Food processing and its problems
The first food processing humans did (after discovering how to make fire) was preparing and cooking food. Then they discovered that they could process food to stop it going bad - preserve it - for eating in hard times like winter or drought. Here are the main ways people preserve food:

• Drying, especially fruits (an example is grapes. They become raisins or sultanas when dry)
• Salting - meat and fish packed in layers of salt don't go bad
• Pickling in vinegar or brine (salty water) - onions, gherkins, olives, some fish
• Canning and bottling - fruits, vegetables, meats, soups
• Freezing and freeze-drying - just about everything can be preserved this way

What's the problem? Today, companies that process food in factories are mostly interested in adding value by making something that tastes good. If it doesn't, no one will buy it and they won't make any money. A single raw potato is worth almost nothing, but if you slice it thinly and fry the slices in fat, the crispy chips you get take up lots of space. So you can package them up in a fancy bag and sell them for many times the original value of the potato. And they taste good, of course! Humans love salt, sugar and fat so foods which have a lot of these are really tasty – but not too good for your health. Too much fat in your diet seems to be the cause of many diseases like cancer and heart disease. You'd be surprised to discover that savoury snacks (like chips or crisps) often contain sugar as well as salt and fat. And sweet snacks (biscuits and stuff) usually contain salt as well as sugar and fat. If you eat lots of sugary foods (including some drinks), your body changes the sugars into fat - which some people can do without.
There's another big problem too: bad food...

Why does food go bad? Processed food is easily messed up (contaminated) by microbes that cause food poisoning. You only need a few bits of bad meat to pollute the machinery that makes it into pies or something, and that would then contaminate thousands of them. Obviously manufacturers are very careful because if they poisoned their customers, they wouldn't make any money.

Poisoning their customers is exactly what tobacco companies do - only the effects take 20 or 30 years rather than a few hours in the case of food poisoning. If cigarettes gave you cancer in a few months, nobody would smoke.

The microbes that do the damage are mostly bacteria. They make poisons (toxins) in the food they affect and it is these - as well as the bacteria themselves - which can make you very ill if you eat bad food.

Microbe facts: More about these killer bugs

• more than a million people die from food poisoning each year round the world [1]
• the US Food and Drug Administration reckons that between 24 million and 81 million Americans get sick from food poisoning bugs each year - and 10,000 of them die [1]
• Campylobacter makes 2 million people sick each year in the US. This bug comes from contaminated chicken and turkey meat. Up to 80 per cent of this type of meat could be contaminated [2]
• E. coli comes from contaminated ground beef. It makes 73,000 Americans ill each year [2]
• Salmonella (this is the one everyone's heard of) kills 600 people and makes 1,400,000 people sick in the US each year. It comes in contaminated meats and eggs [2]
• Listeria food poisoning is mainly a problem with ready-to-eat foods. In the US, it kills around 500 people each year [2]

1. New Scientist, 17/12/1994, 28.
2. A Rogue's Gallery of Foodborne Illness Union of Concerned Scientists