What is food allergy, and what is food intolerance? How do the two differ? The best way to answer this question is to tell the stories of Jane and Susan.

Jane's Story

Jane's health problems began as a baby. She had colic and vomited often, and at the age of three months developed eczema on her face and arms. Her mother had hay fever every summer, and her father had suffered from asthma as a child — both complaints are common allergies. Even before Jane was born, their family dr was well aware that they were an atopic family — in other words, they were prone to allergies. As Jane grew older she developed asthma and hay fever, although only mildly. Her asthma seemed to get worse when there was a cat in the room. Using extracts of grass pollen and cat dander, and inserting minute amounts of them under her skin (a skin-prick test), the dr found that she was indeed allergic to both these substances — her arm had a red, itchy bump where the extract had entered the skin.

Once or twice during her early years Jane's mouth and tongue swelled up enormously after eating, and she had to be rushed to the hospital. After thinking carefully about what she had eaten on these occasions, Jane's mother concluded that it was peanuts that had caused this alarming reaction. The dr used skin-prick tests again, and they confirmed that Jane had a food allergy — she was extremely sensitive to peanuts. Other skin-prick tests were negative, so it seemed that she could eat most foods safely.

Even though Jane avoided peanuts carefully from then on, there were occasional problems. One day when Jane was about eight and her parents were holding a party, she handed a bowl of nuts around to the guests. Later she rubbed her eyelids, and they soon began to swell and itch furiously. Although her hay fever and asthma subsided as Jane grew older, her sensitivity to peanuts remained the same.

As an adult, Jane had a successful career that involved a great deal of traveling and eating out. Wherever she ate she had to be careful to avoid anything with peanuts — even the slightest trace of them. All was well until Jane, by now in her thirties, ordered some cheesecake in a restaurant. She had asked the waiter if the brown powder on the surface of the cheesecake contained any nuts, and he assured her that it was pure chocolate. Usually it was—but the chef had run out of chocolate that day and been forced to use something else. Unfortunately for Jane, that something else was finely grated nuts, including some peanuts.

Within seconds of taking her first mouthful of cheesecake, Jane's mouth was itching. Her tongue began to swell, and her breathing became difficult. She could no longer speak, and, as the swelling blocked her windpipe, she began to turn blue. Within minutes she had collapsed on the floor.

The colleagues she was dining with were horrified and had no idea what to do, but a stranger at the next table intervened. By an extraordinary, and lucky, chance, he was a dr. Grabbing a spoon from the table, he pushed the handle over the back other tongue and managed to open up the blocked windpipe. As he did so Jane gradually turned from blue to pink, but she was still in a state of collapse (known as anaphylactic shock), and her face was still horribly swollen. Meanwhile, someone had telephoned the hospital, and another dr arrived with the life-saving medicines that Jane needed. When these were injected, she slowly regained consciousness.

Thereafter, Jane was even more careful about avoiding peanuts in her food. She realized that she could easily have died had it not been for the presence of a dr. By scrupulously avoiding peanuts, though, she has remained well. She also carries an emergency kit with a syringe of epinephrine that can be used to treat such attacks should she ever eat peanut by accident again.

Susan's Story

Susan is about the same age as Jane. She was reasonably well as a child, apart from frequent colds and chest infections. At the age of twenty-one, however, she suffered a bad bout of diarrhea when traveling abroad. Although she recovered from this, her bowels never really returned to normal: A mild form of diarrhea stayed with her so that she needed to go several times a day, often at the most inconvenient moment. As the years passed this problem gradually worsened, and unpleasant pains began in the lower part of her stomach. When she finally consulted her dr about this problem, she was told that it was irritable bowel syndrome, or IBS, and that she should try to relax more.

For many years Susan also suffered headaches, but thought little of them — she simply took aspirin when she felt one coming on. One day, just after her twenty-eighth birthday, she experienced a strange sort of headache that was on the left side of her head only. She took some aspirin, but the pain did not go away — indeed, it became more intense, and she began to feel slightly sick. Eventually she had to draw the curtains and go to bed because she could not bear the light. There were more of these attacks over the next few months and Susan went to see her dr again. He told her that these were migraines, and again recommended that she should try to worry less and learn to relax. Although she followed his suggestions, the migraines continued, and so did her bowel problems.

Over the next few years Susan had to give up alcohol and chocolate, as these always seemed to bring the migraine attacks on. But despite avoiding these items, her migraines continued to become more frequent. She also felt excessively tired, especially first thing in the morning, and she sometimes felt lightheaded and confused, or very edgy and irritable. To add to these problems, she began to get odd little pains in her knees. These gradually grew worse, and by the time she was thirty-four she could no longer run up the stairs without pain; she was forced to give up jogging and riding a bicycle, too, because these activities made her knees so much worse. The pains spread to some of her other joints and she began to feel that there was something seriously wrong, because she was ill most of the time.

Susan had previously accepted her dr's diagnosis that most of her problems were due to her "nerves," but at this point she began to have doubts. She was now married, and had a good job that she enjoyed. Apart from her health problems she had few worries — indeed she felt more settled and happy than at any time in her life — so why was her health getting worse instead of better? She went to see her dr again, and he gave her a thorough examination but could find nothing wrong. He repeated his earlier diagnosis, and suggested that her joint pains were also psychosomatic.

A few months later Susan read a magazine article about something called "food allergy," which seemed to cause the sort of symptoms she had. She asked her dr's opinion about this and found he was very dismissive of the idea — as far as he could see, her symptoms were nothing like those of food allergy. Another year went past, in which Susan became steadily worse. Then a new dr joined the practice, and when she next called for an appointment, it was suggested that she see him instead, as he had a special interest in patients like herself. When Susan went to see the new dr, he explained that symptoms such as hers could sometimes be caused by food, although there were other potential causes as well. He went on to explain why his colleague had dismissed the idea other having food allergy — the condition he treated was quite different, and he preferred to use the name food intolerance. While he could not guarantee that this was her problem, it was certainly a possibility. He suggested that she try a special diet that avoided all the foods she normally ate. Susan began the diet on a Monday with high hopes, but by Tuesday she felt very ill indeed. Her tiredness was far worse, and she experienced a severe migraine attack — the worst one she had ever suffered — that lasted through Wednesday as well. On Thursday she felt completely washed out from the migraine, and Friday was little better. In desperation, she rang the dr, but he told her that this sort of reaction often occurred — in fact it was a positive sign that foods were the source of the problem, so she should persevere with the diet.

On Saturday Susan woke up quite early, before her alarm clock went off — which was most unusual, because she normally had great difficulty waking up. As she got out of bed, she noticed that her knees did not give their customary painful twinge. She tried walking downstairs and then running up them again. To her amazement, she found that the pains she had endured for two years had suddenly vanished.

As the day went on she realized that she felt altogether different — she was no longer tired, her head felt clearer, and there was no headache or migraine, unlike most weekends. Indeed, she felt better than she had for many years. Over the next few days it became obvious that her bowels were also a great deal better. When she returned to the dr, Susan was jubilant — she simply couldn't believe how much better she felt. Even her irritability, which she had thought was just part of her personality, had now vanished. The dr explained that she must now reintroduce foods, one at a time, to see what effect they had. Over the next two months, she tried out all the foods she normally ate. Some of these had no effect, but others made her very ill — milk, wheat, rye, barley, yeast, oranges, lemons, beef, and tomatoes were the main culprits. By avoiding all these foods, and adding some other, more unusual foods into her diet instead, Susan remained well. Migraines, which had previously afflicted her once or twice a week, were now a thing of the past.

After eight months, the dr suggested that she try out some of the incriminated foods, to see what effect they had. She found that she still reacted to milk, but was fine on the other foods. The dr advised her not to eat them more than once every four days. A year later Susan discovered that she could now drink milk again without ill effects. Interestingly, she discovered that she could also drink alcohol, in moderation, and cat chocolate, as they no longer seemed to trigger migraines. By this stage she had begun to forget what a migraine felt like!

Allergy and Intolerance

Both Jane and Susan were clearly being made ill by the food they ate. But their symptoms were very different — and so was the treatment they received from the medical profession. Food allergy — which caused Jane's dramatic illness — is a recognized complaint whose underlying mechanism is fairly well understood. Food intolerance, on the other hand, is not regarded as a sound diagnosis by the majority of drs. Most would agree that there is such a thing as food intolerance (although they might use a different name for it), but they would argue that it affects relatively few people. Like Susan's dr, they would regard the majority of patients with vague, multiple symptoms, including headache or migraine, fatigue, and diarrhea, as suffering from emotional and mental problems that express themselves in ill health.

This book deals with both food allergy (Jane's problem) and food intolerance (Susan's problem), but it concentrates most attention on food intolerance, since this is the area that has been sadly neglected by conventional medicine. (The reasons for this neglect, and for the continuing controversy over food intolerance, will be examined later, in chapter 6.)

Food Intolerance

Jane could fairly be described as a typical case of food allergy. But Susan is not a typical case of food intolerance, because there is no such thing. Food Intolerance cannot lay claim to any single set of symptoms. Every patient is different, both in the cluster of symptoms displayed and in the foods that cause these symptoms. Nor is there a single, clear-cut mechanism underlying the symptoms, as there is with food allergy. The available evidence indicates that there may be half a dozen or more different factors that contribute to the illness. In other words, food intolerance is a complex subject, and few generalizations can be made.

Nevertheless, there are certain features that characterize this type of food sensitivity and distinguish it from food allergy. Whereas food-allergy reactions are usually immediate, food-intolerance reactions tend to be much slower. The culprits in food intolerance are foods that are eaten very regularly, especially items such as wheat and milk that are consumed at almost every meal. The slowness of the reaction, combined with the fact that the foods are eaten so often, contributes to the masking effect observed by the first drs to study these reactions—the link between food and symptoms is unlikely to be made when the body is subjected to a constant bombardment with the food.

Whereas food-allergy reactions can be provoked by quite small amounts of the food — a smear of the food from a badly washed saucepan for some highly allergic individuals — much larger quantities are needed to provoke the symptoms of food intolerance. Food intolerance is also far more insidious than food allergy: it is often difficult to say when it began, because the symptoms are very mild at first but gradually get worse. There are exceptions to this rule however, for in some cases a bad bout of influenza or diarrhea can spark food intolerance. As in Susan's case, those with food intolerance tend to collect more and more new symptoms as the years go by, and become intolerant of more and more foods.

Food allergy — at least in adults and older children — usually persists for many years, often for a lifetime, even though the food is scrupulously avoided. Food intolerance, on the other hand, may well disappear if the food is not eaten for a few months. But it will tend to recur if the food is ever eaten regularly again.

The symptoms of food intolerance are extraordinarily varied and affect almost every body system. The illustration above summarizes the major symptoms that are generally agreed upon. Most drs working in this field would probably wish to add various other symptoms to this list, and there is intense debate over symptoms that might or might not be attributed to food. Some of these controversial areas are considered in chapter 7, where the symptoms of food intolerance are described in more detail.

An important aspect of food intolerance is that the symptoms are not constant — they tend to come and go and to vary in severity. Nonfood factors may play an important part, particularly stress, which can greatly exacerbate the symptoms. One of the most curious facets of food intolerance is that the person concerned often has a craving for the particular food or foods that cause the problem. In such cases — which account for as many as 50 percent of food-intolerant patients — eating the food initially gives a sense of great well-being. A possible explanation for this bizarre feature of the disease has now been discovered and is described in chapter 12.

Food for Thought

All of us, patients and drs alike, are conditioned to think about food and other aspects of our environment in a particular way. As civilized inhabitants of temperate climes, we can indulge in the luxury of regarding nature as safe and welcoming, and of thinking of food as entirely wholesome and beneficial. These attitudes are part of our culture, another luxury that we simply take for granted, such as armchairs or automobiles. If we are to understand food intolerance, some of these accepted ideas need to be challenged.

Much of the medical prejudice against food intolerance is rooted in the idea that food — as long as it is part of a balanced diet — cannot be bad for you. What is often forgotten is that our foods were not designed specifically for human consumption, but were drawn from a pool of wild plants and animals that were domesticated by the first farmers. In the wild, most food items are reluctant food items. They do not want to be eaten, and their efforts to stay off the menu are part of what Charles Darwin called the "struggle for existence." Most animals can run away, or fight back, but plants do not have this option.

Their defense is based partly on thorns and prickles, but far more important than these is the array of invisible chemical weapons that pervade almost all plant tissues. Some of these simply taste bad; others cause vomiting or other ill effects. A few even mimic the hormones of insects or mammals and thus disrupt their growth or sexual development.

Plant-eating animals have, in the course of their evolution, simply adapted to these chemicals in their food. They can detoxify them sufficiently to be able to feed on their chosen food or foods, and the plants can ward them off sufficiently to stay alive. It is rather like the situation between criminals and the police, where each side becomes increasingly cunning, better armed, and more ruthless, but neither side ever wins and obliterates the other. The term biological arms race aptly describes this situation.