I have been eating orange peels ever since FunkOdyssey posted a link to the DirtDoctor regarding d-limonene and its use in heartburn. Then reading carefully through some of MR's posts he states that he eats the orange peels too. Indeed there does seem to be some very beneficial effects due to this substance (particularly its anti-cancer effect). Unlike many phytochemicals, it is actually absorbed and can be detected in both the plasma and adipose tissue (it is fat soluble) [1], which maybe explains its potent effect in mammary carcinogenesis.
Anyways for some papers on limonene and its anti-cancer effect look at (2,3,4).
From (5) it seems that 2 lemons provide 596mg of d-limonene and from this article (6), lemon has about twice the limonene content of oranges. Each lemon ~100g would contain 298mg, and 1 orange is approximately 150g, thus each orange probably has around 200mg of d-limonene (this is a very very crude estimate).
Looking back at older research there was a ton of studies done on citrus fiber, and its relationship to cholesterol, heart disease and what not (7,8). [For an interesting read on the hemodynamic hypothesis of heart disease see (9)].
Beyond these effects there was a recent paper seeing its effects in rats for diabetes (10). I DON'T have access to this paper so if anyone grab me the paper it would be much appreciated.
(For some folks the limonene may irritate the stomach so maybe give it half a try first, if you want to of course, using lemon rind in your cooking may be better for some).
References
1. Nutr Cancer. 2010;62(6):783-8.Adipose tissue accumulation of d-limonene with the consumption of a lemonade preparation rich in d-limonene content.Miller JA, Hakim IA, Chew W, Thompson P, Thomson CA, Chow HH.
5. Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1472-6.Pharmacokinetics of perillic acid in humans after a single dose administration of a citrus preparation rich in d-limonene content.Chow HH, Salazar D, Hakim IA.
6. http://www.perkinelm...RindsbyGCMS.pdf
7. Clin Cardiol. 1988 Sep;11(9):589-94.The effects of grapefruit pectin on patients at risk for coronary heart disease without altering diet or lifestyle.Cerda JJ, Robbins FL, Burgin CW, Baumgartner TG, Rice RW.
8. Clin Cardiol. 1988 Sep;11(9):597-600.Grapefruit pectin inhibits hypercholesterolemia and atherosclerosis in miniature swine.Baekey PA, Cerda JJ, Burgin CW, Robbins FL, Rice RW, Baumgartner TG.
9. QJM. 2011 Oct;104(10):867-70. Epub 2011 Jun 20.The great cholesterol myth; unfortunate consequences of Brown and Goldstein's mistake.Adams DD.
10. Eur J Nutr. 2011 Mar 29. [Epub ahead of print]Dietary d-limonene alleviates insulin resistance and oxidative stress-induced liver injury in high-fat diet and L-NAME-treated rats.Victor Antony Santiago J, Jayachitra J, Shenbagam M, Nalini N.