Which nutrient is the most difficult to obtain from our diet?

December 8, 2025 •

5 min read

According to the National Institutes of Health, vitamin B12 is found almost exclusively in animal products, making it a particularly challenging nutrient to acquire through a vegan diet. Several other factors, such as age and certain medical conditions, can also impair nutrient absorption, compounding the difficulty for certain populations.

Quick Summary

This article explores the specific nutrients hardest to get from food, focusing on vitamin B12 and vitamin D due to their limited sources and complex absorption processes. It outlines the dietary challenges, common deficiency risks, and reliable solutions like fortification and supplementation.

Key Points

Vitamin B12 is the most challenging nutrient for vegans and vegetarians: Found naturally almost exclusively in animal products, it requires supplementation or fortified foods for those on plant-based diets.
Vitamin D is hard to get from diet alone: Primarily synthesized via sun exposure, its limited presence in foods and reduced synthesis during winter or with sunscreen make dietary sources insufficient.
Absorption is a major factor: Age, certain medications, and digestive issues like Celiac or Crohn's disease can hinder the body's ability to absorb vital nutrients, including B12 and Vitamin D.
Smart food pairings enhance absorption: Combining non-heme iron sources (plant-based) with Vitamin C significantly increases its bioavailability.
Supplements offer a reliable solution: For those with dietary restrictions or absorption issues, targeted supplementation is often the most effective method to ensure adequate intake of difficult-to-obtain nutrients.
Gut health affects nutrient uptake: A healthy gut microbiome, supported by prebiotics and probiotics, can improve the absorption and production of certain nutrients.

The Primary Contenders: Vitamin B12 and Vitamin D

While many nutrients can be challenging to obtain, two stand out due to their specific dietary sources or reliance on external factors: Vitamin B12 and Vitamin D. Vitamin B12's natural occurrence is almost exclusively in animal products, posing a significant hurdle for those on plant-based diets. Vitamin D, while present in some foods, primarily relies on sun exposure for synthesis, making dietary intake alone often insufficient.

Vitamin B12: The Vegan and Vegetarian Challenge

Vitamin B12, or cobalamin, is crucial for nerve function, red blood cell production, and DNA synthesis. Since plants do not produce B12, individuals on a vegan diet must rely on fortified foods or supplements. While lacto-ovo vegetarians consume some animal products like dairy and eggs, these may not provide sufficient amounts, and studies show deficiency is common even in this group. Furthermore, absorption can decrease with age, affecting older adults regardless of diet. The issue is compounded because the high folate content in many vegan diets can mask the megaloblastic anemia caused by B12 deficiency, delaying diagnosis and potentially leading to irreversible neurological damage.

Reliable B12 sources for plant-based diets:

Fortified foods: Many breakfast cereals, plant-based milks (soy, oat), and nutritional yeast are fortified with B12.
Supplements: Regular B12 supplementation is often the most reliable way for vegans and vegetarians to meet their needs.

Vitamin D: The Sun and Food Dilemma

Often called the 'sunshine vitamin', Vitamin D is synthesized in the skin upon exposure to ultraviolet B (UVB) radiation from sunlight. For many, this is the primary source, making dietary intake less significant. However, several factors make relying on sun exposure problematic, including limited sunlight during winter months in higher latitudes, consistent sunscreen use, and darker skin pigmentation. Even for those with adequate sun exposure, few foods naturally contain significant amounts of vitamin D.

Strategies for adequate vitamin D intake:

Dietary sources: Foods like fatty fish (salmon, mackerel), eggs, and some mushrooms contain vitamin D, but often not enough to meet daily requirements.
Fortified products: Cow's milk and some breakfast cereals are fortified with vitamin D.
Supplementation: Given the unreliability of both sun exposure and food sources, supplementation is a common and effective solution for many.

Comparison of Difficult-to-Obtain Nutrients


Nutrient	Primary Challenge	High-Risk Groups	Key Food Sources	Absorption Aids
Vitamin B12	Sourced almost exclusively from animal products; not produced by plants.	Vegans, vegetarians (especially strict), older adults, individuals with malabsorption disorders.	Meat, fish, dairy, eggs, fortified cereals/plant milks, nutritional yeast.	Adequate stomach acid, intrinsic factor.
Vitamin D	Primarily synthesized through sun exposure; limited natural food sources.	Older adults, dark-skinned individuals, those with limited sun exposure, people with fat malabsorption.	Fatty fish, eggs, liver, fortified products.	Exposure to sunlight, healthy fats.
Iron (Non-Heme)	Plant-based form (non-heme) is poorly absorbed compared to animal-based (heme) iron.	Vegans, vegetarians, menstruating women, pregnant individuals.	Legumes, leafy greens, fortified grains, dried fruits.	Vitamin C intake.
Omega-3s (EPA/DHA)	Plant-based sources provide ALA, which must be inefficiently converted to EPA/DHA.	Vegans, vegetarians.	Fatty fish, algae-based supplements.	Healthy digestive system.

Factors Affecting Nutrient Absorption and Mitigation

Beyond the source of a nutrient, several physiological and lifestyle factors can impact how well your body absorbs it. This is particularly relevant for those already at risk of deficiency.

Stomach Acid and Digestive Health

Proper stomach acid (hydrochloric acid) is essential for breaking down food and preparing certain nutrients for absorption, particularly minerals like iron and calcium, and releasing vitamin B12 from food. Conditions causing low stomach acid, or medications that reduce it, can significantly impair absorption.

Fat Malabsorption

Fat-soluble vitamins (A, D, E, K) require dietary fat for optimal absorption. Medical conditions such as Crohn's disease, celiac disease, or gastric bypass surgery can lead to fat malabsorption, increasing the risk of deficiency in these vitamins.

Nutrient Pairings

Some nutrients interact synergistically. For example, consuming vitamin C-rich foods with plant-based iron sources significantly enhances iron absorption. Similarly, vitamin D and vitamin K2 work together to regulate calcium metabolism.

Gut Microbiota

A healthy and diverse gut microbiome plays a crucial role in nutrient absorption and even produces certain B-vitamins. Consuming probiotic and prebiotic foods can support gut health and, in turn, nutrient bioavailability.

Conclusion: Navigating Dietary Challenges

In conclusion, pinpointing a single 'most difficult' nutrient is complex, as it heavily depends on individual factors like diet and physiology. However, Vitamin B12 presents the most significant challenge for anyone avoiding animal products, and Vitamin D is notoriously difficult to obtain from diet alone for the general population. While dietary planning is crucial, recognizing these specific difficulties allows for targeted strategies. For those at risk, incorporating fortified foods and, crucially, high-quality supplements can effectively bridge these nutritional gaps and prevent serious health consequences. Consulting a healthcare professional or registered dietitian is also key for personalized advice and monitoring. The modern diet, with its focus on sustainability and plant-based eating, requires a mindful approach to these nutrient requirements. Taking an informed, proactive stance ensures your body receives all the essential building blocks it needs. For further information on dietary guidelines, consider resources from authoritative health organizations like the National Institutes of Health.

Navigating Nutrient Challenges

Identify Your Risk: Consider your dietary pattern (especially vegan/vegetarian), age, and any existing medical conditions to assess your personal risk for deficiencies like Vitamin B12 or Vitamin D.
Prioritize Fortified Foods: Regularly consume fortified cereals, plant milks, and nutritional yeast to get reliable sources of vitamin B12.
Embrace Targeted Supplements: Given the limitations of dietary sources and sun exposure, using supplements for Vitamin B12 and Vitamin D is often the most reliable strategy.
Practice Smart Food Pairings: To maximize iron absorption, pair plant-based iron sources (like lentils or spinach) with a food rich in Vitamin C (such as tomatoes or citrus).
Optimize Gut Health: Support your gut microbiome by including prebiotic foods (garlic, onions) and probiotic foods (yogurt, kimchi) in your diet to aid overall nutrient absorption.
Monitor Medical Conditions: Individuals with digestive issues (like Crohn's or Celiac disease) or those who have had bariatric surgery should be particularly vigilant about nutrient absorption and consult a healthcare provider for a monitoring plan.
Consider Sun Exposure: Safely manage sun exposure for Vitamin D synthesis, recognizing its limitations based on geography, skin type, and season.
Consult a Professional: When in doubt, seek personalized guidance from a doctor or registered dietitian to ensure you are meeting your unique nutritional needs.

Frequently Asked Questions

Vitamin B12 is produced by microorganisms and is found naturally in animal products like meat, eggs, and dairy. Plants do not produce B12, so a vegan diet, which excludes all animal products, lacks natural dietary sources.

For most people, it is very difficult to get enough vitamin D from food sources alone, as it is primarily synthesized by the body through sun exposure. A few foods contain it naturally, but fortification and supplementation are often necessary.

Groups most at risk for vitamin B12 deficiency include vegans, strict vegetarians, older adults whose absorption ability decreases with age, and individuals with certain medical conditions like pernicious anemia or Celiac disease.

The iron in plant-based foods (non-heme iron) is less bioavailable than animal-based iron. You can significantly enhance its absorption by consuming a source of vitamin C (like citrus fruits, tomatoes, or bell peppers) alongside the meal.

Yes, a healthy gut microbiome with a balance of good bacteria is vital for efficient nutrient absorption. Probiotics and prebiotics can support a healthy gut, improving your body's ability to utilize nutrients from food.

Besides vitamins B12 and D, other nutrients that can be challenging to obtain from certain diets include Omega-3 fatty acids (EPA and DHA), which are less efficiently converted from plant sources, and iron, particularly for those on vegetarian or vegan diets.

For many, supplements are a reliable and effective way to ensure adequate intake of nutrients that are difficult to get from diet alone, such as vitamin B12 and vitamin D. However, they should complement, not replace, a balanced diet and are best discussed with a healthcare provider.