There are 3 parts to a wheat kernel (sometimes  called a wheat berry):

1)  The BRAN is the hard outer covering of the wheat kernel, high in fiber & nutrients. 

2)  The GERM is the nutrient-rich embryo that will sprout and grow into a new wheat plant.  

3)  The ENDOSPERM is the biggest part (83%), the "insides" of the kernel - mostly starch. 

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Diets rich in "whole grain" foods and other plant foods low in total fat, saturated fat, and cholesterol may reduce the risk of heart disease and certain cancers.

 WHITE FLOUR
is made from the endosperm only
= NOT a whole grain

WHOLE WHEAT FLOUR
combines all 3 parts of the wheat berry
= a whole grain