For a long time, popular belief has held that following a plant-based diet necessarily implies deficiencies in nutrients such as iron or protein. However, new international research, in which Spanish scientists participated, challenges this idea . The study, published in the journal Biology, reviews more than a hundred studies and concludes that the human body possesses adaptive mechanisms that allow it to make the most of plant-based nutrients.
The research, led by Miguel López-Moreno of the Francisco de Vitoria University in Madrid and with the collaboration of Hana Kahleova of the Physicians Committee for Responsible Medicine, among other experts from Canada, Peru, and Spain, analyzes how the body responds to sustained dietary changes. Far from being a mere passive conduit, the body adjusts its regulatory systems to maintain nutritional balance, even when the intake of certain compounds decreases.
A paradigm shift in nutrition
Traditionally, nutritional science has established a direct relationship between the amount of a nutrient ingested and its availability in the body. But this study demonstrates that this view is overly simplistic . According to the authors, the body doesn't simply absorb what it's given, but rather activates compensatory mechanisms. For example, when a person reduces their consumption of animal iron, the intestine increases the efficiency of absorbing plant-based iron, thanks to the regulation of the hormone hepcidin. Similarly, the internal production of creatine and carnosine increases to compensate for the lower intake of these compounds, found almost exclusively in meat and fish.
Dr. Kahleova points out that the body doesn't act like a simple tube , but rather regulates its systems to maintain stability. This adaptation isn't immediate, but occurs over weeks or months. In fact, the digestive symptoms that often appear when starting a high-fiber diet, such as bloating or gas, tend to disappear as the gut microbiota changes and becomes more efficient at fermenting complex carbohydrates.
The five nutrients that generate the most questions
The review focuses on five areas where plant-based diets are often questioned: iron, creatine and carnosine, protein, fermentable fiber, and polyphenols. In all cases, the researchers found evidence that the body adapts . Regarding iron, although vegetarians rely on non-heme iron, which is less readily absorbed, long-term studies show that the gut compensates by absorbing a higher proportion. Furthermore, the amount of iron consumed by vegetarians and vegans is often comparable to or even greater than that of omnivores, thanks to the intake of legumes, whole grains, and fortified foods.
Regarding creatine and carnosine , vegetarians tend to have lower muscle reserves , but they maintain normal function and respond favorably to supplements. This indicates lower basal saturation, not a deficiency. Plant-based proteins , on the other hand, are perfectly adequately met with well-planned diets, which preserve muscle mass and strength comparable to omnivorous diets. Fermentable fiber, which may initially cause discomfort, is ultimately better utilized by an adapted gut microbiota. And polyphenols, antioxidant compounds in plants, are transformed by gut bacteria into even more bioactive metabolites, with long-term vegans exhibiting higher concentrations.
Limits of adaptation and recommendations
However, the authors caution that this adaptive capacity has its limits . Situations such as pregnancy, chronic inflammation, inflammatory bowel disease, celiac disease, or severe malnutrition can overwhelm the body's regulatory capacity. Therefore, the review advocates for individualized counseling, rather than offering general reassurance or unwarranted alarm. Dr. Kahleova points out that in her own trial with type 1 diabetic patients, a high-fiber, plant-based diet reduced insulin requirements, demonstrating the importance of evaluating the adaptive response in clinical populations.
The study also calls for longitudinal research that measures adaptation over time , using biomarkers that distinguish between a temporary response and a steady state. According to the authors, this approach is applicable not only to plant-based diets but to any nutritional research that aims to infer long-term status from short-term intake data.
This research provides a more nuanced and realistic view of how the human body responds to plant-based diets. Far from being a source of deficiencies, these diets can be perfectly suitable if planned correctly, thanks to physiological adaptation mechanisms. However, it is essential to consider individual circumstances and seek professional advice when there are health conditions that could compromise the body's ability to adapt. Science continues to advance, dispelling myths and offering evidence-based recommendations.
