Nutrition (20 page)
Oral administration of lactic-acid bacteria has been shown to be safe in several hundred human clinical trials. Caution is needed, however, when considering their use in some immunocompromised patients and in those with intestinal bleeding, although the lack of harmful effects from lactobacilli and bifidobacteria appears to extend across all age groups, including immunocompromised individuals.
Probiotics are immensely popular, and an estimated 20 billion doses are consumed every year around the globe in the form of bio yogurts, fermented dairy drinks, capsules and tablets. According to the World Health Organization, probiotics
by definition
are beneficial for health. Yet the European Food Safety Authority recently refused to accept the evidence for any health claims on product labels. This has caused uproar in academic circles, as swathes of research supported by solid scientific evidence has been rejected and the level of evidence required by the EFSA is widely considered to be too high.
by definition
are beneficial for health. Yet the European Food Safety Authority recently refused to accept the evidence for any health claims on product labels. This has caused uproar in academic circles, as swathes of research supported by solid scientific evidence has been rejected and the level of evidence required by the EFSA is widely considered to be too high.
The best evidence comes from a meta-analysis of data from a number of randomized controlled trials, so let’s see what these can tell us about the efficacy of probiotics.
Cholesterol
A meta-analysis of 13 trials involving 485 participants shows that taking probiotics significantly lowered total cholesterol levels (by 6.4 mg/dl), LDL-cholesterol (by 4.9 mg/dl) and reduced triglycerides by 3.95 mg/dl.
A meta-analysis of 13 trials involving 485 participants shows that taking probiotics significantly lowered total cholesterol levels (by 6.4 mg/dl), LDL-cholesterol (by 4.9 mg/dl) and reduced triglycerides by 3.95 mg/dl.
Upper respiratory tract infections
A rigorous systematic analysis from the Cochrane Collaboration (an international network of researchers dedicated to providing high-quality evidence to inform healthcare decision making) looked at ten clinical trials involving 3,451 participants. This found that probiotics were better than placebo at reducing the number of episodes of upper respiratory infections such as the common cold. Compared with inactive placebo, taking probiotics daily reduced the risk of having at least one cold by 42 per cent, the risk of having at least three colds by 47 per cent and the chance of needing an antibiotic prescription for an upper respiratory infection by 33 per cent.
A rigorous systematic analysis from the Cochrane Collaboration (an international network of researchers dedicated to providing high-quality evidence to inform healthcare decision making) looked at ten clinical trials involving 3,451 participants. This found that probiotics were better than placebo at reducing the number of episodes of upper respiratory infections such as the common cold. Compared with inactive placebo, taking probiotics daily reduced the risk of having at least one cold by 42 per cent, the risk of having at least three colds by 47 per cent and the chance of needing an antibiotic prescription for an upper respiratory infection by 33 per cent.
Antibiotic-associated diarrhoea
Children in hospital receiving broad-spectrum antibiotics can develop diarrhoea as a result of ‘killing off’ the healthy bacteria in their gut. Co-prescribing probiotics is therefore common in many hospitals worldwide and is a standard part of care in Scandinavia. A meta-analysis of three trials involving 1,092 children showed that those given probiotics for the duration of their hospital stay were 63 per cent less likely to develop diarrhoea and 51 per cent less likely to develop rotavirus gastroenteritis. One in five adults taking antibiotics also develop diarrhoea. A similar meta-analysis of adults showed that coadministration of probiotics reduced the risk by 44 per cent, while for
Clostridium difficile
-associated disease – which can be life-threatening – the relative risk was reduced by 71 per cent. A Cochrane Collaboration systematic review of 63 trials involving 8,014 participants showed that when diarrhoea did occur, probiotics had clear beneficial effects in shortening its duration (by at least 24 hours) and reducing stool frequency with effects noticed by day two. They also noted a lack of side effects and stated that they were safe to use alongside rehydration therapy.
Children in hospital receiving broad-spectrum antibiotics can develop diarrhoea as a result of ‘killing off’ the healthy bacteria in their gut. Co-prescribing probiotics is therefore common in many hospitals worldwide and is a standard part of care in Scandinavia. A meta-analysis of three trials involving 1,092 children showed that those given probiotics for the duration of their hospital stay were 63 per cent less likely to develop diarrhoea and 51 per cent less likely to develop rotavirus gastroenteritis. One in five adults taking antibiotics also develop diarrhoea. A similar meta-analysis of adults showed that coadministration of probiotics reduced the risk by 44 per cent, while for
Clostridium difficile
-associated disease – which can be life-threatening – the relative risk was reduced by 71 per cent. A Cochrane Collaboration systematic review of 63 trials involving 8,014 participants showed that when diarrhoea did occur, probiotics had clear beneficial effects in shortening its duration (by at least 24 hours) and reducing stool frequency with effects noticed by day two. They also noted a lack of side effects and stated that they were safe to use alongside rehydration therapy.
Traveller’s diarrhoea
A meta-analysis of 12 studies showed that several probiotic bacteria reduced the risk of developing gastroenteritis when travelling by 15 per cent.
A meta-analysis of 12 studies showed that several probiotic bacteria reduced the risk of developing gastroenteritis when travelling by 15 per cent.
Irritable bowel syndrome
A meta-analysis of 14 trials involving over 1,165 people, and another of ten trials involving 918 people showed that probiotics were better than placebo with noticeable improvements in overall symptoms such as pain, flatulence and bloating.
A meta-analysis of 14 trials involving over 1,165 people, and another of ten trials involving 918 people showed that probiotics were better than placebo with noticeable improvements in overall symptoms such as pain, flatulence and bloating.
Allergies
Mothers-to-be who take probiotics during pregnancy can reduce the chance of their offspring developing allergic conditions such as eczema. This is because, during early development, the immune system has to find a balance between tolerating harmless bacteria while fighting infections, and tolerating harmless dietary and self-identified proteins while attacking foreign proteins. Exposure to beneficial probiotic bacteria appears to help the immune system mature in the correct way. A meta-analysis of seven studies involving 2,843 children whose mothers took probiotics or placebo during pregnancy and breastfeeding showed that taking lactobacilli reduced the risk of developing an allergy by 10.6 per cent.
Mothers-to-be who take probiotics during pregnancy can reduce the chance of their offspring developing allergic conditions such as eczema. This is because, during early development, the immune system has to find a balance between tolerating harmless bacteria while fighting infections, and tolerating harmless dietary and self-identified proteins while attacking foreign proteins. Exposure to beneficial probiotic bacteria appears to help the immune system mature in the correct way. A meta-analysis of seven studies involving 2,843 children whose mothers took probiotics or placebo during pregnancy and breastfeeding showed that taking lactobacilli reduced the risk of developing an allergy by 10.6 per cent.
Prebiotics
Prebiotics are defined as ‘non-digestible food ingredients that selectively stimulate a limited number of bacteria in the colon to improve host health’. They are not digested or absorbed, and travel intact to the large bowel where they act as a fermentable food source to stimulate the growth of probiotic bacteria. They cannot be fermented by other, less beneficial bowel bacteria or by potential pathogens, and therefore act as a food to selectively promote the growth of beneficial probiotic bacteria.
Prebiotics include substances known as fructo-oligosaccharides (FOS), which are a form of soluble fibre found in some foods such as oats, barley, wheat, garlic, onions, bananas, honey and tomatoes. Some prebiotics are now being added to breakfast cereals and other ‘functional’ foods. Probiotics and prebiotics are also increasingly used together, as supplements, in a practice referred to by nutritionists as synbiotics.
Few safety concerns are associated with prebiotics, but it is important that their fermentation should not have undesirable effects on bowel function or habit, or be associated with the production of undesirable products such as excessive gas, which can cause discomfort and bloating. If you choose to take a prebiotic supplement, do not exceed the stated dose.
Your diet must provide all the ingredients needed for energy and all the processes of life including metabolism, reproduction, growth and repair. So far, we’ve considered the macronutrients (carbohydrates, proteins, fat, fibre), essential micronutrients (vitamins, minerals) and phytochemicals in the diet. In addition, the diet contributes five other important components: water, acidity, alcohol, salt (at levels well above those needed for essential micronutrient functions) and food additives.
Water
Water is more important for good nutrition than is generally realized. It is essential for energy metabolism in the citric acid cycle, for nutrient transport, waste disposal and the regulation of body temperature through perspiration.
Water contributes 60 per cent of the weight of an average male – a total of 40 to 50 litres – while the weight of the average female is 55 per cent water (33 to 35 litres), due to the relatively greater percentage of body fat.
Two-thirds of your body water is inside your cells, while the remaining third bathes the outside of your cells and flows through your circulation in the so-called ‘internal sea’ of interstitial fluid. Water molecules constantly move from one fluid compartment to another as nutrients and waste substances are passed to and from your cells.
THE FLUIDS OF LIFE
The body of a man weighing 70 kg contains:
• a total of 42 litres water
• 28 litres within his body cells
• 14 litres outside his body cells, of which 3 to 4 litres are in his circulation
During an averagely active day in a temperate climate the body loses around 2.5 litres of fluid, either through the lungs as water vapour, through the skin as sweat, or through the kidneys as urine. A small amount is also lost through the bowels. If you take vigorous exercise or visit a hot country, it is easy to lose twice this amount. Athletes in hot climates may lose as much as 10 litres of fluid per day.
HOW YOU LOSE WATER
Average daily water losses from the body:
• urine | 1,500 ml |
• sweat and water vapour from the lungs | 800 ml |
• in bowel motions | 200 ml |
Your body normally maintains a fine fluid balance, which is regulated partly by the hormonal control of urine production in the kidneys, and partly by the concentration of salts, sugars and soluble proteins that draw water into your circulation. As long as you replace your daily water losses through adequate drinking and eating, the amount of fluid in your intracellular and extracellular compartments is kept within narrow limits. Excess fluid passes into your circulation and is usually filtered out by the kidneys. If you are dehydrated, you will pass less urine than normal as your body conserves its water stores and triggers a sensation of thirst.
Ideally, men need to obtain at least 2.5 litres of water per day and women 2 litres per day. This is acquired partly from beverages and partly from moisture-rich foods such as soups. Children should drink approximately half this amount, depending on their age. Urine colour is a useful way of checking your hydration status in the workplace – it should be pale in colour. Urine that is dark yellow and concentrated is an important sign of dehydration.
TEA AND HYDRATION
As caffeine has a mild diuretic effect, it is often claimed that caffeinated drinks, such as tea, have a negative effect on hydration. However, research does not support this. A gold-standard randomized, double-blind, placebo-controlled crossover trial involving 21 healthy males aged 20 to 55 years found no difference in hydration levels whether participants drank four mugs (240 ml per mug) of black tea, each containing around 50 mg caffeine, or boiled water (240 ml per mug) at set intervals over one day. Blood samples and a 24-hour urine collection showed no great differences between concentrations of electrolytes, urea, protein or osmolality (a unit of measurement for the amount of a chemical dissolved in a fluid) of body fluids. Urine volume and colour also remained the same. Thus, both tea and water appear to make a similar contribution to fluid requirements that more than offsets the diuretic potential of small caffeine doses.
Although you should ideally drink at least eight glasses of water a day, only one in ten people do so. Over half the population only drink between one and four glasses of water daily.
Unfortunately, thirst receptors are not a sensitive judge of how fluid-deficient you are, and you are already quite dehydrated by the time you feel a craving to drink.
Unfortunately, thirst receptors are not a sensitive judge of how fluid-deficient you are, and you are already quite dehydrated by the time you feel a craving to drink.
The brain is particularly sensitive to changes in fluid balance. Dehydration is a common cause of tiredness, poor concentration, reduced alertness, reduced short-term memory, headache and mood changes, with increasing agitation, impatience and feelings of stress.
Dehydration also contributes to constipation, kidney stones, and, as it increases the thickness and stickiness of blood, can lead to abnormal blood clotting and even precipitate a heart attack or stroke. Therefore, it is important to drink fluids throughout the day rather than just when you are feeling thirsty.
High ambient temperature can quickly lead to dehydration, so adequate fluid intake is especially important during the summer months or when visiting or living in hot climates. If exposure to heat is excessive, it can lead to heatstroke when increased humidity stops sweat evaporating from the skin to cool the body.
Bottled versus tap water
The purity of drinking water is of paramount importance, and strict directives control the quality of both tap water and bottled water in Europe, the US and other developed countries.
Tap (mains) water is obtained from reservoirs, lakes, rivers and aquifers (which are underground geological formations that store rainwater). Water from these sources is treated to remove harmful substances (e.g. agricultural, industrial or sewage contaminants) and disinfected with chlorine. Tap water is of high quality, but some people dislike the slight smell or taste of chlorine. Placing a covered jug of water in the fridge for around an hour until it is cool will help to remove chlorine traces. Use the cooled water within 24 hours. Using a water filter will also remove chlorine and improve flavour. Table water, offered by some restaurants at a high price, is often just bottled tap water that has been filtered to improve its taste.
FLUORIDATION
In some regions, fluoride is added to public water supplies as fluoridation can help to strengthen teeth, to reduce the risk of dental caries. As another benefit, optimal intakes of fluoride can also strengthen bones and may provide some protection against osteoporotic bone fractures. Excess is harmful, however, and can lead to mottling of developing teeth and, paradoxically, brittleness of bones. Fluoridation is therefore controversial.
Spring water must originate from an underground source and must be microbiologically wholesome in its natural state without the need for any treatments. It may be treated to remove certain minerals or undesirable substances, however. Composition does not have to be specified, and spring water is available as still or sparkling.
SPARKLING OR STILL?
Even naturally sparkling water loses the carbon dioxide gas that provides these bubbles during processing, and this gas must be captured and reintroduced under pressure to produce that delightful effervescence. Carbonated water is more acidic than still water as the carbon dioxide gas dissolves to form weak carbonic acid. This can give a slightly sour taste unless there is sufficient bicarbonate present to reduce the acidity. Check labels for the electrolyte composition of bottled water.
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