Intermittent Fasting, Inflammation and the Mediterranean Diet

A randomized controlled trial published online on 21 October 2026 in Cell Metabolism asked a question that is usually left blurry: when a healthy diet lowers inflammation, is it the food or the weight loss? In this study, eight weeks of a fully provided Mediterranean diet did not change the inflammation marker C-reactive protein. The marker fell only after two fasting days a week were added, alongside greater weight loss.

The authors' conclusion is in the title of their paper: weight loss during intermittent fasting, not Mediterranean diet quality alone, is associated with lower inflammation.

The question behind the study

The Mediterranean diet is often credited with anti-inflammatory effects. The trouble is that people who switch to it frequently lose weight as well, and losing weight is itself linked with lower inflammation. If both change together, you cannot tell which one did the work.

This trial pulled them apart by running in two phases. First, change the diet and nothing else. Then keep the diet and add fasting days.

What the study did

The work was led from the University of Sydney, with collaborators including Washington University in St. Louis.

Who	53 adults with metabolic risk factors, 77% female, mean age 54.7 years
How long	16 weeks in total
Weeks 1 to 8	A fully provided Mediterranean diet, or the participants' habitual western diet as the control
Weeks 9 to 16	Twice-weekly fasting days added
Primary outcome	High-sensitivity C-reactive protein (CRP), a blood marker of inflammation
Also measured	Weight, insulin sensitivity, blood pressure, lipids, multi-omic analyses, gut microbiome

Two features make this a careful design. It was a controlled-feeding trial, so the Mediterranean diet was handed to people instead of merely recommended. And the abstract reports "clear dietary separation", meaning the two groups really were eating differently during the first phase.

The abstract does not describe what a fasting day consisted of, so this post does not either.

What it found

Diet-only phase. CRP did not change during the eight weeks of Mediterranean diet alone, despite the clear difference in what the groups ate. Lipids did improve in this phase, so the diet was not doing nothing. It simply did not move the inflammation marker.

Fasting phase. After fasting days began, CRP fell in the Mediterranean-diet group relative to controls. That fall came alongside greater weight loss, improved insulin sensitivity and lower blood pressure.

Deeper measurements. The multi-omic analyses showed parallel reductions in inflammatory signaling. Gut microbiome composition stayed largely stable.

The abstract gives no CRP values and no figures for the weight lost, so none appear here. What it does give is the direction and the timing: nothing during diet alone, a fall once fasting and weight loss arrived.

The authors sum it up this way: diet quality alone does not lower inflammation over 8 weeks, and negative energy balance and weight loss during fasting "appear to be the stronger drivers".

What it does not show

• It is a small trial. Fifty-three people is enough to see a pattern, not enough to settle a question. Most participants were women, and all had metabolic risk factors.
• It is short. Each phase lasted eight weeks. The finding is that diet quality alone did not lower CRP over 8 weeks. A longer period on the diet might look different, and the trial cannot say.
• The order was fixed. Fasting came second for everyone, after eight weeks on the diet. The study cannot fully separate the effect of adding fasting from the effect of simply being on the diet for longer.
• It points at weight loss, not at fasting as such. The authors name negative energy balance and weight loss as the likely drivers. The trial did not compare fasting days with another way of losing the same weight, so it does not show that fasting has an anti-inflammatory effect beyond the weight it takes off.
• "Associated with" is the authors' wording. The CRP fall arrived together with weight loss. That is a strong hint about cause, not a demonstration of it.
• All food was provided. That makes the result cleaner and also less like ordinary life, where people shop, cook and drift.
• CRP is a marker. The trial measured a blood test, not illness. It does not show that anyone avoided a disease.

What this means if you fast

If you have read that a Mediterranean diet "fights inflammation", this trial suggests a more modest version: over eight weeks, in these participants, eating better without losing weight did not shift CRP. The diet still improved lipids, which is a reason to value it on its own terms.

If you fast, the message is not that fasting has special powers. It is that the weight loss and energy deficit that came with fasting days were what lined up with lower inflammation. Two fasting days a week is the shape of the 5:2 schedule, though the trial's exact protocol is not described in the abstract. Daily eating windows are a different pattern, covered in the fasting schedules overview, and this trial did not test them. For choosing between them, see how to choose the right fasting schedule for your lifestyle.

It also suggests the two are not rivals. In the trial, fasting days were added to the Mediterranean diet, not swapped for it.

Fasting is not right for everyone, and this post is general information, not medical advice. If you are pregnant or breastfeeding, have diabetes or take blood-sugar medication, have a history of eating disorders, take other regular medication, or are under 18, talk to a doctor before fasting. The participants here had metabolic risk factors and took part in a supervised study with all meals supplied, which is not the same as trying fasting days alone.

Tracking fasts with QoFast

QoFast is a fasting tracker app for iPhone and Android, for intermittent fasting and multi-day extended fasts. The timer works offline and survives restarts, and you can log water and mood and look back over your fasting history and streaks. QoFast gives general information, not medical advice, and is free to download with an optional Pro subscription on the App Store and Google Play.

FAQ

Does intermittent fasting reduce inflammation? In this trial, CRP fell after twice-weekly fasting days were added to a Mediterranean diet, together with greater weight loss. The authors attribute the change mainly to negative energy balance and weight loss.

Does the Mediterranean diet lower inflammation on its own? Not over eight weeks in this study. CRP did not change during the diet-only phase, although lipids improved.

How much did CRP fall? The abstract does not give CRP values, so this post cannot report a figure.

Did fasting change the gut microbiome? Gut microbiome composition was reported as largely stable.

Sources

• Warmbrunn MV, Tosti V, Biswas RK, and colleagues (senior author Fontana L). "Weight loss during intermittent fasting, not Mediterranean diet quality alone, is associated with lower inflammation: A randomized controlled trial." Cell Metabolism, published online 21 October 2026. DOI: 10.1016/j.cmet.2026.09.017. PubMed: 42906553.