What is clinical nutrition?
Clinical nutrition is the study of the relationship between food and a healthy body. More specifically, it is the science of nutrients and how they are digested, absorbed, transported, metabolized, stored, and eliminated by the body. Besides studying how food works in the body, nutritionists are interested in how the environment affects the quality and safety of foods, and what influence these factors have on health and disease.
What are nutrients?
Nutrients are substances that the body needs to live and grow. The body requires more than 45 nutrients, and the ways they are used are as different as the molecules, cells, and tissues they help to create. Carbohydrates, proteins, and fats -- called macronutrients -- are broken down (metabolized) to provide energy. Vitamins and minerals -- called micronutrients -- are not used for energy themselves, but are needed to help macronutrients be used for energy.
What is the history of clinical nutrition?
The study of nutrition dates back to the 18th century, when the French chemist Lavoisier discovered a relationship between our metabolism of food and the process of breathing. By the early 20th century, scientists had found that diseases -- such as beri beri, rickets, scurvy, and pellagra -- were associated with certain diets. By 1912, the Polish chemist Casimir Funk had found a substance (vitamin B1) that actually prevented beri beri, and he named it "vitamine." Later it was found that these diseases were caused by the lack of specific nutrients -- vitamin B1 (thiamine), vitamin D, vitamin C, and vitamin B3 (niacin) respectively.
In the early 1940s, the National Research Council set Recommended Dietary Allowances (RDAs).
Researchers and scientists continue to find out more about how individual nutrients can help prevent and treat disease. But they are also learning how whole foods may allow nutrients to work together. For example, antioxidants like beta carotene, selenium, vitamin E, and vitamin C, when consumed in foods, appear to protect against the development of heart disease, cancer, and other chronic degenerative diseases.
The old RDAs have been replaced by Dietary Reference Intakes (DRIs), which show how much of a nutrient we need every day to maximize health and lower the risk of chronic disease (in contrast to RDAs, which listed the minimum amount needed to prevent a deficiency). The field of clinical nutrition is now increasingly incorporated into mainstream medical treatment.
What are nutritional supplements?
The term "nutritional supplement" refers to vitamins, minerals, and other nutrients that are used to support good health and treat illness. For example, plant compounds known as phytochemicals (found in tomatoes and soybeans) have powerful disease fighting properties. While it's best to get nutrients through the foods you eat, sometimes taking a supplement can help. For example, taking zinc supplements has been reported to shorten the duration of the common cold and lower the incidence of acute diarrhea in children.
How do vitamins and minerals work?
Vitamins and minerals play an essential role in the body's normal metabolism, growth, and development. For example, while a vitamin is not a source of energy by itself, it can provide the key the body needs to unlock energy stored in food. Some vitamins and minerals work together, such as the mineral zinc and vitamin A. Zinc enables the body to use vitamin A to promote good vision. Not getting enough vitamin A may lead to night blindness, a condition in which the eyes have trouble adjusting to darkness. Zinc supplementation may help prevent this condition by helping the body use vitamin A. Another example is calcium and vitamin D. Calcium, which is very important in bone and heart health, is more readily absorbed if vitamin D is also present.
Taking supplements, however, is not the answer to long term good health. Instead, combining a healthy diet with regular exercise and a positive mental attitude is the best bet for a healthy lifestyle.
What constitutes a healthful diet?
The United States Department of Agriculture (USDA) food plate suggests that we use fat "sparingly," and that our daily diet include 2 - 3 servings of dairy products; 2 - 3 servings of meat, poultry, fish, eggs, beans, or nuts; 3 - 5 servings of vegetables; 2 - 4 servings of fruit; and 6 - 11 servings of bread, cereal, rice, or pasta. But the numbers alone don't tell the whole story. Our food needs are influenced by many factors, including age, gender, body size, pregnancy, and health. A clinical nutritionist or nutritionally oriented doctor can help you determine which type of diet is best for you. No matter what, you can improve your diet by adding more fruits and vegetables and cutting back on overly processed foods and sugar.
What happens during a visit to a clinical nutritionist?
First, the clinical nutritionist will ask you questions about your medical history, family history, and personal lifestyle. The medical history might include questions about your diet, digestion, history of weight loss or gain, sleep and exercise patterns, and relaxation habits. Some clinical nutritionists will ask you to bring a 3 day food diary and list of any herbs, supplements, or medicines that you take regularly. Laboratory tests might be used to find out if you are low in any nutrients and to test your organ function. This way, a nutritionist will get a full picture of your nutritional lifestyle.
During the second part of the visit, the nutritionist will suggest ways that you can fill the gaps and reduce the nutritional "overloads" in your diet. For example, your nutritionist may suggest that you eat your meals at different times or cut down on the amount of carbohydrates that you eat. The nutritionist will also offer advice on specific nutritional supplements if necessary (see below). The nutritionist will then schedule follow up visits to monitor your health.
What is clinical nutrition good for?
Studies show that eating habits play a major role in the development of certain chronic diseases, including heart disease, obesity, cancer, and diabetes. Making changes to your diet can help prevent and treat these conditions. For example, lowering certain fats and cholesterol and adding whole grains to your diet can help prevent atherosclerosis (plaque build up in the arteries), which can lead to heart disease or stroke. Eating fewer calories will help you lose weight. Cutting down on simple sugars (glucose, sucrose, fructose, and lactose) can help prevent diabetes, and diets high in fiber (especially soluble fiber) can help control diabetes.
Scientists have found many other connections between diet and disease. In a clinical study of 20,000 men, for example, eating one fish meal per week was linked to a 52% reduction in the risk of sudden death from a heart attack. Fish is high in omega-3 fatty acids, which can protect the heart from fatal arrhythmias (abnormal heart rhythm).
In another clinical study of more than 42,000 women, those who ate lots of fruits, vegetables, whole grains, low fat dairy, and only lean meats lived longer. High intake of fruits, vegetables, and legumes is associated with a lower risk of developing heart disease.
There are many ongoing studies regarding clinical nutrition. Some interesting results show that:
- Diets high in folate (found in leafy greens, dry beans and peas, fortified cereals and grain products, and some fruits and vegetables) may lower risk of stroke and heart disease.
- Eating small amounts of fish when pregnant may protect against early delivery and low birth weight infants. Some fish may contain higher amounts of mercury, and should only be eaten in moderation. Ask your obstetrician which types of fish are best for you when pregnant. Taking iron supplements improves aerobic training ability in iron depleted women.
- Lutein and zeaxanthin (carotenoids) in the diet may reduce risk of cataracts.
- Lutein from dietary sources (such as kale and spinach) may protect against colon cancer.
- Flavonoids (found in apples, blueberries, broccoli, cabbage, carrots, citrus fruits, onions, and teas) may protect against cancer.
- Omega-3 fatty acids found in cold water fish (such as herring, tuna, and salmon) help reduce inflammation and help prevent certain chronic diseases, such as heart disease, cancer, and arthritis.
- Vitamin E (in the diet from fruits and vegetables) may reduce the risk of angina (chest pain) and heart attack in people with atherosclerosis.
- A higher ratio of sodium to potassium is associated with an increased risk of heart disease.
In hospitals, nutrition is used to improve the overall health of patients with a wide range of conditions. Examples of these conditions are AIDS, cancer, osteoporosis, lung disease, obesity, burns, metabolic disorders, and kidney, liver, and pancreatic disorders. Patients who need surgery are also supported with clinical nutrition.
Is there anything I should watch out for?
Some nutritional supplements can interact with medications; it is very important to tell your doctor about any dietary supplements you are considering taking. Always take supplements according to label directions, unless otherwise directed by a qualified health care practitioner.
There is little scientific information about the effect of so called functional foods -- foods to which vitamins, minerals, herbs, or other dietary substances are added -- despite their growing popularity in the marketplace. Examples include calcium fortified orange juice or snacks containing echinacea.
Some common foods, including nuts, wheat gluten, dairy products, fish, shrimp, soy, bananas, and eggs, may trigger allergic reactions. Your doctor can test for such possible allergies if he suspects you have them.
How can I find a certified clinical nutritionist?
To find a clinical nutritionist in your area, contact:
- The American Board of Nutrition:
- The American College of Nutrition:
- The Clinical Nutrition Certification Board:
- The American Dietetic Association:
Specialists in many alternative health systems (including Traditional Chinese Medicine, ayurveda, and naturopathy) also consider food a vital part of preventing and treating illness.
Albert CM, Hennekens CH, O'Donnell CJ, et al. Fish consumption and risk of sudden cardiac death. JAMA. 1998;279(1):23-28.
Bazzano LA, He J, Ogden LG, et al. Dietary intake of folate and risk of stroke in US men and women: NHANES I Epidemiologic Follow-up Study. National Health and Nutrition Examination Survey. Stroke. 2002;33:1183-1189.
Bazzano LA, He J, Ogden LG, et al. Fruit and vegetable intake and risk of cardiovascular disease in US adults: the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. Am J Clin Nutr. 2002;76(1):93-99.
Bosetti C, Pelucchi C, La Vecchia C. Diet and cancer in Mediterranean countries: carbohydrates and fats. Public Health Nutr. 2009 Sep;12(9A):1595-600.
Bogers RP, Dagnelie PC, Bast A, van Leeuwen M, van Klaveren JD, van den Brandt PA. Effect of increased vegetable and fruit consumption on plasma folate and homocysteine concentrations. Nutrition. 2007;23(2):97-102.
Burke V, Beilin LJ, Cutt HE, Mansour J, Williams A, Mori TA. A lifestyle program for treated hypertensives improved health-related behaviors and cardiovascular risk factors, a randomized controlled trial. J Clin Epidemiol. 2007;60(2):133-41.
Cook RF, Billings DW, Hersch RK, Back AS, Hendrickson A. A field test of a web-based workplace health promotion program to improve dietary practices, reduce stress, and increase physical activity: randomized controlled trial. J Med Internet Res. 2007;9(2):e17.
Dauncey MJ. New insights into nutrition and cognitive neuroscience. Proc Nutr Soc. 2009 Aug 24:1-8.
De Lorgeril M. Essential polyunsaturated fatty acids, inflammation, atherosclerosis and cardiovascular diseases. Subcell Biochem. 2007;42:283-97.
Demark-Wahnefried W, Clipp EC, Lipkus IM, et al. Main outcomes of the FRESH START trial: a sequentially tailored, diet and exercise mailed print intervention among breast and prostate cancer survivors. J Clin Oncol. 2007;25(19):2709-18.
Greenwald P, Anderson D, Nelson SA, Taylor PR. Clinical trials of vitamin and mineral supplements for cancer prevention. Am J Clin Nutr. 2007;85(1):314S-317S.
Hill AM, Fleming JA, Kris-Etherton PM. The role of diet and nutritional supplements in preventing and treating cardiovascular disease. Curr Opin Cardiol. 2009 Sep;24(5):433-41.
Kant AK , Schatzkin A, Graubard BI, Schairer C. A prospective study of diet quality and mortality in women. JAMA. 2000;283(16):2109-2115.
Kiefer I, Prock P, Lawrence C, Wise J, Bieger W, Bayer P, Rathmanner T, Kunze M, Rieder A. Supplementation with mixed fruit and vegetable juice concentrates increased serum antioxidants and folate in healthy adults. J Am Coll Nutr. 2004 Jun;23(3):205-11.
Kilbourne AM, Rofey DL, McCarthy JF, et al. Nutrition and exercise behavior among patients with bipolar disorder.Bipolar Disord. 2007;9(5):443-52.
King JC; Dietary Guidelines Advisory Committee. An evidence-based approach for establishing dietary guidelines. J Nutr. 2007;137(2):480-3.
Kuller LH, Kinzel LS, Pettee KK, Kriska AM, Simkin-Silverman LR, Conroy MB, Averbach F, Pappert WS, Johnson BD. Lifestyle intervention and coronary heart disease risk factor changes over 18 months in postmenopausal women: the Women On the Move through Activity and Nutrition (WOMAN study) clinical trial. J Womens Health (Larchmt). 2006;15(8):962-74.
Ledikwe JH, Rolls BJ, Smiciklas-Wright H, et al. Reductions in dietary energy density are associated with weight loss in overweight and obese participants in the PREMIER trial. Am J Clin Nutr. 2007;85(5):1212-21.
Mann J, McAuley K. Carbohydrates: is the advice to eat less justified for diabetes and cardiovascular health? Curr Opin Lipidol. 2007;18(1):9-12.
McCarthy WJ, Yancey AK, Harrison GG, Leslie J, Siegel JM. Fighting cancer with fitness: dietary outcomes of a randomized, controlled lifestyle change intervention in healthy African-American women. Prev Med. 2007;44(3):246-53.
Mead A, Atkinson G, Albin D, et al. UK Heart Health Group; Thoracic Dietitians Interest Group (Specialist group of the British Dietetic Association). Dietetic guidelines on food and nutrition in the secondary prevention of cardiovascular disease - evidence from systematic reviews of randomized controlled trials (second update, January 2006). J Hum Nutr Diet. 2006;19(6):401-19.
Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health: evaluating the risks and the benefits. JAMA. 2006;296(15):1885-99.
Munoz Garcia M, Perez Menendez-Conde C, Bermejo Viecedo T. Advances in the knowledge of the use of micronutrients in artificial nutrition. Nutr Hosp. 2011;26(1):37-47.
Pérez-López FR, Chedraui P, Haya J, Cuadros JL. Effects of the Mediterranean diet on longevity and age-related morbid conditions. Maturitas. 2009 Aug 31. [Epub ahead of print]
Piirainen T, Isolauri E, Lagstrom H, Laitinen K. Impact of dietary counseling on nutrient intake during pregnancy: a prospective cohort study. Br J Nutr. 2006;96(6):1095-104.
Raviv S, Smith LJ. Diet and asthma. Curr Opin Pulm Med. 2009 Sep 4. [Epub ahead of print]
Razquin C, Martinez JA, Martinez-Gonzalez MA, Mitjavila MT, Estruch R, Marti A. A 3 years follow-up of a Mediterranean diet rich in virgin olive oil is associated with high plasma antioxidant capacity and reduced body weight gain. Eur J Clin Nutr. 2009 Aug 26. [Epub ahead of print]
Sazawal S, Dhingra U, Deb S, Bhan MK, Menon VP, Black RE. Effect of zinc added to multi-vitamin supplementation containing low-dose vitamin A on plasma retinol level in children -- a double-blind randomized, controlled trial. J Health Popul Nutr. 2007;25(1):62-6.
Song Y, Sesso HD, Manson JE, Cook NR, Buring JE, Liu S. Dietary magnesium intake and risk of incident hypertension among middle-aged and older US women in a 10-year follow-up study. Am J Cardiol. 2006;98(12):1616-21.
Soriguer F, Almaraz MC, García-Almeida JM, et al. Intake and home use of olive oil or mixed oils in relation to healthy lifestyles in a Mediterranean population. Findings from the prospective Pizarra study. Br J Nutr. 2009 Sep 14:1-9. [Epub ahead of print]
Swanenburg J, de Bruin ED, Stauffacher M, Mulder T, Uebelhart D. Effects of exercise and nutrition on postural balance and risk of falling in elderly people with decreased bone mineral density: randomized controlled trial pilot study. Clin Rehabil. 2007;21(6):523-34.
Timms L. Effect of nutrition on wound healing in older people: a case study. Br J Nurs. 2011;20(11):S4-10.
Villareal DT, Miller BV 3rd, Banks M, Fontana L, Sinacore DR, Klein S. Effect of lifestyle intervention on metabolic coronary heart disease risk factors in obese older adults. Am J Clin Nutr. 2006;84(6):1317-23.
Wolf AM, Siadaty M, Yaeger B, Conaway MR, et al. Effects of Lifestyle Intervention on Health Care Costs: Improving Control with Activity and Nutrition (ICAN). J Am Diet Assoc. 2007;107(8):1365-73.
Yang Q, Liu T, Kiklina EV, et al. Sodium and potassium intake and mortality among US adults: prospective data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2011;171(13):1183-91.
Yates AA, Schlicker SA, Suitor CW. Dietary Reference Intakes: the new basis for recommendations for calcium and related nutrients, B vitamins, and choline. J Am Diet Assoc. 1998:98(6):699-706.
Yoon SS, Carroll MD, Johnson CL, Gu Q. Cholesterol management in the United States: the national health and nutrition examination survey, 1999 - 2006. Ann Epidemiol. 2011;21(5):318-26.
Last reviewed on: 10/13/2011
Reviewed by: Reviewed by Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.