You are not what you eat. You are what you can digest and absorb. The fundamental design of the human body is a tube â€" a doughnut with a hole in the middle. And we, like other animals, spend our physical lives processing organic matter through this tube for waste. How good you are at this determines your energy level, longevity and state of body and mind, as well as your digestion.

Over a lifetime, no less than 100 tons of food pass along the digestive tract and 300 000 liters of digestive juices are produced by the body to break it down. Our ‘inside skin', a nine meter long tract with a surface area the size of a small football pitch, is only the thickness of a quarter of a sheet of paper. Amazingly, most of the billions of cells that make up this barrier between us and the inside world are renewed every four days.

If you suffer from indigestion, bloating abdominal pain or drowsiness after meals, or if you often get stomach upsets, diarrhea or constipation, there are four simple steps you can take to tune up your digestion.

Your ‘inner skin' gets easily damaged â€" alcohol, antibiotics, food allergens and painkillers are the most common culprits. The result is that the digestive tract becomes more permeable and whole food proteins which aren't on the guest list, so to speak, rather than broken down amino acids which are, get through into the bloodstream. Then your immune system attacks. That's the basis of food allergy.

By avoiding your current food allergens â€" wheat, milk and yeast being the most common â€" you can give your digestive system a break. The good news is that most food allergies aren't for life. If you remove the offending food item strictly for four months, then heal the gut, you can lose your sensitivity to foods.

Another way to lessen the load on your digestive system is to take a digestive enzyme with each meal. These enzymes, called protease, amylase and lipase, literally help digest your food. If you instantly feel better you know you've got a problem with your digestion. If you get bloated after lentils or beans, choose an enzyme that contains glucoamylase.

Next, you can help rebuild your digestive tract by feeding it glutamine. While the rest of your body runs on glucose, your rapidly repairing digestive cells can run on this amino acid. Having a heaped teaspoon, ideally together with other key nutrients such as Vitamin A and zinc, last thing at night in a glass of water, is like a visit to the health farm. Do this every day for a month, or after any kind of infection, alcoholic excess or course of antibiotics.

 Inside your body you have more bacteria than living cells. They flourish in a healthy digestive tract and die off in an unhealthy one. So, once you've improved your digestive ‘re-inoculating' your digestive tract with exactly the right strains of bacteria makes a big difference. These are called lactobacillus acidophilus and bifidus bacteria. Again, having a capsule or powder for up to 30 days is all you need to get your inner flora flourishing.

Then there's maintenance. What damages your digestive tract the most is too much alcohol, deep fried food, burnt meat, coffee and wheat. Wheat contains something called gliadin, not found in oats or rice, which irritates many people's insides. Fresh fruit, vegetables, plus plenty of water, help digestion, as does chewing and not eating just because you're stressed.

Finally, drink lots of water, Dehydration is the most common cause of constipation. We all need eight glasses of water a day.