Nutrition

Maintaining and Improving Health

Geoffrey P. Webb

• Éditeur: CRC Press
• Année: 2019
• ISBN:
  9781351058056
• Édition: 5
• Sujet: Medizin
• Sous-sujet: Klinische Medizin

Following the tradition of its predecessor, the fifth edition of Nutrition: Maintaining and Improving Health continues to offer a wide-ranging coverage of all aspects of nutrition while providing new information to this edition including:

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• Increased coverage of experimental and observational methods used in nutrition

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• In-depth focus on the nutritional implications of the increased adoption of vegetarian and vegan lifestyles

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• Streamlined referencing - a short selected list of key references at the end of each chapter with URL links to free additional resources where possible

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• Discussion of nutrition debates

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• Critical coverage of "medicinal uses of food" including superfoods, functional foods and dietary supplements

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• Updated bullet point summaries of key points after each major topic within each chapter

The author provides an evidence-based evaluation of many key nutrition beliefs and philosophies. The book contains in-depth and critical reviews of the methods used to evaluate nutritional intakes/status and the observational and experimental used to investigate putative links between dietary factors and health outcome. It covers the role of food as a source of energy and nutrients while discussing the non-nutritional roles of food and the social and psychological factors that influence food choice. Presenting a critical discussion on the value of nutrition research linking specific foods or nutrients to specific diseases which encourages students to question the value of some current nutrition research.

This is essential reading for all nutrition and dietetics students with different backgrounds who are studying nutrition as a specific discipline for the first time.

PART 1
CONCEPTS AND PRINCIPLES

1 Changing priorities in nutrition

2 Food selection

3 Methods of nutritional assessment and surveillance

4 Investigating links between diet and health outcomes

5 Investigating links between diet and health – amalgamation, synthesis and decision making

6 Dietary guidelines and recommendations

1 Changing priorities in nutrition

Ensuring adequacy and use of food groups

A new priority – reducing the chronic diseases of ageing populations

Plates and pyramids: food guides to reflect modern nutritional priorities

Failure to fully implement better nutritional knowledge and understanding

The future of nutrition research

Yoghurt and ovarian cancer? A case study of unproductive research

Key reference

Ensuring adequacy and use of food groups

During the first half of the twentieth century, the focus of nutrition research was to identify the essential nutrients and to quantify our requirements for these nutrients.

Essential nutrients are split into two major categories.

• The macronutrients – carbohydrates, fats and protein are required in relatively large quantities and are the main sources of dietary energy. Within the fats category, small amounts of certain polyunsaturated fatty acids are specifically essential and needed for vitamin-like functions; one of them was originally designated vitamin F. Within the protein component, nine or ten amino acids are termed essential because they are needed for protein synthesis and cannot be made from the other 10/11 so-called non-essential amino acids; some are also needed in other synthetic pathways. We can synthesise glucose from some amino acids and from the glycerol component of fat, but in most healthy diets, carbohydrates would be expected to provide more than half of the calories.
• The micronutrients – vitamins and minerals are only required in small (milligram or microgram) quantities and do not act as sources of energy. There are 13 vitamins and 15 unequivocally established essential minerals.

The following list gives the criteria for establishing that a nutrient is essential.

• The substance is essential for growth, health and survival.
• Characteristic signs of deficiency result from inadequate intakes and these are only cured by administration of the nutrient or a specific precursor.
• The severity of the deficiency symptoms is dose-dependent; they get worse as the intake of nutrient decreases.
• The substance is not synthesised in the body, or only synthesised from a specific dietary precursor, and so is required throughout life. Note that a strict application of this rule would eliminate vitamin D, which can be synthesised in the skin in sufficient amounts by a photochemical reaction, provided it is regularly exposed to summer sunlight.

During the first half of the twentieth century, most of these essential nutrients were identified and their ability to cure or prevent certain deficiency diseases was confirmed. These deficiency diseases have been major causes of ill-health and mortality and in a few cases still are.

• Between 1900 and 1950 there were 3 million cases and 100,000 deaths from pellagra in the USA, a disease that was shown to be caused by a lack of niacin or vitamin B₃. It has been a major cause of ill-health in many places where maize was the dominant staple food.
• In the early 1900s, there were 30,000 deaths per year from beriberi in British Malaya and up to 20,000 in the American-occupied Philippines. Beriberi was shown to be caused by a lack of thiamin (vitamin B₁) and was prominent in other countries where white (polished) rice was the dominant source of dietary calories.
• In the late nineteenth and early twentieth centuries, up to 75% of children in some British industrial cities and some northern US cities like Boston suffered from rickets caused by vitamin D deficiency. Inadequate exposure of the skin to summer sunlight was the major underlying cause.
• Prior to the 1920s, a diagnosis of pernicious anaemia meant death was almost inevitable until it was found that eating raw liver (a very rich source of vitamin B₁₂) could alleviate this condition. The condition is caused by an inability to absorb vitamin B₁₂.

The impact of this work was such that several Nobel Prizes for Physiology or Medicine and for Chemistry were awarded for vitamin-related work; between 1929 and 1943 a total of 14 individuals shared seven Nobel prizes for such work.

In most cases, these nutrients have not only been identified but firm estimates of average requirements have also been made. Selenium was the last of the 28 micronutrients to have its essentiality established in 1957. Many governments and international agencies use these estimates of requirements to publish lists of dietary standards that can act as yardsticks to test the adequacy of diets or food supplies. These standards are variously termed Recommended Dietary/Daily Allowances (RDA) or Dietary Reference Values (DRV) and they are discussed fully in Chapter 3.

During these early decades of the twentieth century, our understanding of the nature, roles and requirements for essential nutrients was established and ensuring adequacy became the overriding priority in nutrition. Good nutrition was all about making sure that people got enough energy and protein and adequate amounts of all of the essential nutrients. The quality of a diet would have been judged upon its ability to supply all of the essential nutrients and to prevent nutritional inadequacy.

The official priorities for improving the nutritional health of the British population during the 1930s were the following:

• To reduce the consumption of bread and starchy foods.
• To increase the consumption of nutrient-rich, so-called “protective foods”, like milk, butter, cheese, eggs, fruit and green vegetables.

The following benefits were expected to result from these changes:

• A taller, more active and mentally alert population.
• Less of the deficiency diseases like goitre, rickets and anaemia.
• A reduced toll of death and incapacity due to infectious diseases like pneumonia, tuberculosis and rheumatic fever.

These aims have largely been achieved. The average height of Britons has increased and they are now much taller now than in the first half of the twentieth century. Occurrences of overt deficiency diseases are now rare and usually confined to particular high-risk sectors of the population like those with chronic illnesses or those at the extremes of social and economic deprivation. Children now mature faster and reach puberty earlier. The potential physical capability of the population has undoubtedly increased even though many of us are unfit because we are not required to do any hard physical work and can choose to lead very inactive lives. Infectious diseases now account for less than 1% of deaths in Britain.

There are still many populations around the world where people struggle to obtain enough food to eat and where malnutrition and certain deficiency diseases are still prevalent; ensuring dietary adequacy remains the nutritional priority for such populations. Even within affluent countries, those at the extremes of social and economic deprivation may still struggle to achieve sufficient dietary adequacy to prevent overt indications of deficiency or malnutrition. Prolonged periods of ill-health may also precipitate malnutrition. Many people in the UK without visible symptoms of deficiency still have intakes of vitamins and minerals that are considered inadequate and/or have biochemical indicators that are below the threshold values taken to indicate poor status for particular nutrients.

Right up until the 1990s the guidance tools used by those seeking to give public health advice about diet and nutrition reflected this prioritising of adequacy. Foods were grouped according to their ability to supply important elements of an adequate diet and clients advised to eat food from each of these groups each day. A food chart poster produced by the Ministry of Food in Britain during World War II (WW2) splits foods up into four groups and recommends that people “eat something from each group every day”.

The four groups used were:

• Body-building foods – these were all high protein, animal foods: milk, meat, eggs, cheese and fish. In a footnote it is acknowledged that many vegetable foods like peas, beans, bread and potatoes help in body-building but ar...