Grain, the Double Edged Sword

"Consumption of high levels of whole grain cereal products impairs bone metabolism not only by limiting calcium intake, but by indirectly altering vitamin D metabolism. In animal studies it has been long recognized that excessive consumption of cereal grains can induce vitamin D deficiencies in a wide variety of animals [81–83] including primates [84]. Epidemiological studies of populations consuming high levels of unleavened whole grain breads show vitamin D deficiency to be widespread [85–87]. A study of radiolabelled 25-hydroxyvitamin D3 (25(OH)D3) in humans consuming 60 g of wheat bran daily for 30 days clearly demonstrated an enhanced elimination of 25(OH)D3 in the intestinal lumen [88]. The mechanism by which cereal grain consumption influences vitamin D is unclear. Some investigators have suggested that cereal grains may interfere with the enterohepatic circulation of vitamin D or its metabolites [84, 88], whereas others have shown that calcium deficiency in- creases the rate of inactivation of vitamin D in the liver [89]. This effect is mediated by 1,25-dihydroxyvitamin D (1,25(OH)2D) produced in response to secondary hyperparathyroidism, which promotes hepatic conversion of vitamin D to polar inactivation products which are excreted in bile [89]. Consequently, the low Ca/P ratio of cereal grains has the ability to elevate PTH which in turn stimulates increased production of 1,25(OH)2D which causes an acceler- ated loss of 25-hydroxyvitamin D."

http://www.direct-ms.org/pdf/EvolutionPaleolithic/Cereal%20Sword.pdf

So, in case you needed another reason not to eat bread (whole grain or otherwise):

- besides the fact that it has a high calorie to nutrient ratio, and

- rapidly digests into simple sugar and thus drives blood sugars to unhealthy levels resulting in the insulin cascade, and 

- the fact that it has many 'anti-nutrient qualities', and 

- the fact that most bread doesn't taste good enough to eat by itself (how much sugar and/or butter do you slather on your bread to make it desirable?);

Here's another thing we don't need - it interferes with vitamin D utilization.