A nut is a fruit composed of a hard shell and a seed, where the hard-shelled fruit does not open to release the seed (indehiscent). So, while, in a culinary context, a wide variety of dried seeds are often called nuts, in a botanical context, only ones that include the indehiscent fruit are considered true nuts. The translation of “nut” in certain languages frequently requires paraphrases as the concept is ambiguous.
Most seeds come from fruits that naturally free themselves from the shell, unlike nuts such as hazelnuts, chestnuts, and acorns, which have hard shell walls and originate from a compound ovary. Culinary usage of the term is less restrictive, and some nuts as defined in food preparation, like pistachios and Brazil nuts, are not nuts in a botanical sense. Common usage of the term often refers to any hard-walled, edible kernel as a nut.
Several epidemiological studies have revealed that people who consume nuts regularly are less likely to suffer from coronary heart disease (CHD). Nuts were first linked to protection against CHD in 1993. Since then many clinical trials have found that consumption of various nuts such as almonds and walnuts can lower serum LDLcholesterol concentrations. Although nuts contain various substances thought to possess cardioprotective effects, scientists believe that their Omega 3 fatty acid profile is at least in part responsible for the hypolipidemic response observed in clinical trials.