If you’re searching for the best collagen for leaky gut, you may find plenty of articles recommending a particular collagen type, usually Type I, marine collagen, or hydrolyzed collagen. The problem is that the scientific evidence does not currently support choosing one collagen supplement as a proven treatment for increased intestinal permeability.

Collagen is an important structural protein in the human body, and collagen peptides provide amino acids such as glycine, proline, and hydroxyproline. That gives collagen a biologically plausible role in connective-tissue biology. But biological plausibility is not the same as demonstrating that a supplement repairs the intestinal barrier in humans.

So, if your goal is specifically to improve intestinal permeability, there is currently no collagen type that can be confidently called the clinically proven “best” option. Research into collagen peptides and gastrointestinal health is developing, but direct human evidence remains limited.

Quick answer: What is the best collagen for leaky gut?

There is currently no collagen supplement proven to repair or reverse increased intestinal permeability in humans. Hydrolyzed collagen peptides may be a convenient source of collagen-derived amino acids, but evidence specifically connecting collagen supplementation with improved intestinal barrier function is still limited. Type I collagen is common in supplements, but it has not been established as superior to Type II or Type III collagen for gut health. [1–4]

What is a “leaky gut”?

“Leaky gut” is a popular term used to describe increased intestinal permeability.

The intestine is not supposed to be an impenetrable wall. Its barrier has to allow nutrients, water and other useful substances to cross into the body while limiting the uncontrolled passage of potentially harmful substances.

The intestinal barrier is complex. It includes the mucus layer, intestinal epithelial cells, tight junctions between cells, immune components and interactions with the gut microbiota. Intestinal permeability is therefore only one part of overall intestinal barrier function. [5]

Normal intestinal permeability

Some substances naturally cross the intestinal lining. This is essential for digestion and nutrient absorption.

The important question is not whether the intestine is permeable, but how permeable it is and under what circumstances.

Increased intestinal permeability

When barrier function is altered, substances can cross the intestinal lining differently than they normally would.

Research has associated altered intestinal permeability with several gastrointestinal and systemic conditions. However, an association does not necessarily mean that increased permeability is the original cause of the condition.

“Leaky gut” is not a diagnosis by itself

The phrase “leaky gut” is widely used online, but it should not be treated as a diagnosis for unexplained digestive symptoms.

Bloating, abdominal pain, diarrhea, constipation, reflux and other symptoms can have many possible causes. Conditions such as celiac disease, inflammatory bowel disease and irritable bowel syndrome require appropriate clinical assessment rather than simply assuming that intestinal permeability is responsible.

This distinction matters when evaluating collagen supplements. If a person has a genuine gastrointestinal disorder, taking collagen should not be considered a substitute for diagnosis or evidence-based treatment.

Does collagen actually help leaky gut?

At present, there is not enough high-quality human evidence to say that collagen supplementation repairs a damaged intestinal barrier or reliably reduces intestinal permeability.

This is the most important point in the entire article.

There is a plausible biological argument for collagen because collagen is abundant in connective tissues and contains distinctive amino acids, particularly glycine, proline and hydroxyproline. But eating collagen does not mean that intact collagen travels directly to the intestinal wall and becomes new intestinal tissue.

Dietary collagen is digested and absorbed as amino acids and small peptides. The body then uses those building blocks according to its physiological needs.

That is very different from demonstrating that orally consumed collagen selectively rebuilds or “seals” the gut barrier.

What the evidence currently looks like

The evidence can be divided into several levels:

Evidence level	What it tells us about collagen and gut health
Biological plausibility	Collagen contains amino acids involved in protein and connective-tissue biology.
Cell/laboratory research	May provide clues about mechanisms, but does not establish benefits from taking collagen supplements.
Animal research	Can identify possible biological effects, but results cannot automatically be applied to humans.
Observational research	Can identify associations but cannot prove collagen causes improved gut health.
Small human trials	Potentially useful, but results may be preliminary.
Randomized controlled trials	The most useful design for determining whether supplementation causes an outcome.
Systematic reviews/meta-analyses	Can provide stronger evidence when enough good-quality trials exist.

For collagen and intestinal permeability specifically, the evidence base is still developing rather than established.

As of 2026, a randomized, double-blind, placebo-controlled trial involving 116 adults with gastrointestinal symptoms has been completed, but the public ClinicalTrials.gov record does not yet contain results. The study examined gastrointestinal symptoms and included intestinal permeability-related outcomes. [6]

Another randomized trial is currently investigating whether 2.5 g, 5 g or 10 g of collagen peptides taken daily for 45 days affects intestinal permeability following an aspirin challenge. Its primary permeability outcome uses a urinary lactulose-to-mannitol measurement. [7]

The existence of these trials is important because it shows that researchers are still testing the question rather than having already established collagen as an effective treatment.

What does collagen do in the body?

Collagen is a major structural protein.

It contributes to tissues including:

• skin
• bone
• cartilage
• tendons
• ligaments
• blood vessels
• connective tissue
• basement membranes and other structural components

There are many collagen types in the human body, each with different distributions and functions. Types I, II and III are among the most abundant. [8,9]

Collagen is characterized by a distinctive triple-helix structure and a high proportion of glycine, proline and hydroxyproline.

When you consume collagen peptides, however, your digestive system does not simply deliver whole collagen molecules to a specific body part.

The protein is broken down during digestion into smaller peptides and amino acids, which can then be absorbed and used by the body.

This is why the statement:

“Collagen is found in connective tissue, therefore eating collagen repairs the gut lining”

is an oversimplification.

The first part is true.

The conclusion does not automatically follow.

Which type of collagen is best for gut health?

If you are comparing collagen products, you will commonly encounter Type I, Type II and Type III collagen.

But it is important not to confuse where a collagen type naturally occurs in the body with evidence that consuming that collagen type produces a particular health outcome.

Type I collagen

Type I is the most abundant collagen type in the human body.

It is prominent in:

• skin
• bone
• tendons
• ligaments
• teeth
• several other connective tissues

Many bovine and marine collagen products are predominantly Type I collagen. [8,9]

Because Type I collagen is so common in supplements, it is frequently marketed as the best collagen for gut health.

However, being common in supplements does not establish that Type I collagen repairs intestinal permeability.

Evidence for gut health: Limited.

Bottom line: Type I is a reasonable description of the collagen in many products, but it is not clinically proven to be the best collagen for a leaky gut.

Type II collagen

Type II collagen is particularly associated with cartilage.

It is therefore much more commonly discussed in relation to joint and cartilage health than intestinal health. [8,9]

Some supplements specifically contain Type II collagen, including products derived from chicken cartilage.

There is no strong clinical evidence establishing Type II collagen as a superior choice for intestinal permeability.

Evidence for gut health: Insufficient to recommend it specifically for this purpose.

Type III collagen

Type III collagen occurs alongside Type I collagen in several tissues, including skin, blood vessels and connective tissues. [8,9]

It is often present naturally in bovine-derived collagen products.

Again, its presence in tissues does not mean that consuming Type III collagen specifically improves intestinal barrier function.

Evidence for gut health: Insufficient.

So which type should you choose?

If your only reason for buying collagen is to treat “leaky gut,” there is currently no evidence-based reason to say that Type I, Type II or Type III is definitively the best.

A supplement containing Type I collagen may be perfectly reasonable for someone who wants collagen for another purpose, but that is a different question from whether it treats increased intestinal permeability.

Collagen peptides vs. gelatin

These terms are related but are not identical.

What are collagen peptides?

Collagen peptides are collagen that has been broken down into smaller peptide chains, usually through enzymatic hydrolysis.

You may also see products described as:

• hydrolyzed collagen
• collagen hydrolysate
• collagen peptides

These terms generally refer to collagen that has been processed to produce smaller peptides that are easier to dissolve and use in foods and supplements. [10]

What is gelatin?

Gelatin is produced by processing collagen and partially breaking down its structure.

Unlike many collagen peptide powders, gelatin forms a gel under appropriate conditions.

Both gelatin and collagen peptides originate from collagen-rich animal tissues, but their physical properties differ.

Is collagen peptides better than gelatin for gut health?

There is not enough direct evidence to conclude that collagen peptides are superior to gelatin for intestinal permeability.

Collagen peptides are often more convenient because they dissolve easily in liquids and do not gel in the same way.

That is a practical advantage, not proof of a greater gut-health effect.

Bovine vs. marine vs. chicken collagen

Another common question is whether the source of collagen makes one supplement better for the gut.

The major sources include:

Bovine collagen

Bovine collagen is commonly derived from cattle hides or bones and is frequently rich in Type I collagen, sometimes with Type III collagen.

Potential advantages:

• widely available
• commonly used in collagen peptide products
• often relatively economical

Limitations:

• animal-derived
• unsuitable for people avoiding bovine products
• allergen and dietary considerations may apply

There is no good evidence showing that bovine collagen is inherently better for intestinal permeability.

Marine collagen

Marine collagen is generally obtained from fish skin, scales or other fish-derived materials.

It is commonly associated with Type I collagen. [10]

Potential advantages:

• useful alternative for people who prefer fish-derived collagen
• often used in Type I collagen products

Limitations:

• fish allergy is relevant
• source and sustainability vary
• often more expensive

There is currently no convincing clinical evidence showing that marine collagen is superior to bovine collagen for gut health.

Chicken collagen

Chicken collagen is often associated with Type II collagen, particularly when cartilage is used as the source.

It is commonly marketed toward joint and cartilage support rather than gut health.

There is currently insufficient evidence to recommend chicken collagen specifically for intestinal permeability.

Which source is best for the gut?

None has been established as the best.

Choose based on dietary preferences, allergies, source transparency, product quality and your actual reason for using collagen rather than assuming that one animal source will repair the gut barrier better than another.

What does the human research actually show?

This is where collagen marketing and scientific evidence often diverge.

There is human research on collagen supplementation, but much of it examines outcomes such as skin, joints, connective tissue or exercise-related outcomes rather than intestinal permeability.

For example, systematic reviews and meta-analyses have investigated collagen peptides for musculoskeletal outcomes and found some potentially useful effects, although certainty varies by outcome and study quality. [11,12]

A 2024 systematic review and meta-analysis included 19 studies involving 768 participants and reported statistically significant effects for several exercise-related outcomes, including fat-free mass, tendon morphology, muscle architecture and maximal strength. However, the certainty of evidence ranged from very low to moderate depending on the outcome. [12]

This is useful evidence—but it is not evidence that collagen heals leaky gut.

Similarly, systematic reviews have examined hydrolyzed collagen for skin outcomes. Some have reported improvements in skin hydration or elasticity, while newer analyses have raised important questions about study quality and funding bias. [13,14]

Again, these results should not be transferred to intestinal permeability.

Why this distinction matters

Suppose a collagen trial finds improved skin elasticity.

That supports a statement about skin.

It does not support:

“Collagen improves gut barrier function.”

Likewise, evidence that collagen peptides may influence connective-tissue remodeling does not establish that they repair the intestinal barrier.

This is one of the most important principles when reading supplement research:

Evidence for one outcome cannot automatically be transferred to another outcome.

Can collagen improve intestinal permeability?

The honest answer is:

We don’t know yet.

There is enough biological interest to justify research, but not enough high-quality human evidence to make collagen a proven treatment for increased intestinal permeability.

Researchers are now conducting trials that directly measure gut-related outcomes.

One completed randomized trial involving 116 adults with gastrointestinal symptoms investigated collagen peptides versus placebo and included an intestinal permeability outcome based on serum lipopolysaccharide levels. The study was completed in November 2025, but the public registry still reports no posted results. [6]

A separate trial that began in 2026 is specifically examining whether daily collagen peptide supplementation changes intestinal permeability after an aspirin challenge. The study is designed to compare 2.5 g, 5 g and 10 g doses with placebo and uses the urinary lactulose-to-mannitol ratio as its primary permeability measurement. [7]

These studies are particularly relevant because they move beyond theoretical arguments and actually test intestinal-barrier outcomes in humans.

Until results from well-designed human trials are available, claims that collagen “seals,” “repairs” or “heals” the gut should be treated cautiously.

Why collagen’s amino acids don’t prove that it repairs the gut

You will often see glycine and proline highlighted in collagen marketing.

These amino acids are genuinely abundant in collagen.

That does not mean that consuming more collagen automatically directs those amino acids toward repairing intestinal tissue.

The body continuously breaks down and synthesizes proteins. Amino acids from food become part of a larger metabolic pool.

Your body decides how those nutrients are used.

So it is reasonable to say:

Collagen provides amino acids that participate in protein metabolism and connective-tissue biology.

It is not reasonable to automatically turn that into:

Collagen supplements repair intestinal permeability.

The second statement requires direct clinical evidence.

Potential benefits of collagen that have better evidence

If someone is considering collagen supplementation, it is useful to look beyond the gut.

Research on collagen peptides has investigated several areas, including:

• joint pain and function
• connective-tissue remodeling
• exercise recovery
• tendon-related outcomes
• body composition
• skin hydration and elasticity

Some systematic reviews report potentially beneficial effects, but the quality and certainty of evidence varies substantially. [11–14]

For example, a systematic review of 15 randomized controlled trials found evidence suggesting collagen supplementation may improve joint functionality and reduce joint pain in certain populations, although the authors also identified limitations and called for additional research. [11]

A newer systematic review and meta-analysis of 19 studies involving 768 participants found benefits for several musculoskeletal outcomes, but certainty ranged from very low to moderate depending on the outcome. [12]

The evidence therefore gives a more balanced picture:

Collagen may have useful applications, but those applications should not be confused with treatment for intestinal permeability.

How to choose a collagen supplement

If you decide to use collagen despite the uncertainty around gut-specific benefits, focus on product quality rather than exaggerated health claims.

1. Look at the collagen source

Check whether the product is:

• bovine
• marine
• chicken
• another animal-derived source

This is particularly important if you have allergies or dietary restrictions.

2. Consider collagen peptides

Hydrolyzed collagen or collagen peptides are commonly used because they are convenient, soluble and processed into smaller peptides.

That does not automatically make them better for gut health, but they are a practical supplement form.

3. Read the ingredient list

A simpler ingredient list can make it easier to understand what you are actually consuming.

Be cautious of products that combine collagen with a long list of ingredients while making broad claims about gut repair.

4. Check allergen information

Marine collagen may be relevant to people with fish allergies.

Other collagen sources may have their own dietary considerations.

Always check the manufacturer’s allergen information.

5. Look for quality testing

Where possible, consider products from manufacturers that provide meaningful information about manufacturing standards and independent or third-party testing.

Testing and quality assurance do not prove that a collagen product works for leaky gut—but they can provide additional confidence about product identity and quality.

6. Don’t assume “premium” means better for the gut

Terms such as:

• grass-fed
• wild-caught
• organic
• clean
• premium
• pharmaceutical grade

may describe sourcing or manufacturing characteristics, but they do not automatically demonstrate superior effects on intestinal permeability.

A more expensive collagen supplement is not necessarily a more effective gut-health supplement.

How much collagen should you take?

There is no established collagen dosage specifically proven to treat increased intestinal permeability.

Collagen studies have used a wide range of doses depending on the outcome being investigated.

For example, research involving musculoskeletal outcomes has commonly examined doses in the several-gram-per-day range, while ongoing gut-related trials are testing different doses specifically to determine whether gastrointestinal or intestinal-permeability outcomes change. [7,11,12]

Therefore, it would be misleading to tell someone:

“Take X grams of collagen to heal your leaky gut.”

There is currently no well-established evidence-based dosage for that purpose.

If you choose to take collagen, follow the product’s directions unless a qualified healthcare professional has advised you differently.

Is collagen safe?

Collagen supplements are generally tolerated by many people, but “natural” does not mean “risk-free.”

Possible considerations include:

• digestive discomfort
• unpleasant taste or aftertaste
• intolerance to other ingredients in the product
• allergic reactions to the source
• interactions or dietary considerations depending on the individual product

Product quality also matters because supplements can differ considerably in ingredients and manufacturing standards.

If you have a diagnosed gastrointestinal condition, significant unexplained digestive symptoms, food allergies, are pregnant or breastfeeding, or take medications that require dietary or supplement considerations, discuss supplementation with an appropriate healthcare professional.

Collagen should not replace treatment for a diagnosed gastrointestinal disease.

Who may want to avoid or reconsider collagen?

Collagen may not be appropriate for everyone.

You may want to reconsider it if:

You have an allergy to the collagen source

For example, marine collagen may be unsuitable for someone with a relevant fish allergy.

You follow a dietary restriction

Collagen is animal-derived. People following vegetarian or vegan diets generally cannot obtain true collagen from plant foods.

Products marketed as “vegan collagen” typically do not contain animal collagen itself. Instead, they may contain nutrients or ingredients marketed as supporting the body’s own collagen production.

You are using collagen to self-treat unexplained symptoms

If you have persistent:

• diarrhea
• constipation
• abdominal pain
• unexplained weight loss
• blood in the stool
• persistent vomiting
• severe or worsening digestive symptoms

the priority should be appropriate medical evaluation rather than trying different supplements.

What else supports gut health?

This may be more important than choosing between Type I, Type II or Type III collagen.

A healthy gut is influenced by multiple factors, including diet, physical activity, sleep, medications, underlying diseases and interactions between the intestinal barrier and gut microbiota.

There is no single supplement that can replace those factors.

Eat enough dietary fiber

Fiber is found in foods such as:

• vegetables
• fruit
• legumes
• whole grains
• nuts
• seeds

Individual tolerance varies, especially in people with gastrointestinal disorders, so increasing fiber rapidly may cause temporary digestive symptoms.

Eat a diverse range of plant foods

A varied diet provides different types of fiber and other compounds that interact with the gut microbiota.

However, individual dietary needs differ, and people with diagnosed gastrointestinal disorders may need personalized dietary advice.

Maintain adequate nutrition

Protein, vitamins, minerals and sufficient overall energy intake are important for normal tissue maintenance.

Rather than focusing on one supplement, consider whether your overall diet is meeting your nutritional needs.

Stay physically active

Regular physical activity is associated with many aspects of better overall health and may also influence gastrointestinal function.

Prioritize sleep

Poor sleep can affect multiple physiological systems, including metabolic and immune function.

Address underlying gastrointestinal conditions

If intestinal symptoms are caused by an underlying condition, treating that condition is more important than simply adding collagen.

For example, someone with celiac disease needs appropriate management of celiac disease rather than relying on collagen supplements.

What about diet and intestinal permeability?

Dietary research is still developing.

A 2024 systematic review examining dietary interventions and intestinal permeability in healthy people found only 12 eligible studies from more than 3,700 records and concluded that there was not strong evidence overall for dietary interventions consistently increasing or decreasing intestinal permeability in healthy populations. [15]

That is a useful reminder that even apparently simple gut-health claims require careful interpretation.

Does collagen help digestion?

There is not enough evidence to say that collagen generally improves digestion.

Some collagen products are marketed for:

• easier digestion
• reduced bloating
• improved gut comfort
• better bowel function

But these claims should not automatically be accepted as established effects.

A completed randomized trial specifically investigated collagen peptides and gastrointestinal discomfort in adults with gastrointestinal symptoms. It included measures of reflux, diarrhea, abdominal pain, indigestion and constipation, as well as other outcomes. However, the public registry currently does not provide the trial results. [6]

Therefore, it is premature to conclude that collagen improves digestion based on that study.

Does collagen help IBS?

There is currently insufficient evidence to recommend collagen as a treatment for irritable bowel syndrome (IBS).

IBS is a defined gastrointestinal disorder with multiple potential contributing factors.

If someone with IBS happens to feel better after taking collagen, that individual experience does not establish that collagen treats IBS.

It is also worth noting that the completed collagen gastrointestinal trial specifically excluded people with diagnosed IBS and several other chronic gastrointestinal conditions. [6]

That means its eventual results—once posted—would not necessarily tell us whether collagen benefits people who actually have IBS.

Does collagen help bloating?

There is not enough evidence to say that collagen reliably reduces bloating.

Bloating can have many causes, including diet, constipation, gastrointestinal disorders and changes in gut motility.

If bloating is persistent or severe, looking for the underlying cause is more useful than assuming it is caused by “leaky gut.”

Collagen may be convenient for some people as a protein supplement, but it should not be marketed as a proven anti-bloating treatment.

Is collagen necessary for a healthy gut?

No.

There is no evidence that people need a collagen supplement in order to maintain normal intestinal barrier function.

Your body makes collagen naturally.

Dietary protein provides amino acids that can be used for many physiological processes, including the synthesis of body proteins.

A collagen supplement may be useful for some people for particular reasons, but that is very different from saying that everyone needs collagen for gut health.

The bottom line

If you’re looking for the best collagen for leaky gut, the most scientifically accurate answer is that no specific collagen type has been proven to repair increased intestinal permeability in humans.

Type I collagen is common in bovine and marine collagen supplements, while Type II is strongly associated with cartilage and Type III commonly occurs alongside Type I in several connective tissues. But the natural location of a collagen type does not prove that consuming it produces a specific gut-health benefit.

Hydrolyzed collagen and collagen peptides are convenient forms of collagen, but there is currently insufficient evidence to say that they are an established treatment for “leaky gut.”

The human research on collagen is more developed for areas such as joint and connective-tissue outcomes than for intestinal permeability. Even in those areas, the certainty of evidence varies. [11,12]

Most importantly, researchers are still conducting controlled human trials specifically examining collagen, gastrointestinal symptoms and intestinal permeability. One completed 116-person trial has not yet posted results, while another trial is currently testing different collagen peptide doses against placebo using direct permeability measurements. [6,7]

So if you want to take collagen, it can be reasonable to consider it as one part of your diet depending on your individual circumstances—but you do not need to buy an expensive “gut healing” collagen product simply because the label promises to seal or repair your intestinal lining.

For overall gut health, a balanced diet, adequate fiber and nutrition, regular physical activity, sufficient sleep and appropriate management of underlying gastrointestinal conditions are more important than finding a supposedly perfect collagen type.

Collagen may be interesting for gut health. It is not yet proven to be a treatment for leaky gut.

Frequently Asked Questions

What is the best collagen for leaky gut?

No specific collagen type has been proven to repair increased intestinal permeability in humans. Type I collagen is common in supplements, but there is not enough evidence to establish it as superior to Type II or Type III collagen for gut health.

Does Type I collagen help gut health?

Type I collagen is an important structural protein in tissues such as skin, bone, tendons and ligaments. However, evidence that taking Type I collagen specifically improves intestinal permeability is currently limited.

Is marine collagen better for the gut?

There is no convincing clinical evidence showing that marine collagen is better than bovine or other collagen sources for intestinal permeability. Marine collagen is often Type I collagen, but source alone does not establish a gut-health advantage.

Are collagen peptides good for digestion?

Collagen peptides are hydrolyzed collagen and are commonly used because they are soluble and convenient. However, there is not enough human evidence to conclude that collagen peptides generally improve digestion.

Is collagen the same as gelatin?

No. Both originate from collagen, but they have different physical properties and processing characteristics. Gelatin can form a gel, while collagen peptides are processed into smaller peptides and generally dissolve more readily.

Can collagen repair intestinal permeability?

There is currently insufficient high-quality human evidence to say that collagen repairs or reverses increased intestinal permeability. Research specifically testing this question is ongoing.

How much collagen should you take for leaky gut?

There is no scientifically established collagen dosage specifically proven to treat increased intestinal permeability. Studies investigating collagen for other outcomes use different doses, and ongoing gut-related trials are also testing different amounts.

Can collagen cause digestive problems?

Some people may experience digestive discomfort or intolerance after taking collagen or other ingredients in a supplement. Individual responses vary, and people with allergies should check the collagen source and complete ingredient list.

Is collagen safe to take every day?

Collagen supplements are generally tolerated by many people, but safety depends on the specific product and individual circumstances. Follow product directions and seek professional advice if you have relevant medical conditions, allergies or concerns about supplementation.

Does collagen help IBS?

There is currently insufficient evidence to recommend collagen as an IBS treatment. IBS has multiple potential causes and should be appropriately assessed and managed rather than assumed to be caused by a “leaky gut.”

Does collagen help bloating?

There is not enough evidence to conclude that collagen reliably reduces bloating. Persistent bloating can have many causes, so identifying the underlying issue is more useful than assuming collagen will resolve it.

What is the difference between Type I and Type II collagen?

Type I collagen is abundant in tissues such as skin, bone, tendons and ligaments, while Type II collagen is predominantly associated with cartilage. Neither has been established as the best collagen type for intestinal permeability.

Sources & Evidence

1. Intestinal barrier and permeability

Effects of dietary components on intestinal permeability in health and disease
Neurogastroenterology & Motility, 2020.
Evidence type: Human-focused review of intestinal barrier and dietary factors.
Supports the explanation of intestinal permeability and the multifactorial nature of the intestinal barrier. [5]

2. Collagen structure and sources

Hydrolyzed Collagen—Sources and Applications
Authors: reviewed in Biotechnology and related literature.
2020.
Evidence type: Scientific review.
Supports information on collagen structure, hydrolyzed collagen, collagen sources and collagen types. [10]

3. Collagen types and tissue distribution

Pharmacological Functions, Synthesis, and Delivery Progress for Collagen as Biodrug and Biomaterial
2023.
Evidence type: Scientific review.
Supports descriptions of Type I, II, III and other collagen types and their tissue distribution. [9]

4. Collagen and connective-tissue outcomes

The effects of collagen peptide supplementation on body composition, collagen synthesis, and recovery from joint injury and exercise: a systematic review
Mishti Khatri et al.
Amino Acids, 2021.
DOI: 10.1007/s00726-021-03072-x
Evidence type: Systematic review of randomized controlled trials.
Supports the discussion of collagen evidence for joint, connective-tissue and exercise-related outcomes. [11]

5. Collagen peptides and exercise/musculoskeletal outcomes

Impact of Collagen Peptide Supplementation in Combination with Long-Term Physical Training on Strength, Musculotendinous Remodeling, Functional Recovery, and Body Composition in Healthy Adults: A Systematic Review with Meta-analysis
Kevin Bischof et al.
Sports Medicine, 2024.
DOI: 10.1007/s40279-024-02079-0
Evidence type: Systematic review and meta-analysis of randomized controlled trials.
Included 19 studies and 768 participants. [12]

6. Hydrolyzed collagen and skin

Effects of Oral Collagen for Skin Anti-Aging: A Systematic Review and Meta-Analysis
Szu-Yu Pu et al.
Nutrients, 2023; 15(9):2080.
DOI: 10.3390/nu15092080
Evidence type: Systematic review and meta-analysis of 26 RCTs involving 1,721 participants. [13]

7. More recent evidence on collagen and skin

Effects of Collagen Supplements on Skin Aging: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
The American Journal of Medicine, 2025; 138(9):1264–1277.
DOI: 10.1016/j.amjmed.2025.04.034
Evidence type: Systematic review and meta-analysis of 23 RCTs involving 1,474 participants.
Important because analyses by funding source and study quality produced substantially less favorable results. [14]

8. Collagen and gastrointestinal symptoms

ClinicalTrials.gov NCT06937801: A Randomized, Double-blind, Placebo-controlled Clinical Trial to Assess the Effect of Collagen Peptide on Perceived Gastrointestinal Discomfort in Healthy Adult Participants With Presence of Gastrointestinal Symptoms.
Enrollment: 116 participants.
Completed November 2025; results not posted on the registry as of the latest available record.
Evidence type: Randomized, double-blind, placebo-controlled clinical trial; registered protocol, not published results. [6]

9. Collagen and intestinal permeability

ClinicalTrials.gov NCT07586930: Effects of Collagen Peptide on Intestinal Permeability Following an Acute Aspirin Challenge in Adults With Moderate GI Symptoms.
Planned enrollment: 92 participants.
Intervention: 2.5 g, 5 g or 10 g collagen peptides versus placebo.
Evidence type: Ongoing randomized clinical trial; results not yet available. [7]

10. Diet and intestinal permeability

Can Diet Alter the Intestinal Barrier Permeability in Healthy People? A Systematic Review
Nutrients, 2024; 16(12):1871.
DOI: 10.3390/nu16121871
Evidence type: Systematic review.
Twelve eligible studies were identified, with the authors concluding that strong evidence remains limited in healthy populations. [15]