Does fasting reset your immune system?
Fasting lowers inflammatory markers and has measurable effects on the gut microbiome that appear to be beneficial for the immune system. For healthy people who want to address low-grade inflammation, time-restricted eating is a practical starting point.
Fasting demonstrably lowers inflammatory markers in the blood, such as the protein CRP. This effect has been found in healthy people who practised time-restricted eating or alternate-day fasting. Notably, the effect on metabolic inflammation sometimes occurs even without weight loss, through interaction between the liver, adipose tissue, muscles and immune cells. This suggests that fasting itself makes the difference, not just weight loss.
The link with the gut microbiome is interesting. Time-restricted eating improves the composition of gut bacteria and the functioning of circadian clock genes, the genes that regulate the day-night rhythm in cells. Researchers believe this is an important mechanism through which fasting ultimately influences the immune system.
In autoimmune diseases, the evidence is still preliminary. In conditions such as rheumatoid arthritis and lupus, disease activity sometimes decreases, but for conditions such as MS, thyroid diseases and psoriasis the results are contradictory and long-term guidelines are lacking. In mouse studies, fasting improved the course of an MS model. A small pilot study in MS patients saw similar shifts in gut microbiome composition and blood values, but it involved only a handful of people, so that does not yet constitute proof.
There is also research into a fasting-mimicking diet for intestinal inflammation (IBD). In mice with colitis it restored the intestinal wall; in a small human study, inflammatory markers decreased. Note: the lead researcher has a financial interest in a company that sells this diet, which puts the results in a different light. Complete water fasting also improved those markers, but did not reverse tissue damage.
Whether fasting slows the long-term ageing of the immune system remains unclear. The indications exist, but the evidence is too thin to draw conclusions from. The combination of fasting and chemotherapy showed more attacking T cells in tumours in mouse studies, but whether this works in humans has not been investigated.
This answer draws on several review studies and a number of smaller human studies, including one small randomised study in MS patients. The evidence for lowering inflammatory markers in healthy people is reasonably consistent. For autoimmune diseases, IBD and cancer, the findings largely come from animal research or very small human studies, in which cause and effect have rarely been firmly established. The researchers themselves emphasise that long-term human data are lacking for most applications.
How does nutrition strengthen your immune system?
Nutrition has a clear influence on the immune system: deficiencies weaken your defences, and correcting a demonstrable deficiency (especially of vitamin D, C and zinc) helps. In people without a deficiency, the case for extra supplementation is less convincingly proven.
Can you slow down the ageing of your immune system?
The immune system demonstrably ages, and there are promising avenues for slowing that process, but no single approach has been proven safe and effective in humans. Eating less processed food is the only step you can concretely take right now; everything else requires more research in humans before any conclusions can be drawn.
Can you strengthen your immune system by eating more fibre?
Eating more fibre has a clear biological mechanism, but in healthy people it does not automatically lead to a measurably stronger immune system. Fermented foods appear to work more reliably for your gut flora; probiotic supplements are even risky in the context of immunotherapy.
Can you test your immune system with a blood test?
A blood test can partially map the immune system, but the results are only meaningful when a doctor interprets them in the context of your health and medication use.
Does fasting help your cells clean themselves up?
Some forms of fasting clearly set the self-cleaning process of cells in motion in people. A time-window eating schedule or a multi-day period of substantial calorie restriction has the most support for achieving this.
Can fasting really rejuvenate your cells?
Animal studies show convincing signs of cellular rejuvenation through fasting, and the first studies in people point in the same direction.