Only half the minerals actually become available for absorption
Uma pesquisa conduzida na Universidade Federal de São Paulo lança luz sobre uma lacuna silenciosa entre o que os alimentos contêm e o que o corpo humano efetivamente consegue aproveitar. Ao simular laboratorialmente o processo digestivo, cientistas descobriram que castanhas de caju e castanhas-do-brasil liberam apenas metade — ou menos — de seus minerais durante a digestão. O achado convida a uma reflexão mais honesta sobre como lemos rótulos nutricionais e construímos expectativas em torno de alimentos considerados saudáveis.
- A crença popular de que comer castanhas garante boa absorção de minerais como cobre e magnésio é colocada em xeque por dados laboratoriais concretos.
- A simulação digestiva revelou que até 72% do magnésio da castanha-do-brasil simplesmente não se torna disponível para o organismo durante a digestão.
- Manganês e zinco, presentes nas castanhas, sequer puderam ser quantificados — suas concentrações ficaram abaixo do limite de detecção dos instrumentos.
- Pesquisadores alertam que bioacessibilidade e biodisponibilidade são conceitos distintos, e que estudos em humanos ainda são necessários para completar esse mapa.
- A conclusão prática aponta para dietas variadas: castanhas são aliadas nutricionais, não fontes exclusivas de minerais essenciais.
Pesquisadores da Universidade Federal de São Paulo se debruçaram sobre uma pergunta aparentemente simples: ao comer castanhas de caju ou castanhas-do-brasil, quanto dos minerais presentes no alimento realmente chega à corrente sanguínea? A resposta, publicada na revista Química Nova, é menos animadora do que muitos consumidores imaginariam.
O estudo, liderado pelo químico Angerson Nogueira do Nascimento com apoio da FAPESP, não se limitou a medir o conteúdo mineral total das castanhas. Os pesquisadores foram além: simularam em laboratório as condições do sistema digestivo humano — temperatura, acidez, enzimas e movimentos mecânicos do estômago e intestinos — para verificar quais minerais de fato se tornavam acessíveis ao organismo.
Quatro minerais foram monitorados: cobre, magnésio, manganês e zinco. Os resultados expuseram uma diferença expressiva entre o que o alimento contém e o que o corpo consegue usar. Nas castanhas de caju, cerca de 56% do cobre e 52% do magnésio mostraram-se bioacessíveis. Nas castanhas-do-brasil, os índices foram menores: aproximadamente 50% do cobre e apenas 28% do magnésio. Manganês e zinco estavam presentes em quantidades tão reduzidas que ficaram abaixo da capacidade de detecção dos equipamentos.
Nascimento destacou que os resultados devem mudar a forma como interpretamos informações nutricionais. O conteúdo total de um mineral em um alimento conta apenas parte da história — o que importa é quanto desse mineral é liberado durante a digestão e, posteriormente, absorvido pelo organismo. Castanhas seguem sendo alimentos nutritivos e valiosos, mas devem ser vistas como parte de uma dieta equilibrada e diversificada, não como fontes exclusivas de minerais essenciais.
A team of researchers at São Paulo's Federal University set out to answer a question that sounds simple but turns out to matter: when you eat a handful of cashews or Brazil nuts, how much of the mineral content actually makes it into your bloodstream? The answer, published this spring in the journal Química Nova, is less than you might hope.
The study, led by chemist Angerson Nogueira do Nascimento and conducted with support from the São Paulo Research Foundation, focused on two nuts widely consumed across Brazil—cashews and Brazil nuts. Rather than simply measuring the total mineral content of these foods, the researchers did something more revealing: they simulated human digestion in a laboratory, recreating the temperature, acidity, enzyme composition, and mechanical action of the stomach and intestines to see which minerals actually became available for the body to absorb.
Four minerals were tracked: copper, which helps form red blood cells and supports immune function; magnesium, essential for bone health and muscle contraction; manganese, which acts as an antioxidant and aids in bone formation; and zinc, critical for immunity, wound healing, and protein synthesis. The researchers first measured the total concentration of each mineral in the nuts, then ran them through their digestive simulation to determine what fraction actually became accessible.
The results revealed a significant gap between what's in the food and what the body can use. In cashews, approximately 56 percent of the copper and 52 percent of the magnesium were bioaccessible—meaning they were released from the food matrix during digestion and theoretically available for absorption. Brazil nuts showed slightly lower rates: about 50 percent of copper and 28 percent of magnesium. Manganese and zinc were present in such small quantities that they fell below the detection threshold of the laboratory instruments.
The distinction between bioaccessibility and bioavailability matters here. Bioaccessibility refers to the fraction of a nutrient that gets released from food during digestion and becomes potentially available for the body to absorb—something that can be measured in a laboratory. Bioavailability, by contrast, describes the portion that actually gets absorbed and used by the body, accounting for metabolism, distribution, and excretion. That requires human or animal studies, which demand significant resources and ethical approval. What the Unifesp team measured was the first part of that chain: the liberation of minerals from the food itself.
Nascimento emphasized that the findings should reshape how we think about nutritional labeling and dietary guidance. A food's total mineral content tells only part of the story. Two foods might contain identical amounts of copper, but if one releases that copper during digestion while the other locks it away in indigestible compounds, their nutritional value to the body is fundamentally different. The research suggests that nuts like cashews and Brazil nuts should be understood not as exclusive sources of these minerals but as complementary contributors to a varied, balanced diet—part of the picture, not the whole picture.
Notable Quotes
The evaluation of a food's nutritional value should not be limited to the total concentration of nutrients. It is fundamental to also investigate how these elements behave under conditions that simulate the digestive system.— Angerson Nogueira do Nascimento, lead researcher
The Hearth Conversation Another angle on the story
So the nuts actually contain these minerals, but the body can't get to them?
Not quite. The minerals are there, but the digestive process only releases about half of them. The other half stays bound up in the food matrix and passes through.
Why does that happen? What's holding the minerals back?
The researchers didn't detail the specific mechanisms in this study—that's a question for follow-up work. But it's likely compounds in the nuts themselves, like fiber or certain plant compounds, that bind to the minerals and prevent them from being released during digestion.
So if I eat Brazil nuts for magnesium, I'm only getting 28 percent of what the label says?
Roughly, yes. The label shows total content. But based on this simulation, only about 28 percent of the magnesium in Brazil nuts becomes available for your body to actually absorb during digestion.
Does cooking or processing change that?
This study tested the nuts as they're typically consumed, but the researchers didn't explore whether roasting, blanching, or other preparation methods might improve mineral release. That's another open question.
Should people stop eating nuts?
No. The study shows nuts still contribute meaningful minerals to the diet. They're just not as concentrated a source as the raw numbers suggest. They work best as part of a varied diet with other mineral sources.