Study analysis · The Journal of nutrition · 2021
Eating berries won't help your gut like apples do—here's why.
People who eat more fruit (except berries) have more of a special gut bacteria called Lachnospira that helps break down fiber.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study looked at what people ate and what bacteria were in their poop, and found that people who ate more fruit had more of a certain kind of bacteria. But it didn't change anyone's diet to see if that caused the change—so we don't know if the fruit made the bacteria grow, or if people with those bacteria just liked fruit more.
What’s the bottom line?
Scientists looked at what people ate and what bacteria lived in their poop. They found that eating 30+ kinds of plants a week and more fiber from fruits (like apples and bananas, not berries) was linked to more diverse and healthier gut bugs.
How strong is this study?
The researchers did a pretty good job measuring what people ate and what bacteria were in their poop, and they studied a lot of people. But since they didn't change anyone's diet or control other things like exercise or sleep, we can't be totally sure the results are because of the fruit alone.
65 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availability+25/25
21 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=343)+16.4/20
- Follow-upno follow-up reported
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registration+15/15
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. This is a cross-sectional observational study with no randomization, no control group, and no intervention. It measures associations at a single point in time, making it impossible to determine if diet causes changes in gut microbiota or if the reverse is true, or if other factors are responsible.
No Conflicts
No conflicts of interest identified
No conflicts of interest were declared, and the study was funded by the USDA Agricultural Research Service, a government agency with no commercial interest in the outcomes.
Funders
Conflict Details
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
All authors are employed by the USDA, a government entity with no commercial stake in the study outcomes. The funding source is public and non-industrial. The study design, analysis, and publication appear independent. No industry ties or financial conflicts are disclosed or implied.
Key takeaways
- 01
People who ate more fiber from fruits had 21% stronger link to gut diversity (r=0.213).
- 02
Those who ate more cooked grains had more Bifidobacterium.
- 03
Lachnospira bacteria grew more when people ate fruit fiber.
- 04
Yes—this suggests eating a wide variety of plant foods, especially fruits, may help your gut bacteria thrive, which is linked to better digestion and overall health.
Surprising findings
- Berries, often touted as gut superfoods, showed no significant link to Lachnospira, while non-berry fruits did.Public health messaging heavily promotes berries for antioxidants and fiber, but this study shows they don’t drive the same gut bacterial response as apples or bananas.
- Cooked grains (not raw or whole) were the strongest carb correlate for Bifidobacterium.Most gut health advice avoids refined carbs—yet this study links them to a beneficial bacterium, suggesting cooking method matters more than 'whole' vs. 'refined'.
Practical takeaways
Swap one berry snack per day for an apple, pear, or banana to boost Lachnospira.
This is correlational—not proof that eating more apples will change your gut bacteria overnight.
medium confidenceInclude cooked grains like pasta or rice in your meals if you want to support Bifidobacterium.
Don’t overdo it—this doesn’t mean you should eat only white bread. Balance with vegetables and legumes.
medium confidenceAim for 30 different plant foods per week—not just fruits, but also legumes, nuts, whole grains, and vegetables.
The study used self-reported data, so accuracy may vary. Use a simple app or checklist to track.
medium confidenceWhy this study matters
Fruit Fiber > Berry Fiber for Gut Health
The study found that dietary fiber from fruits excluding berries (like apples and bananas) was robustly linked to higher levels of Lachnospira, a fiber-digesting gut bacterium (FDR-corrected P < 0.05). Berries showed no such association, despite being high in fiber.
Most people think all fruits are equally good for gut bacteria—this flips that assumption and shows specific types of fruit matter more than others.
Cooked Grains Boost Bifidobacterium
Higher intake of total carbohydrates from cooked grains—like pasta, bread, and rice—was correlated with increased abundance of Bifidobacterium, a probiotic-linked genus (Figure 2B).
This challenges the idea that all carbs are bad—cooked grains may actually feed beneficial gut bacteria, not harm them.
30+ Plants a Week = Healthier Gut
Dietary diversity—measured as eating 30 or more distinct plant types per week—was correlated with 17.1% higher gut microbial diversity (r = 0.171).
You don’t need fancy superfoods—just variety. This makes gut health feel achievable, not overwhelming.
Tree-Based Diet Analysis Beats Traditional Methods
By tracking not just nutrients but the actual food items and their macronutrient grams (e.g., grams of fiber from apples vs. oats), the tree method found stronger links than standard nutrient-only approaches.
This isn’t just about ‘eat more fiber’—it’s about *what kind* of fiber and *where it comes from*. The method itself is a breakthrough.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists looked at what people ate and what bacteria lived in their poop. They found that eating 30+ kinds of plants a week and more fiber from fruits (like apples and bananas, not berries) was linked to more diverse and healthier gut bugs.
Research results
People who ate more fiber from fruits had 21% stronger link to gut diversity (r=0.213). Those who ate more cooked grains had more Bifidobacterium. Lachnospira bacteria grew more when people ate fruit fiber.
What this means - more context
Yes—this suggests eating a wide variety of plant foods, especially fruits, may help your gut bacteria thrive, which is linked to better digestion and overall health.
This study investigates reproducible associations between dietary patterns and gut microbiota composition in a healthy U.S. adult cohort.
Using tree-based dietary analysis, the study found that higher dietary fiber intake—especially from fruits excluding berries—is correlated with increased gut microbial diversity and enrichment of Lachnospira, while carbohydrate intake from cooked grains correlates with Bifidobacterium abundance. The method outperformed traditional nutrient-only approaches.
Methods Used
343 healthy U.S. adults provided 2–3 automated 24-hour dietary recalls and one stool sample. Dietary data were structured into a tree format annotated with macronutrient grams (dry weight, fiber, carbs, etc.). Gut microbiota was profiled via 16S rRNA sequencing (QIIME2), and associations were analyzed using Faith’s phylogenetic diversity, k-means clustering, and DESeq2 differential abundance testing.
Main Finding
Dietary fiber intake showed the strongest correlation with gut microbial alpha diversity (r = 0.213), and fiber from fruits excluding berries was robustly associated with increased Lachnospira abundance (FDR-corrected P < 0.05). Total carbohydrate from cooked grains correlated with Bifidobacterium enrichment.
Confidence Level
Moderate—correlational design limits causal inference; robust statistical methods and replication of key findings (e.g., Lachnospira-fruit link) in prior studies support reliability.
Study Flags
Red Flags
- •Cross-sectional design—cannot prove causation
- •Self-reported dietary data prone to recall bias
- •Single stool sample limits temporal understanding of microbiome dynamics
Surprising Findings
Berries, often touted as gut superfoods, showed no significant link to Lachnospira, while non-berry fruits did.
Public health messaging heavily promotes berries for antioxidants and fiber, but this study shows they don’t drive the same gut bacterial response as apples or bananas.
Practical Takeaways
Swap one berry snack per day for an apple, pear, or banana to boost Lachnospira.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Moderate probability
on the GRADE evidence scale
This study looked at what people ate and what bacteria were in their poop, and found that people who ate more fruit had more of a certain kind of bacteria. But it didn't change anyone's diet to see if that caused the change—so we don't know if the fruit made the bacteria grow, or if people with those bacteria just liked fruit more.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Large sample size (n=343) for an observational microbiome study
- Use of repeated 24-hour dietary recalls (2–3 per participant) to improve dietary assessment
- Standardized stool collection and sequencing methods (QIIME 2, 16S rRNA)
Weaknesses
- Cross-sectional design prevents determination of temporal direction
- No control group or intervention to test causality
- Blinding status unknown, and no randomization
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists looked at what people ate and what bacteria lived in their poop. They found that eating 30+ kinds of plants a week and more fiber from fruits (like apples and bananas, not berries) was linked to more diverse and healthier gut bugs.
Research results
People who ate more fiber from fruits had 21% stronger link to gut diversity (r=0.213). Those who ate more cooked grains had more Bifidobacterium. Lachnospira bacteria grew more when people ate fruit fiber.
What this means - more context
Yes—this suggests eating a wide variety of plant foods, especially fruits, may help your gut bacteria thrive, which is linked to better digestion and overall health.
This study investigates reproducible associations between dietary patterns and gut microbiota composition in a healthy U.S. adult cohort.
Using tree-based dietary analysis, the study found that higher dietary fiber intake—especially from fruits excluding berries—is correlated with increased gut microbial diversity and enrichment of Lachnospira, while carbohydrate intake from cooked grains correlates with Bifidobacterium abundance. The method outperformed traditional nutrient-only approaches.
Methods Used
343 healthy U.S. adults provided 2–3 automated 24-hour dietary recalls and one stool sample. Dietary data were structured into a tree format annotated with macronutrient grams (dry weight, fiber, carbs, etc.). Gut microbiota was profiled via 16S rRNA sequencing (QIIME2), and associations were analyzed using Faith’s phylogenetic diversity, k-means clustering, and DESeq2 differential abundance testing.
Main Finding
Dietary fiber intake showed the strongest correlation with gut microbial alpha diversity (r = 0.213), and fiber from fruits excluding berries was robustly associated with increased Lachnospira abundance (FDR-corrected P < 0.05). Total carbohydrate from cooked grains correlated with Bifidobacterium enrichment.
Confidence Level
Moderate—correlational design limits causal inference; robust statistical methods and replication of key findings (e.g., Lachnospira-fruit link) in prior studies support reliability.
Study Flags
Red Flags
- •Cross-sectional design—cannot prove causation
- •Self-reported dietary data prone to recall bias
- •Single stool sample limits temporal understanding of microbiome dynamics
Surprising Findings
Berries, often touted as gut superfoods, showed no significant link to Lachnospira, while non-berry fruits did.
Public health messaging heavily promotes berries for antioxidants and fiber, but this study shows they don’t drive the same gut bacterial response as apples or bananas.
Practical Takeaways
Swap one berry snack per day for an apple, pear, or banana to boost Lachnospira.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Moderate probability
on the GRADE evidence scale
This study looked at what people ate and what bacteria were in their poop, and found that people who ate more fruit had more of a certain kind of bacteria. But it didn't change anyone's diet to see if that caused the change—so we don't know if the fruit made the bacteria grow, or if people with those bacteria just liked fruit more.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Large sample size (n=343) for an observational microbiome study
- Use of repeated 24-hour dietary recalls (2–3 per participant) to improve dietary assessment
- Standardized stool collection and sequencing methods (QIIME 2, 16S rRNA)
Weaknesses
- Cross-sectional design prevents determination of temporal direction
- No control group or intervention to test causality
- Blinding status unknown, and no randomization
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The researchers did a pretty good job measuring what people ate and what bacteria were in their poop, and they studied a lot of people. But since they didn't change anyone's diet or control other things like exercise or sleep, we can't be totally sure the results are because of the fruit alone.
65 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availability+25/25
21 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=343)+16.4/20
- Follow-upno follow-up reported
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registration+15/15
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. This is a cross-sectional observational study with no randomization, no control group, and no intervention. It measures associations at a single point in time, making it impossible to determine if diet causes changes in gut microbiota or if the reverse is true, or if other factors are responsible.
No Conflicts
No conflicts of interest identified
No conflicts of interest were declared, and the study was funded by the USDA Agricultural Research Service, a government agency with no commercial interest in the outcomes.
Funders
Conflict Details
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
USDA Agricultural Research Service: Author employed by USDA ARS; study funded by internal USDA grants
All authors are employed by the USDA, a government entity with no commercial stake in the study outcomes. The funding source is public and non-industrial. The study design, analysis, and publication appear independent. No industry ties or financial conflicts are disclosed or implied.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
1 video from Big Think Clips cite this study, drawing 1 claim from it.
- Very strong evidence
Randomized or controlled trials support this claim, alongside consistent supporting evidence.
Evidence
Authored by
5 researchersIf this is your work, this is how we attribute it on Fit Body Science. Mary E. Kable is listed as the lead author.