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Diet and digestive health

  • Angie Jefferson
clinical update
When all is going right we barely notice
the process of digestion, but when
things start to go wrong we quickly find
that discomfort associated with eating – one of the
great pleasures in life – soon becomes intolerable.
An efficient digestive system is essential to good
health and well-being. Every year hundreds of
thousands of people in the UK suffer from diges-
tive disorders, ranging from 10 per cent of the pop-
ulation who are regularly constipated, to the
35,000 afflicted by bowel cancer. Estimates are that
disorders of the digestive system account for 1.1
million hospital consultations each year (Depart-
ment of Health 1998). Even greater is the suffering
of the millions who never mention a digestive prob-
lem to a health professional, but self-treat common
ailments such as heartburn, constipation and piles.
In many cases these problems could be prevented
Angie Jefferson outlines the essential role that fibre – particularly that from vegetables and
fruit – plays in maintaining a healthy digestive system
Diet and
primary health care | Vol 15 No 1 | February 2005 27
clinical update
by eating a more balanced diet, and leading a
healthy lifestyle.
Often, digestive complaints are not discussed by
patients due to embarrassment and social stigma,
which means that they may be missing out on sim-
ple information which could resolve their problem,
or be delaying vital investigations into more serious
diseases, such as bowel cancer. Providing informa-
tion in the health centre or practice may be all that
some people need, or could be the stimulus to dis-
cussing a problem. Establishing a trusting relation-
ship, and prompting patients while using their own
language, could help to overcome some of the diffi-
culties and social taboo surrounding digestive prob-
lems in the UK.
The digestive system
Very simply, the digestive system processes the food
and drinks that we take in to release the energy and
nutrients needed for growth, everyday living, and
wear and tear, with anything that is not used
expelled as waste (Box 1). This process starts at the
mouth, where food enters the body, and ends at
the anus, where waste leaves. Far from being a sim-
ple organ, however, the digestive system consists of
a complex series of chambers, each with specific
functions: the mouth where food is chewed into
small pieces; the stomach where acid is mixed with
food to break it down further; the small intestine
where digestion is completed and most nutrients
absorbed; and the large intestine where the remains
of the process are solidified and bacteria ferment
any remaining carbohydrates. Malfunction in any
part of the digestive tract has a major impact on the
efficient performance of the rest of the system,
resulting in a wide range of side-effects (Box 2). But
by far the most common cause of digestive mal-
function is lack of attention to the diet, failing to
provide the digestive tract with what it needs to
operate at its best.
To function efficiently the digestive tract needs the
Regular feeding – digestion responds best to reg-
ular small meals rather than infrequent large meals.
Topping up the system regularly will help to keep
everything moving nicely in the right direction.
Fibre – a neglected nutrient of which 80 per cent
of us eat too little. Fibre acts like a sponge, absorb-
ing fluid to form a soft bulky mass that can easily
move through the digestive tract.
Fluid – to allow fibre to work. Without fluid fibre
remains hard and compacted and could result in
Food for gut bacteria – the lower digestive tract
is full of bacteria that are essential to our health
and well-being. What we eat affects their survival
and ultimately our health.
Activity – gravity and movement both help to pro-
pel food along the digestive tract.
Good habits – defecation is a learned habit which
we need to maintain. Ignoring the urge to defecate
results in the stools drying out and constipation.
Dietary fibre
Few people consider whether they are eating enough
fibre, and eight out of 10 of the UK population fail
to reach the recommended intake of 18g of fibre
each day (Henderson et al 2003). Eating enough fibre
not only has a major impact on digestive health in
the short- and longer-term, but also affects our
energy levels and how we feel each day. Strictly
speaking, fibre is not a nutrient because it is not
digested, but is essential in the diet to act as a lubri-
cant for digestion. Fibre passes down through the gut
largely unchanged, taking with it the waste products
that we need to get rid of.
Fibre is found in the tough fibrous part of fruit and
vegetables, particularly in the stalk and skins of fruits,
seeds or grains, and especially wholegrains (bran is
the outer covering of wheat grains), and also in soft
parts of fruit and vegetables that are not digested by
the small intestine. Much of the food we eat is
digested in the stomach and small intestine, but fibre
cannot be digested and passes relatively unchanged
into the large intestine (colon). Here, fibre acts like
blotting paper, drawing water into the stool, and pro-
vides a food source for the bacteria in the colon.
Increased bacterial numbers and the water absorp-
tive effects of fibre make the stool larger, softer and
easier to pass.
People who eat too little fibre, and are constipated,
tend to feel sluggish and tired. For women this tends
to be made worse during pregnancy, and around the
time of a period, due to changing levels of hormones
which tend to slow down activity of the gut. Even
We each eat about 500kg of food per year
Almost two litres of saliva is produced each day
Muscles contract in waves to move the food down the oesophagus. This means that food would
get to a person's stomach, even if they were standing on their head
The stomach produces 0.5 per cent hydrochloric acid, which is strong enough to dissolve bone
The gut is approx 9 metres long, but has an absorptive surface of more than 4,500 square metres
Every day 11.5 litres of digested food, liquids and digestive juices flow through the digestive sys-
tem, but only 100mls is lost in faeces
In the mouth, food is either cooled or warmed to a more suitable temperature
Food takes between 1.5 to three days to travel the length of the digestive tract
28 primary health care | Vol 15 No 1 | February 2005
Box 1. Digestive facts
clinical update
primary health care | Vol 15 No 1 | February 2005 29
Box 2. Common digestive disorders
Bowel (Colon)
Stomach ache
Sense of fullness
Furred tongue
Loss of appetite
Fatigue and depression
Abdominal pain, often
in lower left abdomen
Abdominal distension
Irregular bowel habit
with pellet-like stools
Sometimes small quan-
tities of blood passed
with bowel actions
Cramping pain often
colicky in nature
Feeling of fullness
Disruption of bowel
habit – constipation or
diarrhoea Abdominal
pain relieved by
defecation or passing
of wind
Pattern associated with
the menstrual cycle
Bright red blood
covering the stool,
on toilet paper, or in
the toilet bowl
Blood on stool
Abdominal pain
Straining feeling
in rectum
Changes in bowel
habit, such as unusual
episodes of diarrhoea
or constipation
Increased amount of
mucus in the stool
1% population consult
GP 10-12% population
UK laxative market
worth £40 million –
85% of this is spent on
self treatment
On average we pass
flatus (wind) 15 times
each day – odour can
be a problem
50% those >70 years
have diverticula in
large intestine
10-20% UK population
True incidence thought
to be higher
50% UK population
by 50 years of age
35,000 new cases in
UK each year
Low fibre intake
Low fluid intake
Overuse of laxatives
Underactive thyroid
Iron tablets
painkillers and cough
Some antidepressants
Air swallowing
Bacterial fermentation
Eating rapidly
Chewing gum
Loose dentures
Low-fibre diet and
high intestinal pressure
Some may have diver-
ticula from birth
Not fully known
Oversensitive bowel
leading to spasm
Exacerbated by spices,
large rich meals,
alcohol, coffee, stress
Straining to pass
hard stools
Low fibre diet
Family history
Benign polyps in bowel
Ulcerative colitis or
>3 bowel open-
Pain, discomfort
or straining at
least 25% of
Small hard or dry
stools at least
25% time
A sensation of
incomplete evac-
uation on more
than 25% of
Symptom history
Examination to
exclude other
Barium enema
Full symptom
Laboratory tests,
X-rays and
endoscopy to
exclude other
Visual examination
Examination with
a gloved, lubri-
cated finger to feel
for abnormalities.
may be used to
view internal
Barium enema
where a biopsy
> fibre
> fluid
> activity
Bulking laxative
e.g. ispaghula husk;
and sterculia
Osmotic laxative
e.g. lactulose
Avoid purgative or
stimulant laxatives
& faecal softeners
for general use
< fizzy drinks & beer
Slow eating to <
swallowing of air
Modify fibre intake
Activated charcoal
or defoaming
agents containing
> fibre – but some
people helped by
< fibre
> fluid
> activity
Antibiotics if fever
Regular small meals
> fibre – but some
people helped by <
Avoid triggers
Treat anxiety
and depression if
> fibre
> fluid
> activity
Warm water baths
Ice packs
cream or supposito-
Bulking laxatives
Surgical removal
> fibre from cereals,
fruit and vegetables
> fluid
> activity
> fibre from cereals,
fruit and vegetables
> fluid
> activity
> fibre from cereals,
fruit and vegetables
> fluid
> activity
Avoid straining
> fibre from cereals,
fruit and vegetables
> fluid
> activity
Maintain normal
body weight
Good calcium
Avoid common
gas producers e.g.
cabbage, Brussel
sprouts, cauliflower,
onions, garlic, leeks
and some seeds
such as fennel,
sunflower and
poppy seeds
clinical update
30 primary health care | Vol 15 No 1 | February 2005
mild constipation can result in considerable discom-
fort, and have a significant effect on our mood and
how we feel. Andrew Smith, Professor of Psychology
at Cardiff University, has looked at the effect that a
low fibre intake can have on well-being (Smith 2004
Q. 2001 in refs?). Even among people who were not
constipated, increasing fibre intake by the simple step
of eating a bran cereal for breakfast resulted in a 10
per cent improvement in mood within two weeks of
starting the dietary change. Benefits reported
included improved mood, better sleeping patterns
and feeling happier.
A second benefit of high fibre foods is the fact
that they tend to keep you feeling fuller for longer.
Of concern to us all is that it seems ever more diffi-
cult to stay in shape. Fibre acts something like a
sponge, absorbing fluids and swelling up inside the
stomach. The bulk provided by a high-fibre diet helps
to stave off hunger and so leaves us more able to
resist temptation, thus helping us to keep trim (Swin-
burn et al 2004). Lifestyle changes aimed at body
weight reduction can help prevent type-2 diabetes,
and a higher-fibre diet is one of factors with the
potential to significantly reduce the incidence of this
type of diabetes (Parillo and Riccardi 2004).
Over recent years there has been some degree of
disagreement in the literature as to the extent of the
protective effect of dietary fibre against colon can-
cer. Compelling new evidence was, however, pub-
lished in two studies during 2003, highlighting the
crucial role of a high fibre diet in cancer prevention:
Results from the European Prospective Investiga-
tion into Cancer and Nutrition (EPIC) study (Bing-
ham et al 2003) found that people who eat the
most fibre have 25 per cent less risk of develop-
ing cancer, compared to those with the lowest
fibre intakes. Furthermore the study predicted
that in populations with low average intakes of
fibre (such as the UK), doubling intakes of fibre
could reduce their risk of developing colon can-
cer by up 40 per cent.
The second study was the US Prostate, Lung, Col-
orectal and Ovarian (PLOC) Screening Trial (Peters
et al 2003), which offered further support for the
role of fibre in reducing the risk of colon cancer.
High intakes of dietary fibre were associated with
a 27 per cent reduction in risk of colorectal ade-
noma (a precursor of colon cancer). The associa-
tion was strongest for fibre from grains, cereals
and fruits.
The uniqueness of the EPIC study is its sheer size and
diversity, with half a million participants from 10 dif-
ferent countries across Europe, consuming widely dif-
ferent diets. This study confirms that eating a diet
rich in plant foods and especially fruit, vegetables,
and high-fibre cereals, probably remains the best
option for reducing the risk of colon cancer, and for
more general health and well-being.
However, the current UK recommendations to eat
at least 18g of fibre a day is lower than the levels
suggested by these studies to protect against cancer.
On average in the UK people eat just 13g per day.
What is clear is that many Britons could benefit sub-
stantially from increasing their intake of fibre rich
foods such as high-fibre cereals, fruit and vegetables.
The protective effects of fibre
There are several ways that fibre helps to reduce can-
cer risk:
Fibre is broken down in the gut, by good bacteria
to produce health-promoting substances such as
butyrate (a fatty acid), which can help keep the
cells of the bowel wall healthy and inhibit the
growth of cancerous cells.
Fibre speeds up the passage of food waste
through the bowel, reducing the likelihood of
damage by toxic substances such as carcinogens.
Foods supplying fibre (Box 3) are also rich
sources of phytochemicals that have been linked
to cancer protection. It is likely that a combina-
tion of these actions arising from a high fibre
consumption that can help to reduce the risk of
colon cancer.
Few people think about what’s inside the gut, and,
if they did, most would squirm at the thought of it
being full of bacteria. Popular belief is that all bacte-
ria are bad, but many gut bacteria are positively
friendly and of benefit to health. When we are born
the gut is sterile and contains no bugs, but we rap-
idly build up this natural defence over the first few
weeks of life. On average our gut bugs number
some 100,000 billion and weigh around 2lbs (1kg).
Over recent years we have increasingly come to
recognise the value of these gut bacteria to health,
and how we can positively influence the composi-
tion of the intestinal flora.
Billions of ‘friendly’ and ‘unfriendly’ bacteria live
side by side in the lower gut influencing health both
day-to-day and year-to-year. Beneficial bacteria (for
example, lactobacillus and bifidobacteria) are able to
use particular types of carbohydrate (called fructo-
oligosaccharides) which are resistant to digestion in
the upper digestive tract to produce a source of
energy. These non-digestible food ingredients,
known as prebiotics, selectively stimulate the growth
of good bacteria in the colon, and inhibit the growth
of less friendly types, such as staphylococcus and sal-
monella (Gibson and Roberfroid 1995).
Bingham SA et al (2003) Dietary
fibre in food and protection
against colorectal cancer in the
European Prospective
Investigation into Cancer and
Nutrition (EPIC): an observational
study. The Lancet. 361, 9368,
Department of Health (1998)
Hospital Episode Statistics.
London, DoH.
Gibson GR, Roberfroid MB (1995)
Dietary modulation of the
human colonic microbiota:
introducing the concept of
prebiotics. Journal of Nutrition.
125, 6. 1401-1412.
Guarner F, Malagelada JR (2003)
Gut flora in health and disease.
The Lancet. 360, 9356, 512-519.
Henderson et al (2003) National
Diet and Nutrition Survey: Adults
Aged 19-64 Years. London, The
Stationery Office.
Parillo M, Riccardi G (2004)
Diet composition and the risk of
type 2 diabetes: epidemiological
and clinical evidence. British
Journal of Nutrition. 92, 1, 7-19.
Peters U et al (2003) Dietary fibre
and colorectal adenoma in a
colorectal cancer early detection
programme. The Lancet. 361,
93368, 1491-1495.
Smith A et al (2001) High fibre
breakfast cereals reduce fatigue.
Appetite. 37, 3, 249-250.
Swinburn BA et al (2004)
Diet, nutrition and the
prevention of excess weight
gain and obesity. Public Health
Nutrition. 7, 1A, 123-146.
clinical update
primary health care | Vol 15 No 1 | February 2005 31
A thriving community of bacteria helps to fight off
the bugs that cause stomach upsets, which is espe-
cially important for children who are more vulnera-
ble to these than adults. In addition, friendly bacteria
help with:
absorption of nutrients reaching the lower gut
synthesis of vitamins
reduction of blood cholesterol levels
lowering the risk for bowel cancer
boosting immune function – both in the gut and
body wide (Guarner and Malagelada 2003).
Prebiotics, such as inulin, are found naturally in small
quantities in fruits and vegetables such as onions,
garlic, leeks, asparagus and bananas. However,
many Western diets may not contain enough of
these foods to optimise digestive health. Food man-
ufacturers have recently begun adding prebiotic
ingredients like inulin, extracted from the chicory
root, to foods such as breakfast cereals, offering a
convenient way to top up prebiotic intake. As inulin
is also a form of dietary fibre, it carries the added
benefits of the nutritional and health effects associ-
ated with fibre.
The probiotic approach adds living bacteria to food
in sufficient numbers to survive passage through the
stomach and reach the intestine, where they exert
their positive function. Most probiotics (usually
yoghurt or yoghurt drinks with added live bacteria)
contain just one single type of bacteria, usually from
the lactobacillus family. However the friendly bifi-
dobacteria and lactobacillus families contain a wide
range of different species. So while taking a probi-
otic drink will boost just the one type of bacteria in
the gut, eating a diet rich in prebiotics helps to sup-
port the entire family.
Looking after our digestive system is relatively easy
to do with a few positive dietary and lifestyle choices
(Box 4), and the benefits extend far beyond preven-
tion of constipation into weight control, cholesterol
and diabetes management, and boosting mood and
immunity. Providing patients with good information
regarding digestive health not only could reduce indi-
vidual suffering and the need for prescription of lax-
atives or the purchase of over-the-counter remedies,
but could also leave us feeling more energised, hap-
pier and able to deal with daily life
Angie Jefferson BSc, RD, RPHNutr,
Consultant Dietitian
Food Fibre content (g)
Baked Beans (small tin – 200g) 13.2g
40g of all-bran cereal [Q. is this All Bran the brand?] 12.0g
150g chickpea dhal 8.4g
1 serving frozen peas 8.1g
An average (150g) portion of wholemeal spaghetti 6.0g
Bran muffin 6.0g
4 dried apricots 5.4g
15 blackberries 5.3g
2 slices wholemeal bread 5.2g
8 dried prunes 4.8g
30g bran flakes 4.5g
40g fruit and fibre cereal 3.5g
2 weetabix 3.4g
A medium jacket potato (with skin) 3.2g
A medium orange 3.4g
2 slices white bread 2.9g
1 serving brown rice 2.5g
1 medium banana 2.4g
1 pear 2.3g
1 serving boiled carrot 1.8g
1 serving boiled cabbage 1.7g
2 digestive biscuits 1.4g
1 serving white rice 1.3g
Box 3. Foods to boost fibre intake
Eat plenty of fibre such as bran, wholemeal bread, cereals, fruit, leafy vegetables, potato skins,
beans, dried peas.
Have a regular routine in the morning and allow your bowels time to work. The best time to go
is in the hour after breakfast.
Reduce your intake of processed foods such as cheese and white bread.
Drink more water and avoid caffeine, alcohol and fizzy drinks.
Incorporate foods rich in prebiotics into your diet.
Eat breakfast to give the system a head start for the day.
Never ignore the urge to go to the toilet or the stools will just get drier and harder.
Keep active by exercising regularly.
Avoid sitting regularly for long periods, get up and move around.
Box 4. Tips for great digestive health
The Digestive Disorders Foundation
PO Box 251
Telephone 020 7486 0341
Fax 020 7224 2012
Useful organisations
... A number of scientific studies have shown a link between eating a high fibre diet and a range of health benefits (e.g. cardiovascular health, Pereira et al., 2004;diabetes, Liu et al., 2003; digestive health, Jefferson, 2005; weight loss, Ludwig et al., 1999;and cancer, Bingham, 2006). Research has also shown that increasing dietary fibre from wheat bran cereals decreases fatigue increases energy (Smith et al., 2001). ...
Full-text available
Research has shown that breakfast cereal consumption leads to a more positive mood and improved memory. The present study investigated the acute effects of having a fibre cereal bar for breakfast on mood and memory. Twenty volunteers (15 male, 5 female; mean age 22 years) were tested at 09.00 following an overnight fast. They carried out a free recall task involving recall of a list of 20 words and rated their mood using bi-polar visual analogue scales. The volunteers then had a 40 minute break and half of the volunteers consumed cereal bars (37g; 606KJ/144KCcal; 26g carbohydrate, 1.5g protein; 3.74g fat and 1.5g fibre) at the start of the break whereas the others abstained from eating. Following the break the volunteers repeated the memory task and mood rating. The results showed that consumption of the cereal bar led to a more positive mood (greater alertness; being more happy/sociable; and being calmer). Recall of the list of words was also significantly greater in the cereal bar condition. Overall, the results extend previous findings and show that acute benefits of breakfast can be identified following consumption of a fibre cereal bar.
Full-text available
To review the evidence on the diet and nutrition causes of obesity and to recommend strategies to reduce obesity prevalence. The evidence for potential aetiological factors and strategies to reduce obesity prevalence was reviewed, and recommendations for public health action, population nutrition goals and further research were made. Protective factors against obesity were considered to be: regular physical activity (convincing); a high intake of dietary non-starch polysaccharides (NSP)/fibre (convincing); supportive home and school environments for children (probable); and breastfeeding (probable). Risk factors for obesity were considered to be sedentary lifestyles (convincing); a high intake of energy-dense, micronutrient-poor foods (convincing); heavy marketing of energy-dense foods and fast food outlets (probable); sugar-sweetened soft drinks and fruit juices (probable); adverse social and economic conditions-developed countries, especially in women (probable). A broad range of strategies were recommended to reduce obesity prevalence including: influencing the food supply to make healthy choices easier; reducing the marketing of energy dense foods and beverages to children; influencing urban environments and transport systems to promote physical activity; developing community-wide programmes in multiple settings; increased communications about healthy eating and physical activity; and improved health services to promote breastfeeding and manage currently overweight or obese people. The increasing prevalence of obesity is a major health threat in both low- and high income countries. Comprehensive programmes will be needed to turn the epidemic around.
Full-text available
In the last 10 years nutritional research on diabetes has improved dramatically in terms of both number of studies produced and quality of methodologies employed. Therefore, it is now possible to attempt to provide the evidence on which nutritional recommendations for the prevention of type 2 diabetes could be based. We therefore performed a literature search and, among the papers published in indexed journals, we selected relevant epidemiological (mostly prospective) and controlled intervention studies. Lifestyle factors that have, so far, been consistently associated with increased risk of type 2 diabetes are overweight and physical inactivity. However, recent evidence from epidemiological studies has shown that the risk of type 2 diabetes is also associated with diet composition, particularly with: (1) low fibre intake; (2) a high trans fatty acid intake and a low unsaturated:saturated fat intake ratio; (3) absence of or excess alcohol consumption. All these factors are extremely common in Western populations and therefore the potential impact of any intervention on them is large: indeed, >90 % of the general population has one or more of these risk factors. The ability to correct these behaviours in the population is estimated to reduce the incidence of diabetes by as much as 87 %. Recent intervention studies have shown that type 2 diabetes can be prevented by lifestyle changes aimed at body-weight reduction, increased physical activity and multiple changes in the composition of the diet. Within this context, the average amount of weight loss needed is not large, about 5 % initial weight, which is much less than the weight loss traditionally considered to be clinically significant for prevention of type 2 diabetes. In conclusion, new emphasis on prevention by multiple lifestyle modifications, including moderate changes in the composition of the habitual diet, might limit the dramatic increase in incidence of type 2 diabetes envisaged worldwide.
Because the human gut microbiota can play a major role in host health, there is currently some interest in the manipulation of the composition of the gut flora towards a potentially more remedial community. Attempts have been made to increase bacterial groups such as Bifidobacterium and Lactobacillus that are perceived as exerting health-promoting properties. Probiotics, defined as microbial food supplements that beneficially affect the host by improving its intestinal microbial balance, have been used to change the composition of colonic microbiota. However, such changes may be transient, and the implantation of exogenous bacteria therefore becomes limited. In contrast, prebiotics are nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacterial species already resident in the colon, and thus attempt to improve host health. Intake of prebiotics can significantly modulate the colonic microbiota by increasing the number of specific bacteria and thus changing the composition of the microbiota. Nondigestible oligosaccharides in general, and fructooligosaccharides in particular, are prebiotics. They have been shown to stimulate the growth of endogenous bifidobacteria, which, after a short feeding period, become predominant in human feces. Moreover, these prebiotics modulate lipid metabolism, most likely via fermentation products. By combining the rationale of pro- and prebiotics, the concept of synbiotics is proposed to characterize some colonic foods with interesting nutritional properties that make these compounds candidates for classification as health-enhancing functional food ingredients.
The human gut is the natural habitat for a large and dynamic bacterial community, but a substantial part of these bacterial populations are still to be described. However, the relevance and effect of resident bacteria on a host's physiology and pathology has been well documented. Major functions of the gut microflora include metabolic activities that result in salvage of energy and absorbable nutrients, important trophic effects on intestinal epithelia and on immune structure and function, and protection of the colonised host against invasion by alien microbes. Gut flora might also be an essential factor in certain pathological disorders, including multisystem organ failure, colon cancer, and inflammatory bowel diseases. Nevertheless, bacteria are also useful in promotion of human health. Probiotics and prebiotics are known to have a role in prevention or treatment of some diseases.
Hospital Episode Statistics
Department of Health (1998) Hospital Episode Statistics. London, DoH.
National Diet and Nutrition Survey: Adults Aged 19-64 Years
  • Henderson
Henderson et al (2003) National Diet and Nutrition Survey: Adults Aged 19-64 Years. London, The Stationery Office.