When you're ill, your appetite often disappears. That's partly the immune system redirecting energy and partly the effects of cytokines on appetite-regulating brain circuits. Most of the time, this is fine short-term.
But some foods genuinely support immune function and recovery. And some do the opposite. Here's what the evidence says.
Hydration: Non-Negotiable First Priority
Before food: fluids. Dehydration impairs virtually every immune function. It thickens mucus (making it harder to clear pathogens), reduces circulation of immune cells, and worsens fever's already-dehydrating effects.
Water, herbal teas, warm broth, and diluted juice all count. Aim to drink consistently even without thirst - the thirst mechanism is suppressed by fever in some people.
Hot drinks specifically have evidence beyond just hydration. A 2008 study at Cardiff University tested hot drinks vs. the same drinks at room temperature in cold and flu patients. Hot drinks produced significantly better symptom relief for runny nose, cough, sneezing, sore throat, and tiredness - through a combination of steam inhalation, soothing mucous membrane effects, and psychophysiological relief. It's a real effect.
Chicken Soup: Actually Evidence-Based
This isn't folk medicine. It has genuine scientific support.
A 1993 study by pulmonologist Dr Stephen Rennard (University of Nebraska) tested multiple chicken soup recipes and found they inhibited neutrophil migration - which is the mechanism behind the inflammation-driven symptoms of upper respiratory infections. The broth, vegetables, and chicken combination all contributed; the effect wasn't from any single ingredient.
The mechanisms: warm broth keeps mucous membranes moist, promotes fluid intake, provides electrolytes (sodium supports fluid absorption), and the vegetables provide anti-inflammatory compounds. A 2000 follow-up study confirmed the anti-inflammatory effects in in-vitro testing.
Practically: homemade or good-quality store-bought chicken soup with vegetables. The evidence is for the full soup, not just plain broth.
Zinc-Rich Foods: Critical for Immune Cell Function
Zinc is one of the better-evidenced nutrients for immune function. It's required for the development and activation of T-cells (the lymphocytes that directly attack infected cells and coordinate the adaptive immune response). Zinc deficiency significantly impairs immune function.
A 2013 Cochrane review found that zinc supplementation within 24 hours of cold symptom onset reduced the duration of the common cold by roughly one day on average. The effect is most reliable for zinc lozenges (which allow zinc to reach the upper respiratory tract directly) rather than oral tablets alone.
Food sources of zinc:
- Oysters - highest zinc density of any food (~74mg per 100g)
- Beef and lamb - good zinc sources
- Pumpkin seeds - reasonable plant-based zinc
- Chickpeas and lentils - moderate zinc (with lower bioavailability than meat)
Note: plant-based zinc is less bioavailable than animal sources due to phytates binding zinc in plants. Vegetarians and vegans benefit from soaking or sprouting legumes to reduce phytate content.
Garlic: The Most Evidence-Based Food for Cold Prevention
Garlic's active compound allicin has been studied specifically for immune effects. The best clinical evidence comes from cold prevention rather than treatment.
A 2001 RCT in Advances in Therapy gave 146 volunteers either garlic extract or placebo for 12 weeks through winter. The garlic group had 63% fewer colds. Garlic-takers who did get a cold recovered significantly faster (average 1.52 days vs 5.01 days).
A 2014 Cochrane review found insufficient evidence to draw strong conclusions about garlic for established cold treatment (mainly due to insufficient trials) but noted the 2001 trial's findings as promising.
The practical recommendation: add garlic liberally to soup and food when sick. Crush or chop and let it sit for 5-10 minutes before cooking - this allows allicin formation, which is then heat-stable for light cooking.
Ginger
Ginger has direct antiviral properties in laboratory studies and anti-inflammatory effects in human research. A 2013 study in the Journal of Ethnopharmacology found fresh ginger (not dried) inhibited human respiratory syncytial virus (HRSV) attachment to respiratory cells in vitro - a mechanism that could reduce how severe a respiratory infection becomes.
For nausea specifically (common with stomach bugs and some fevers), ginger is one of the most evidence-based natural interventions - significantly better than placebo in multiple RCTs.
Practical use: fresh ginger tea (steeped slices in hot water), added to soups, or mixed with honey and lemon. The fresh form has better antiviral evidence than dried.
Honey: The Best Evidence for Sore Throats
Honey has antimicrobial properties (it's low pH, high osmolarity, and contains hydrogen peroxide) and is a well-evidenced sore throat remedy.
A 2012 Cochrane review and subsequent guidelines now recommend honey as the first-line treatment for acute cough in children over 1 year (under 1 year, it's contraindicated due to botulism risk). It outperformed diphenhydramine (an antihistamine) and placebo for cough frequency and severity in multiple trials.
A teaspoon of honey in warm water or tea, or taken directly, before bed is the most evidence-based home remedy for night-time cough and sore throat.
Foods Rich in Vitamin C
Vitamin C's role in preventing or treating colds has been oversold. A 2013 Cochrane review found that regular vitamin C supplementation (200mg+ daily) did not prevent colds in the general population - but did modestly reduce cold duration by ~8-14% and severity.
However, vitamin C is essential for neutrophil and lymphocyte function, and deficiency significantly impairs immune response. Ensuring adequate vitamin C through food during illness is sensible.
Best sources: red and yellow bell peppers (highest vitamin C density - more than citrus), kiwi, strawberries, broccoli, citrus fruit.
Fermented Foods and Gut Microbiome Health
70% of the immune system is in the gut. Gut-associated lymphoid tissue (GALT) coordinates much of the immune response to pathogens. The gut microbiome directly trains and regulates this immune tissue.
Maintaining fermented food intake when sick (yogurt, kefir) supports the gut microbiome's contribution to immunity. A 2021 meta-analysis found probiotic supplementation reduced the incidence and duration of upper respiratory tract infections by about 25% and 1-1.5 days respectively in multiple RCTs.
You may not feel like eating much fermented food when sick, but plain yogurt is one of the more appetising options for someone with low appetite.
What to Avoid When Sick
Alcohol: Directly suppresses the immune system - reduces white blood cell proliferation, impairs macrophage function, and compromises the gut barrier. Even moderate alcohol impairs immune recovery. Avoid for the duration of an illness.
Excess sugar: Elevated blood glucose transiently reduces neutrophil activity. A 1973 study found that consuming 100g of glucose significantly reduced neutrophil phagocytosis (the immune cells' ability to engulf and destroy bacteria) for up to 5 hours. A glass of orange juice won't meaningfully impair immunity, but a diet high in added sugar over the course of an illness isn't helping.
Ultra-processed food: Low nutrient density when the body needs micronutrients for immune function, and can disrupt the gut microbiome at a time when gut immunity matters.
Not eating at all: Loss of appetite when sick is normal but going too long without calories impairs immune function - the immune system is metabolically expensive and requires energy. Small, nutrient-dense meals are better than nothing. Easily digested options: rice with broth, scrambled eggs, plain yogurt, banana.
The Inflammation Context
What happens when you're sick is fundamentally an inflammatory process - the immune system releasing cytokines, increasing blood flow, raising temperature. The anti-inflammatory foods that support long-term immune health are also beneficial acutely. The difference is that acute inflammation during illness is necessary and therapeutic - you don't want to suppress it entirely.
The goal with food during illness isn't to suppress the immune response but to support it running efficiently.