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: • availability • nutritional quality • affordability • clean and uncontaminated

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	Reduced levels of folate, vitamins B2, B3, B5, B6, B12 Increased serum levels of vitamin A
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).

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.

MULTIVITAMINS FOR PREVENTATIVE HEALTH?

In 2003, the Lewin Report quantified the preventative health benefits of multivitamin supplementation using the US health insurance model.⁵ It was established that multivitamin use by older adults could lead to more than US $1.6 billion in Medicare cost savings over the next 5 years in the United States. The significant cost savings were based on improved immune function and a reduction in relative risk of coronary artery disease achievable with daily multivitamin supplementation in people over 65 years old. Furthermore, the authors state that this is a conservative estimate that does not take into account cost savings from decreased ambulatory care and assumes that only one-third of adults will experience benefits. Reductions in the incidence of other diseases such as cancer were not considered in this review but may also be reduced.

An extension of this work was carried out by Huang and colleagues, who conducted another comprehensive review of the published literature to determine whether evidence supported the use of multivitamin/mineral supplements and certain single-nutrient supplements in the primary prevention of chronic disease in the general adult population.⁶ Their review concluded that multivitamin/mineral supplement use may prevent cancer in individuals with poor or suboptimal nutritional status.

Given their relative safety and general health benefits, the evidence suggests that multivitamins may extend the benefits afforded by healthy eating. Accordingly, it would be prudent for all adults to take multivitamins regularly to prevent chronic disease.^4,7 In particular, they should be recommended for people with barely adequate diets, older adults, alcohol-dependent individuals, fussy eaters and those with malabsorption syndromes and intolerances.

WHAT DEFINES AN ESSENTIAL NUTRIENT TODAY?

Clearly, the line between essential and non-essential nutrients has blurred as a result of modern scientific enquiry and experimentation.⁸ In the first half of the twentieth century, nutrients were termed ‘essential’ when their removal from the diet caused severe organ dysfunction or death. Since then, modern scientific techniques have enabled us to detect finer gradations of inadequacy well before severe organ failure sets in, such as a decline in health status or ability to function optimally. This raises the question of whether nutrients and food components that are vital for optimal function and disease prevention should also be termed ‘essential’. This would assume that the traditional aim of clinical nutrition has broadened beyond preventing deficiency to include the promotion of wellness and optimal health.

Many nutrients currently classified as non-essential may in future prove to be essential, if a longer-term view is taken than has been previously. For example, it is feasible that organ failure and death may result from years of inadequate intake and not be apparent in the short term or only manifest after a long latency period. While identifying which non-essential nutrients and food components may turn out to be essential is a difficult task, evidence suggests that some specific diets consisting of multiple food components have substantial health-promoting effects. In particular, evidence to support the Mediterranean diet stands out—this may be the ‘essential diet’.

FOOD AS MEDICINE

Food provides us with physical and emotional nourishment. Most obviously, it provides macronutrients (carbohydrates, protein, fat) and micronutrients (vitamins, minerals) that help to sustain health. Many foods also contain a variety of active phytochemicals that exert pharmacological effects, giving those foods health benefits beyond their nutritional content. These non-nutrient constituents are sometimes known as functional components. Identification of functional components in everyday foods has led to a greater understanding of their health-giving properties. Table 10.3 provides examples of functional components found in everyday foods.

TABLE 10.3 Examples of functional food components

Food component	Source	Potential benefit
Carotenoids
Beta carotene	Carrots, various fruits and vegetables	Boosts cellular antioxidant protection; may reduce risk of CHD and contribute to healthy vision
Zeaxanthin/lutein	Collards, spinach, corn, egg yolk, orange peppers	May contribute to healthy vision and reduce incidence of several cancers
Dietary fibre
Beta glucan	Oat bran, rolled oats	May reduce risk of CHD and aid metabolic control in diabetes
Soluble fibre	Psyllium seed husk	May reduce risk of CHD and aid metabolic control in diabetes
Fatty acids
Omega-3 fatty acids	Deep sea oily fish (e.g. mackerel, salmon, tuna)	May reduce risk of CHD; reduces all-cause mortality; numerous other health benefits
Flavonoids
Anthocyanidins	Red berries, red grapes	Boosts cellular antioxidant protection; numerous health benefits
Proanthocyanidins	Apples, pears, cranberries, cocoa, wine (esp. red), grapes, peanuts	Boosts cellular antioxidant protection; numerous health benefits
Isothyocyanates
Indole-3-carbinol and sulphorafane	Cauliflower, broccoli, cabbage, kale, brussels sprouts	Boosts cellular antioxidant protection and influences detoxification pathways; may reduce incidence of various cancers
Phenols
Caffeic acid, ferulic acid	Coffee, apple, brown rice, citrus fruits, pears and some vegetables	Boosts cellular antioxidant protection; may contribute to healthy vision and heart and reduce incidence of various cancers
Stanols and sterols
Stanols/sterol esters	Fortified table spreads	May reduce risk of CHD
Prebiotics/probiotics
Inulin	Whole grains, some fruit, onions	May improve gastrointestinal health and immune function
Bifidobacteria and lactobacilli	Fermented milk products (e.g. yoghurt)	May improve gastrointestinal health and immune function
Phyto-oestrogens
Isoflavones	Soy-based foods	May reduce risk of CHD
Sulfides/thiols
Diallyl sulfinate (allicin)/allyl methyltrisulfide	Garlic, onion, leek (found in allium vegetables)	Boosts cellular antioxidant protection and influences detoxification pathways; may maintain healthy heart and immune function

Source: adapted from the International Food Information Council Foundation⁹

FUNCTIONAL FOODS AND FOOD SUPPLEMENTS

The term ‘functional food’ is widely used to describe foods that provide more health benefits than mere nutritional content alone. In many cases, functional attributes are being discovered for everyday fruits and vegetables, causing the mainstream media to call them ‘superfoods’. Food technology has allowed the development of food products that may provide even greater health benefits than nature has provided, such as fortified foods. Nutraceutical companies take this one step further and manufacture concentrated food supplements, such as fish oil products with predefined levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and concentrated probiotic supplements containing specific bacterial strains. In many cases, the supplemental forms contain a higher concentration of the functional component than is naturally found in food. There may be other advantages to food supplements, such as more stringent quality control (e.g. fish oil products being tested for heavy metal contamination, whereas fish in the local market are not), consistency in concentration of key active ingredients using standardisation techniques, and palatability, for fussy eaters.

THE HEALTHIEST DIET: MEDITERRANEAN?

Defining what constitutes a healthy diet is difficult and open to debate. Nutritional pyramids developed by government agencies provide a general guide; however, every few years another dietary approach emerges (e.g. Pritikin, Atkins, vegan) that challenges accepted thought and reminds us how little we truly know about nutrition.

The substantial health benefits afforded to people who adhere to the Mediterranean diet in the long term is a consistent finding in the peer-reviewed literature, making it a strong candidate for the healthiest diet. In 2002, Panagiotakos and colleagues found that a combination of Mediterranean diet and healthy lifestyle (non-smoking, physically active, moderate drinking) was associated with a greater than 50% lower rate of all-causes and cause-specific mortality (e.g. from coronary heart disease, cardiovascular diseases and cancer).¹³ The cohort study involved 1507 apparently healthy men and 832 women, aged 70 to 90 years, in 11 European countries. A year later, Trichopoulou also reported a positive association between longevity and the Mediterranean diet that was significant in people aged 55 years or older.¹⁴ More recently, a 2004 review of five cohort studies confirmed these findings and concluded that there is now sufficient evidence to show that diet does indeed influence longevity.¹⁵

Table 10.4 lists the main foods typically included in the Mediterranean diet. Not surprisingly, many contain functional components discussed in this chapter.

TABLE 10.4 Summary of foods typically included in the Mediterranean diet and modification generally required to the Western diet

Food	Recommendations for a Mediterranean style of eating
Fish	Increase intake to at least three times a week
Olives, olive oil	Replace current oils and spreads with olive oil
Nuts	Eat regularly, especially walnuts
Vegetables	Eat regularly, especially dark-green leafy types and coloured vegetables (e.g. cooked tomatoes)
Fruit	Eat regularly, especially fresh fruit grown locally in season
Garlic	Eat regularly
Red wine	Moderate amounts taken with meals (1 glass daily)
Red meat—eaten only on occasion	Decrease consumption
Dairy products—eaten only on occasion	Decrease consumption (especially trans fatty acids)
Processed foods—eaten only on occasion	Decrease consumption (especially high glycaemic index foods)

NUTRITIONAL SUPPLEMENTS

Nutritional supplements can never replace a balanced diet or provide all the health benefits of a whole food, but they can provide nutritional assistance and therapeutic effects in three different ways, as discussed below.

PRESCRIBING NUTRITIONAL AND FOOD SUPPLEMENTS

Nutritional and food supplements can play an important role in general practice and provide practitioners with many additional therapeutic tools. While the fully fledged practice of dietetics and clinical nutrition requires several years of specialised training, general practitioners can successfully integrate some simple, pre-prepared treatments into their practice (Box 10.1).

A practitioner who lacks confidence or knowledge about nutrition and food concentrates should consider referring the patient to an accredited dietician for food-based solutions, or a naturopath for both food-based and supplement-based approaches. Some pharmacists have undergone additional training and can provide general information about popular over-the-counter products. For general practitioners who are keen to learn more about this expanding area, several GP-specific short courses are provided by accredited course providers such as the Australasian College of Nutritional and Environmental Medicine (ACNEM).