Dietary Antioxidants and Intestinal Barrier Protection During Inflammation

Daniel Chen, Alan Wang, Ying Chen, Xinxin Li

September 9, 2026

This preprint reports new research that has not been peer-reviewed and revised at the time of posting

Categories: Biology

Abstract

The intestinal barrier helps the body absorb nutrients while protecting it from harmful substances. Inflammation can damage this barrier by weakening the connections between intestinal cells. We hypothesized that digested spinach would better protect intestinal barrier function during inflammation than digested bread, particularly when applied before inflammatory damage occurred. Spinach and bread were first passed through a laboratory digestion process that simulated the mouth, stomach, and small intestine. Their antioxidant capacities were measured before and after digestion, with vitamin E used as a positive control. The digested food samples were then added to Caco-2 intestinal cell layers either before or after inflammation was induced. Barrier health was measured using TEER, ZO-1 staining, and scanning electron microscopy. Spinach had a higher antioxidant capacity than bread, even after digestion. Cells treated with spinach before inflammation maintained stronger barrier function, more organized tight junctions, and better-preserved surface structures than cells treated with bread. Spinach added after inflammation was less effective. These results suggest that digested spinach may help protect the intestinal barrier during inflammation, especially when it is present before damage begins. However, spinach contains many nutrients and natural compounds, so the protective effects cannot be linked to antioxidants alone.

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Scientific Feedback

Graduate Student | Emory University

September 29, 2026

What do you like most about this manuscript?

I think the introduction is incredibly on point! You did a really good job at addressing all the background information needed to understand the rationale of your experiment. The experimental design is thorough, well supported, and diverse enough to consider different aspects that are impacted by inflammation and antioxidants. The variety of tests you did and the consideration of using digested and undigested food samples is remarkable.

How effectively did the background information support the research question? What additional information would be helpful for the reader?

Your background information is quite comprehensive and covers most of the themes/topics that concern your study. I particularly liked the way you explained the different approaches you are using to study digestion (with INFOGEST) and antioxidant activity/inflammation (with ORAC, ZO-1, and TEER).

Some suggestions I have to improve your background information are:

Usually, your background information is best-written in an "inverted pyramid" shape where you start with the "big picture" of your research and get progressively more detailed. Since the "big picture" of your study is the role of antioxidants in preventing/treating inflammation, I think your first paragraph could focus first on why inflammation is a problem (maybe talking about how common it is, ways in which people get inflammation, or diseases that are related with inflammation). Then, you could explain how antioxidants help with this (expanding on what you already have talking about free radical), and then start talking about antioxidants being in foods and considerations about bioavailability (which is what you already have). This would give your study an even greater impact by informing your readers about the importance of antioxidants.
You have explained how digestion can help release antioxidants from foods to increase their bioavailability. However, in your hypothesis you talk about foods "retaining" their antioxidant capabilities after digestion, which suggests that digestion can also cause a decrease in antioxidant activity. I think you could add a sentence or two explaining how that decrease due to digestion occurs.
In your second paragraph you mention spinach and bread as some foods that have changes in their antioxidant ability based on digestion. I think it would help you to introduce them (or maybe just spinach) as a food known to be rich in antioxidants before talking about the INFOGEST method. This would explain better why you decided to use spinach and bread for your studies.

What are the strengths of the hypothesis? How could it be improved?

Your hypothesis is testable, specific, and clearly related with your study's goals. Some ways in which I think you could improve it are:

Instead of having three separate hypotheses, try combining them into a single statement. The hypotheses you have right now cover each of your experiments, so I would suggest to try to come up with one that covers the entire study. I think focusing on "preventive treatment" and "decreased intestinal lining damage" would be best.
I think something you could consider is whether you want to compare spinach and bread against each other or if each of them can decrease the effects of inflammation. Either way makes sense but I personally think that you do not need to face them against each other and instead frame your study on whether they can help with the effects of inflammation.

What are the strengths of the experimental design? Can you think of accessible experiments or analysis that would help the authors strengthen their study?

As I mentioned before, I think the use of different approaches to perform your study is truly remarkable and the way you wrote your Methods section is incredibly complete. Some suggestions I have to make it even better are:

You could add some more detailed about the spinach and bread samples you used. Specially for the bread, what kind did you use? In your introduction you mentioned that different types of bread differ in their antioxidant activity, so I think that is an important detail to include in your paper (and allows you to suggest studying other kinds of bread in your discussion!)
I think you could be more specific in the Methods section for your ORAC assay to include the mass and volume you used for your samples. It is understandable to not include the entire protocol since you are using the one from the manufacturer but I think you should still include some details like the output you are measuring from the experiment.
In your antioxidant capacity experiment (Fig. 2), you mention that all of the undigested samples had a greater capacity than the digested ones. You should include/mention statistical tests to determine whether that difference is significant (like an ANOVA with Tukey HSD post-hoc test). More information of that can be find here: https://emerginginvestigators.org/documents/stats_guide. Also for this graph, it would be good to add a negative control/blank (one with no food/sample) to show what the basal readings are. If you already considered that, make sure to mention it in the figure legend (mentioning that you normalized with a blank sample) and in the Methods section.
In Fig. 4E, is there a reason why the nuclei of the cells did not fluoresce? Since the DAPI staining serves as a form of control to show the presence of cells, is there something about bread pretreatment that would affect the cells like that? I do not know if it is possible for you to repeat this experiment but, if not, I would definitely consider discussing the possibilities of there having been experimental error or possible explanations for why you are not getting fluorescence in the DAPI channel.
In Fig. 5, I think it would be good to include pictures from your inflammation sample with no digesta treatment to show what damaged tissue looks like. I would also suggest including pictures from that inflammation control and your digesta treatment samples at the lower magnification to show how the monolayer is affected.

What are the successes and the areas for improvement in the Discussion? Consider factors such as how clearly results are summarized, how well the results support the conclusions, how key takeaways are communicated, how limitations or next steps are discussed, etc.

I think your Discussion section is really well written and does a good job at summarizing your findings, talking about limitations, and suggesting future steps. I particularly appreciated your understanding to not oversell your results by knowing that your digesta samples include many more components besides antioxidants. Great job!

The only suggestion I have would be, as I mentioned before, to elaborate a little more about the specific type of bread you studied and how others may lead to different results.

How effective is the authors’ communication style? Could someone who has never heard of this topic understand what the authors have written in the text or shown in their figures? Are there changes the authors can make to improve how they are communicating verbally and visually?

Overall, I think all of the paper is very well written and that all of the topics you covered are well explained. Your Methods section is detailed enough that anyone could replicate the studies you made. The only suggestions I have in this area are:

In Fig. 3, I think changing the label from "control" to "untreated control" would be clearer. I think you could also add some dashed vertical lines on Days 2 and 19 to signify your treatment timepoints in the graphs. You should also state what statistical test you used for your analysis in the figure caption.
In Fig. 4 and 5, I think you could add titles over the microscope images to make it easier for your readers to know what each of them correspond to (and not have to go to the caption to figure that out).

A scientist with subject-specific expertise provided this feedback. Constructive feedback plays a key role in the scientific process because it allows researchers to learn from other scientists, be encouraged, and refine their ideas, research, and presentation.