Mediterranean diet modestly improved VO₂max

May 4, 2026

The Mediterranean diet is often framed as a general health win, but this study asked a more runner-relevant question: could it help trained endurance athletes adapt to training? The answer was promising, but not earth-shaking.

Reference: Lu et al. Mediterranean diet enhances endurance training adaptation through gut microbiota-derived short-chain fatty acids. Frontiers in Nutrition (2026) DOI: 10.3389/fnut.2026.1795528.

Study snapshot

A quick, practical summary for runners and coaches.

Quick answer

The study tested whether the Mediterranean diet could support gut-related changes and improve VO₂max during endurance training. The Mediterranean diet group improved VO₂max slightly more than the control group. The result is useful, but modest, and the study did not test race performance directly.

Key takeaways

The Mediterranean diet looked like a sensible training diet, not a guaranteed performance hack.
The study found gut-related changes alongside a modest VO₂max improvement.
The evidence is relevant to endurance athletes, but not specific to marathon, trail, or ultra runners.
Runners should not make sudden race-week diet changes based on this one study.

How confident should we be?

Evidence confidence: Moderate

The study used a useful randomized design in trained endurance athletes, but it was small, short, unblinded, and not runner-specific. The findings are promising, but the real-world performance value remains uncertain.

Bottom line

A Mediterranean-style diet may be a sensible option during endurance training, especially for athletes whose usual diet is low in fibre and plant foods. But this study does not prove that runners should expect major performance gains.

Read the deep-dive below for the full results, study details, limitations, practical interpretation, My thoughts, and my Rating of Perceived scientific Enjoyment.

Running science research reviews for endurance runners

The deep dive

The details behind the headline result, including the practical meaning, full findings, study design, limitations, and my interpretation.

Practical meaning

What does this research mean for runners and coaches?

The study supports a sensible idea: the Mediterranean diet may be a useful base diet during endurance training. It may support training adaptation partly by increasing fibre intake, shifting gut microbiota, and increasing some short-chain fatty acids.

That said, this is still interpretation, not a direct race-performance finding. The study measured VO₂max and time to exhaustion, not marathon time, trail race performance, ultra performance, fuelling tolerance, or recovery across a full season.

For runners

For marathon runners, trail runners, and ultra runners, the practical message is fairly simple. A Mediterranean-style diet may be a good default pattern during general training. Think whole grains, legumes, fruit, vegetables, nuts, olive oil, and enough carbohydrate to support the work.

The findings do not mean runners should suddenly double fibre intake before long runs or races. Fibre can support gut health, but it can also cause gastrointestinal problems if increased too quickly or placed too close to hard sessions. Build it gradually. Keep the lentil enthusiasm away from race morning.

For coaches

For coaches, the study supports using the Mediterranean diet as a broad nutrition framework for endurance athletes. It may be useful for athletes whose usual diet is low in plants, low in fibre, or heavy on refined foods.

But the coach still needs to individualise. Some runners tolerate higher fibre well. Others need careful timing, especially before intervals, long runs, races, or sessions with race-pace fuelling.

Practical decision

Should runners change anything?

Maybe. Runners do not need to overhaul the diet overnight. But if the current diet is low in plants, low in fibre, and heavy on refined foods, this study supports moving toward a Mediterranean-style pattern during normal training.

Consider this if

You want a sensible base diet for endurance training.
Your fibre intake is low and your gut tolerates gradual increases.
You want to improve diet quality without relying on supplements.
You are in a general training block, not the final few days before a race.

Do not overreact if

You already eat a varied, plant-rich diet.
You have a sensitive gut and high-fibre foods cause problems.
You are racing soon and have not practised the diet.
You want a guaranteed performance boost. The study does not offer that.

A sensible next step

Gradually build the diet around whole grains, legumes, fruit, vegetables, nuts, and olive oil, while keeping enough carbohydrate for training. Increase fibre slowly over several weeks. Keep new high-fibre meals away from key sessions and race day.

Never make any major changes to your training or lifestyle habits based on the findings of one study, especially if the study is small or provides low-quality evidence. Check whether other trials confirm the findings. If there is a meta-analysis on the topic, look at the effect size, the variability between studies, and the quality of evidence.

Expert interpretation

My thoughts

Running science from Thomas Solomon at Veohtu

The study is useful because it tested a realistic dietary pattern in trained endurance athletes. That gives it more practical value than a supplement trial in untrained students or a microbiome study in mice wearing the tiny lab coats of destiny.

The findings are also nicely boring, in the best possible way. The intervention was not exotic. It was a Mediterranean-style diet with more fibre, more plant foods, more olive oil, and less processed food. For many endurance athletes, that is already a sensible direction.

But I would not treat the study as proof that the Mediterranean diet improves race performance. The effect on VO₂max was modest. The sample was small. The athletes came from different endurance sports. And the gut-muscle mechanism, while interesting, still needs stronger confirmation.

The sensible next step would be a larger runner-specific trial with longer follow-up, better real-world outcomes, and careful tracking of gastrointestinal tolerance. I would especially like to see this tested in marathon and ultra runners, where fibre timing, fuelling comfort, and gut resilience can matter quite a lot.

My Rating of Perceived scientific Enjoyment

RPsE: 7/10

I experienced moderate scientific enjoyment because the study used a solid randomized design, reported the methods clearly, and measured meaningful endurance and gut-related outcomes. The enjoyment was capped because the trial was small, short, unblinded, not runner-specific, and the mechanism was interesting rather than fully nailed down.

Research question

What did the researchers ask?

The researchers asked whether following the Mediterranean diet during endurance training could improve gut microbiota, increase short-chain fatty acids, and enhance VO₂max.

In plain English, the study tested whether a plant-rich, fibre-rich dietary pattern could help trained endurance athletes adapt slightly better to training.

Study design

What type of study was this?

The study was a 12-week parallel-group randomized controlled trial. The researchers randomly assigned athletes to either the Mediterranean diet group or the control group. Both groups followed the same general endurance training programme.

A randomized controlled trial can test whether an intervention caused a change under the study conditions. That is useful. But this was still a small nutrition trial, and the participants and study staff could not be blinded to the diet. That means expectations, behaviour, and adherence could have influenced the results.

Participants

Who took part?

The study enrolled 60 competitive endurance athletes: 30 in the Mediterranean diet group and 30 in the control group. Fifty-five athletes completed the full intervention: 27 in the Mediterranean diet group and 28 in the control group.

The athletes were 18–35 years old and had at least 2 years of structured endurance training. They trained for at least 8 hours per week. The study included runners, cyclists, and triathletes recruited from local clubs and groups.

At baseline, the Mediterranean diet group included 18 males and 12 females. The control group included 17 males and 13 females. The groups were similar for age, sex distribution, body mass index, training experience, weekly training volume, baseline diet, and VO₂max. The mean baseline VO₂max was 54.8 mL/kg/min in the Mediterranean diet group and 55.3 mL/kg/min in the control group.

The study excluded athletes who had used antibiotics or probiotics in the previous 3 months, had symptoms of gastrointestinal disease, followed a ketogenic or vegetarian diet, or had a recent injury that stopped training.

Methods

What did the researchers do?

The Mediterranean diet group received personalised diet plans from registered dietitians. The diet emphasised whole grains, legumes, vegetables, fruits, nuts, and extra virgin olive oil. It included moderate fish and poultry, and restricted red meat, processed meat, and refined sugars. The target fibre intake was 30–35 g/day.

The control group maintained their usual diet. To balance attention between groups, the control group received general nutrition advice about hydration and macronutrient intake, but without a focus on fibre or the Mediterranean diet.

Both groups followed a 12-week periodised endurance training programme designed by professional coaches. The programme included 4–6 sessions per week, with long runs or rides, tempo sessions, and intervals. Training volume was individualised, with a target of 8–12 hours per week.

The researchers measured dietary intake, Mediterranean diet adherence, gut microbiota, faecal and plasma short-chain fatty acids, VO₂max, time to exhaustion, and lactate threshold. VO₂max was measured using a graded exercise test on either a treadmill or cycle ergometer, depending on the athlete’s main sport.

Main findings

What did the study find?

VO₂max Modestly improved

Gut markers Changed favourably

Race performance Not tested

The Mediterranean diet group increased the Mediterranean diet adherence score from 5.8 to 10.4 points. The control group stayed about the same, increasing from 5.6 to 5.9 points. Fibre intake increased from 18.2 to 32.8 g/day in the Mediterranean diet group, while the control group stayed near 18 g/day.

Training load looked similar between groups. Weekly training volume, mean training heart rate, training impulse, session RPE, and training compliance did not differ meaningfully between groups. That matters because it makes the diet comparison more believable.

The Mediterranean diet group showed greater changes in the gut microbiota. The Shannon diversity index, a measure of gut microbiota diversity, increased by 11.2%. The researchers also reported increases in bacteria linked with short-chain fatty acid production, including Faecalibacterium and Roseburia.

Short-chain fatty acids also changed. Plasma propionate increased by 42.1%, and plasma butyrate increased by 57.9% in the Mediterranean diet group. Plasma acetate increased modestly, but that result was not statistically significant.

The main performance result was VO₂max. The Mediterranean diet group improved by 2.4 ± 1.6 mL/kg/min. The control group improved by 1.3 ± 1.4 mL/kg/min. After adjustment for baseline VO₂max, age, sex, and body mass index, the between-group difference was 1.1 mL/kg/min, with a 95% confidence interval from 0.3 to 1.9 mL/kg/min. The p-value was 0.006, and Cohen’s d was 0.73.

Time to exhaustion improved more in the Mediterranean diet group than in the control group: 9.8% versus 5.2%. Lactate threshold showed a trend toward greater improvement in the Mediterranean diet group, but this did not reach statistical significance.

The researchers also reported moderate positive correlations between changes in plasma propionate and butyrate and improvements in VO₂max. Mediation analysis suggested that plasma propionate accounted for about 23% of the dietary effect on VO₂max. That supports a possible gut-muscle mechanism, but it does not prove that short-chain fatty acids were the main reason performance improved. Mediation models are useful. They are not tiny truth machines.

What helps confidence?

What were the strengths?

The study used a randomized controlled design.
The researchers studied trained endurance athletes, not sedentary volunteers.
Both groups followed a structured endurance training programme.
The researchers monitored training load and dietary adherence.
The study measured both practical outcomes and biological markers, including VO₂max, gut microbiota, and short-chain fatty acids.

What limits confidence?

What were the limitations?

The study was small, with 55 athletes completing the full intervention.
The intervention lasted only 12 weeks.
The diet intervention could not be blinded.
The study included runners, cyclists, and triathletes, so the evidence is not specific to runners.
VO₂max and time to exhaustion are useful, but they are not the same as race performance.
The mediation analysis supports a possible mechanism, but it does not prove that short-chain fatty acids caused the performance improvement.
The study was not powered for sex-specific analyses.
The real-world importance of a 1.1 mL/kg/min between-group VO₂max difference depends on the athlete, event, and baseline fitness.

Funding and conflicts

Who funded the study?

The authors reported financial support from the Liaoning Provincial Higher Education Fundamental Research Project. The authors declared no commercial or financial relationships that could be considered a potential conflict of interest.

That is reassuring because the study does not appear to be funded by a food company, supplement company, or commercial diet programme. Still, no funding statement removes the need for caution. Small nutrition trials can be influenced by adherence, expectations, outcome choice, and ordinary human messiness.

FAQ

Does the Mediterranean diet improve VO₂max in runners?

This study found a modest VO₂max improvement in trained endurance athletes following the Mediterranean diet. The athletes included runners, cyclists, and triathletes, so the result is relevant but not runner-specific.

Is the Mediterranean diet good for marathon training?

It can be. The Mediterranean diet can provide carbohydrate, fibre, healthy fats, and micronutrients. But marathon runners still need to practise race fuelling separately.

Should ultra runners eat more fibre?

Maybe, but timing matters. A higher-fibre diet may support gut health during training, but too much fibre before long runs or races can cause gut trouble.

Did gut bacteria improve endurance performance?

The study found associations between short-chain fatty acids and VO₂max improvement, and the randomized diet intervention changed both. That supports a possible gut-muscle link, but it does not prove the gut changes fully caused the performance gain.

How long does the Mediterranean diet take to affect endurance training?

The study lasted 12 weeks, and some diet and gut-related changes were measured during that period. This looks more like a training-block strategy than a quick pre-race trick.