The Doc

Ever since I've been around on these boards I've picked up some interesting and unusual information about food, nutrition and the human body. I figured I should probably put some of them down in writing before I totally forget the information. This thread will just be a sounding board/journal of interesting nutritional info I've picked up that might actually interest some of you. Hopefully at least one person will learn something they did not know before they read my posts.

The first one is about the nutritional info on the packaging of the foods we buy, and why sometimes the exact same portion of the exact same food can have two completely different sets of nutitional information.The quick and easy answer is that the interpertation of the information is up to the manufacturer themselves and which method they choose to use determines what you read on the box. This was brought to my attention when 2 different containers of Oat Bran had vastly different nutritional info for the same quantity of the same food:

1)Mothers Oat bran, ingredients: 100% Natural Oat Bran

Per 100g
364 Cals
8g Fat, 1 sat
63g carbs, 14g fiber
17g protein

2)Plain oat bran, bulk, raw: ingredients: 100% Natural Oat Bran

Per 100g
246 Cals
7g Fat, 1g sat
66g Carbs, 15g fiber
17g protein

Now how can the Oat Bran that has 3g more carbs and only 1g less of fat have 118 fewer calories than the other package of Bran? Is it somehow different than the other product even though they are both simply 100% Natural Oat Bran? No, the companies just used 2 totally different methods of obtaining their nutritional info. I'll explain:

The first thing you need to know is that carbs are usually estimated in nutritional values. They take 100g and then subtract the Protein, Fat, Water and Ash content and the number that's left is the Carbs. Now after that is done they can use different "systems" of evaluation to get the nutritional info to put on the package. In the 2 examples you have above the Mothers Oat Bran is valued using the Atwater General Factor System and the Plain/Bulk Oat Bran is valued using the Atwater Specific Factor System (which was actually introduced in 1955 by Merrill and Watt ).

The Atwater General Factor System is the one most people know where the values are based on METABOLIZABLE ENERGY (ME), or the amount of energy available for total (whole body) heat production at nitrogen and energy balance. We know these numbers as:
1g fat=9 calories
1g protein=4 calories
1g carbs=4 calories
50% of all fiber in undigestable

Most people accept this at face value since it is so easy to use and understand even though it is not entirely accurate. Depending on the food source the actual calories per gram vary for protein, carbs, and fat:

Protein: 2.44-4.36 calories per gram
Carbs: 2.70-4.16 calories per gram
Fats: 8.37-9.02 calories per gram

The Atwater General Factor System is how the Mothers numbers were figured out.

Fat: 7.9g x 9 = 71.7 calories
Protein: 17.025g x 4 = 68.1 calories
Carbs: 63g-7g fiber = 56g x 4 = 224 calories
Total calories = 363.8

Now The Atwater Specific Factor System, a refinement based on re-examination of the Atwater system, was introduced in 1955 by Merrill and Watt. It integrates the results of 50 years of research and derives different factors for proteins, fats and carbohydrates, depending on the foods in which they are found. So the above numbers have little to do with figuring out the nutritional value except for the fat. You actually have to look at the energy factor of the source of carbs, and the Protein Rating of the protein source to get your nutritional values. This method has a lot to do with "Food Energy".

Here's how they figured out the nutritional values for the Plain Oat Bran using The Atwater Specific Factor System.

The conversion factor for the digestible portion of the fat is 37 kJ/g (9 kcal/g).
Fat: 6.533g x 9 = 58.8 calories or 6.533 x 37= 241.72 divided by 4.18= 57.8 calories, so there's actually a 1 calorie discrepancy in the math.

Calculating the Protein Rating

% Protein = 14.2
Reasonable Daily Intake = 30g
Protein in a Reasonable Daily Intake = 0.142 X 30 g = 4.26/4.3
PER = 1.8
Protein Rating = 4.3 X 1.8 = 7.74
7.74 x 17g protein = 131.58 kj divided by 4.18 kj/g= 31.47 calories/31.5

Carbs: 15g (fiber) x .06(energy value fiber)=.9, 66g - 0.9= 65.1 x 10kj=651kj, 651 kj divided by 4.18kj/g = 155.74 calories/156
Total calories= 246.3

As you can imagine this actually took me about 10 hour of reading and research to find all of the equations and ratings to prove the numbers mathematically (yeah, I need a life ).So as you can see the nutritioal information is actually at the mercy of the manufacturer if they want to represent it as direct analysis or food energy conversion factors. You can safely use the smaller numbers if you believe that different foods require more energy for the body to digest thus leaving less for the body to use or store accordingly. That is basically why there is a sizable difference in the nutritional values of the same portions of the same food.

I hope that wasn't to complicated .

The Doc

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SouthCaliDiva

Okay Doc, you know I'm dietetically challenged, and you come in here with this!

I'll have to print this out and marinate on it a little bit.







{Also, I'm taking Exercise Physiology this semester and this would be excellent for a study group. }

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GameDayDog

Dayum dude.. Great post...

Although, I have a question, I guess 2... If I'm lookin' at the nutritional info on stuff, how do I know which method of calculation was used??

Is it safe to always assume that the General Factor will always have the higher caloric number??

Peace..~G

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nuge7076

Great post! Thanks for sharing...

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Apootheosis

uh, so basically your saying food is inaccurately labeled?

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The Doc

When you look at these 2 you will notice that the higher calorie bran actually adds up when you use the "normal" method calories per gram (minus 1/2 of the fiber from the carbs), so it's obviously the General Factor System. As for your second question, the majority of companies just use the method that you are used to. But some companies want to make their product appear healthier so they will use whatever method accomplishes this. You should have bells going of in your head when you see something with 66g of carbs and only 246 calories .

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The Doc

Yes and no, it's not exactly precise. The estimations we normally use for the food we eat are fine, and everyone finds them much easier to accept and use. The actual grams of the protein, carbs, and fat may be very accurate, it is how many calories each gram contains that is subjective. Basically when you see a food label that doesn't come close to adding up in your mind they are telling you that science believes the body will have to work harder to break them down, thus expending more energy to make those grams of food useable. Sort of like the old rumor that celery actually has negative calories because the body has to epend more energy to digest celery than are actually in it.

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The Doc

Since part 1 of my thread seems a little confusing I will try to be more specific and actually explain how all this works over the next couple of days. I'll try not to overload each thread, we don't want anyone's head exploding . Today I'll start explaining ENERGY CONTENT OF FOODS, JOULES AND CALORIES, THE FRAMEWORK FOR AN UNDERSTANDING OF FOOD ENERGY CONVERSION FACTORS, and A BRIEF OVERVIEW OF FLOW OF ENERGY THROUGH THE BODY.

The translation of human energy requirements into recommended intakes of food and the assessment of how well the available food supplies or diets of populations (or even of individuals) satisfy these requirements require knowledge of the amounts of available energy in individual foods. Determining the energy content of foods depends on the following: 1) the components of food that provide energy (protein, fat, carbohydrate, alcohol, polyols, organic acids and novel compounds) should be determined by appropriate analytical methods; 2) the quantity of each individual component must be converted to food energy using a generally accepted factor that expresses the amount of available energy per unit of weight; and 3) the food energies of all components must be added together to represent the nutritional energy value of the food for humans. The energy conversion factors and the models currently used assume that each component of a food has an energy factor that is fixed and that does not vary according to the proportions of other components in the food or diet.

JOULES AND CALORIES
The unit of energy in the International System of Units (SI) is the joule (J). A joule is the energy expended when 1 kg is moved 1 m by a force of 1 Newton. This is the accepted standard unit of energy used in human energetics and it should also be used for the expression of energy in foods. Because nutritionists and food scientists are concerned with large amounts of energy, they generally use kiloJoules or megaJoules. For many decades, food energy has been expressed in calories, which is not a coherent unit of thermochemical energy. Despite the recommendation of more than 30 years ago to use only joules, many scientists, non-scientists and consumers still find it difficult to abandon the use of calories. This is evident in that both joules (kJ) and calories (kcal) are used side by side in most regulatory frameworks. Thus, while the use of joules alone is recommended by international convention, values for food energy in the following post are given in both joules and calories, with kilojoules given first and kilocalories second, within parenthesis and in a different font. The conversion factors for joules and calories are: 1 kJ = 0.239 kcal; and 1 kcal = 4.184 kJ.

FRAMEWORK FOR AN UNDERSTANDING OF FOOD ENERGY CONVERSION FACTORS
Humans need food energy to cover the basal metabolic rate; the metabolic response to food; the energy cost of physical activities; and accretion of new tissue during growth and pregnancy, as well as the production of milk during lactation. “Energy balance is achieved when input (or dietary energy intake) is equal to output (or energy expenditure), plus the energy cost of growth in childhood and pregnancy, or the energy cost to produce milk during lactation”.

The total combustible energy content (or theoretical maximum energy content) of a food can be measured using bomb calorimetry. Not all combustible energy is available to the human for maintaining energy balance (constant weight) and meeting the needs of growth, pregnancy and lactation. First, foods are not completely digested and absorbed, and consequently food energy is lost in the faeces. The degree of incomplete absorption is a function of the food itself (its matrix and the amounts and types of protein, fat and carbohydrate), how the food has been prepared, and - in some instances (e.g. infancy, illness) - the physiological state of the individual consuming the food. Second, compounds derived from incomplete catabolism of protein are lost in the urine. Third, the capture of energy (conversion to adenosine triphosphate [ATP]) from food is less than completely efficient in intermediary metabolism . Conceptually, food energy conversion factors should reflect the amount of energy in food components (protein, fat, carbohydrate, alcohol, novel compounds, polyols and organic acids) that can ultimately be utilized by the human organism, thereby representing the input factor in the energy balance equation.

FLOW OF ENERGY THROUGH THE BODY - A BRIEF OVERVIEW
Food that is ingested contains energy - the maximum amount being reflected in the heat that is measured after complete combustion to carbon dioxide (CO2) and water in a bomb calorimeter. This energy is referred to as ingested energy (IE) or gross energy (GE). Incomplete digestion of food in the small intestine, in some cases accompanied by fermentation of unabsorbed carbohydrate in the colon, results in losses of energy as faecal energy (FE) and so-called gaseous energy (GaE) in the form of combustible gases (e.g. hydrogen and methane). Short-chain (volatile) fatty acids are also formed in the process, some of which are absorbed and available as energy. Most of the energy that is absorbed is available to human metabolism, but some is lost as urinary energy (UE), mainly in the form of nitrogenous waste compounds derived from incomplete catabolism of protein. A small amount of energy is also lost from the body surface (surface energy [SE]). The energy that remains after accounting for the important losses is known as “metabolizable energy” (ME).

Not all metabolizable energy is available for the production of ATP. Some energy is utilized during the metabolic processes associated with digestion, absorption and intermediary metabolism of food and can be measured as heat production; this is referred to as dietary-induced thermogenesis (DIT), or thermic effect of food, and varies with the type of food ingested. This can be considered an obligatory energy expenditure and, theoretically, it can be related to the energy factors assigned to foods. When the energy lost to microbial fermentation and obligatory thermogenesis are subtracted from ME, the result is an expression of the energy content of food, which is referred to as net metabolizable energy (NME).

Some energy is also lost as the heat produced by metabolic processes associated with other forms of thermogenesis, such as the effects of cold, hormones, certain drugs, bioactive compounds and stimulants. In none of these cases is the amount of heat produced dependent on the type of food ingested alone; consequently, these energy losses have generally not been taken into consideration when assigning energy factors to foods. The energy that remains after subtracting these heat losses from NME is referred to as net energy for maintenance (NE), which is the energy that can be used by the human to support basal metabolism, physical activity and the energy needed for growth, pregnancy and lactation.

I think that's enough for today . Tommorow we'll get into the diffrent systems and how they determine what numbers go on the nutrition label.

The Doc

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Peaked_18

http://www.fao.org/documents/show_cd...E/y5022e04.htm


...

The Doc

Man I actually read the book, oh well at least I can archive it on my computer now insted of going through 5000 pages of notes . You don't happen to have a link to any thing related to "The energy value of foods using specific factors from the latest revisions of USDA Agriculture Handbook No. 8: Composition of Foods". I used to have the book with all the specific factors of every food, I still have all my notes but it's nice to have a direct reference.

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DarkFalcon

That's pretty intresting Doc. I wonder if Canadian labeling varies as much or if it's standarized.

The Doc

It's actually pretty much the same as everywhere else. I have some info on the Canadian Labeling guidelines around here somewhere, I'll send them to you after I find them if you would like them.

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builtbeast

Good post doc. I noticed food labels using Joules instead of Calories when I was in Europe.

The Doc

I'll just post the info for the 3 general methods for energy conversion of food, so you can see where different manufaturers come up with their numbers.

1)The Atwater general factor system

This is the one that most of us are familiar with, the 4/4/9 calories for protein/carbs/fat. The system is based on the heats of combustion of protein, fat and carbohydrate, which are corrected for losses in digestion, absorption and urinary excretion of urea. It uses a single factor for each of the energy-yielding substrates (protein, fat, carbohydrate), regardless of the food in which it is found. The energy values are 17 kJ/g (4.0 kcal/g) for protein, 37 kJ/g (9.0 kcal/g) for fat and 17 kJ/g (4.0 kcal/g) for carbohydrates. The Atwater general system also includes alcohol with a rounded value of 29 kJ/g (7.0 kcal/g or an unrounded value of 6.9 kcal/g). As originally described by Atwater, carbohydrate is determined by difference, and thus includes fibre. The Atwater system has been widely used, in part because of its obvious simplicity.

2)The extensive general factor system

A more extensive general factor system has been derived by modifying, refining and making additions to the Atwater general factor system. For example, separate factors were needed so that the division of total carbohydrate into available carbohydrate and fibre could be taken into account. In 1970, Southgate and Durnin added a factor for available carbohydrate expressed as monosaccharide (16 kJ/g [3.75 kcal/g]). This change recognized the fact that different weights for available carbohydrate are obtained depending on whether the carbohydrate is measured by difference or directly. In recent years, an energy factor for dietary fibre of 8.0 kJ/g (2.0 kcal/g) has been recommended, but has not yet been implemented.

In arriving at this factor, fibre is assumed to be 70 percent fermentable. It should also be recognized that some of the energy generated by fermentation is lost as gas and some is incorporated into colonic bacteria and lost in the faeces. As already mentioned, there are also general factors in use for alcohol (29 kJ/g [7.0 kcal/g]), organic acids (13 kJ/g [3.0 kcal/g]) and polyols (10k J/g (2.4 kcal/g]), as well as individual factors for specific polyols and for different organic acids.

The Atwater specific factor system

The Atwater specific factor system, a refinement based on re-examination of the Atwater system, was introduced in 1955 by Merrill and Watt. It integrates the results of 50 years of research and derives different factors for proteins, fats and carbohydrates, depending on the foods in which they are found. Whereas Atwater used average values of protein, fat and total carbohydrate, Merrill and Watt emphasized that there are ranges in the heats of combustion and in the coefficients of digestibility of different proteins, fats and carbohydrates, and these should be reflected in the energy values applied to them. The following two examples help to make this clearer: 1) Because proteins differ in their amino acid composition, they also differ in their heats of combustion. Thus, the heat of combustion of protein in rice is approximately 20 percent higher than that of protein in potatoes, and different energy factors should be used for each. 2) Digestibility (and fibre content) of a grain may be affected by how it is milled. Thus, the available energy from equal amounts (weight) of whole-wheat flour (100 percent extraction) and extensively milled wheat flour (70 percent extraction) will be different.

Based on these considerations, a system was created with substantial variability in the energy factors applied to various foods. Among the foods that provide substantial amounts of energy as protein in the ordinary diet, energy conversion factors in the Atwater specific factor system vary, for example, from 10.2 kJ/g (2.44 kcal/g) for some vegetable proteins to 18.2 kJ/g (4.36 kcal/g) for eggs. Factors for fat vary from 35 kJ/g (8.37 kcal/g) to 37.7 kJ/g (9.02 kcal/g), and those for total carbohydrate from 11.3 kJ/g (2.70 kcal/g) in lemon and lime juices to 17.4 kJ/g (4.16 kcal/g) in polished rice. These ranges for protein, fat and carbohydrate are, respectively, 44, 7 and 35 percent.

So as you can see by the info provided by The Food and Agriculture Organization of the United Nations (FAO) there are diffrent methods available to find the true usable energy in different foods. Obviously everybody here knows how to eat clean and the proper ratios in their diet, I just found this useless info interesting.

The Doc

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