Carbohydrates, fiber, and protein

Important nutrients for the body

Nutrients in the food we eat have many roles in our body, including regulating metabolic processes. Nutrients can be classified into two different groups. Essential nutrients cannot be made by the body and must be in the food eaten. Nonessential nutrients are those the body can make on its own. For example, the body makes vitamin D from sun exposure on the skin. However, this synthesis is often not enough on its own, so dietary vitamin D may still be needed. Foods can also be described as follows:

• Nutrient rich (also called nutrient dense): Foods high in nutrients (e.g., vitamins, minerals, complex carbohydrates, healthy fats, and lean protein) and low in calories.
• Non-nutrient rich: Foods lacking vitamins, minerals, and fiber. They provide “empty calories” and can cause people to gain weight.

The following sections will examine nutrients important in our diet.

Carbohydrates

Carbohydrates are nutrients found in our diet. About 45% to 65% of our daily calories should come from carbohydrates. Carbohydrates are used for energy and to regulate protein and fat metabolism. This nutrient encompasses a broad range of simple sugars, starches, and fiber.

Simple sugars

There are many types of simple sugars. Nutrient-rich foods containing simple sugars include the following:

• Fruits and vegetables, which contain fructose and glucose
• Milk and milk products, which contain lactose

Non-nutrient-rich foods and food additives containing simple sugars include desserts (cookies, cakes), candy, soda, syrups (including regular and high-fructose corn syrups), white sugar (sucrose), honey, and molasses.

During digestion, most sugars (except lactose from milk) break down into fructose and glucose. Lactose breaks down into glucose and galactose. Simple sugars are rapidly absorbed and quickly raise blood glucose levels. They provide a quick source of energy.

Starches

Starches are called complex carbohydrates. Food sources of complex carbohydrates include the following:

• Nutrient-rich starches: Legumes (e.g., split peas, beans [kidney, black, garbanzo, and pinto]), starchy vegetables (e.g., corn, green peas, and potatoes), and whole grains (e.g., oats, barley, quinoa, seeds, and brown rice)
• Non-nutrient-rich starches: White bread, crackers, and white rice

Complex carbohydrates are digested in the intestine before being absorbed. They break down into simple sugars and become a source of energy. The glucose from the simple sugars and starches raises the blood glucose level. With the help of insulin, glucose is moved out of the bloodstream and into cells; it is then used for energy. Some glucose is stored in the liver and muscles as glycogen. The body uses the stored glycogen in between meals and during strenuous exercise. As the blood glucose levels start to drop, glucagon works in the liver to release the stored glycogen. Glycogen is released back into the blood and raises the blood glucose level.

It is important to remember that excessive carbohydrates can be converted into fat. The following are smart carbohydrate dietary choices:

• Eat a variety of whole grains, fruits, vegetables, legumes, and low-fat or nonfat dairy products.
• At least half of all grains eaten should be whole grains.
• Limit processed foods in your diet, especially those with added sugar, salt, and fat.
• Eat enriched refined grains, if eating refined grains.

Whole grains and refined grains

Foods made from wheat, oats, cornmeal, rice, and barley are grain products. Grains are divided into whole grains and refined grains:

• Whole grains: Use the entire grain kernel (e.g., bran, germ, and endosperm); they include whole-wheat flour, cracked wheat (bulgur), whole cornmeal, oatmeal, and brown rice.
• Refined grains: Are milled, and the bran and germ are removed to create a finer texture and longer shelf life. Examples include white flour, degermed cornmeal, white rice, and white bread.

During the milling process, dietary fiber, iron, and many B vitamins are removed. For this reason, most refined grains are enriched. This means certain B vitamins and iron are added back to the grains. Fiber is not added back into the product.

Glycemic index

The glycemic index (GI) is a numeric index used to indicate how much a carbohydrate food raises the blood glucose level. The foods are ranked from 0 to 100. Carbohydrates that are rapidly digested, absorbed, and considerably raise the blood glucose level are considered high-GI foods (≥70). Low-GI foods (≤55) produce a smaller change in the blood glucose level. The goal is to eat more low-GI foods to reduce the risk of type 2 diabetes mellitus and heart disease. Low-GI foods can also help maintain weight loss. The table below shows the GI values of some common foods.

Fiber

Fiber is different from simple sugars and starches. It cannot be digested by the body, and thus, it does not raise the blood glucose level. Fiber helps a person feel full and can help with weight management. There are two types of fiber: soluble fiber and insoluble fiber.

Soluble fiber dissolves in water and forms a gel-like substance. Soluble fiber softens the stool. It lowers the blood glucose level by slowing sugar absorption. Soluble fiber lowers the low-density lipoprotein (or bad cholesterol) level by binding to fatty acids. Examples of soluble fiber foods include the following:

• Nutrient-rich: Legumes, oats, barley, fruits (e.g., avocados, apples, and citrus fruits), and carrots
• Non-nutrient-rich: Processed and refined goods

Insoluble fiber bulks up the stool and helps to prevent constipation. Examples of insoluble fiber include the following:

• Nutrient-rich: Whole grains (whole wheat and brown rice), vegetables (corn, broccoli, green beans, cauliflower, and potatoes with skins), nuts and seeds, popcorn, and prunes.
• Non-nutrient-rich: Processed and refined goods

Fiber supplements are usually taken to reduce constipation. They can help a person be “regular.” The active ingredient in the supplements can vary between natural and synthetic soluble fiber. Consider the following:

• Metamucil contains psyllium husk, a natural substance that contains about 70% soluble fiber and 30% insoluble fiber.
• Citrucel contains methylcellulose, a semisynthetic soluble fiber.
• Fibercon contains calcium polycarbophil, a synthetic soluble fiber.

It is important to drink plenty of water when taking fiber supplements. Some fiber supplements have been shown to lower blood pressure, blood glucose, and the risk of heart disease.

Protein

Protein is a nutrient in our diet. About 10% to 35% of our daily calories should come from protein. The following sections examine the role of protein in the body and the types of amino acids.

Role of protein in the body

Proteins are broken down into amino acids. Amino acids can be used as a source of energy in the absence of carbohydrates. Amino acids are also used to make proteins to help the body:

• Break down food (e.g., enzymes)
• Grow and repair body tissues (e.g., connective tissue, hair, nails, muscles)
• Perform other functions (e.g., those related to hemoglobin, antibodies, and hormones)

Proteins and amino acids are considered the building blocks of life. The body needs several amino acids in large enough amounts to maintain good health. Protein malnutrition is seen around the world and can lead to kwashiorkor. A lack of dietary protein can cause growth failure, loss of muscle mass, anemia, edema and potbelly, skin depigmentation and hair loss, weakening of the circulatory and respiratory systems, decreased immunity, and death.

Amino acids

Amino acids are classified into three groups:

Definitions

Essential amino acids

Cannot be made by the body, thus must come from food eaten throughout the day.

Nonessential amino acids

Can be made by the body from essential amino acids or in the normal breakdown of proteins.

Conditional amino acids

Usually not essential except in times of illness and stress.

Foods that have all the essential amino acids to support the body are called complete proteins. Foods that are considered complete proteins are fish, meat, poultry, dairy products, quinoa seeds, buckwheat, chia seeds, and eggs. Foods that do not contain all the essential amino acids are called incomplete proteins. Nuts, legumes, grains, and vegetables are examples of incomplete proteins.

Smart protein choices include the following:

• Choose lean or low-fat meat and poultry.
• Eat seafood rich in omega-3 fatty acids, such as salmon, trout, herring, Pacific oysters, and Atlantic and Pacific mackerel.
• Limit processed meats (e.g., ham, sausage, and deli meats), which contain added salt (sodium).
• Eat unsalted nuts and seeds to keep sodium intake low.