25. Nutrition. Food and Diet




Energy Drinks-Hype or Help?

Check the ingredient list.

Energy drinks are marketed to appeal to young people. They claim to provide energy for physical activity. What are the facts?

Many energy drinks do contain various kinds of sugar that are a source of Calories. The amount of sugar is generally similar to that in soft drinks. Some energy drinks are sugar-free.

The primary ingredients in all energy drinks are substances that stimulate the nervous system. Caffeine is usually shown as an ingredient and is typically in an amount equivalent to that found in a cup of coffee, although some brands have higher amounts. Two herbal ingredients commonly found in energy drinks are also known to be stimulants—guarana and yerba mate. Because they are herbal products, it is not required that companies provide detailed information about their quantities and effects. Both of these ingredients are extracts of South American plants. So, energy drinks containing guarana or yerba mate have additional stimulants that have effects similar to caffeine.

Taurine is another ingredient commonly found in energy drinks. It is naturally produced by the body and is a major ingredient of liver bile. It is present in meat and fish. Although it is often called an amino acid, it is not. However, it is produced in the body from the amino acid cysteine. It appears to have a variety of effects in the body but it is unclear if additional quantities have any beneficial effect. Its presence in energy drinks is probably related to some evidence that it improves the endurance of muscles. Its name is also of interest. It was first isolated from the bile of an ox, so it was given the name taurine after Taurus the bull. It appears that high doses are not harmful.

So, it appears that the primary effect of these drinks is to stimulate the nervous system so that people are more alert. They are not sources of energy in the metabolic sense.

• What is the nutritional content of an energy drink?

• What role does caffeine play in metabolism?

• Should marketers of energy drinks be required to prove their claims?


ü  Background Check

Concepts you should understand in order to get the most out of this chapter:

• The basic principles of chemistry (chapter 2)

• The basic principles of organic chemistry (chapter 3)

• How enzymes work in processing energy and matter (chapter 5)

• The structure and function of the digestive system (chapter 24)


25.1. Living Things as Chemical. Factories: Matter and Energy. Manipulators


Organisms maintain themselves by constantly processing molecules to obtain energy and building blocks for new living material. Autotrophs can manufacture organic molecules from inorganic molecules, but heterotrophs must consume organic molecules to get what they need. Nutrients are all the molecules required to support living things. Some nutrients are elements, such as calcium, iron, and potassium; others are organic molecules, such as carbohydrates, proteins, fats, and vitamins. All heterotrophs obtain the nutrients they need from food, and each kind of heterotroph has particular nutritional requirements. This chapter examines the nutritional requirements of humans.


Diet and Nutrition Defined

The word nutrition is used in two contexts. First, nutrition is the branch of science that seeks to understand food, its nutrients, how the body uses nutrients, and how inappropriate combinations or quantities of nutrients lead to ill health. The word nutrition also refers to all the processes by which we take in food and use it, including ingestion, digestion, absorption, and assimilation. Ingestion is the process of taking food into the body through eating. Digestion is the breakdown of complex food molecules to simpler molecules. Absorption is the movement of simple molecules from the digestive system to the circulatory system for dispersal throughout the body. Assimilation is the modification and incorporation of absorbed molecules into the structure of the organism.

Many of the nutrients that enter living cells undergo chemical changes before they are incorporated into the body. These interconversion processes are ultimately under the control of the cell’s genetic material. It is DNA that codes the information necessary to manufacture the enzymes required to extract energy from chemical bonds and to convert raw materials (nutrients) into the structure (anatomy) of the organism.

Diet is the food and drink consumed by a person from day to day. It must contain the minimal nutrients necessary to manufacture and maintain the body’s structure (e.g., the bones, skin, tendon, muscle) and regulatory molecules (enzymes and hormones) and to supply the energy (ATP) needed to run the body’s machinery. If the diet is deficient in nutrients, or if a person’s body cannot process nutrients efficiently, a dietary deficiency and ill health may result. A good understanding of nutrition can promote good health; it requires an understanding of the energy and nutrient content in various foods (figure 25.1).




FIGURE 25.1. Diet

Your diet is what you eat on a daily basis.


Energy Content of Food

The kilocalorie (kcal) is the unit used to measure the amount of energy in foods. One kilocalorie is the amount of energy needed to raise the temperature of 1 kilogram of water 1°C. Remember that the prefix kilo- means “1,000 times” the value listed. Therefore, a kilocalorie is 1,000 times more heat energy than a calorie. A calorie is the amount of heat energy needed to raise the temperature of 1 gram of water 1°C. Although the energy unit for nutrition is a kilocalorie, it is usually called a Calorie with a capital C. This is unfortunate because it is easy to confuse a dietary Calorie, which is really a kilocalorie, with a calorie. Most books on nutrition and dieting use the term Calorie to refer to food calories (How Science Works 25.1).



Measuring the Caloric Value of Foods

A bomb calorimeter is an instrument used to determine the energy content of food. This is done by determining how much heat a given amount of food produces when it is burned. To operate the instrument, a small food sample is formed into a pellet and sealed inside a strong container called a bomb. The bomb is filled with oxygen under 30 atmospheres of pressure and is then placed in a surrounding jacket filled with water. The sample is electrically ignited. As it reacts with the oxygen (burns), the food sample in the bomb produces heat that is transferred to the water in the jacket that surrounds the bomb. The increase in temperature of the water is recorded. A kilocalorie (Calorie) is the amount of heat energy needed to increase the temperature of 1 kilogram of water 1°C. Therefore, if 1 gram of food results in a water temperature increase of 4°C for each kilogram of water, that food has 4 kilocalories (Calories).




1. What is a nutrient?

2. What is the difference between digestion and assimilation?

3. How is the energy content of food measured?