What is Nutrition?

Healthy food on a plate

If a visitor from another planet asked, “What is nutrition?” would you know how to answer? The definition can be simple or complex, depending upon your perspective. According to the National Cancer Institute, nutrition is defined as “the taking in and use of food and other nourishing material by the body.” The NCI describes nutrition as existing in three parts: the consuming of food and drink, the breaking down of food and drink by the body into nutrients, and the travel of those nutrients through the bloodstream to various parts of the body, which use them for purposes such as fuel.

For those who plan to study nutrition, the scope of their studies encompasses much more than this. The science of human nutrition involves diet and how that interacts with development, growth, physiology, composition, and metabolism of the human body. The study of nutrition examines the role that nutrition plays in all types of people, the ways in which nutrition impacts wellness and disease, and how diets, people, and their environments interact. 

Of course, nutrition can be studied in all types of living organisms. After a brief mention of the types of nutrition, however, for our purposes, we will stick to examining human nutrition here. 

Heterotrophic vs. Autotrophic Nutrition

Before we closely study human nutrition, we will discuss the two types of nutrition based on mode and organism. These are heterotrophic and autotrophic nutrition.

Heterotrophic nutrition

Heterotrophic nutrition is found in heterotrophs; that is, organisms that cannot produce food on their own and depend on other sources for nutrition. These include herbivores (plant eaters), carnivores (meat eaters), and omnivores (those who eat plants and meat). There are three types of heterotrophs:

  • Holozoic – This type of heterotroph includes humans and other types of animals, and involves ingesting, digesting, absorbing and assimilating solid and liquid material
  • Saprophytes – Mushrooms, fungi, and other microorganisms that feed on dead or decaying organic matter
  • Parasites – Leeches, ticks, and other organisms that live in or on an organism of another species (a host) and gets its nutrients at the expense of that host

Autotrophic nutrition

Autotrophic nutrition is a type of nutrition in which organisms synthesize their own food, through the usage of sunlight, water, and carbon dioxide. A prime example of an autotroph is green plants. 

Dietary Patterns in Humans

Another important consideration in the study of human nutrition is dietary patterns. These can be described as the combinations of foods and beverages that make up a person’s complete dietary intake over a period of time. Changing dietary patterns can greatly improve a person’s nutritional intake, health and wellness, and is often a focus of a nutritionist’s work.

Nutrient-Dense Foods 

We all need certain nutrients, which we will discuss further below. Foods that are nutrient-dense provide vitamins, minerals and other healthy components, with little to no added sugar, saturated fat, and sodium. Foods considered to be nutrient-dense, according to the United States Department of Agriculture (USDA), include fruits, vegetables, whole grains, eggs, seafood, peas, beans, nuts, seeds, lentils, low-fat dairy products, lean meats, and poultry. It is always recommended to get most of our nutrients from nutrient-dense foods rather than through taking vitamin and mineral supplements, but be sure to follow your health practitioner’s advice regarding any supplementation.

The Four Basic Nutrients All Humans Need

Now that we understand that humans are holozoic heterotrophs, we can examine the four essential nutrients that all humans should consume daily. The USDA updates its nutritional guidelines every five years. The most recent update covers the years 2020 to 2025. In this update, the USDA reported that Americans are lacking in four basic nutrients, namely, vitamin D, calcium, potassium, and dietary fiber. 

The amounts of these nutrients that each person should consume is based upon their dietary aims and how many calories they consume daily. (A calorie is a measure of the energy content of food).

Calorie Recommendations Based Upon Gender and Age

  • Women ages 19 to 50 who are not trying to gain or lose weight should consume between 1800 and 2000 calories per day
  • Women ages 51 and over who are not trying to gain or lose weight should consume 1600 calories daily
  • Men ages 19 to 50 who are not trying to gain or lose weight should consume between 2200 and 2400 calories per day
  • Men ages 51 and over who are not trying to gain or lose weight should consume 2000 calories daily

Nutrient Recommendations Based Upon Gender

  • Calcium: Women need 1000 to 1200 mg/day, and men need 1000 mg/day. Calcium can be found in dairy foods, spinach, and tofu.
  • Potassium: Women need 2600 mg/day, and men need 3400 mg/day. Potassium is found in foods such as lima beans, baked potato, banana, and tuna.
  • Dietary fiber: Women need 22 to 28 mg/day, and men need 28 to 34 mg/day. Fiber is found in foods such as popcorn, navy or white beans, shredded wheat cereal, and berries.
  • Vitamin D: Women and men both need 600 IU/day. Vitamin D is found in milk, tuna, yogurt, and fortified orange juice.

Food Groups and Guidelines

The USDA has become a bit more flexible in regards to its nutritional recommendations for how much we should eat from each food group daily. They have allowed for differences based upon cultural traditions, personal preferences, and varying budgets. Their dietary guidelines are now seen as more of a framework that is designed to meet people where they are and to ensure that they are fulfilling their nutritional needs. The USDA advises that we focus on meeting our food group needs through the consuming of nutrient-dense foods and beverages, while remaining within our calorie limits.

The main food groups, and their recommended intakes, are:

  • Vegetables: This includes dark green vegetables, red and orange vegetables, beans, peas and lentils, starchy vegetables, and other vegetables. The average adult consuming 2000 calories per day should strive to consume 2 ½ cups of vegetables daily.
  • Fruits: This includes fresh, frozen and canned fruits and 100% fruit juices. An adult consuming 2000 calories per day should aim to consume 2 cups of fruit daily.
  • Grains: This includes whole grains (such as barley, brown rice and quinoa) and refined grains (such as white bread, white rice, and pasta). An adult eating 2000 calories per day should try to consume 6 ounces of grains daily.
  • Dairy: This includes milk, soy beverages, yogurt, dairy desserts, and cheeses. An adult consuming 2000 calories per day should strive to consume 3 cups of dairy foods daily.
  • Protein foods: This includes meats, poultry, eggs, seafood, nuts, seeds, and soy products, as well as beans, peas and lentils (although they are also part of the vegetable group, when consumed, they should be counted as one group only). An adult on a 2000 calorie a day diet should consume 5.5 ounces of protein daily.
  • Oils: These include canola, olive, corn, peanut, soybean, and other oils, and provide essential fatty acids in our diet. An adult eating 2000 calories per day should consume 27 grams of oils daily.

In addition, the USDA recommends limiting added sugars in our diets to less than 10 percent of the total calories consumed in a day. Saturated fat should also be limited to less than 10 percent of total daily caloric intake. Sodium should be limited to less than 2300 mg. daily. Alcoholic beverages should be limited to two drinks per day for men and one drink per day for women.

Now that we understand the basics of nutrition, let’s take a closer look at some of the issues nutritionists and dietitians study in humans and how nutrition contributes to them.

Eating Disorders

Some nutritionists specialize in working with people who have eating disorders, most commonly referred to by the profession as disordered eating. People can develop eating disorders at any age or stage of life, and they affect people of all genders, races, backgrounds, and body weights. Eating disorders that nutritionists may encounter include, but are by no means limited to:

  • Anorexia nervosa– This eating disorder is characterized by the restriction or avoidance of food. There are two subtypes: restrictive, in which people severely limit the amount and type of food they consume; and binge-purge, in which people may limit their foods and have episodes in which they binge eat large amounts of food in a short time, followed by vomiting or using laxatives or diuretics to get rid of the food they consumed.  Because those suffering from anorexia nervosa are not getting the proper nutrients from foods, they can develop many health concerns, including:
    • Anemia
    • Constipation
    • Muscle wasting and weakness
    • Brain damage
    • Infertility
    • Organ failure
  • Bulimia nervosa- This eating disorder is characterized by recurrent episodes of eating large amounts of food, followed by behavior to compensate for this and prevent weight gain, such as vomiting, laxative or diuretic use, or a combination of these. Health problems that can develop from the lack of proper nutrition include:
    • Dehydration
    • Electrolyte imbalance which can lead to heart attack or stroke
    • Worn tooth enamel
    • Chronically inflamed sore throat
  • Binge-eating disorder-This eating disorder is characterized by periods of unrestricted eating of large amounts of food, not followed by purging, excessive exercise or fasting. Health problems that can develop from this include:
    • Obesity
    • High blood pressure
    • High cholesterol
    • Cardiovascular disease
  • Avoidant restrictive food disorder (ARFID)- This eating disorder is characterized by selective eating, or restricting the amount and/or types of foods eaten. People with ARFID restrict their calories and nutrients so much that this restriction can affect growth and development, as well as overall health. Health problems that can arise from ARFID include:
    • Menstrual irregularities
    • Slowed heart rate
    • Sleeping problems
    • Anemia
    • Low immunity

Nutrition and Wellness

Proper nutrition contributes to overall health and wellness, and may prevent the onset of disease. Good nutrition is vital to our health and development, as it strengthens immunity, contributes to safer pregnancy and childbirth, and lowers the risk of contracting certain diseases, such as cardiovascular disease and diabetes. Nutrition also contributes to greater longevity. 

Those who are malnourished, or are not consuming the proper nutrition, have health problems. The World Health Organization (WHO) defines malnutrition as both undernutrition (wasting away or stunting growth) and overweight (including obesity). Both forms of malnutrition result from the inadequate intake of minerals and vitamins, and can result in diet-related health problems such as anemia and high blood pressure, as well as noncommunicable diseases, such as diabetes and cardiovascular disease. 

The WHO estimates that 1.9 billion adults worldwide are obese, and 38.9 million children are overweight. When it comes to undernutrition, 149.2 million children worldwide have stunted growth (too short for their age) and 45.4 million are wasted (too thin for their height). Forty-five percent of worldwide child deaths under the age of 5 result from undernutrition.

Nutritionists are trained and educated to work with all types of individuals – those who are healthy, those who are malnourished, those who are overweight or obese, and those who have various diseases. Becoming a nutritionist is a challenging, yet rewarding, profession in which you will likely deal with persons from diverse backgrounds and cultures. Understanding not only the science of nutrition, but the complexities of humanity, will enable you to be a more effective nutritionist.