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With the onset of adulthood, good nutrition can help young adults enjoy an active lifestyle. For most people, this is the time when their bodies are in the best condition. The body of an adult does not need to devote its energy and resources to support the rapid growth and development that characterizes youth. However, the choices made during those formative years can have a lasting impact. Eating habits and preferences developed during childhood and adolescence influence health and fitness into adulthood. Some adults have gotten a healthy start and have established a sound diet and regular activity program, which helps them remain in good condition from young adulthood into the later years. Others carry childhood obesity into adulthood, which adversely affects their health. However, it is not too late to change course and develop healthier habits and lifestyle choices. Therefore, adults must monitor their dietary decisions and make sure their caloric intake provides the energy that they require, without going into excess.
At this time, growth is completed and people reach their physical peak. Major organs and body systems have fully matured by this stage of the life cycle. For example, the human body reaches maximum cardiac output between ages twenty and thirty. Also, bone and muscle mass are at optimal levels, and physical activity helps to improve muscle strength, endurance, and tone.Elaine U. Polan, RNC, MS and Daphne R. Taylor, RN, MS, Journey Across the Life Span: Human Development and Health Promotion (Philadelphia: F. A. Davis Company, 2003), 192–193. In order to maintain health and fitness at this age, it is important to continue to practice good nutrition. Healthy eating habits promote metabolic functioning, assist repair and regeneration, and prevent the development of chronic conditions. In addition, the goals of a young adult, such as beginning a career or seeking out romantic relationships, can be supported with good habits.
Young men typically have higher nutrient needs than young women. For ages nineteen to thirty, the energy requirements for women are 1,800 to 2,400 calories, and 2,400 to 3,000 calories for men, depending on activity level. These estimates do not include women who are pregnant or breastfeeding, who require a higher energy intake (see Chapter 12 "Nutrition through the Life Cycle: From Pregnancy to the Toddler Years").
For carbohydrates, the AMDR is 45 to 65 percent of daily calories. All adults, young and old, should eat fewer energy-dense carbohydrates, especially refined, sugar-dense sources, particularly for those who lead a more sedentary lifestyle. The AMDR for protein is 10 to 35 percent of total daily calories, and should include a variety of lean meat and poultry, eggs, beans, peas, nuts, and seeds. The guidelines also recommend that adults eat two 4-ounce servings (or one 8-ounce serving) of seafood per week.
It is also important to replace proteins that are high in trans fats and saturated fat with ones that are lower in solid fats and calories. All adults should limit total fat to 20 to 35 percent of their daily calories and keep saturated fatty acids to less than 10 percent of total calories by replacing them with monounsaturated and polyunsaturated fatty acids. Avoid trans fats by limiting foods that contain synthetic sources, such as partially hydrogenated oils. The AMDR for fiber is 22 to 28 grams per day for women and 28 to 34 grams per day for men. Soluble fiber may help improve cholesterol and blood sugar levels, while insoluble fiber can help prevent constipation.
A healthy diet of nutrient-rich meals incorporates a variety of whole foods. Whole foods are unprocessed or unrefined, or have been created with as little processing as possible. They do not include a lot of added ingredients, such as sugar, sodium, or fat, and are free of preservatives or other chemicals that are often added to food products. Examples of whole foods with no processing include legumes and fresh fruits and vegetables. Examples of whole foods with minimal processing include whole-grain breads and cereals. Dietitians recommend consuming whole foods for a variety of reasons. Whole foods provide nutrients in their natural state, with all of the vitamins and minerals intact. Food processing can remove some nutrients during manufacturing. Also, diets rich in whole foods contain high concentrations of fiber and antioxidants, and can protect against chronic disease.
Micronutrient needs in adults differ slightly according to sex. Young men and women who are very athletic and perspire a great deal also require extra sodium, potassium, and magnesium. Males require more of vitamins C and K, along with thiamine, riboflavin, and niacin. Females require extra iron due to menstruation. Therefore, it can be beneficial for some young adults to follow a daily multivitamin regimen to help meet nutrient needs. But as always, it is important to remember “food first, supplements second.” Table 13.4 "Micronutrient Levels during Adulthood" shows the micronutrient recommendations for adult men and women.
Table 13.4 Micronutrient Levels during Adulthood
|Nutrient||Adult Males||Adult Females|
|Vitamin A (mcg)||900.0||700.0|
|Vitamin B6 (mg)||1.3||1.3|
|Vitamin B12 (mcg)||2.4||2.4|
|Vitamin C (mg)||90.0||75.0|
|Vitamin D (mcg)||5.0||5.0|
|Vitamin E (mg)||15.0||15.0|
|Vitamin K (mcg)||120.0||90.0|
|Niacin (B3) (mg)||16.0||14.0|
|Riboflavin (B2) (mg)||1.3||1.1|
|Thiamine (B1) (mg)||1.2||1.1|
Source: Institute of Medicine. http://www.iom.edu.
There are a number of intake recommendations for young adults. According to the IOM, an adequate intake (AI) of fluids for men is 3.7 liters per day, from both food and liquids. The AI for women is 2.7 liters per day, from food and liquids.Institute of Medicine. “Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate.” Accessed March 5, 2012. http://www.iom.edu/Reports/2004/Dietary-Reference-Intakes-Water-Potassium-Sodium-Chloride-and-Sulfate.aspx.
It is best when fluid intake is from water, instead of sugary beverages, such as soda. Fresh fruits and vegetables, including watermelon and cucumbers, are excellent food sources of fluid.
In addition, young adults should avoid consuming excessive amounts of sodium. The health consequences of high sodium intake include high blood pressure and its complications. Therefore, it is best to limit sodium to less than 2,300 milligrams per day.
Good nutrition during the young adult years can help to support gastrointestinal integrity and prevent digestive disorders, such as constipation and diarrhea. Dietary fiber helps bind indigestible food together and normalize bowel movements. It also holds more water in the stool to make it softer for those who suffer from constipation. Excellent sources of fiber include oats, barley, rye, wheat, brown rice, celery, carrots, nuts, seeds, dried beans, oranges, and apples. In addition, healthy intestinal microflora can be supported by prebiotics, which stimulate the growth of beneficial bacteria already in the colon and are found in fruits and vegetables, and probiotics, which change or improve the bacterial balance in the gut and are found in yogurt.
Obesity remains a major concern into young adulthood. For adults, a BMI above 25 is considered overweight, and a BMI of 30 or higher is obese. By that measurement, about two-thirds of all adults in the United States are overweight or obese, with 35.7 percent considered to be obese.Centers for Disease Control, National Center for Health Statistics. “Prevalence of Obesity in the United States, 2009–2010.” NCHS Data Brief, No. 82, January 2012, accessed on March 5, 2012. http://www.cdc.gov/nchs/data/databriefs/db82.pdf. As during childhood and adolescence, physical inactivity and poor dietary choices are major contributors to obesity in adulthood. Solid fats, alcohol, and added sugars (SoFAAS) make up 35 percent of total calories for most people, leading to high levels of saturated fat and cholesterol and insufficient dietary fiber. Therefore, it is important to limit unrefined carbohydrates and processed foods.