There's a great deal of uncertainty about the nutritional value of certain foods, herbs and vitamin/mineral supplements, because the bioavailability of such vitamins and minerals is not fully understood and depends on so many variable factors which are difficult to include in tests of humans groups.
For example, raw nuts and seeds, such as Brazil nuts, Almonds, Chia seeds, wholegrain rice, and so on, are considered to be very high in many important nutrients, such as Iron, Manganese, Magnesium, Zinc, Selenium, various vitamins, and so on.
However, what is not so often mentioned is that such raw nuts and seeds contain 'anti-nutrients', which can significantly reduce the bioavailability of such nutrients.
The anti-nutrients are described as 'Phytates' or 'Phytic Acid'. Their role is to preserve the nutrients in the seeds for as long as possible, so that when the conditions are right for the seeds to germinate and sprout, the seeds still have all the nutrients they needs in order to grow and flourish.
As the seeds sprout, the Phytates are reduced and the nutrients are released. However, if we eat the nuts and seeds before they sprout, as we often do, the Phytates, which bind the nutrients, will prevent the digestive system from absorbing and processing the nutrients.
Even more alarming, is the research which suggests if you eat the nuts as part of your main meal, the Phytates and Phytic Acid might also reduce the bioavailability of the nutrients in the main meal, so one often comes across advice to snack on nuts between meals, in order to reduce this effect.