Principles of Biochemistry Volume 3 - A. Lehninger 1985

Certain aspects of human biochemistry
Human nutrition
Special food labels serve the interests of consumers

Consumer protection laws in the United States require food packaging labels to display nutritional information. By comparing these data with unit prices, shoppers can quantitatively evaluate the "unit cost" of various food products of the same type. The nutritional information on breakfast cereal boxes, which are available in A wide variety, is particularly valuable. Table 26-15 presents nutritional data for a widely advertised brand of children's breakfast cereal (flakes), a key characteristic of which is its high free sugar content. Note that the only natural ingredient in this product is milled corn, while the rest consists of flavorings, preservatives, Vitamins, and minerals. A one-ounce (28.4 g) serving of this product contains 26 g of CARBOHYDRATES, 2 g of protein, and zero fat, meaning that carbohydrates account for 93% of the cereal's weight. The carbohydrates are split equally between starch and sugars, with free sugars making up about 47%—significantly exceeding the optimal daily intake recommended for A balanced diet (see Fig. 26-2). Such a high free sugar content is undesirable as it promotes tooth decay in children. Milk added to the cereal provides 67% of the protein and nearly 40% of the calories. The cereal is fortified with various vitamins, as well as iron and zinc ions. The sodium content listed on the label is particularly important for individuals with Hypertension.

Class="center">Table 26-15. Nutritional information printed on a box of popular U.S. corn flakes

Percentage of U.S. Recommended Daily Allowances (% U.S. RDA)

Ingredients: milled corn, sugar, salt, malt flavoring, ascorbic acid, vitamin A palmitate, niacinamide, reduced iron, pyridoxine hydrochloride, riboflavin, thiamine hydrochloride, Folic acid, and vitamin D₃. BHA (butylated hydroxyanisole) added to help preserve freshness.

References

General

Davidson S., Passmore R., Brock J. F., Truswell A. S. (eds.). Human Nutrition and Dietetics, 6th ed., Churchill Livingstone, Edinburgh, 1975.

Human Nutrition: Readings from Scientific American, Freeman, San Francisco, 1978.

The Nutrition of Man, special issue of the British Medical Journal, vol. 37 (1981).

Underwood E. J. Trace Elements in Human and Animal Nutrition, Academic Press, New York, 1977.

Specialized

Chisholm J. J., Jr. Lead Poisoning, Sсi. Am., 224, 15-23 February (1971).

Feenstrom W. D., Wurtman R. J. Nutrition and the Brain, Sсi. Am., 230, 84-91 February (1974).

Food and Agriculture, Sсi. Am., 235 September (1976). A comprehensive review of articles on this topic.

Goldwater L. J. Mercury in the Environment, Sсi. Am., 224, 15-21 May (1971).

Harpstead D. D. High-Lysine Corn, Sсi. Am., 225, 34-42, August (1971).

Janick J., Noller C. H., Rhykerd C. L. The Cycles of PLANT AND ANIMAL Nutrition, Sсi. Am., 235, 74-86, September (1976).

Kermode G. O. Food Additives, Sсi. Am. 226, 15-21, March (1972).

Kretchmer N. Lactose and Lactase, Sсi. Am., 227, 70-78, October (1972).

Lieber C. S. The METABOLISM of Alcohol, Sсi. Am., 234, 25-33, March (1976).

Loomis W. F. Rickets, Sсi. Am., 223, 76-91, December (1970).

Mayer J. The Dimensions of Human Hunger, Sсi. Am., 235, 40-49, September (1976). Nutrition Misinformation and Food Faddism, Nutrition Reviews, Special Supplement, July (1974).

Questions and Problems

1. Recommendations for daily dietary intake. Why do the figures for the daily diet recommended by the Food and Nutrition Board (Table 26-2) differ from the minimum daily requirements?

2. ATP derived from glucose or Fatty acids. Calculate how many moles of ATP are synthesized via Oxidative Phosphorylation from 1 g of glucose and 1 g of palmitic acid under standard conditions. Compare your results with The amount of heat released upon the combustion of 1 g of glucose and 1 g of palmitic acid in a bomb calorimeter (Table 26-5).

3. Weight loss during fasting. When a person adopts a "crash" or strict diet, the initial weight loss is primarily due to dehydration of the body. Why? During prolonged fasting, the daily weight loss is less than during the initial period. How would you explain this?

4. The Link Between diet and obesity. Long-term consumption of foods whose caloric content exceeds recommended levels can lead to obesity. Which type of diet—one rich in sugars or one rich in fats—promotes obesity more? Explain your answer.

5. Food calorimetry. A 9.5 g sample of wheat flakes was subjected to complete oxidation to CO₂ and H₂O by combustion in a bomb calorimeter. As a result, the 2500 g of Water surrounding the calorimeter was heated from 15 to 27 °C.

a) Calculate the caloric content of the wheat flakes in kilocalories per gram.

b) If the initial moisture content of the wheat flakes was 25%, What is the caloric content of the dry flakes?

c) Based on the data above and other considerations, formulate a hypothesis as to whether carbohydrates, proteins, or fats are the main component of wheat flakes. Explain your answer.

d) If a person eats these wheat flakes, is the same amount of energy released in the body as in the calorimeter? If not, why?

6. Calorie balance. A young female college senior discovered that she had gained too much weight over the past year. Her diet provided 2400 kcal/day. Standard tables correlating height, build, age, and weight indicated that she was about 20% overweight. To maintain her weight at a normal level on a constant basis, she needs an average intake of 2100 kcal per day. Using the data provided in this chapter, suggest six different foods that this woman should consume in restricted amounts to maintain a normal weight.

7. Nitrogen balance and dietary proteins. A healthy young man on a diet containing balanced amounts of Essential Amino Acids exhibits a positive nitrogen balance—that is, the total amount of nitrogen ingested per day exceeds the total amount excreted per day. In contrast, an individual on a diet deficient in one or more essential amino acids exhibits a negative nitrogen balance, meaning that the total daily nitrogen intake is less than the total daily nitrogen excretion. Explain why this occurs.

8. Experimental Determination of Amino acid requirements. Describe the design of an experiment that would determine the minimum daily requirement of The amino acid phenylalanine for a white rat.

9. Initial weight loss during the Treatment of kwashiorkor. When young children suffering from kwashiorkor are placed on a nutritious diet, they initially lose weight. Explain why.

10. Nutrition and Kidney disease. People with renal failure lose The ability to excrete Metabolic waste products at a sufficient rate. They must undergo regular dialysis, during which Blood is dialyzed across a membrane to wash out wastes such as urea and uric acid. In addition, their diet must contain limited amounts of certain proteins. Explain why. Which protein source is preferable for their diet—eggs or corn? Why?

11. Vitamin B₆ requirement and diet. When a person switches to a high-protein diet, their requirement for vitamin B₆ increases. Provide a possible explanation for this phenomenon.

12. Nutritional studies and intestinal Bacteria. One of the difficulties in human nutrition research is the uncertainty associated with The Effect of an experimental diet on intestinal bacteria. Why must this factor be taken into account?

13. The necessity of specific foods. It is a common belief that milk is a supreme food and must be included in everyone's diet for proper nutrition. Is this true? Provide a biochemical rationale for your answer.

14. Provisions for mountaineers. Suppose you need to compile a food list for a mountaineer embarking on a 48-hour ascent of one of the Himalayan peaks.

a) What characteristics and requirements would you consider paramount for a diet in this situation?

b) What specific types of foods would you include?

c) What foods would you consider unnecessary?

d) What VITAMINS AND MINERALS would you suggest supplementing the diet with? Explain your Answers.

15. Alcohol as a precursor to fats and carbohydrates. Ethanol is completely converted into triacylglycerols, but it cannot be converted into glucose or Glycogen. Why?

15. Caloric content of beer. A college senior who maintains a constant weight on a diet corresponding to an intake of 2900 kcal/day also acquired the habit of drinking one 350 g can of beer per day. How much new fat tissue will he accumulate after 3 years, assuming all other factors, such as physical activity, remain constant? (The actual increase in his body weight will be greater because fat deposition in adipose tissue requires an increase in blood volume and extracellular fluid volume.)

17. Meat as a calorie source. In several Regions of the world with readily accessible natural resources, it is customary to consume large quantities of meat at every meal. If meat lovers eat it in amounts exceeding their caloric requirements, they may gain "excess" weight.

a) Through which metabolic pathway can protein-rich meat lead to the deposition of triacylglycerols?

b) What other metabolic changes can occur as a result of such a diet?