From a Dietitian’s Perspective

AS SEEN ON MY NEW SUBSTACK – COMPLEXDIETITIAN.SUBSTACK

This post is not medical advice. Please consult your personal physician or dietitian to discuss testing and management that is appropriate for you.

What is MTHFR?

Methylenetetrahydrofolate reductase (MTHFR) polymorphisms—often referred to as “the MTHFR gene”—are common genetic variants that can influence folate metabolism and related biochemical pathways involving vitamin B12. With the increased availability of direct-to-consumer genetic testing, many individuals are now learning their MTHFR status. Alongside this rise in testing has come ongoing discussion: How clinically meaningful is MTHFR testing, and how should it be interpreted in the context of patient care?

As a registered dietitian, nutrient metabolism and reviewing laboratory data is a large part of my work (and educational training). Questions about MTHFR testing come up frequently in my practice, particularly among patients managing fatigue, neurologic symptoms, or complex chronic conditions. This post reflects how I currently think about MTHFR, folate, and vitamin B12 based on available evidence and clinical experience.

Factors Contributing to Folate and Vitamin B12 Deficiency

Folate and vitamin B12 deficiencies can occur for a variety of reasons. While genetic variation in metabolism maycontribute in some cases, deficiencies are often more closely linked to factors such as dietary intake, absorption, medication use, or underlying gastrointestinal or autoimmune conditions.

Potential contributors can include:

Malabsorption-related conditions

• Celiac disease
• Small intestinal bacterial overgrowth (SIBO)
• Short bowel syndrome

Medication-related factors

• Proton pump inhibitors (PPIs)
• H2 receptor blockers

Nutritional intake considerations

• Malnutrition
• Restrictive or limited diets

Additional gastrointestinal or autoimmune conditions

• Pancreatic insufficiency
• Autoimmune gastritis
• Pernicious anemia
• Inflammatory bowel disease involving the small intestine

In many cases, nutrient deficiencies appear to be multifactorial, with genetics representing one possible influence rather than a primary driver.

When Lab Testing May Be Worth Considering

My role as a dietitian is always collaborative and aligned with physician-directed care. Importantly, current evidence-based guidelines for testing and management of folate and vitamin B12 deficiencies do not change based on MTHFR status.

What often matters more is the broader clinical picture.

Blood testing is often considered when individuals present with:

• Symptoms that could suggest malabsorption (such as loose stools, gas, bloating, or abdominal pain)
• Prolonged use of PPIs or H2 blockers
• A history of bowel resection
• Known or suspected celiac disease
• Small intestinal Crohn’s disease
• Restrictive dietary patterns
• Neurologic symptoms such as peripheral neuropathy
• Significant or unexplained fatigue

In my work with patients who have conditions such as POTS, MCAS, and Ehlers-Danlos syndrome (EDS), nutrient deficiencies can be present. In these contexts, lab testing can help clarify contributing factors and inform how repletion is approached.

Any decision to test is best made in conjunction with a physician, with results interpreted alongside symptoms, dietary patterns, and medical history.

MTHFR Genetic Testing Is Not Recommended

Professional organizations, including the American College of Medical Genetics and Genomics (ACMG), do not recommend MTHFR genetic testing. This position reflects findings that MTHFR status does not consistently alter clinical decision-making for folate or vitamin B12 deficiency. While folate and B12 metabolism can play a role in the cardiovascular disease risk (likely a topic for another day), MTHFR genetic testing is not recommended in the setting of determining cardiovascular disease risk or blood clot risk. There are separate blood tests available for this that are best determined by a cardiologist. 

In many scenarios:

• The diagnostic workup for deficiency remains similar regardless of MTHFR status
• Management strategies often do not differ meaningfully

Additionally, MTHFR testing can be costly—often ranging from $100 to $800 or more—and testing quality may vary between companies. Some individuals are left with results that are difficult to interpret or contextualize without clinical guidance.

What About Methylated Vitamins?

A common follow-up question is whether methylated forms of folate or vitamin B12 are necessary or preferable.

Current evidence suggests:

• Folic acid remains the most extensively studied form of folate for correcting deficiency.
• Methylated forms of folate and B12 are widely available and may be well tolerated by some individuals, though comparative research remains limited.
• Individual responses to different supplement forms can vary.

One consistent consideration is monitoring. Supplementation—regardless of form—is ideally guided by laboratory values and reassessed over time. Excessive intake of certain nutrients can carry risks, and more supplementation is not always better.

For this reason, addressing deficiencies with oversight from both a physician and a dietitian can help balance safety with effectiveness.

Closing Thoughts

Concerns about folate and vitamin B12 metabolism are understandable. These nutrients can play important roles in neurologic function, cardiovascular disease risk, and overall health. At the same time, genetics represent only one part of a much larger clinical picture.

Some general considerations:

• Be cautious of approaches that emphasize MTHFR genetic testing as a primary diagnostic tool
• Be mindful of supplement protocols that are not guided by labs or clinical context
• Consider care models that encourage collaboration between physicians and dietitians
• When deficiencies are suspected, testing and monitoring over time may help guide appropriate repletion

TL;DR for Patients

• MTHFR is a genetic variation that can influence how folate is processed in the body, but it is only one of many factors involved in folate and vitamin B12 status.
• Low folate or B12 levels are often related to absorption issues, medications, dietary intake, or underlying health conditions, rather than genetics alone.
• At this time, major medical organizations do not routinely recommend MTHFR genetic testing, as it does not consistently change how deficiencies are evaluated or managed.
• Testing blood levels of folate and vitamin B12—when symptoms or risk factors are present—can be a more practical starting point.
• Different forms of folate and B12 supplements exist. Some people report feeling better with certain forms, but responses can vary, and research in this area continues to evolve.
• Supplementation is generally safest when guided by lab values and monitored over time with a healthcare professional.

If you’re experiencing symptoms, asking thoughtful questions and seeking collaborative care can be a reasonable approach—especially when navigating complex or chronic health concerns.

Patients: Your concerns are valid, and advocating for yourself can be important. Evidence-informed care and thoughtful interpretation of results may help reduce unnecessary interventions.

Physicians and fellow dietitians: I’m interested in hearing how others approach MTHFR-related questions in practice, particularly as genetic testing becomes more accessible. I am always open to respectful and open dialogue.

Thanks for reading,
Crystal McLean, MS, RD, LDN

Check out my new sub stack – https://complexdietitian.substack.com

Additional Reading Material and Resources:

Centers for Disease Control and Prevention. MTHFR gene variant and folic acid facts. Updated May 15, 2024. Accessed January 24, 2026. https://www.cdc.gov/folic-acid/data-research/mthfr/index.html

Hickey SE, Curry CJ, Toriello HV. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing. Genet Med. 2013;15(2):153-156. doi:10.1038/gim.2012.165

Liu C, Yao H, Wang F. Effect of nutritional supplements for reducing homocysteine levels in healthy adults: a systematic review and network meta-analysis of randomized trials. Nutr Rev. 2025;.

Colson NJ, Naug HL, Nikbakht E, Zhang P, McCormack JThe impact of MTHFR 677 C/T genotypes on folate status markers: a meta-analysis of folic acid intervention studies.Eur J Nutr.(2017-Feb)

Quigley EMM, Murray JA, Pimentel M. AGA clinical practice update on small intestinal bacterial overgrowth: expert review. Gastroenterology. 2020;159(4):1526-1532.

Skavinska O, Rossokha Z, Stefanyshyn V, et al. Comparative analysis of treatment with folate forms in clinical practice. Nutr Rev. 2025.

Aziz Q, Harris LA, Goodman BP, Simrén M, Shin A. AGA clinical practice update on gastrointestinal manifestations and autonomic or immune dysfunction in hypermobile Ehlers-Danlos syndrome: expert review. Clin Gastroenterol Hepatol.2025.

Green R. Indicators for assessing folate and vitamin B-12 status and for monitoring the efficacy of intervention strategies. Am J Clin Nutr. 2011;94(2):666S-672S.

Wolffenbuttel BHR, McCaddon A, Ahmadi KR, Green R. A brief overview of the diagnosis and treatment of cobalamin (B12) deficiency. Food Nutr Bull. 2024;45(1).

Topan R, Pandya S, Chance P, et al. Nutrient intake, dietary patterns, and relationship to symptoms and comorbidities in hypermobile Ehlers-Danlos syndrome. Clin Nutr. 2025.