Introduction to clinical nutrition: food and supplements

chapter 10 Introduction to clinical nutrition: food and supplements



INTRODUCTION AND OVERVIEW


A healthy diet and lifestyle are prerequisites for wellness and the prevention of many chronic diseases. Identifying specific components in the diet that promote health remains a challenge, as the relationships are complex and often multifactorial. Nutritional epidemiology and interventional research with specific food components and nutritional supplements provide evidence that helps us to better understand the role of nutrition in health promotion and disease and provide patients with better advice.


Early studies in nutrition originated from observations of deficiency and its signs and symptoms. Probably the best known of these is the identification of scurvy as a diet-related disease with a potentially fatal outcome, sometime in the fifteenth century. Approximately 200 years later, James Lind identified citrus fruits as both a preventative treatment and a cure; however, it wasn’t until the 1920s that vitamin C was isolated and identified as the true source of the treatment’s success.


Contemporary research using more sophisticated methodologies has allowed new approaches to be used in nutritional studies. These include large prevalence and community studies, cohort and case-control studies and randomised trials. Generally, food intake diaries and surveys, biomarkers (e.g. vitamin C in urine), clinical indicators (e.g. cholesterol) and anthropometry are used as key measurements. Although these measures are useful, they are not without limitations, and research is still being conducted to identify new and more accurate measures and methods of assessment.


Clinical nutrition is the use of this information in diagnosis, disease prevention and treatment, and health promotion. Treatment consists of dietary manipulation and using food and nutritional supplements as medicine, based on individual assessment.



INADEQUATE NUTRITIONAL INTAKE


Many factors can affect an individual’s nutritional status. The most obvious factors are human biological factors and physiological phases, such as age, gender and the stages of growth, pregnancy, lactation and older age. Less obvious but just as influential can be system factors such as the healthcare system, the education system and the food supply system (industry, agriculture and institutions).


Factors affecting nutritional status can be divided into three broad categories: external, internal and food factors. These are listed in Table 10.1.


TABLE 10.1 Factors affecting food choices and nutritional status















































External factors Internal factors Food factors
Educational system: nutrition and health knowledge Age, gender and genetics affecting nutritional requirements Food supply chain:



Peer beliefs and practices Physiological phases affecting nutritional requirements, e.g. growth, pregnancy, lactation, older age Quantity of food consumed
Family beliefs and practices Altered organ function or metabolism, e.g. malabsorption syndromes, intolerances Flavour and palatability of food
Ethnicity and cultural influences Personal attitudes, beliefs and behaviours, e.g. following a fad diet, vegetarianism Texture of food
Religious beliefs and practices Appetite, e.g. poor appetite due to disease or disease treatment Appearance of food
Occupation Dental health, e.g. ill-fitting dentures, sensitive teeth, gum disease Odour of food
Media and advertising Physical disabilities making it difficult to shop for fresh produce, prepare food, self-feed, chew and/or swallow food Availability of nutrients in foods, e.g. binding to other food components
Economic influences, e.g. household finances, economy of community/country Gastrointestinal symptoms, e.g. nausea, vomiting  
Medication use (see Table 10.2) Psychosocial factors, e.g. isolation, confusion, loneliness  
Cooking techniques, e.g. up to 100% of vitamin C can be lost through cooking Everyday moods and emotions, e.g. comfort eating  

Source: adapted from Braun & Cohen (2007)1


One factor that tends to be overlooked is the effect of medication use on nutritional status and the possibility of inducing deficiency with long-term use. Table 10.2 gives examples of some commonly used drugs and the nutrients that can be affected. In particular, clinicians should consider the nutritional result of chronic medication use in individuals who have a barely adequate diet, take multiple drugs or are elderly and frail.


TABLE 10.2 Examples of drugs and their interactions with nutrients



























Drug or drug class Nutrient(s) affected
Loop diuretics Increased urinary excretion of vitamin B1, magnesium and zinc
Oral contraceptive pill

Corticosteroids Reduced calcium, vitamin D, calcium and iron
Antibiotics Reduced endogenous synthesis of vitamins B1, B5
Proton pump inhibitors and H2 antagonists Reduced dietary absorption of folate, iron, vitamin B12
Orlistat Reduced dietary absorption of vitamins A, D, E, K
L-thyroxine Insoluble complexes formed with iron, magnesium, calcium and zinc, resulting in reduced drug and nutrient absorption

Source: Braun & Cohen 2007.1



RDAs AND RDIs


The concept of recommended daily allowances (RDAs) originated in the United States in the 1940s as a basis for setting the poverty threshold and food stamp allotments for the military and civilian populations during times of war and/or economic depression.2 At this time, the first RDAs were determined for vitamins A, C, D, E, thiamine, riboflavin, niacin, energy, protein and the minerals calcium and iron. These levels were established by observing a healthy population’s usual dietary intakes and extrapolating from this information.


Over the subsequent 50 years, new ideas about and scientific research into health and nutrition emerged, and as a result the original concept of RDAs required modification. The key ideas to emerge were as follows:







As a result of these developments, a new framework was set up in the mid-1990s. It aimed to establish new nutrient intake recommendations to meet a variety of uses and to base nutrient requirements on the reduction of chronic disease risk, with a clear rationale for the endpoints chosen. The new guidelines still contain RDAs but have been expanded to include three new intake recommendations: estimated average requirements (EARs), adequate intake (AI) and upper level (UL) intake.


Revisions were also afoot in Australia and New Zealand, and in 2006 the National Health and Medical Research Council (NHMRC) published its newly adjusted nutritional guidelines.3 These new guidelines are far more comprehensive than previous versions and have incorporated some of the new initiatives developed in the United States.


The guidelines are for healthy people and have been differentiated into gender and age requirements, assuming an average body weight for the adult male as 76 kg and female as 61 kg. Four key terms used in the document are defined here:






In some instances, the new RDI values for specific nutrients have increased substantially since the previous guidelines (e.g. for iron and folate), whereas others have increased marginally (e.g. for calcium) or decreased (e.g. zinc requirements for adult females).



PITFALLS OF THIS SYSTEM


Setting nutrient reference values presents many challenges. Russell,2 from the Human Nutrition Research Center on Aging at Tufts University in the USA has outlined eight obstacles.










Overall, for many nutrients and food components there is no adequate database to confidently set an RDI or UL, and the scientific basis for many of the reference values is weak. Clearly the reference values we now use can only be a general approximation and loosely relevant to the general healthy population, with even less relevance to the individual with comorbidities or special needs.


To create a set of reference values with greater accuracy and relevance, substantial research funding is required. Even then, some values such as ULs may never be entirely accurate, as ethical considerations would prevent such research from ever being conducted.



MOVING BEYOND RDIs: OPTIMAL NUTRITION


There is now strong international awareness that nutritional intakes at levels beyond RDI have a role in the prevention of many degenerative diseases such as cancer, cardiovascular disease, macular degeneration and cataract, cognitive decline and Alzheimer’s dementia, and developmental conditions such as neural tube defects.1 The new NHMRC guidelines for the adequate intake of vitamins and minerals recognise this fact and state that ‘there is some evidence that a range of nutrients could have benefits in chronic disease aetiology at levels above the RDI or AI’.3


This has given rise to a new concept, of ‘suboptimal nutrition’. A major systematic review of the international literature conducted by Fairfield and Fletcher describes suboptimal nutrition as a state in which nutritional intake is sufficient to prevent the classical symptoms and signs of deficiency, yet insufficient to significantly reduce the risk of developmental or degenerative diseases.4


As such, avoiding a state of suboptimal nutrition requires adequate dietary intakes of all key food groups, and possibly the use of additional nutritional supplements. Nutrients associated with a reduced risk of chronic disease when consumed in quantities higher than the RDI are many and include the antioxidant vitamins C, E and A, the mineral selenium and nutrients such as folate, omega-3 fatty acids and dietary fibre.3 It is also becoming clear that the balance between nutrients or macronutrients is important for optimal health and disease prevention—examples are the ratio of omega-3 to omega-6 fatty acids and high to low glycaemic carbohydrates.

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Jun 3, 2017 | Posted by in GENERAL SURGERY | Comments Off on Introduction to clinical nutrition: food and supplements

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