Programmes to prevent childhood overweight and obesity, which focus on
modification of dietary behaviour, increasing physical activity or reducing
sedentary behaviour, have been underway for a number of years in countries all
over the world. Encouraging results have provided useful data for the
development of future initiatives. This is the second in a series of articles
discussing current research on the prevention of childhood obesity.
The Diet
Any obesity prevention programme that targets the general child population cannot have a
dietary regimen that specifically aims to reduce calorie intake, as this might cause unwanted
weight loss in nonoverweight children. Ideally any public health programme would aim to
decrease both over and underweight in children, thus studies have looked to improve the
general ‘healthiness’ of the diet for example by reducing fat intake (1), increasing portions
of fruit and vegetables (2) or reducing the consumption of carbonated drinks (3).
Physical activity at school
The demands of modern school curricula make it difficult to include any additional physical activity as there are fears this may
have a negative impact on academic performance. However an Australian primary school study which introduced 1¼ hours of
fitness training each day found no loss of academic ability (assessed by arithmetic and reading tests) despite 4060 minutes less
formal teaching per day (4). The study reported improved physical work capacity and significant decreases in body fat compared
to children following the usual physical education programme. This programme has since been adopted by 60% of primary
schools in the state of South Australia. Nothing similar has yet been measured in secondary schools where the pressure to
succeed at exams is intense.
Physical activity at leisure
Leisure activities are also important especially for older children who are starting to make choices about how they spend their free
time. The ongoing French ICAPS study (5) has an emphasis on increasing the recreational and dailylife physical activity of
adolescents. Classroom debates and educational activities were used, in the intervention group, to develop positive attitudes
towards exercise, and taster sessions of attractive activities were offered during break times and after school. Practical support
came from extending the school bus service (flexible timing) and adapting times and places for activities. The emphasis was on
having fun, being sociable and making friends in a noncompetitive environment. After six months of intervention the proportion
of both boys and girls engaged in leisure physical activities was significantly increased in the intervention group, whereas it was
unchanged among control children. After 2 years they were 20% less overweight children in the group "action " versus the group "
control". Other studies have incorporated a similar approach of classroom education and community support to encourage
adolescents to be more active in their daily lives (2).
Sedentary behaviour
Some of the most successful studies have worked on reducing the number of hours spent being sedentary. A small study in the
US provided 8 and 9 year old children in one school with an 18 lesson, 6 month classroom curriculum focused on reducing
television viewing and computer games (6). Compared with a matched control school, children receiving the intervention had lower
average body mass index (a measure of weight relative to height) and skinfold thickness. Parents also reported decreases in
children’s television viewing. No studies in older children have focused solely on reducing TV viewing but the ‘Planet Health’ study
in the US (2) found that TV viewing and obesity were clearly linked in adolescent girls (but not boys), and that for each hour
reduction in TV watching there was a 15% reduction in the risk of obesity. The ICAPS study mentioned above (5) has reported a
reduction in the number of adolescents watching more than 3 hours of TV/day, but again with greater success amongst girls than
boys.
References
1. Caballero B et al (2003) Pathways: a schoolbased randomised controlled trial for the prevention of obesity in American Indian
schoolchildren The American Journal of Clinical Nutrition 78:10301038
2. Gortmaker SL et al (1999) Reducing obesity via a schoolbased interdisciplinary intervention among youth: Planet Health. Archives
of Pediatric Adolescent Medicine 153:409418
3. James J et al (2004) Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled
trial. British Medical Journal 328: 1237
4. Dwyer T et al (1983) An investigation of the effects of daily physical activity on the health of primary school students in South
Australia. International Journal of Epidemiology 12:308313
5. Simon C et al (2004) Intervention centred on adolescents’ physical activity and sedentary behaviour (ICAPS): concept and 6month
results. International Journal of Obesity 28:(Supplement 3) S96S103
6. Robinson TN (1999) Reducing children's viewing to prevent obesity, Journal of the American Medical Association 282:15611567
Preventing childhood obesity examining what initiatives work (2/4)
Salt is the common name we use for sodium chloride (NaCl). Salt is essential for life
and for good health. High blood pressure is a risk factor for cardiovascular disease,
and stroke. It is related to high sodium and low potassium intakes, but can
recommendations to reduce our salt intakes make a difference?
The importance of salt
Salt, or sodium chloride, is used to preserve and flavour food. It is also present naturally in all
food. As a rough guide, 1 g sodium is equivalent to 2.5g salt.
Sodium and chloride help to regulate blood pressure, control fluid balance and maintain the
right conditions for muscle and nerve functioning. Sodium facilitates absorption of nutrients
such as glucose and amino acids.
An average adult man’s body contains about 90g sodium of which half is in blood and other
body fluids, over a third is in bone and the rest inside the body’s cells.
Average sodium intakes range from 2 to 6g per day, although health in adults can be
maintained on less than 0.5g. Requirements increase when losses are high such as during
menstruation, lactation and heavy sweating.
Salt intake is of high priority in the public health response to hypertension because of the potential to shift downwards the blood
pressure distribution in the entire population.
Potassium
Potassium is naturally present in most foods, fruits and vegetables being especially good sources.
In our body, potassium is mainly found inside the cells. It has important roles throughout the body and is involved in the same
functions as sodium but with a complementary role and the balance between the two elements is critical.
Blood pressure – contrasting effects of sodium and potassium
The kidney’s ability to excrete or conserve sodium is a key factor for blood pressure regulation.
Most studies show that a reduction in salt intake reduces blood pressure, the effect being greatest in those with high blood
pressure, the obese and the elderly. Response to salt reduction is highly variable between individuals and may not provide
measurable benefits to people already within normal ranges.
In contrast, reduced blood pressure is linked to increased potassium intakes which may be due to potassium’s ability to increase
sodium excretion and the vasoactive effects of potassium on blood vessels.
Foods High in Potassium, Low in Sodium
The best sources of potassium are fresh foods with limited processing, because processing can impact the potassium level. On
the other hand, raw foods are naturally low in sodium and processed foods are our main dietary source of sodium.
Table 1 indicates food sources high in potassium and low in sodium.
Table 1 : A selection of Foods High in Potassium, Low in Sodium (when unprocessed)
The biggest effect on blood pressure is our lifestyle
Obesity, low levels of physical activity and low intakes of potassium have greater effects on blood pressure than high sodium
Salt, potassium and the control of blood pressure
Avocado,
apricot &
other stone
fruit
Banana
Beans as
lentils, kidney
beans, split
peas
Dates, raisins &
other dried fruits
Herbs &spices
e.g. parsley
and chilli :
fresh or dried
Kale, spinach, lettuce and
other green leafy vegetables
Fish such as
cod,
sardines, trout,
tuna
Mushrooms :
fresh or dried
Orange and
other citrus
fruits & juices
Melon, watermelon, apple, and
other seeded fruits
Peanuts,
walnuts
and other nuts
Potato and sweet
potato
Red and white
meat
Soy beans, curd, milk
Tomato and
tomato
products
Yoghurt &
low fat dairy
(except cheese)
2
intakes. Low calcium and magnesium intakes and a high ratio of saturated fats to n3 polyunsaturated fats have also been
implicated. Most recent interest has been in the benefits of the DASH (Dietary Approaches to Stop Hypertension) diet, rich in
fruits, vegetables and grain products (to increase potassium and fibre) and including low fat dairy products, fish, legumes, poultry
and lean meats. When salt intake was kept constant, blood pressure fell significantly.
Table 2 illustrates potential benefits to blood pressure of various lifestyle modifications.
Table2: Potential blood pressure benefits, by lifestyle change
Experts recommend reductions in salt intake
The evidence linking dietary salt to blood pressure has been exhaustively reviewed in the scientific literature over the past two
decades, and the public health policy implications of this evidence have been carefully considered by expert committees in many
countries worldwide, including the UK and the USA.
As we do not need our current high intakes, reductions to 56g salt (22.4g sodium) per day are recommended. It is also
recommended to consume 5 portions of fruit and vegetables per day which has been shown to have many health benefits
including increasing potassium intake.
Practical implications
The body can adapt to reduced sodium intakes from salt; acceptance of a sodium intake half of that accustomed to takes 23
months. We are turning to alternative ways of flavouring foods with greater use of pepper, fresh and dried herbs and spices. Salt
substitutes, based on potassium compounds, can help too whilst also contributing to an increased potassium intake. Although
taste and a lower food preservative value compared with salt have limited their usage, more recently products have been
developed by the food industry to overcome these problems.
Further Information
1. Geleijnse, J.M., F.J. Kok, and D.E. Grobbee, Blood pressure response to changes in sodium and potassium intake: a
metaregression analysis of randomised trials. Journal of Human Hypertension, 2003. 17: p. 471480.
2. Geleijnse, J.M., F.J. Kok, and D.E. Grobbee, Impact of dietary and lifestyle factors on the prevalence of hypertension in
Western populations. European Journal of Public Health, 2004. 14: p. 235239.
3. Institute of Medicine, Dietary reference intakes for water, potassium, sodium, chloride, and sulfate. 2004, The National
Academies Press: Washington.
4. Sacks, F.M., et al., Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop
hypertension (DASH) diet. New England Journal of Medicine, 2001. 344: p. 310.
5. U.S. Department of Health and Human Services, 7th Report of the US Joint National Committee on prevention, Detection
Evaluation, Treatment of Hypertension, JNC 7 Express, 2003. p. 8
6. Bertino, M., Beauchamp, G.K., Engelman, K., Longterm reduction in dietary sodium alters the taste of salt, American
Journal of Clinical Nutrition, 1982. 36: p.11341144
7. Blais, C.A., et al., Effect of dietary sodium restriction on taste responses to sodium chloride: a longitudinal study.
American Journal of Clinical Nutrition, 1986. 44: p. 232243.
8. Geleijnse, J.M., Grobbee, D.E. and Kok, F.J., Impact of dietary and lifestyle factors on the prevalence of hypertension
in Western populations. Journal of Human Hypertension, 2005. 19: p. S1–S4.
Modification
Recommendation
Approximate
Systolic Blood
Pressure Reduction
(Range)
Weight Reduction Maintain normal body weight (body
mass index 18.5 – 24.9 kg/m2)
5 20 mmHg/10 kg
weight loss
Adopt DASH
Eating Plan
Consume a diet rich in fruits,
vegetables and lowfat dairy products
with a reduced content of saturated
and total fat
8 – 14 mmHg
Dietary Sodium
Reduction
Reduce dietary sodium intake to no
more than 2.4g sodium or 6 g salt per
day
2 – 8 mmHg
Physical Activity
Engage in regular aerobic physical
activity such as brisk walking (at least
30 min per day, most days of the
week)
4 – 9 mmHg
Moderation of
Alcohol
Consumption
Limit consumption to maximum 3 units
of alcohol per day in men and 2 units
of alcohol per day for women and
lighter weight men.
(1 unit of alcohol = 10 gr of pure
alcohol = 1 glass of beer (25 cL) or
wine (10 cL) or whiskey (3 cL))
2 – 4 mmHg
3
Nanotechnology is the development of new products and processes using matter
with dimensions in the range of approximately 0.1 to 100 nanometres. A
nanometre is onebillionth of a metre (or onemillionth of a millimetre), making this
truly the ‘science of the small’. To put this in perspective, the width of one atom is
approximately onetenth of a nanometre, a DNA molecule is about 2.5
nanometres wide and the thickness of a human hair is approximately 80,000
nanometres.
At a recent conference in Amsterdam: 'Nano and Microtechnologies in the Food and
Healthfood Industries' (25
th
26
th
October 2006), participants learned that nanotechnology
exploits the fact that at the nanoscale, the properties of a material can differ substantially,
and in potentially useful ways, from those of the same material at a larger scale. This
pioneering technology, which has actually been around for decades, has the potential to
revolutionise everyday life in areas as diverse as Information Technologies,
communications, energy, cosmetics, textiles, healthcare and food.
Nanotechnology and food
Many food companies are now investing in nanotechnology research that could provide us with safer, healthier, more nutritious
and tastier food. Food production costs will be lowered as techniques become more efficient, using less energy, water and
chemicals, and producing less waste.
Although there are currently only a handful of foodrelated products on the market that incorporate nanotechnology, many more
exciting new applications are in various stages of development. Some of the key areas in which this emerging science will play a
valuable role include food packaging and food safety, and ‘interactive foods’. Imagine icecream that has the taste and texture
of icecream without the use of fat!
Food packaging and food safety
‘Smart packaging’ systems are being developed that will result in better protection of food and improved monitoring techniques
that allow food to be traced from ‘farm to fork’. Lighter, more flexible packaging materials that are more resistant to heat, light,
mechanical and other damage, and materials that can absorb oxygen and moisture, will help to keep foods fresher for longer.
Nanoparticles with antimicrobial properties, and dirtrepellent surfaces, are also expected to have widespread application for
packaging materials and in machines used in food production processes.
Further down the pipeline are materials that can adjust their properties according to external or internal conditions, such as
temperature, and those that can repair themselves when torn or punctured. Another innovative idea is the use of embedded
‘nanosensors’ in packaging, which can detect minute quantities of chemicals such as those released when a food starts to spoil.
The consumer is alerted to the spoilage or contamination by a colour change in the packaging.
Functional / interactive foods
New food systems are being developed with enhanced functional properties. Visions for the future include low sodium foods that
still taste salty due to interactions with the tongue, and nutrient delivery systems that use nanocapsules to deliver micronutrients,
antioxidants or even drugs to specific target areas of the body at designated times. Ultimately, ‘nanosensors’ could be
developed that detect an individual’s personal profile and trigger the release of appropriate molecules from the product. In this
way, foods could be customised according to the specific taste and smell preferences of the consumer, along with their needs
related to health status, nutrient deficiencies or allergies. Potential applications include foods that can release an appropriate
amount of calcium in consumers with early osteoporosis, or those with ‘smart filters’ that are shaped to trap molecules that might
cause an allergic reaction.
Consumer concerns
Although nanotechnology holds great promise for the future, as with any new technology, consumers naturally have concerns
about the possible risks to human health and the environment. Although current EU regulations are considered broad enough to
cover existing nanotechnologies, this is currently under review. Thorough premarket testing of products, focussing on particle
size as well as composition, is one way in which consumers want governments to act. Research Institutes and government
organisations in the UK and Germany are currently leading in this area. A consultation process, involving both experts and
consumers, is being undertaken by the German Federal Institute for Risk Assessment (BfR), and should be completed by the end
of 2006.
Further information:
1.
Nanotechnology: Innovation for tomorrow's world.
2.
International Food Information Council.
3.
The National Nanotechnology Initiative.
4.
5.
6.
European Nanotechnology Gateway (nanoforum.org). Report on Nanotechnology in Agriculture and food
A big future for the science of the small
4
7.
The Royal Society/Royal Academy of Engineering Report: Nonoscience and nanotechnologies:
opportunities and uncertainties
8.
Federal Institute for Risk Assessment
9.
http://www.foodtechinternational.com/papers/nanotechnology.htm
10.
http://www.foodtechinternational.com/papers/applicationnano.htm
5