Counting Calories

 Counting Calories
June 1996 -- QA/QC

By: Ray Marsili
Contributing Editor

  Nearly everyone who works in the food industry knows how the total calories of a food or beverage product are determined. Simple, right? The process involves a series of proximate analyses followed by a calculation. First, protein, fat, moisture and ash are determined. Then the total carbohydrate (CHO) content is calculated by difference, since protein, fat, CHO, ash (minerals), and moisture usually comprise nearly the entire content of most food and beverage products.  The final step involves another calculation:
Calories/serving = (gm protein/serving x 4 Cal/gm) + (gm fat/serving x 9 Cal/gm) + (gm CHO/serving x 4 Cal/gm)  This is the "4-9-4" rule for estimating calories in foods. It is used by almost everyone for nutritional labeling purposes. But how accurate is this calculated calorie result? Is bomb calorimetry preferred? Are there more accurate ways to estimate the total caloric content of foods?  While the 4-9-4 rule does, indeed, accurately estimate the calorie content of most food products, it's a drastic oversimplification in some cases. Two basic problems could invalidate the calculation for some foodstuffs: 1) Nutrients from different food sources are not utilized (assimilated) by the human body with the same efficiency; and 2) some food materials contain significant levels of ingredients other than protein, fat, CHO, ash and water.Nutrients aren't created equal  A subtle but significant difference exists between nutrient testing and chemical testing. Meaningful nutrient testing should take into account not just how much of a specific chemical nutrient is present in the food sample, but also how much is actually metabolized when the product is consumed. According to data in the USDA Handbook No. 8, for instance, the coefficient of digestibility of egg protein is 97% and it contributes 3.9 Cal/gm, while the coefficient of digestibility for egg "fat" is 95% and contributes 9.02 Cal/gm.  On the other hand, wheat bran's protein coefficient of digestibility is only 40% and its protein calorie contribution is just 1.82 Cal/gm - significantly less than the 4 Cal/gm estimated by the 4-9-4 rule. Furthermore, the coefficient of digestibility of wheat bran carbohydrate is 56%, and its calorie contribution is only 2.35 Cal/gm - again, far below the 4 Cal/gm used in the 4-94 calculation.Calculated source of error  Calculating CHO by difference is not always accurate and can lead to significant under- or over-estimation of total calories. For example, some confectionery products and pet foods contain propylene glycol as a humectant and flavor solvent. When the CHO content is determined by difference, the propylene glycol is calculated as CHO, even though it is a polyhydric alcohol and probably is not digestible or capable of contributing calories when consumed. Another example of calculated values for CHO that lead to an overestimation of calories is when foods contain high levels of insoluble complex CHOs, which pass through the body either undigested or only partially digested. Insoluble fiber would contribute far fewer calories than the 4 Cal/gm estimated by the 4-94 rule.  The 4-9-4 rule doesn't work well with alcoholic beverages, and the higher the alcohol content, the greater the error in underestimation of the caloric content of the beverage. During the proximate analysis for moisture determination, the alcohol in the sample is driven off with the water and it shows up as an increase in moisture content. Since it is not calculated as protein, fat or CHO, its calorie contribution, which is actually 6.93 Cal/gm (for ingested alcohol, according to Handbook No. 8), is zero when the 4-9-4 rule is applied.  According to Jon DeVries, Ph.D., technical manager for Medallion Laboratories (Minneapolis), there are five official ways to estimate the caloric content of food products:The 4-9-4 rule.Using the general 4-9-4 factors, but not counting calories contributed by insoluble fiber. Rather than calculating total CHO by difference and multiplying by 4 Cal/gm, the insoluble fiber portion of the CHO is subtracted from the total CHO difference value before multiplying by 4 Cal/gm.The Atwater System. Using digestibility factors and bomb calorimetry data, the Atwater System tabulates data for specific food factors approved by FDA for particular foods or ingredients. Consider the estimation of total calories obtained from eating 1 gram of potato. Bomb calorimetry experiments are used to determine the heat of combustion of potato protein. This number, 3.75 Cal/gm, is multiplied by 74%, the coefficient of digestibility for potato protein, to give a value of 2.78 Cal/gm. The process is repeated for potato fat and potato CHO, and then all three values are summed to estimate the total calories per each gram of potato consumed.Bomb calorimetry measurements. One might expect that bomb calorimetry, a direct measurement with a scientific instrument, would be the most accurate way to estimate the caloric content of foods. In reality, bomb calorimetry data is seldom used in the food industry to estimate calories. The method is expensive to run, and results tend to overestimate actual calories when food is digested because digestibility factors, which are difficult to obtain, are not considered. Today, few contract nutritional laboratories are even equipped with bomb calorimeters.  "Bomb calorimetry tends to give the maximum possible caloric content of the product," says Lars Reimann, vice president of operations for Woodson-Tenent Laboratories, Memphis, TN. "Consider hair. It's nearly pure protein and, according to bomb calorimetry, has about 4 Cal/gm. But in reality it contributes 0 Cal/gm since it cannot be digested."  Bomb calorimetry is sometimes used for pet and animal foods. Reimann says that the American Assoc. of Feed Control Officials requires bomb caloric measurement of raw feed and fecal matter to determine the actual calories (by difference) contributed by feed when it is consumed by the animal. While this is an accurate way to determine actual calories, it is also time-consuming and expensive.Consideration of calorie contribution by special ingredients. For example, laboratory experiments show that polydextrose, a popular bulking agent used in many reduced fat foods, contributes 1 Cal/gm.  Another example of an ingredient requiring special consideration for its caloric content is salatrim. The credit for Nabisco's ability to deliver a lowfat, fudge-dipped granola bar goes to this ingredient. Although salatrim is a real fat, only 55% is used by the body. Therefore, it only contributes 5 Cal/gm - not the usual 9 Cal/gm.Counting getting more difficult  The trend toward more reduced fat and no-fat products continues to gain momentum and shows no signs of abating. Fiber, gums, bulking agents, and specially engineered new ingredients like salatrim and olestra will be appearing more often and in higher concentrations in processed foods.  Olestra, a sucrose polyester, can be used in frying of savory snacks without adding calories. It joins an elite family of only four other food additives that cannot be regarded as GRAS but have been approved since 1970. These are TBHQ (1972), aspartame (1981), polydextrose (1981), acesulfame K (1988) and now, olestra. Currently, the FDA's approval for olestra only permits its use in savory snacks. For olestra to be used in other applications, Procter & Gamble would have to file another petition and have that approved.  The usage levels of olestra are different from other more common food additives. Olestra will be consumed at relatively high intakes of 30% to 40%, compared with the 1% to 2% for most other approved food additives.  When food additives like olestra are used at such high levels, their impact on calorie estimation becomes highly significant. To estimate calories accurately in these types of foods, the food chemist can no longer simply perform proximate analysis, calculate CHO by difference, and apply the 4-9-4 rule. The new challenge is to develop accurate tests to quantitate the level of olestra, salatrim, and other fat replacers now being used so that their individual calorie contributions can be determined. This is no simple task. With the list of these newly developed ingredients to replace fat growing at a rapid pace, counting calories becomes much more difficult.  Even the more commonly used bulking agents that are added to mimic the mouthfeel of fat complicate the determination of calories. CHOs are the most common types of bulking agents used in prepared foods. They may be totally digestible, partially digestible, or undigestible, as well as soluble or insoluble. Most bulking agents are polysaccharides and are obtained from industrial gums, modified starches, and plant cell walls, which are largely a combination of cellulose, hemicelluloses and a small amount of lignin. Most of the un-derivatized starches are digested in the human gastrointestinal system. However, ungelatinized starch is not completely digested. Most other industrial polysaccharides pass through the large intestine with little breakdown, since no naturally occurring enzymes are present to cause cleavage.  An important consequence of the fat-replacer revolution is that it will become considerably more difficult for food companies to identify how competitors are achieving the calorie reductions they are reporting on their product labels. To monitor the calorie content of competing products, more testing for specific types of ingredients will be required. In addition, the FDA and other regulatory labs will have a more difficult task in making sure the calorie content reported on food labels is what's present in the products being sold.The calorie-counting consumer  Fat is the No. 1 consumer nutrition concern and saturated fat is No. 2, according to a recent telephone interview of 1,500 adults sampled nationwide by The United Soybean Board. Calories ranked No. 8 of the 12 consumer nutrition concerns mentioned.  Despite the shift to eating foods with lower levels of fat, consumers are heavier than ever. A recent survey by the National Center for Health Statistics (NCHS) shows that 33% of American adults are now overweight - an 8% increase over 10 years ago. A study by the National Institutes of Health revealed that in 1992-1993 the average weight of Americans age 25-30 was 171 lbs. The same age group had an average weight of only 161 lbs. in 1985-1986. Excess caloric intake from nonfat sources is undoubtedly contributing to this weight gain. A recent National Health and Nutrition Examination Survey showed that the total daily calorie intake for adults rose from 1,969 Cal. in 1978 to 2,200 Cal. in 1990.  Consumers are learning that merely reducing the amount of fat in their diet does not automatically lead to weight control. Calories contributed by CHOs are an important factor. The net calories available to your body is a critical factor, whether those calories come from fat or carbohydrates. No matter what the source, if you eat more calories than you burn the excess is stored in the body as fat. People are gaining weight from too many calories from low-fat ice cream, cakes, cookies, mayonnaise and margarine.  It is likely that consumers will be paying more attention to calorie intake in the future. But although consumers will probably be even more likely to check calorie counts on foods, accurately determining a food product's caloric content is becoming increasingly more difficult and less accurate. Even now, the calories per serving reported on many food products are ball-park estimates at best.  Despite the inherent inaccuracies associated with calorie determinations, American consumers are, in some cases, making purchase decisions based on these numbers. For example, one brand of macaroni and cheese may list 390 Call/serving on its nutrition label, while another may list 400 Call/serving. A substantial number of consumers will choose to purchase the one that lists fewer calories on the nutrition panel even though, in reality, the other macaroni and cheese product may actually contain fewer calories per serving. Consumers are relying too heavily on the accuracy of reported calories per serving that appear on food labels.  One problem that seems to persist is consumers' perception of what constitutes healthy eating. In this regard, consumers have persistently demonstrated a tendency to be myopic. Too often they focus on avoiding one or two "bad" food concerns (e.g., fat or saturated fat) and don't consider the contribution of vitamins, minerals and other desirable nutrients. Highly engineered foods that contain increasingly larger proportions of fat replacers and bulking agents may indeed contain less fat and fewer calories, but in many cases, they also may contain significantly reduced levels of beneficial nutrients. The education part of the NLEA must be improved for consumers to benefit from nutrition labels. Good nutrition involves more than counting calories. Fat and Calorie Reduction for 1 oz. of Potatoand Tortilla Chips with Olestra Product Fat (g) Calories Regular Potato Chips 10 150 Potato Chips w/ Olestra 0 70 Regular Tortilla Chips 7 140 Tortilla Chips w/ Olestra 1 90Source: USDA Handbook No. 8 and Procter & GambleBack to top<