Since food purchase, preparation and eating occupy a significant part of our lives, it is not surprising that there is a great deal of interest in food and in trying to explain the various phenomena associated with it.

What is the ecological place and function of an oyster? Given that seeds support the early life of plants, what nutritional properties might they have? What is happening to fruit as it ripens? To meat as it is barbecued? To bread as it bakes? What makes us feel hungry, or satisfied?

Science offers one way of explaining these phenomena. What distinguishes science from other systems of knowledge is the predictability of a particular outcome when a practice or event is repeated. Ideas are the starting point, but they are not enough. Explanations must also be consistent, no matter how tested. The establishment of a scientific fact depends on well-designed, extensive and rigorous testing. Ideas and explanations must be able to stand up to full evaluation by other scientists.

Biological systems, including food and the human organism, are exceedingly complex. In seeking to understand such systems the scientist must unravel many interacting factors. The effect observed after a certain event may be modified, enhanced or diminished by other factors. For example, for a particular level of cigarette smoking the risk of lung cancer can be decreased by a regular intake of green leafy and yellow vegetables. The risk of cancer of the throat from cigarette smoking can be increased by regular intake of alcohol.

Pseudo-science is rife. Many people now use a scientific vocabulary to inspire confidence in what they say or write. But careful analysis often reveals that their case is phoney.

For example, you might read that 'stomach enzymes do not work on vegetables and fish at the same time and therefore these foods should not be eaten together'. Sounds scientific! How should you examine such a statement? First you might note that most people at some time combine these foods, and that doctors and government health officials now recommend consumption of these foods to promote good health and a long life. You might still want to seek more information on the suggestion that combining the foods is not a good idea. The explanation offered is inaccurate. Firstly, the stomach is only one site of digestion, and much more digestion takes place in the small intestine under the action of pancreatic secretions and other digestive enzymes. Secondly, both vegetables and fish contain different nutrient components, such as protein, carbohydrate and fat, which must be digested. We do know that some plant foods contain substances that inhibit some of the enzymes that digest proteins or carbohydrates, but this is usually not of practical importance; and, if it were, it would affect the digestion of both plant and animal-derived foods. Even if a particular food component is incompletely digested, this may not be a problem, and could even be an advantage.

Some starch, for example from cereal and bananas, is not digested in the small intestine, but is further processed by the bacteria in the large bowel, yielding gases like carbon dioxide, methane and hydrogen and other body fuels. These are used in the lining of the large bowel and are also absorbed into the bloodstream for use in the liver and other tissues. These processes may play an important role in the function of the large bowel.

To come back to the original proposition about eating fish and vegetables together, so far there is no scientific evidence that combining vegetables and fish is a risk to human health. The point of this example is that biological and especially physiological knowledge is required to evaluate nutritional claims, and not just scientific jargon. Since such basic physiological knowledge is often lacking, many interested and well meaning, even 'educated' individuals are victims of bogus nutritional claims.