Exploring the Impact of Retinol, Vitamin K2, Carnitine, and Creatine in Plant-Based Diets 

Plant-based diets have gained significant attention for their association with reduced risks of chronic diseases such as heart disease, diabetes, and certain cancers. However, concerns have been raised about the potential implications of lower dietary intakes of certain non-essential nutrients—retinol, vitamin K2, carnitine, and creatine—which are predominantly found in animal-derived foods. This narrative review delves into the physiological roles of these nutrients and evaluates whether their absence in plant-based diets could negatively impact health outcomes. 

Retinol: Meeting Needs Through Plant-Based Sources 

Retinol, a form of vitamin A, is essential for vision, immune function, and cellular communication. While animal products like liver and dairy are rich sources of retinol, plant-based diets rely on provitamin A carotenoids, such as beta-carotene, which the body converts into retinol. Although genetic variations can affect the efficiency of this conversion, studies show that even individuals with reduced conversion rates can meet their retinol requirements through a well-planned plant-based diet. Foods like carrots, sweet potatoes, and leafy greens are excellent sources of beta-carotene, ensuring that plant-based eaters are not at a disadvantage. 

Vitamin K2: Endogenous Synthesis vs. Dietary Intake 

Vitamin K2, known for its role in bone and cardiovascular health, is primarily found in fermented foods and animal products. However, the human body can synthesize vitamin K2 endogenously through the action of gut bacteria. Current research does not consistently demonstrate that dietary vitamin K2 provides additional benefits beyond what is produced naturally. While some studies suggest a potential link between dietary vitamin K2 and improved bone density or reduced arterial calcification, the evidence remains inconclusive. For individuals on plant-based diets, maintaining a healthy gut microbiome appears sufficient to meet physiological needs. 

Carnitine: Muscle Function and Metabolic Health 

Carnitine, a compound involved in energy production by transporting fatty acids into mitochondria, is abundant in red meat. While plant-based diets typically contain lower levels of carnitine, the body can synthesize it from the amino acids lysine and methionine. Research indicates that carnitine levels in vegetarians and vegans are often lower than in omnivores, but this difference does not translate into compromised muscle function, cognitive health, or metabolic outcomes. Supplemental carnitine is rarely necessary, as the body’s endogenous production appears adequate to meet needs. 

Creatine: Cognitive and Physical Performance 

Creatine, primarily found in meat and fish, plays a critical role in energy metabolism, particularly during high-intensity exercise. While plant-based diets are naturally low in creatine, studies show that vegetarians and vegans have lower muscle creatine stores compared to omnivores. However, this difference does not necessarily result in impaired physical performance or cognitive function. Some research suggests that creatine supplementation may benefit vegetarians and vegans, particularly in activities requiring short bursts of energy, but the overall impact on long-term health remains unclear. 

Conclusion: No Significant Disadvantages for Plant-Based Diets 

The current body of evidence does not support the notion that the absence of retinol, vitamin K2, carnitine, and creatine in plant-based diets adversely affects health. Provitamin A carotenoids, endogenous vitamin K2 synthesis, and the body’s ability to produce carnitine and creatine ensure that plant-based eaters can meet their physiological needs without compromising health outcomes. While individual variations and specific health goals may warrant targeted supplementation, a well-planned plant-based diet remains a viable and healthful choice for most individuals. 

Commentary by SuppBase columnist Alice Winters

The narrative review provides a balanced and evidence-based perspective on the role of non-essential nutrients in plant-based diets. It effectively addresses common concerns about retinol, vitamin K2, carnitine, and creatine, offering reassurance to those considering or already following a plant-based lifestyle. 

One of the strengths of the review is its emphasis on the body’s ability to adapt and synthesize certain nutrients endogenously. For instance, the discussion on vitamin K2 highlights the importance of gut health, which is often overlooked in conversations about plant-based nutrition. Similarly, the review’s nuanced take on creatine supplementation acknowledges potential benefits for specific populations without overstating their necessity. 

However, the review could have delved deeper into the practical implications of these findings. For example, while provitamin A carotenoids can meet retinol needs, the review might have provided more specific dietary recommendations or portion sizes to help readers optimize their intake. Additionally, the discussion on creatine could have explored the potential cognitive benefits of supplementation for vegetarians and vegans, particularly in aging populations or those with high cognitive demands. 

Another area for further exploration is the interplay between these nutrients and other dietary components. For instance, how does the presence of dietary fats affect the absorption of provitamin A carotenoids? Are there synergistic effects between vitamin K2 and other nutrients like vitamin D in bone health? Addressing these questions could provide a more holistic understanding of plant-based nutrition. 

Finally, the review’s conclusion is well-supported but could have emphasized the importance of individualized nutrition. While the evidence suggests that most individuals can thrive on a plant-based diet, genetic variations, lifestyle factors, and health conditions may influence nutrient needs. Encouraging readers to consult with healthcare professionals or dietitians could enhance the practical applicability of the review. 

In summary, this narrative review offers a thorough and insightful analysis of non-essential nutrients in plant-based diets. It successfully dispels common myths and provides a solid foundation for further exploration. By addressing practical considerations and individual variability, future research could build on this work to offer even more actionable guidance for plant-based eaters.