It is not possible to talk about feeding or starving of fevers and colds without firstly defining what they are and what they do.
What is a fever?
The normal body temperature is not as clearly defined as we might think. The mean oral temperature of adults is 36.8ºC plus or minus 0.4ºC, but it also fluctuates in a circadian pattern as shown in Table 1.
The normal temperature also differs with place of measurement (Table 2); rectal measurement is the most accurate, but the least popular. Tympanic and/or axillary in children are generally approved methods of measurement.
Fever is a very common reason for parents to present their children to general practitioners (GPs) and emergency departments, as many believe that a fever is harmful and fear perceived consequences such as fits and serious infections.1–3
Table 1. Circadian temperature fluctuation in adults
|
|
Normal adult oral temperature range in degrees centrigrade1
|
|---|
|
Average
|
Maximum morning (6 am)
|
Maximum afternoon (4 pm)
|
|
36.8 (±0. 4)
|
37.2
|
37.7
|
Table 2. Temperature values in adults and children defined as normal and fever1
|
|
Site of
measurement
|
Normal low
|
Normal high
|
Single measure fever
|
Multiple
measures fever
|
|---|
|
Axilla
|
35.5
|
37.0
|
>37.5
|
–
|
|
Oral
|
35.6
|
37.7
|
>37.8
|
>37.2
|
|
Rectal
|
34.4
|
37.8
|
>38.0
|
>37.5
|
|
Tympanic
|
35.4
|
37.8
|
>38.0
|
–
|
|
Any
|
–
|
–
|
–
|
>1.1 over baseline
|
What is a cold?
Symptoms of a cold include runny nose, sneezing, sore throat, cough and headache. Symptoms climax on days 2–3 and last, on average, 7–10 days, but some symptoms may persist beyond 3 weeks. Many different viruses cause a cold, the most common are rhinovirus (30–50%) and corona virus (10–15%), while influenza is the third most likely (5–15%). Symptoms of cough and fever are the most predictive for influenza, but imprecise. The most common way of catching a cold is to touch secretions and auto-inoculate the virus, which is shed mostly on the second day of the illness and for up to 3 weeks after.4,5
Most upper respiratory tract infections (URTIs) in primary care are caused by ‘cold viruses’, and these often induce fever and anorexia.6-8 The febrile response to colds is greater in children than adults.9
Is fever beneficial or harmful?
Febrile convulsions occur in 2–4% of children under 5 years of age, but they are usually not associated with neurological or other problems.2 In fact, it is well established that a fever is not as predictive of serious illness as the overall clinical condition,1 which is probably why most GPs use other parameters to guide their judgement on the severity of an illness.
Fever generally enhances the activity of the immune system. The majority of evidence suggests that fever associated with infection is beneficial to survival.10
The impact of feeding and starving on fever and immune response
Hippocrates used starvation to treat fever, a method which persisted until the early nineteenth century when Dr Robert Graves revolutionised common practice from ‘starve a fever’ to ‘feed a fever’.11,12
This was probably in recognition of the hugely increased metabolic demands of fever, namely a 10% increase in metabolic rate for every 1ºC increase in temperature.10 Clearly there is a need for food to sustain energy and retain body mass.
Starvation (long-term caloric restriction) lowers core body temperature and gut induced vagal stimulation, which promotes immunity towards bacteria but not viruses. Fasting and dehydration increase the immunity against bacterial infections (extracellular antibody mediated) and reduce the antiviral immune response (intracellular). Thus, the anorexic response to URTIs is not a helpful one, as invariably in the community setting most URTIs and most fevers are of a viral aetiology.6,7,13
In summary, feeding changes immune responses by promoting interferon production (augmenting intracellular immunity), which mostly fights viral infections, the most common cause of fever in the primary care setting. However starvation biases the immune response towards bacterial infections, a far less likely cause of infection.
The impact of feeding and starving on a cold
Despite searching widely on feeding and starving colds, evidence is sparse. A Cochrane review cautions on potential harm from excess fluids.14 Another randomised study found no effect from feeding a milk-rich diet to people with colds on severity of illness or other features such as mucous and cough.15 A recent extensive review of cold treatments stated that evidence about preventing and treating the common cold is frequently of poor quality, and results are inconsistent.9 No study came closer to these on aspects of feeding or starving colds.
Feeding fever with medications: Is treating fever beneficial?
If fever enhances survival then it should be no surprise to discover that treatments that cool are not associated with improved survival, and may even increase mortality in some settings.16
Common justifications for treating fever are to prevent seizures and provide comfort. However feeding febrile children antipyretics (paracetamol, aspirin or ibuprofen) does not prevent seizures. More so, antipyretic use has been shown to increase the spread of infection and prolong influenza, chicken pox and common colds.2,17,18
Uncomplicated fever may be best left untreated, but analgesia will relieve aches and pains, which may create more benefit.
Conclusion
It would seem that feeding (while avoiding excess use of fluids) is the best option, most of the time, for improved outcomes. Feeding patients analgesic antipyretics routinely is not supported by evidence, nor is the use of starvation in the management of fevers or colds. Common sense and clinical judgement should continue to guide management.
Competing interests: Jane Smith is paid as a board member of the Therapeutic Goods Administration’s Advisory Committee on the Safety of Medicines, Australian Medicines Handbook.
Provenance and peer review: Commissioned, externally peer reviewed.