Types of reactions to foods

09 June 2014

Marcia Pitman © 2014

The body has four possible reactions to substances. The first two are natural responses when the body encounters an overdose or lacks the enzymes to digest foods. In contrast, the second two – intolerance and allergy – involve abnormal responses, or hyper-sensitivity, of the immune system.

Toxic Reactions

A toxic reaction occurs when we are exposed to an acute, high dose or to cumulative low doses of a substance. The resulting toxic reactions are not pathological, but are natural responses of the body to an overdose.

Impaired Digestion

When we lack the digestive enzyme needed to break down a particular food, we will not be able to digest it properly nor absorb its nutrients. People, for example, who lack the enzyme lactase will be unable to digest lactose (the sugar in milk). In regions where milk has not historically been a common part of the diet, lactase production declines by 90 percent in the first four years of life,1 with those who can tolerate milk after that age having a genetic mutation that permits the continued production of lactase.2 Perhaps as many as onethird of those of Anglo-Celtic origin, 80 percent of American Blacks, 93 percent of Asians, and 56 percent of those from Latin America and Mediterranean countries do not produce lactase after weaning.3 Although termed ‘lactose intolerance’, it is not an immune reaction but simply an inability to metabolise milk sugars. A second common case is when individuals lack enzymes for the digestion of legumes (alfalfa, beans, peas, lentils, soy and peanuts, for example).


With an intolerance, the reaction is said to be cell-mediated because it is largely carried out by white blood cells (leucocytes) whose enzymes swallow up and destroy the antigen.4 T cells also activate what are known as macrophages and neutrophils, natural killer cells, and cytotoxic (cell-killing) substances, all of which directly attack, destroy, or ingest microbes or cellular debris. When the immune system identifies the presence of partially digested protein (peptides) in the bloodstream, it activates these responses to destroy them. This process is, of course, vital to protect the body from harmful foreign substances and to prevent the proliferation of damaged or cancerous cells. However, in this case, the body is reading benign substances as foreign and then activating an emergency response in an effort to eradicate them – that is, it is reacting adversely to substances that are normally safe.5 This is an over-reaction.


In 1906, Clemens Von Pirquet defined allergy as an acquired, specific, altered capacity of the tissues of the body to react to given substances.6 The reactions can be as harmless as a mild rash at the point of contact, or as potentially fatal as anaphylaxis, which is a systemic response, the most dangerous features of which are lowered blood pressure, breathing difficulties, shock, and loss of consciousness.7

In true allergies, reactions are antibody-mediated. That is, B cells change into plasma cells that produce proteins known as antibodies. It is these antibodies (not the B cells themselves) that attack foreign particles.8 In Western medicine’s understanding, only these reactions involving antibody responses are considered to be true allergies.9 However, one estimate is that just 10 percent of cases of hypersensitivity involve antibodies.10

Figure 1 Reactions to substances

As you can see in Figure 1, both intolerant and allergic reactions cause inflammation via the production of histamine. Histamine dilates the blood vessels so that more lymphocytes can congregate there, and to speed up the metabolism of cells.11 Too much histamine, however, results in excessive inflammation. Inflammation produces symptoms which can target any organ or system. An allergy or intolerance attacking the lungs might cause asthma; one that targets the bowel will produce abdominal bloating, diarrhoea, constipation or flatulence; one that attacks the joints will produce aching and stiffness, and so on. With cumulative assaults over time, other organ systems can become weakened. This is what causes symptoms to shift over time. For example, a baby might have eczema but develops asthma in childhood and migraines later in life. Observing that the eczema has disappeared, a parent is likely to conclude that the child ‘grew out of’ the allergy, not realising that in fact the child is still sensitised but is displaying symptoms elsewhere in the body.


Alexander, P. (1997). It could be allergy and it can be cured. (3rd ed.) Sydney: Ethicare.

Bayless, T.M., Rothfeld, B., Massa, C., Wise, L., Paige, D. & Bedine, M.S. (1975). Lactose and milk intolerance: Clinical implications. New England Journal of Medicine, 292 (22), 1156-1159.

Campbell-McBride, N. (2010). Gut and psychology syndrome. Cambridge, UK: Medinform.

Collison, D.R. & Hall, T. (1989). Why do I feel so awful? Melbourne: Angus and Robertson.

Griffiths, S. (1996). Allergy overload: Are foods and chemicals killing you? Sydney: Harper Collins.

Lebenthal, E. (1979). Lactose malabsorption and milk consumption in infants and children. American Journal of Diseases of Childhood, 131 (1), 21-23.

Mackarness, R. (1990). Not all in the mind. London: Thorsons.

St Aubyn Crump, V. (2009). Allergies: New Zealand’s growing epidemic. Auckland, NZ: David Bateman.

Tortora, G.J. & Derrickson, B. (2006). Principles of anatomy and physiology. (11th ed.) New York: Wiley.

Woteki, C.E., Weser, E., & Young, E.A. (1977). Lactose malabsorption in Mexican-American adults. The American Journal of Clinical Nutrition, 30 (4), 470-475.


  1. St Aubyn Crump 2009,: 20
  2. Lebenthal 1979: 22 & 23
  3. Bayless et al. 1975; Collison & Hall 1989: 172-173; Woteki et al. 1977
  4. Tortora & Derrickson 2006: 820
  5. Griffiths 1996: 1
  6. Mackarness 1990: 10
  7. St Aubyn Crump 2009: 47
  8. Collison & Hall 1989: 33
  9. Campbell-McBride 2010: 30
  10. Collison & Hall 1989: 42
  11. Alexander 1997: 22