Researchers studied nearly 1,000 people in Singapore to see what happens to important vitamins when people eat less meat and more plant-based foods. They found that replacing fish with plant proteins may lower vitamin B12 levels, which your body needs for energy and healthy nerves. However, eating more vegetables and nuts instead of processed meat actually boosted folate levels, another important vitamin. The study suggests that if you’re moving toward plant-based eating, you need to be smart about which plant foods you choose to avoid vitamin deficiencies.

The Quick Take

  • What they studied: How switching from animal-based proteins (meat and fish) to plant-based proteins affects two important vitamins: B12 and folate
  • Who participated: 993 adults living in Singapore, aged 21-75 years, from different ethnic backgrounds
  • Key finding: Replacing fish with plant proteins increased the risk of B12 deficiency by 62-123%, but replacing processed meat with vegetables or nuts actually improved folate levels
  • What it means for you: If you’re reducing meat and fish intake, you may need to pay special attention to getting enough B12 through fortified foods or supplements, while plant-based swaps can actually help with folate levels

The Research Details

Researchers looked at information from 993 people in Singapore and compared what they ate with their blood vitamin levels. They used a detailed food questionnaire to understand each person’s diet and took blood samples to measure B12 and folate. They then used statistical analysis to see if people who ate less animal protein and more plant protein had different vitamin levels. This type of study is like taking a snapshot at one moment in time rather than following people over years.

This research is important because many people are switching to plant-based diets for health and environmental reasons, but we need to understand how this affects essential vitamins. B12 is naturally found mostly in animal products, so people eating more plants need to know if they’re at risk. Understanding these connections helps doctors and nutritionists give better advice to people changing their diets.

This study looked at real people’s actual diets and measured their actual blood vitamin levels, which is stronger than just asking people to remember what they ate. However, because it’s a snapshot study rather than following people over time, we can’t be completely sure that diet changes caused the vitamin changes. The study included diverse ethnic groups, which makes the findings more relevant to Asian populations.

What the Results Show

When people replaced fish (both white fish and oily fish like salmon) with plant proteins, their risk of B12 deficiency went up significantly. Replacing white fish with 30 grams of plant protein daily increased B12 deficiency risk by 62-85%, while replacing oily fish increased it by 98-123%. This is concerning because B12 is harder to find in plant foods. When people replaced a mix of all meats with refined grains like white rice, their B12 deficiency risk also increased by 12%. However, the good news came when people replaced processed meats and processed seafood with vegetables or nuts and seeds—their folate levels actually improved, suggesting these plant swaps have real benefits for this vitamin.

The study found that completely eliminating all meats and replacing them with refined grains (like white rice or white bread) poses a bigger risk for B12 deficiency than just reducing individual types of meat. This suggests that the type of plant food you choose matters—refined grains don’t provide the same nutritional benefits as whole grains, vegetables, nuts, and seeds. The findings highlight that a plant-based diet can work well if you choose nutrient-rich plant foods rather than just any plant-based option.

Previous research has shown that B12 is naturally found mainly in animal products, so this study confirms what nutrition experts already suspected. However, this is one of the first studies to look specifically at Asian populations and to show that the type of plant protein matters. The finding that vegetables and nuts improve folate levels aligns with what we know about these foods being naturally rich in folate, confirming that plant-based swaps can work well for some nutrients.

This study only looked at one point in time, so we can’t prove that changing diets causes vitamin changes—only that they’re connected. The study was done in Singapore, so results might be different in other Asian countries with different food cultures. The study didn’t track whether people were taking supplements, which could affect their vitamin levels. We also don’t know if people maintained these dietary changes long-term or how quickly vitamin levels might change.

The Bottom Line

If you’re reducing meat and fish intake: (1) Make sure you get B12 from fortified plant-based milks, cereals, or supplements—this is especially important if you’re replacing fish; (2) Choose whole plant proteins like legumes, nuts, seeds, and whole grains rather than refined grains; (3) Include plenty of vegetables, which naturally contain folate and other nutrients. These recommendations have moderate confidence because the study is solid but limited to one time point.

This matters most for people in Asian communities who are reducing or eliminating fish and meat, especially those replacing these foods with refined grains. Vegetarians and vegans should pay special attention to B12. People with existing B12 deficiency should be cautious about reducing fish intake. This may be less relevant for people eating a balanced diet that includes fish or fortified foods.

Vitamin B12 deficiency doesn’t develop overnight—your body stores B12 for several years. However, folate changes may happen more quickly, within weeks to months. If you’re making dietary changes, it’s wise to get your B12 and folate levels checked after 6-12 months to see if you need supplements.

Want to Apply This Research?

  • Track weekly servings of B12-rich foods (fish, fortified plant milks, nutritional yeast) and plant proteins (legumes, nuts, seeds) separately to ensure you’re getting both. Set a goal of at least 2-3 servings of B12 sources and 3-4 servings of plant proteins weekly.
  • If reducing fish intake, add one fortified plant-based milk or B12-containing food to your daily routine. When replacing processed meats, specifically choose vegetables, nuts, or seeds rather than refined grains to maximize nutrient benefits.
  • Log your protein sources daily and categorize them as animal-based or plant-based. Every 3 months, review your B12 source intake and adjust if needed. Consider setting a reminder to discuss blood work with your doctor annually if making significant dietary changes.

This research shows associations between diet changes and vitamin levels but doesn’t prove one causes the other. Individual vitamin needs vary based on age, health conditions, medications, and genetics. Before making major dietary changes, especially if you have existing health conditions or take medications, consult with your doctor or registered dietitian. If you’re concerned about B12 or folate deficiency, ask your healthcare provider about blood tests and appropriate supplementation rather than relying on diet alone. This information is educational and should not replace professional medical advice.