and beans. One serving has 50 g of each, and 5 g of the cooking medium. The portion of curd consumed “ at the meal weighs 200 g.

1.15 The next step is to find the published nutrient value of ingredients.

We need the nutrient value of wheat, rice, green gram, potato, green beans, curd and the cooking medium.

Before we consult the Tables for these values, you may like to draw on a piece of paper columns of the type shown in the next slide.¹

1.16 Take a large piece of paper to draw these columns.

1.17 Here are the values you need.

As you can see for yourself, if you know the carbohydrate, protein and fat content of a food, you can easily calculate its energy content. Carbohydrates and proteins provide 4 Calories² per gram each, while fats provide 9 Calories per gram. Thus the energy content of wheat flour will be 12.1 multiplied by 4, plusl .7 multiplied by 9, plus 69.4 multiplied by 4.

1.8 Finally, the last step is to calculate the food value of the meal. You will find the table you have drawn handy.

The exercise is so simple that you should switch off the tape recorder, go back to do the previous slide and settle down to do some simple mathematics.

A calculator will improve your efficiency, but is not essential.

1.19 If you are through with the exercise, you may confirm your results by having a look at the next few slides.

1.20 Here are the calculations for the chapaties.

1.21 Here are the calculations for rice and dal.

1.22 Here are the calculations for vegetable and curd.

1.23 Here is the composition and energy content of the meal. As you would understand, the figures are the result of adding the values obtained in the previous three slides.

1.24 The vitamin, mineral or dietary fibre content of a meal can be calculated along the same lines. If you find the nutritive value of all the meals consumed during a day, you can derive from them the corresponding values for the whole day's intake.

1.25 Calculation of nutrient composition and energy content of a diet by the method illustrated above is simple, logical and accurate but time consuming. For quick calculation, one may make use of ‘food exchanges’. Food exchange system is based on the principle that foods with similar nutrient composition have been grouped together, and the approximate nutrient content of one helping or unit serving worked out in advance.

1.26 Carbohydrate-rich foods are included in the cereal exchange. The wheat content of one chapatie (20 g) is taken as a unit, and equivalent amounts of other carbohydrate rich foods listed. One unit of each food in the exchange gives approximately 15 g carbohydrates, 2 g protein and 70 Calories. Some examples of one cereal exchange include one chapatie, one large slice of bread, 3 tablespoonfuls of rice, one medium-sized idli, 3 tablespoonfuls of corn flakes, or 3 to 5 biscuits, depending on the size. What it means is that these portions of these foods are, nutritionally speaking, roughly equivalent.15

1.27 High-protein grains, the pulses, are included in the legume exchange. Each unit of legume exchange provides 15 g carbohydrate, 6 g protein and 85 Calories. 25 g of almost any legume constitutes one unit in this exchange.

1.28 Vegetables are rather heterogeneous in their composition. Therefore, they have been grouped into at least two exchanges. Group A includes green leafy vegetables with high water, vitamin and mineral content, but very low calorific value. One unit in this group consists of 100 g of the vegetable, and provides only 20 Calories. These vegetables may be neglected while considering the energy content of a diet.

1.29 Group B includes other vegetables but not starchyroots and tubers. These vegetables provide a little more energy than group A vegetables.17

1.30 Starchy roots and tubers being rich in carbohydrate may be included in the cereal exchange, or treated separately.

1.31 Fruit exchange is somewhat similar to the group B vegetable exchange with two important differences. First, the protein content of fruits is negligible. Secondly, fruits being more expensive than vegetables, while framing a diet, the number of fruit exchanges suggested should depend on the 18socioeconomic status of the patient. If we feel that the patient cannot afford fruits, a balanced diet can be framed using vegetables instead of fruits, provided the patient takes part of the vegetables in the raw form.

1.32 Next we come to the milk exchange, which includes milk and milk products. This group of foods is the only one which contains significant quantities of carbohydrates, proteins as well as fats.

1.33 The meat exchange includes various animal foods including egg and cheese.

1.34 Lastly, we come to the fat exchange. As you may notice, different cooking media have the same calorific value. The main difference lies in the degree of saturation of theirfatty acid content.

1.35 Now let us examine how the exchange system can help in quick calculation of the composition and calorific value of a diet. For the sake of illustration, let us take the same meal which we discussed earlier.

As is clear, there is considerable error in using the method of exchanges. But it saves so much time that it is quite acceptable when the workload is heavy. In any case, it is well to keep in mind that in dietetics the impression of accuracy conveyed by figures is illusory. Even if the nutrient content is calculated by direct use of detailed food composition tables, inaccuracy is inevitable in real life situations because the size of the helpings actually consumed, and the ratio of ingredients in a recipe, are seldom measured or fixed. Accuracy is possible only in the laboratory, which belongs to the realm of experimental nutrition, not everyday dietetics.

1.36 Even more important than knowing something is to know how to learn it, or where to find it. In nutrition plenty of factual data is available in many easily accessible publications. But food is such a commonplace topic of conversation that you will be asked questions about it at several social gatherings. Since you can neither carry nutritional tables with you everywhere, nor can you remember them, it is good to keep some simple figures in mind all the time. The questions you will be generally asked will be of two types. One type is related to the composition of foods; for example, how much protein does soyabean contain. The other type is related to the energy content of units of foods as consumed, e.g. how many Calories does a samosa contain. If, being a doctor, you cannot answer such questions, you make a very poor impression on others. The next few slides will help you not only avoid cutting a sorry figure, but also enable you to make a meaningful contribution to such discussions.

1.37 Here is the approximate composition of a few classes of foodstuffs. Cereals have about 70% carbohydrate and about 10% protein. The remaining 20%, as you know, is water. Pulses have about 10% more protein than cereals, and correspondingly their carbohydrate content is 10% less. With these figures you can easily dispel the popular misconceptions that cereals are simply starch while pulses are full of protein. They both have a lot of starch, and also some protein. Although the protein content of pulses is more than that of cereals, the contribution of cereals to our protein intake is greater than that of pulses because we consume much more of cereals than pulses. In an Indian diet, as much as 80% of the protein intake may come from cereals. The importance of pulse protein lies not in its quantity but in its quality. Although both cereal and pulse proteins are poor in quality in comparison with animal protein, they are complementary. Cereals compensate for the methionine deficiency of pulse protein, and pulses make up the lysine deficiency of cereal protein. If our food contains about one-fifth as much pulses as the cereals, the mixture of proteins that we get is quite satisfactory in quality. Alternatively, the quality of cereal protein can be improved, of course at a much higher cost, by supplementing it with animal protein.

Soyabean is a class by itself, and its composition is unique. However, it is good to remember that it is neither indispensable, nor a miracle food. Whatever quantity of protein it provides can also be obtained from double the quantity of any other legume.

Fruits and vegetables make very little contribution to energy intake. Their main role is to provide us vitamins and minerals. The main difference between fruits and vegetables, from a nutritional point of view, is that fruits are consumed 23raw, and therefore their vitamin and mineral content is better preserved. But that does not fully justify their much higher cost. All the benefits of fruits can be obtained from vegetables provided at least a part of our daily vegetables are consumed raw, and the rest are cooked with adequate precautions to minimise vitamin and mineral loss.

Dry fruits are not a major item of the diet but a common subject of discussion. Many popular misconceptions can be cleared by knowing that nuts, in general, are high calorie foods, providing about 600 kcal per 100 g. This is due to their high fat content. In this respect, there is no difference between costly nuts such as almonds or cashewnuts, and relatively less expensive nuts such as walnuts or peanuts. Coming to finer points, the modest walnut is emerging a sort of winner because of its fat having substantial n-3 type of PUFA, which is often deficient in diets currently popular. But all the same, the basic fact remains that all nuts, including walnuts, are high calorie foods. Hence including them in the diet may necessitate excluding something else so that the energy intake does not exceed the energy expenditure. A positive energy balance will lead to obesity, which would enhance the risk for several diseases, no matter which nuts disturbed the energy balance.

1.38 Here are some expensive and prestigious items of food, none of which is indispensable. Milk contains all the three major nutrients in significant, and roughly equal, amount. That is why it is called a complete food. But it is only during the first six months of an infant's life that milk alone constitutes a satisfactory diet.

Egg is a good source of high quality protein, and because of its high fat content, also a good source of energy. It is a supplement of high nutritive value at moderate expense.

Meat is basically 20% protein of good quality. Some meats also have a significant quantity of fat.

Fats and oils are 100% fat, and sugar is 100% carbohydrate. But, for once, purity is not supreme. Foods having a mixture of nutrients are much more valuable and dependable sources of nourishment than these foods which provide just one nutrient.

Honey is a generally overrated food. It is basically a highly concentrated solution of a mixture of sugars. It also has some vitamins. But honey is not a unique source of any important nutrient.

1.39 Another type of information, which should become as much a part of your awareness as your name, is the calorific value of a samosa or an orange, and so on. There is so much variation in the size of such items that any value will be highly approximate, but still a plausible guess is generally possible.

The portions of a majority of foods as commonly served provide about 100 Calories. Therefore if you have any doubt about the calorific value of a food, the safest guess to hazard is 100 Calories. However, if common sense warns you that the food in question has definitely much less or much more energy than that, take 50 Calories away from, or add 100 Calories to the norm. In this slide and the next few, you see some foods which actually provide about 100 Calories.

As you see in this slide, one unit of almost every item of the everyday diet provides about 100 Calories.

1.40 Here are some of the items commonly consumed with tea, which provide about 100 Calories.26

1.41 Here are some sweets and fruits providing about 100 Calories each.

1.42 Here are a few lightweights providing only about 50 Calories. Raw leafy vegetables provide so little energy that they can be consumed in almost unlimited quantity even by the calorie-conscious.

1.43 Some foods, especially fried ones, provide about 150 Calories in the quantities commonly consumed.

1.44 Some still heavier items provide about 200 Calories.

1.45 And here are the real heavy weights providing more than 200 Calories.

1.46 Now you are well equipped to make an informed contribution to a discussion on food values. You may not be able to answer all the questions—nobody really can—but you would not feel embarrassed. However, as a scientist, do not forget that there is an error involved in using even the most accurate tables. When we use exchanges or any other form of approximate information, we accept additional error for the sake of convenience.

1.47 Now you may find it interesting to calculate the composition and energy content of your own dietary intake on a typical day. For this you would have to get hold of a collection of food composition tables, perhaps the ICMR book Nutritive Value of Indian Foods, referred to earlier. You may choose the exact method, or some approximate method; or still better, both, to see how much difference it makes.³