Does intermittent fasting help your gut health?
For healthy people and people with metabolic syndrome there is reasonably consistent evidence that intermittent fasting has a beneficial effect on gut bacteria and inflammation markers. If you have a chronic bowel disease, discuss fasting with your doctor first, as evidence in that group is still lacking.
In a randomised trial involving people with metabolic syndrome, intermittent fasting increased the production of short-chain fatty acids: substances that nourish the gut lining and help suppress inflammation. At the same time, pro-inflammatory substances derived from bacteria dropped in the blood. These effects were statistically significant after 8 weeks, during which participants ate 69% fewer calories on fasting days.
The composition of gut bacteria also changes noticeably. A randomised trial showed shifts in bacterial families linked to improved metabolism. A separate study with 49 participants, without a control group, found that a 16:8 schedule (16 hours fasting, 8 hours eating) increased the amount of protective gut bacteria and gave the bacterial composition a younger structure. Because there was no control group, these findings cannot be fully attributed to the fasting.
For people with a chronic bowel disease such as Crohn's disease or ulcerative colitis the situation is different. No randomised trials using time-restricted eating or alternate-day fasting have yet been conducted in this patient group. Ramadan fasting had virtually no effect on gut inflammation in people with bowel disease. Animal research does show promising signals: a fasting-mimicking diet of 4 days low in calories reduced gut inflammation and stimulated the production of protective gut bacteria in mice. A smaller clinical study in humans also found lower systemic inflammation markers after three such cycles, but the principal investigator has a financial interest in a company that sells this diet.
Combinations of intermittent fasting with high-protein nutrition improved gut complaints more than ordinary calorie reduction in a randomised study with 41 participants over 8 weeks. That study was partly funded by a commercial party, which should be taken into account when interpreting the results.
Based on multiple randomised trials in humans, one review of 20 studies, and several smaller trials without a control group. For IBD patients, randomised evidence in humans is lacking; animal research is positive but cannot be directly translated to humans.
Does eating flaxseed help your gut?
Through its fibre and lignans, flaxseed has a plausible positive effect on the gut, but for the gut as a specific target the evidence in humans is still limited. If you want to take concrete action, opt for at least 30 grams of ground flaxseed per day.
What does fasting one day a week do to your gut microbiome?
Intermittent fasting demonstrably changes your gut microbiome, but the effects are likely temporary if you stop; for healthy people, the benefit is not yet well substantiated.
Are fermented foods and probiotics good for your gut?
Fermented foods, particularly yoghurt and kefir, show positive indications for gut health; for most other products such as kimchi and kombucha, this has not yet been demonstrated in humans.
Does eating a varied diet help your gut bacteria?
Fermented products have the strongest evidence base for increasing gut bacterial diversity. Eating broadly varied meals also helps, but above all avoid heavily processed products containing emulsifiers such as CMC.
Is intermittent fasting good for longevity?
Intermittent fasting improves health markers such as weight and insulin sensitivity, but whether it also makes you live longer has not yet been proven in humans. It is worth considering, but discuss it with your doctor first if you belong to a risk group.
What does intermittent fasting do to your insulin sensitivity?
Intermittent fasting improves insulin sensitivity in most people, but be aware of possible muscle loss and hormonal effects, especially if you combine it with intensive exercise.