Diet and Fever: What to Eat?

Fever and hyperpyrexia

Fever and hyperthermia represent two different pathological mechanisms, but they both generate pyrexia, a NOT physiological condition characterized by "abnormal increase in body temperature".

Both fever and hyperthermia cause the body to overheat, but through two totally different pathogenetic mechanisms:

  • Fever is triggered by chemical damage by cytokines (chemical mediators) on the hypothalamic central regulation "thermostat", which in turn generates excessive heating;
  • Hyperthermia is generated by the imbalance between thermogenesis (production of body heat) or external heating (such as solar radiation) and the thermal dispersion system (cutaneous vasodilation, sweating, etc.) which results in a progressive accumulation of heat.


From the above, it can be deduced that the therapeutic approach between the two forms of pyrexia is completely different; in hyperthermia it is essential to rapidly cool the body (for example with cold water) while in fever, antipyretic drugs are useful, which act by restoring the hypothalamic "set-point" (but also in this case the usefulness of cooling by conduction is not excluded , for example by sponging with cold water).

Classification Body temperature
Febrile sub 37,0-37,3 °C (77°F)
Fever 37,4-37,6 °C (77°F)
Moderate fever 37,7-38,9 °C (77°F)
High fever 39,0-39,9 °C (77°F)
Iperpiressia > 40 ° C

Note: treating fever and reducing pyrexia do not always follow the same therapeutic process; in case of temperature alteration it is first of all fundamental to identify (if possible) the etiopathological agent (ie the cause: inflammation, viral infection, burn etc.) responsible for the body alteration, then eliminate it. The use of antipyretic drugs (such as paracetamol) is useful for reducing the pyretic symptoms of fever but is NOT an effective cure. Obviously, if it is not possible or indispensable to intervene on the primary cause of the fever, antipyretics represent the only applicable pharmacological intervention.

Diet for Fever

Fever is an ACTIVE process that deliberately seeks an increase in body temperature; this condition is metabolically essential to accelerate the enzymatic processes of the whole organism, in order to optimize the immune reaction and speed up healing. For this reason it is essential to reduce the fever only if it exceeds the tolerance limit of the subject.
From the metabolic point of view, fever significantly increases the energy expenditure measurable through the consumption of basal oxygen; the estimates made on the general population indicate that for each degree centigrade (° C) above 37, the organism needs 13% more oxygen to meet the requirements of all physiological and para-physiological processes. This means that, with the same amount of energy introduced with the diet, fever (by increasing the oxidative energy processes) can favor the reduction of the reserve energy substrates (fat and glycogen), consequently also decreasing body weight; having said that, it might seem obvious that in the presence of fever it is essential to modify the diet by increasing the energy intake to cover the minimum requirement for maintaining body weight; eg:

Assuming that the subject "X" normally has an energy expenditure of 2000kcal, in the event of a fever at 39 ° C (2 ° C above the threshold of 37 ° C) he would need a caloric surplus of 26% (13% multiplied by the 2 ° C), or 520kcal. On balance, subject "X" should correct their diet by increasing caloric intake as follows:

  • 2000kcal + 520kcal = 2520kcal

NB. It is advisable to maintain a normal protein intake and proportionally increase both lipids and carbohydrates.

In the event that the subject "X" maintains an energy intake of 2000kcal and the fever at 39 ° C is constant for 14 days, the algebraic sum between the calories introduced with the diet and the calories burned in the presence of fever would be NEGATIVE, giving rise to weight loss:

  • [(2000*14)-(2520*14)]=(28000-35280)= -7280kcal

Furthermore, knowing that PHYSIOLOGICALLY to eliminate 1 kg of fat it is necessary to burn about 7000kcal, it is possible to state that the subject "x", during 14 days of fever at 39 ° C in which he did NOT follow an adequate diet, could suffer a weight loss about 1kg.

Obviously, this example DOES NOT take into account the presence of many variables (FOR EXAMPLE THE REDUCTION OF THE PHYSICAL ACTIVITY LEVEL) that contribute to determining the final energy balance, therefore it must be considered as an absolute SIMPLIFICATION.
NB. If the reader is seduced by the possibility of facilitating weight loss NOT by treating fever or the causative agent that generates it, we remind you that the increase in expenditure associated with bed rest or immobilization of the patient determines a NON-selective weight loss that negatively affects both on the trophism of muscle mass and on the consistency of hepatic and muscle glycogen reserves.


To get a more realistic picture of the metabolic impact of fever on the body, the following key points should also be considered:

  1. Dehydration: fever generates an increase in body temperature which often requires greater heat dispersion, therefore leads to an increase in sweating; therefore, if the diet does not contain sufficient water, the reduction in body weight could indicate more general dehydration than a depletion of energy reserves. It follows that the diet for fever MUST first of all guarantee the basal water requirement, compensate for sweating and facilitate the renal drainage of any pharmacological catabolites
  2. The increase in basic energy expenditure is compensated by the subject's physical INACTIVITY: it is advisable to consider that (usually) the fever does NOT allow the carrying out of common work, recreational and sports activities; considering that the energy expenditure of a person still in bed is almost comparable to his basal metabolic rate (MB) while the Physical Activity Level (LAF) fluctuates between + 33% and 110% more than the same basal metabolism, it is possible affirm that normally the fever diet of a BED OR SICK SUBJECT should provide a LOWER quantity of energy than that normally introduced with diet DESPITE the fever generates a basal increase of 13% every 1 ° C. Eg, for subject "Y" who has a basal metabolic rate of 1300kcal and a Physical Activity Level that increases energy expenditure by 55%, FOR A TOTAL OF 2015KCAL, stay in bed with a fever of 2 ° C (+ 26% of calories) it would mean having a total expenditure of 1638kcal… WELL 377kcal less than normal!
  3. Vomiting and malabsorption linked to the morbid condition: in the event that the causative agent is a pathogen (virus, bacteria, protozoa or other parasites), or an intoxication from ethyl alcohol or other nerves, and the fever is accompanied by vomiting and diarrhea, the diet must undergo modifications drastic. First of all, remember that vomiting and diarrhea cause accelerated dehydration, therefore, the reduction in body weight is mainly related to the volume deficit (volume) of the blood plasma; secondly, the inability to retain food in the stomach or the decrease in intestinal absorption reduce (sometimes severely) the amount of energy and essential elements introduced by the diet. Therefore, in addition to a state of transient general malnutrition, there is a degradation of the reserve energy substrates as well as of muscle tissue (favored by the immobility of the patient) found in indiscriminate weight loss (both lean and fat mass). In this case, the fever diet should favor the gastric passage without inducing vomiting and prepare for proper digestion and absorption; in this regard, it is very useful to make use of moderately protein foods with a higher content of carbohydrates and vegetable oils (semolina enriched with pureed legumes and seasoned with extra virgin olive oil and a little grated cheese), easily digestible (simple and not prolonged cooking) , favor semi-liquid foods (NOT totally liquid, because the digestive tract can react to the sense of fullness with the urge to vomit), with moderate and rather frequent portions; furthermore, it would be better to AVOID foods that contain nutrients that are difficult to tolerate such as lactose.
  4. Transient anorexia: from a behavioral point of view, patients suffering from fever do not feel the need (or the physiological stimulus) to eat and drink. If the fever diet is not drawn up and followed carefully, in addition to the risk of malnutrition, by reducing the water supply, both the potential for heat dispersion and the renal filtration capacity are worsened; with regard to the latter, on the contrary, it should be encouraged thus facilitating the elimination of endogenous and pharmacological catabolites.

The diet in fever must take into account all these factors in order to optimize the healing process and avoid any secondary effects related to malnutrition; it is advisable to pay particular attention to the water, saline and vitamin intake but not to neglect (if possible) also the intake of foods containing the other essential molecules (omega 3 fatty acids and amino acids deriving from proteins of high biological value).

Practical Tips

  • In the presence of fever, especially if associated with vomiting and / or diarrhea, the first concern is to ensure proper hydration. Generally, in adults, water - drunk in small and frequent sips - is sufficient, while in children specific rehydrating formulations are recommended (eg Pedialyte). In case of prolonged fasting it is possible to resort to special rehydrating and alkalizing formulations, based on sodium and / or potassium citrate (eg bioketase). In case of prolonged vomiting, rehydration can also take place intravenously.
  • In case of nausea and vomiting, solid oral feeding should be gradually restored as soon as possible, and pursued according to the patient's tolerability: water and rehydrating liquids → fruit jams and jellies → vegetable puree → pasta or rice in broth → meat veal, chicken and fish, possibly minced to make it more digestible
  •  Associated with rest, the diet must be light, therefore containing easily digestible foods without cooking fats. The lipids will be limited to adding raw oil and butter as a condiment to the dishes.
  • The fever diet favors lean carbohydrates and proteins. The carbohydrates, easy to digest, allow to save muscle proteins from the catabolic phenomena induced by calorie and carbohydrate depletion; moreover, they allow to avoid the ketosis due to the hyperactivation of the lipid metabolism, typical of the conditions of prolonged fasting.
  • Semi-skimmed milk, recommended by some doctors in the presence of fever, should be avoided by lactose intolerant individuals. The text "Terapia medica reasoned" by Aldo Zangara suggests that "the nutrition of the patient with a febrile infectious disease is initially based on the consumption of milk - which is introduced as the main food in the average quantity of one and a half liters per day (950 KCal and 46g of protein) - eggs, homogenized meat dissolved in soups, pasta, rice, semolina, biscuits, white bread, mashed and sweetened cooked fruit, drinks, etc. (meat broths have low caloric value). " Protein sources richer in fat and connective tissue (e.g. muscle bundles, rinds, bones) should therefore be avoided, preferring softer cuts that are easier to digest.
  • The diet for fever involves the consumption of numerous small rations, to avoid excessive burdening of the digestive functions.
  • Particular warnings in certain situations naturally require that the last word, on the adequacy of a particular diet in case of fever, belongs to the doctor; eg:
    • in case of prolonged therapy with corticosteroids it is necessary to limit the sodium intake with the diet and increase that of potassium, since these drugs determine sodium retention and increase the excretion of potassium
    • in case of fever associated with diarrhea, dairy products and sugary foods (sweets, jams) should be avoided, as they could aggravate the condition due to osmotic reasons. Among the fruit juices - foods notoriously useful for the hydrosaline and vitamin rebalancing - those without added sugars, or better still those prepared at home, will be preferred, given that sweeteners with a marked laxative effect are sometimes added instead of sugar in industrial products (for example for example polyols: sorbitol, mannitol, xylitol and others).
    • dairy products must be taken at least 3-4 hours after the oral administration of tetracyclines, as they could inactivate the drug by precipitation in the intestine
    • in case of fever associated with severe hepatitis, the diet should be low protein


  • Treatise on clinical and surgical therapy. Volume 1 - - Piccin - page 54:57
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