Table 2.1 shows the relationships between nutrients and food products (or product groups) and the chronic diseases, where the WHO/FAO expert commission has identi-fied ‘convincing evidence’ or ‘probable evidence’ of such relationships. The table has been adapted to reflect the situation in the Netherlands, insofar as information rela-ting to fish salted in the Chinese manner, aflatoxins, excessive fluoride, hypocal-caemia and vitamin C deficiency has been omitted as irrelevant.
The extent to which dietary factors and certain diseases are interrelated is discussed below. However, this consideration is limited to those dietary factors for which ‘con-vincing evidence’ of a relationship exists, i.e. energy balance, fatty acid pattern, fruit and vegetables, fibre and sugar, certain vitamins and minerals, and alcohol consump-tion. Where possible, references to relevant reports of the Gezondheidsraad2 are given, since these are directly applicable to the Dutch situation. Established relation-ships between dietary factors and less prevalent disorders, such as that between folic acid and neural tube defects, are not discussed in this chapter.
Energy balance
The food we eat is the source of energy for the human body. The main sources of ener-gy in food are the carbohydrates and fats, with a small contribution being made by proteins and possibly by alcohol. In healthy people, the energy intake should be in balance with energy expenditure. Regular monitoring of body weight is a simple way of assessing whether this is the case. A slight positive energy balance over a longer period will lead to an increase in body weight. This may eventually lead to over-weight, either moderate or severe. A negative energy balance can lead to under-weight. The definitions of the terms ‘overweight’ and ‘underweight’ are given in textbox 2.1.
Overweight
During the period 1998 to 2001, 55% of Dutch men and 45% of Dutch women aged between 20 and 70 were overweight. Clinical obesity (severe overweight) could be seen in 10% of men in this age category, and in 12% of women (Blokstra & Schuit, 2003). This represents a twofold increase over the previous 25-year period (Visscher et al., 2002). It is predicted that the number of adults with obesity will rise by a further 50% over the coming 20 years (Bemelmans et al., 2004). The prevalence of overweight and obesity among children has also risen. Between 1980 and 1997, the number of young children with overweight more than doubled (see figure 2.2). Depending on age, the proportion of boys with overweight was between 7.1% and 15.5% in 1997, the figure for girls being between 8.2% and 16.1% (Fredriks et al., 2000).
2 Health Council of the Netherlands, The Hague
Table 2.1: Summary of the evidence for relationships between dietary factors and obesity, diabetes mellitus type 2, cardiovascular diseases, cancer, dental disorders and osteoporosis, adapted to reflect the situation in the Netherlands (WHO, 2003).
Obesity Type 2 Cardiovascular Cancer Dental Osteo-diabetes diseases disorders porosis Energy and fats
High intake of energy-dense food ↑↑
Saturated fatty acids ↑ ↑↑
Trans fatty acids ↑↑
Dietary cholesterol ↑
Myristic acid and palmitic acid ↑↑
Linoleic acid ↓↓
High intake of dietary fibre ↓↓ ↓ ↓
Free sugars (frequency and ↑↑
quantity)
Products preserved in salt ↑
and salt
Sugar-sweetened soft drink ↑ ↑
and fruit juice
Very hot beverages (and food) ↑
Unfiltered boiled coffee ↑
Alcoholic beverages
High alcohol intake ↑↑ ↑↑ ↑↑
Low to moderate alcohol intake ↓↓
Other dietary factors
Hard cheese ↓
Exclusive breastfeeding (a) ↓
Legend:↑↑ = convincingly increases risk; ↑ = probably increases risk; ↓↓ = convincingly decreases risk; ↓ = probably decreases risk; — = convincingly unrelated; - = probably unrelated;
(a) this relates solely to the effect of receiving breastfeeding, not of giving it (see textbox 2.4).
In the Netherlands, among persons with a lower level of education (i.e. no formal edu-cation or primary level only), the prevalence of obesity is approximately three times greater than among those with a degree or higher vocational qualification (Van Lin-dert et al., 2004). However, the increase in the number of persons with obesity may be across the board, regardless of education (Blokstra & Schuit, 2003). Among adults of Moroccan, Turkish, Surinamese and Antillean descent, obesity is more common than in the ‘native’ Dutch population. This is particularly true among women: the percent-age of adult females with obesity varies from 20% in the Antillean ethnic group and 26% among the Turkish, compared to 12% in the mainstream Dutch population (Van Lindert et al., 2004). Little information is available concerning the other ethnic groups. Obesity is also more common among Turkish and Moroccan children than among those of Dutch descent (Brussaard et al., 1999).
Obesity is an important risk factor for a large number of chronic conditions (Gezond-heidsraad, 2003a). Morbidity and co-morbidity rise in direct proportion to the body The World Health Organization uses the ‘body
mass index’ (BMI) as the indicator of a person’s body fat in relation to his or her height. The body mass index is calculated by dividing weight by the
square of the height (kg/m2). The BMI categories shown in table 2.2. apply to Western adults. Dif-ferent cut-off points apply in the case of children and ethnic groups.
Table 2.2: BMI classifications.
Classification of body weight BMI
Underweight < 18.5 kg/m2
Normal weight 18.5-24.9 kg/m2
Overweight ≥25 kg/m2
Moderate overweight 25-29.9 kg/m2
Severely overweight or obese ≥30 kg/m2 Textbox 2.1: Classification of body weight.
Figure 2.2: Prevalence of overweight in Dutch children, by gender and age (after Fredriks et al., 2000).
0 3 6 9 12 15
aged 6 aged 12 aged 18
boys girls
aged 6 aged 12 aged 18
1980 1997
prevalence (%)
mass index (BMI). This is particularly true of diabetes mellitus type 2, but also holds for cardiovascular diseases, gallbladder diseases, conditions which impair mobility (such as arthritis), and various forms of cancer. An expert commission appointed by the International Agency for Research on Cancer (an official WHO agency) found ‘con-vincing evidence’ to suggest that obesity represents an increased likelihood of devel-oping cancer of the colon, breast (post-menopause), uterus, kidney or oesophagus (IARC, 2002). Risk factors for cardiovascular diseases, glucose intolerance and (in the United States) diabetes mellitus type 2 are more prevalent among obese children than others of the same age. The reduced quality of life experienced by persons with obesi-ty is not only due to the increased likelihood of (co-)morbidiobesi-ty, but also to psychologi-cal and social problems, including a higher rate of employment incapacity. The Health Council of the Netherlands states that treatment for obesity does not usually result in any permanent weight loss. It is therefore important to prevent obesity from developing in the first place (Gezondheidsraad, 2003a).
The Health Council arrives at similar conclusions to those of the WHO with regard to the relationship between the risk of developing obesity and dietary factors, physical activity and environmental factors (see column 1 of table 2.1). It summarizes current knowledge of dietary factors as follows. The likelihood of over-consumption (i.e. ener-gy intake in excess of enerener-gy expenditure) is greatest with a diet rich in fats, as opposed to a low-fat, high fibre diet. This is particularly so in combination with a lack of physical activity. The influence of various types of carbohydrates on the regulation of the energy balance is not yet fully understood. Various other dietary factors will also affect energy intake, including the energy density of the diet, the quantity con-sumed (portion size), and the frequency of meals (with particular regard to ‘snack-ing’). The diet which is likely to do most to help maintain an appropriate energy balance is one with a low energy density, i.e. containing a large proportion of fruit, vegetables and cereal products (Gezondheidsraad, 2003a).
Underweight
A negative energy balance can lead to undernutrition and to underweight (BMI <
18.5 kg/m2). Gradual, unintentional weight loss is an important indicator of insuffi-cient energy intake. Persons who lose five or more kilograms over a period of five years have a higher risk of death than those who do not. Among older men, this level of weight loss is associated with an increase in the risk of death in the order of 2.2 (De Groot et al., 2002). Unintentional weight loss of 4% per year has been shown to be an independent indicator of increased risk of death. Undernutrition is often accompa-nied by impaired physical functioning and a decrease in the quality of life (De Jong, 1999; Mathey, 2000).
With the exception of a number of specific groups, undernutrition is relatively uncommon in the Netherlands. The groups with a high prevalence of undernutrition are elderly persons in (residential) care, the chronically ill, and those addicted to alco-hol or drugs. In one survey of ‘apparently healthy’ Dutch citizens aged between 70 and 75, 14% of men and 31% of women were found to have lost five or more kilograms
in body weight over a period of ten years (De Groot et al., 2002). Of elderly persons admitted to a long-term residential care facility, 30% are suffering from undernutri-tion (Anon., 2001), while among those admitted to hospital, the prevalence of under-nutrition can rise to as much as 62% (Naber et al., 1997; see also RIVM, 2004).
Fatty acids
Fatty acids in our diet play a particularly important part in the atherothrombotic process which underlies the development of coronary heart diseases. Various (classes of) fatty acids have various effects. The differences between the various classes of fatty acids is explained in textbox 2.2.
Quantitative relationships have mostly been described between the intake of fatty acids on the one hand and intermediary risk factors, such as high concentrations of serum cholesterol fractions, on the other. In the case of saturated fatty acids, the rela-tionship with serum LDL cholesterol (‘bad’ cholesterol) is the most important. The level of LDL cholesterol has a strong correlation with the total cholesterol level. Inter-vention studies have demonstrated that the replacement of one energy per cent satu-rated fatty acids by carbohydrates is accompanied by a reduction in the total serum cholesterol of 0.052 mmol/l; replacement with monounsaturated fatty acids results in a reduction of 0.048 mmol/l (Clarke et al., 1997).
Trans fatty acids raise the LDL cholesterol level and lower that of HDL cholesterol (‘good’ cholesterol). Besides the adverse effects on serum cholesterol fractions, other adverse effects can be seen, having a link with the risk of coronary heart diseases such as thrombosis. On the basis of cohort studies, it is estimated that an increase in trans fatty acid intake equivalent to two energy per cent will produce a 25% increase in the risk of coronary heart diseases (Oomen, 2001).
Substitution of saturated fatty acids by polyunsaturated acids was shown to reduce the risk of coronary heart diseases in three of the four long-term intervention studies undertaken. The Health Council therefore concludes that the effect may be attribut-able to linoleic acid, although α-linolenic acid could also be responsible for the find-ings (Gezondheidsraad, 2001).
The n-3 or omega-3 unsaturated fatty acids listed in textbox 2.2 are known to reduce the risk of fatal cardiovascular diseases. Fish is a rich source of these lipids. Epidemio-logical research and intervention studies have established that the consumption of Textbox 2.2: Types of fatty acids in the diet.
Fat in our diet is mostly in the form of triglyc-erides, made up of glycerol and fatty acids.
Fatty acids may be saturated (e.g. myristic acid and palmitic acid) or unsaturated, which means that they have one or more double bonds between the carbon atoms. The number of double bonds determines whether the fatty acid is
monounsatu-rated (e.g. oleic acid) or polyunsatumonounsatu-rated (e.g.
linoleic acid). The site of the double bond is repre-sented, for instance, as n-3 (α-linoleic acid, fish fatty acids) or n-6 (linoleic acid). The symbol omega (ω) is sometimes used instead of the ‘n’.
Double bonds can occur either in the cis or trans form.
fish reduces the risk of death from cardiovascular diseases. A daily intake of 400 mg fish fatty acids (the equivalent of eating fish once or twice per week) reduces the risk of coronary heart diseases by approximately 25%, compared to a situation in which no fish fatty acids are consumed (Bucher et al., 2002; Whelton et al., 2004, He et al., 2004).
Fruit and vegetables
Fruit and vegetables are important sources of dietary fibre and various vitamins, and help to prevent nutritional deficiencies. Moreover, a high consumption of fruit and vegetables reduces the risk of certain chronic diseases.
Based on cohort studies, it is estimated that the risk of coronary heart diseases can be reduced by 20% with a high consumption of fruit and vegetables, compared to a situa-tion in which consumpsitua-tion is low (Liu et al., 2000; Hirvonen et al., 2001; Joshipura et al., 2001; Bazzano et al., 2002; Steffen et al., 2003). In the case of stroke, such a relative risk reduction can also be seen for the consumption of fruit and vegetables in combi-nation (Joshipura et al., 1999; Hirvonen et al., 2000; Johnsen et al., 2003; Bazzano et al., 2002; Steffen et al., 2003). However, the results of cohort studies examining the consumption of fruit and vegetables separately are less consistent. In the largest cohort study, no relationship was established between the consumption of vegetables and the risk of stroke, but high consumption of fruit was estimated to reduce the risk by 30% (Joshipura et al., 1999). The relative risks established by the largest cohort stud-ies have been used as the basis for the modelling in section 2.4 (see table 2.3).
In the early 1990s, it was estimated that high consumption of fruit and vegetables would reduce the risk of cancer, particularly its epithelial forms, by approximately 50%
(Block et al., 1992). This risk reduction has since been subject to some downwards adjustment, and a discrepancy between patient-control and cohort studies has been noted. Both the IARC (2003) and the Signalling Committee Cancer of the Dutch Can-cer Society (Signaleringscommissie Kanker KWF, 2004) have made an inventory of the evidence for a relationship between the consumption of fruit and/or vegetables and cancer. Both conclude that consumption is indeed likely to reduce the risk of cancer of the mouth and throat, oesophagus, stomach and lung. The IARC adds that there is some evidence, albeit limited, to suggest that the consumption of fruit and vegetables has a preventive effect with regard to cancers of the colon, ovary, bladder and kidney.
If the evidence from cohort studies is considered in isolation, then the incidence of lung, stomach and breast cancer would appear to have an inverse relationship to the consumption of fruit, while cancer of the lung has a similar relationship to that of vegetables. As shown in table 2.3, the risk reductions are in the order of 20% (IARC, 2003). However, these estimates are based on some considerable uncertainties and with the exception of breast cancer, they are also conservative estimates. Moreover, exactly how high consumption of fruit and vegetables must be in order to achieve these risk reductions is not clear, since each study has compared different intake levels.
Besides nutrients, fruit and vegetables contain a wide range of non-nutrients, such as flavonoids and other polyphenols, which may also play a role in reducing the risks of
chronic diseases. Furthermore, the as yet unknown constituents of fruit and vegeta-bles will probably have some significance in relation to health as well. To date, it has not been possible to demonstrate exactly how or why fruit and vegetables can offer protection against chronic disease.
Dietary fibre
Dietary fibre comprises indigestible carbohydrates. The main sources of fibre are brown, wholemeal and mixed-grain bread, potatoes, fruit and vegetables. Dietary fibre has a preventative effect with regard to obesity, coronary heart diseases and diabetes type 2. The possible effect with regard to bowel cancer remains disputed since the evi-dence, although based on well-conducted cohort studies (Park et al., 2003; Bingham et al., 2003) appears to be conflicting (KWF, 2004). A diet rich in fibre is more important in preventing overweight than one low in fat (Gezondheidsraad, 2003a). However, fibre supplements have not been consistently shown to have any positive effect in pre-venting obesity. Cohort studies reveal that an increase in daily fibre intake of more than 10 grams (for women) and 15 grams (for men) is associated with a 20-30% reduc-tion in the risk of developing coronary heart diseases (Pietinen et al., 1996; Rimm et al., 1996; Wolk et al., 1999; Mozaffarian et al., 2003; Bazzano et al., 2003). Various observa-tion and intervenobserva-tion studies support the hypothesis that dietary fibre also reduces the risk of developing diabetes type 2 (Institute of Medicine, Food and Nutrition Board, 2002; Montonen et al., 2003). The effects in terms of coronary heart diseases and dia-betes type 2 are mostly attributed to dietary fibre derived from cereal products.
Sugar
The consumption of carbohydrates always entails some impact on the teeth. Whether that impact will lead to caries varies from individual to individual and, apart from the frequency of carbohydrate intake, will depend on the individual’s oral hygiene regi-men. With effective administration of fluoride, good oral hygiene and a relatively infrequent intake of carbohydrates, the risk of developing caries is small. Accordingly, the Health Council has not produced a dietary standard or guideline for sugar con-sumption (Gezondheidsraad, 2001).
Minerals and vitamins
The intake of the mineral sodium is positively related to blood pressure, while potas-sium has the opposite effect. Intervention studies demonstrate that a reduction of the Table 2.3: Estimated health effects (relative risks) of high versus low consumption of fruit and vegetables.
Diseases Reference Fruit Vegetables
Coronary heart diseases Joshipura et al., 2001 0.80 0.80
Stroke Joshipura et al., 1999 0.70 ns
Lung cancer IARC, 2003 0.77 0.80
Stomach cancer IARC, 2003 0.85 ns
Breast cancer IARC, 2003 0.82 ns
ns = not significant
daily sodium intake of one gram (almost 30% of the average estimated Dutch intake) by persons with no history of hypertension will result in a limited reduction of the sys-tolic blood pressure of no more than 1 mm Hg. For those who do suffer from hyper-tension, the reduction is 2.5 mm Hg (Gezondheidsraad, 2000a). A meta-analysis of intervention studies of potassium intake suggests that potassium suppletion will reduce systolic blood pressure by 1.8 mm Hg in subjects who do not have elevated blood pressure, and by 4.4 mm Hg in those who do. Fruit and vegetables are good sources of potassium (Geleijnse & Grobbee, 2003). A diet which includes a high pro-portion of fruit, vegetables, fish, nuts, low-fat dairy products, and a low propro-portion of total fat and saturated fat has been shown to have a positive effect on blood pressure (Gezondheidsraad, 2000a).
Calcium and vitamin D are, alongside physical activity, two important factors in the development and maintenance of the skeleton. Among the elderly, a high intake of both calcium and vitamin D has been related to a lower risk of developing osteoporo-sis and bone fractures (Gezondheidsraad, 2000b; Ooms, 1994). A high consumption of milk and milk products, as well as a high intake of calcium (more than 1000 mg per day) demonstrate a slight but consistent reduction in the risk of bowel cancer (KWF, 2004).
This report does not examine the diet as a source of fluoride, since in the Netherlands, toothpaste containing fluoride is considered a far more important contributor to the prevention of oral health problems than the quantity of fluoride in the diet.
Alcohol
The consumption of alcohol, particularly in excess, can have many adverse effects (Klatsky & Friedman, 1995). According to the figures published by Statistics Nether-lands (CBS), 831 people died in the NetherNether-lands from an alcohol-related condition (e.g. alcoholic cirrhosis and alcoholic hepatitis) in the year 2000, where alcohol could be identified as an explicit contributory factor. This figure must be regarded as a minimum, since it does not include deaths which are indirectly related to alcohol con-sumption. For example, each year approximately 200-250 people die in road accidents in which at least one driver is under the influence of alcohol, with a further 3,000 to 3,500 individuals suffering serious injury.
Excessive alcohol consumption is also an important cause of osteoporosis and hyper-tension, the latter increasing the risk of stroke and coronary heart diseases (WHO, 2003). Alcohol consumption is also a risk factor in cancers of the mouth, throat,
Excessive alcohol consumption is also an important cause of osteoporosis and hyper-tension, the latter increasing the risk of stroke and coronary heart diseases (WHO, 2003). Alcohol consumption is also a risk factor in cancers of the mouth, throat,