Part I: Life Science
Although nutritionists themselves don’t always agree about what constitutes a healthy diet, certain facts are clear. The human body requires a combination of protein, carbohydrates, fat, minerals, vitamins, and fiber. Proteins, carbohydrates, and fats (macronutrients) are necessary to provide energy. Minerals and vitamins (micronutrients) , along with fiber, are necessary to maintain proper bodily functions.
Proteins are necessary for the body’s maintenance, growth, and repair. Animal proteins are contained in meat, fish, eggs, and cheese. Vegetable proteins are found in peas, beans, nuts, and some grains.
Carbohydrates include both starches and sugars. They are major sources of energy for the body. Starches are found in bread, cereal, rice, potatoes, and pasta. Sugars are found in fruits, cane sugar, and beets, as well as processed foods.
Fats also provide energy for the body. There are three types of fats: saturated, monounsaturated, and polyunsaturated. Saturated fats can raise bad cholesterol (LDL), but mono- and polyunsaturated fats can actually decrease levels of bad cholesterol. Diets high in saturated fat can lead to high cholesterol, which can cause heart disease or stroke. Sources of saturated fats include meats, shellfish, eggs, milk, and milk products. Sources of monounsaturated fats include olives and olive oil, almonds, cashews, Brazil nuts, and avocados. Sources of polyunsaturated fats include corn oil, flaxseed oil, pumpkin seed oil, safflower oil, soybean oil, and sunflower oil.
Fiber is an important part of a healthy diet that provides bulk to help the large intestine carry away waste matter. Good sources of dietary fiber include leafy green vegetables, carrots, turnips, peas, beans, and potatoes, as well as raw and cooked fruits, cereals, and whole-grain foods.
Water is also essential for survival. The body loses approximately four pints of water each day, which must be replenished. Most foods contain water, facilitating proper water maintenance, although it is still necessary to drink water as well! Insufficient water consumption leads to dehydration, which can cause muscle cramps, dizziness, and, if not remedied, even death.
Minerals in small quantities are needed for a balanced diet. Some necessary minerals are iron, zinc, calcium, magnesium, and sodium chloride (salt). Calcium is important for building strong teeth and bones. Iron, on the other hand, is necessary for red blood cell development. Minerals play many different roles in the development and maintenance of a healthy body.
Vitamins, such as vitamins C and D, are organic compounds that are necessary for a wide variety of physiological processes from bone hardness to healthy gums. Fruits and vegetables are rich sources of vitamins. Vitamin D is unique in that one of the best sources comes not from your diet, but from the sun. Exposure to sunlight allows your body to synthesize its own vitamin D.
A lack of the proper amount of certain necessary nutrients in the diet can lead to deficiency diseases. One such disease is iron-deficiency anemia, which may cause weakness, dizziness, and headaches. It is especially common among children, young adults, and pregnant women who do not get enough iron in their diets. Another example of a deficiency disease is scurvy, which is caused by a lack of vitamin C. Though at one time very common among pirates and sailors who did not have access to fresh fruits and vegetables, scurvy is now relatively rare.
The following table lists a selection of nutrients and their sources.
| Vitamin/Mineral | Sources | Benefits |
|---|---|---|
| Iron | Meat (especially liver), beans, whole grains | Allows red blood cells to transfer oxygen to body tissues |
| Calcium | Dairy products like milk, yogurt, and cheese; spinach | Bone growth, muscle function |
| Magnesium | Nuts, whole grains, green leafy vegetables, fortified foods | Bone development, muscle and nerve function, enzyme function |
| Potassium | Bananas, sweet potatoes, nuts and seeds | Balances fluid levels in the body |
| Vitamin A | Liver, milk, eggs, carrots, spinach | Vision, immune system, cell growth |
| Vitamin C | Red and green peppers, citrus, broccoli | Collagen formation, immune system function, antioxidant (helps protect cells from damage) |
| Vitamin D | Fortified milk, juice, or cereal; body makes majority of vitamin D when exposed to sunlight | Bone strength (by helping the body absorb calcium), muscle and nerve function, immune system |
Take a look at how an expert test taker might approach an ASVAB question about health and nutrition.
| Question | Analysis |
|---|---|
| A pregnant woman feels dizzy and has a headache. Which of the following would be the most likely diagnosis? (A) iron-deficiency anemia (B) scurvy (C) cancer (D) diabetes |
Step 1: You’re given three important facts: the woman is pregnant, has a headache, and is feeling dizzy. Step 2: What condition that causes headache and dizziness is common in pregnant women? Step 3: Those symptoms match iron-deficient anemia, which is especially common among pregnant women. Step 4: Select choice (A). |
Now try one on your own.
A person with high cholesterol should limit their intake of saturated fat. The only choice here that is high in saturated fat is (B) red meat. The others are filled with healthier fats (mono- and polyunsaturated fats) that could possibly help lower high cholesterol.