Constipation is a clinical diagnosis. A normal person on a good diet should open their bowels daily (on average) and effortlessly (no straining) to produce a large stool (oh dear, I've never weighed one!) - about 10-12 inches long, thick as a cucumber, soft, brown and fairly inoffensive. Help is at hand with the Bristol Stool Chart so you can now grade 'em!
Food should pass through the gut in about 24-48 hours. You can easily measure your gut transit time by eating some beetroot (as the purple colouring goes straight through in many people) or sweetcorn which is poorly digested. If food stays in the gut too long, it gets fermented to toxic substances which poison the system and may act as a carcinogen. Inflammation in the gut will cause a faster gut transit.
Two thirds of stool weight are comprised of bacteria, so getting the gut flora right, together with foods that the gut flora like to ferment is probably the single most important intervention. Dehydration is a common cause of constipation, especially amongst the elderly who simply forget to drink enough water. However, water follows minerals, so water taken in isolation without being balanced up by adequate minerals in the diet or as a supplement, will actually dehydrate further. This is because when we pee we do not pee pure water, there are always minerals attached.
So in order of priority the commonest causes of constipation are:
Getting the gut flora right
Food for the Probiotics - these are called prebiotics. The best known of these is fructo-oligosaccharides, which are naturally present in many plants. However, the major source of prebiotics come from vegetables, particularly artichokes, onion, brassicas, pulses, nuts and seeds. Some dried fruits are also rich in prebiotics and have a reputation for improving constipation such as prunes. One can also take prebiotics as fructooligosaccharides - they arer naturally sweet and can be used to sweeten foods such as berries. The usual dose is 5-10grams daily, but start with small doses and build up because they may cause wind. Normally they should be fermented to methane and hydrogen which is inoffensive. Although they are meant for friendly bacteria such as bifidobacteria, they may also fuel less desirables such as clostridia - this means they do not suit everyone!
Faeces contain a high proportion of water and simple dehydration will remove water from faeces so that they become small, hard and difficult to pass. However, this cannot be corrected simply by drinking pure water. The reason for this is that one cannot pee pure water, there are always minerals attached. So if one tries to re-hydrate just by drinking extra water without this being balanced by adequate minerals either in the water or in the diet, actually this will result in further dehydration. Indeed the worst mineral deficiencies I see occur in people who think it is healthy to drink several litres of water a day and in doing so wash out all their minerals.
The body cannot put water into any one compartment, water actually follows minerals around. The biologists will understand that this is all about osmosis. One example of this is how drinking water with too much mineral in it, such as sea water, also results in dehydration. The salt is peed out in the kidneys, but carries with it an awful lot more water than is contained in sea water. Drinking sea water causes massive dehydration and rapid death.
So in addition to making sure one drinks adequate water, it is very important to ensure good trace element status. Because of modern farming practices and the fact that we are less physically active and so we need to eat less means that mineral deficiencies are extremely common. So everybody should be taking nutritional supplements
Allergies can certainly present with constipation and the commonest cause is cow's milk allergy. Allergy to grains can cause constipation or diarrhoea.
Exercise is a powerful stimulant to the gut and another reason to take a daily constitutional. Unfortunately this is impossible for patients with chronic fatigue syndrome since this will make them worse and therefore they need to pay more attention to other factors.
The gut can become blocked by strictures which can result after surgery, after inflammation (such as inflammatory bowel disease), or as a result of drug side effects. Aspirin like drugs will cause severe bowel strictures in a minority of people.
Many medications are constipating because of their effect on the nerves which control gut movements. The commonest of these are the codeine like analgesics, but many anticholinergic drugs such as antidepressants have a similar effect.