Publish Date

January 3, 2023

In response to the inaccurate, unscientific article by Thomas Lodi, M.D. on oxalates1 in the December 2015 issue of Townsend Letter, I will make the following point-by-point responses:

1 – Cartoons about Popeye.
I will not use any cartoons in my response. Anyone interested in cartoons should immediately stop reading this article and start reading their local paper’s comic section.

2 – Inaccurate references.
The tone for accuracy of the author is set in the very first paragraph of his article in which his first reference, #23, has nothing to do with my green smoothie article, which is reference #24. A better reference would actually be #2 from my article2. When the clock strikes 13, the accuracy of the other 12 hours of the clock is in serious question.

3 – Inaccuracy about the contribution of endogenous production to total oxalate load.
Lodi states that 80-90% of oxalates in the body are endogenously produced. Unfortunately, the best scientific study refutes his assertion. According to Holmes et al3, who did extremely well-controlled studies on every aspect of oxalate metabolism and has published forty-one scientific articles on oxalates in the peer-reviewed literature, the mean dietary oxalate contribution to total oxalate in the diet is 52.6% on a high oxalate diet which was defined as a diet of 250 mg oxalate per day. The person drinking a green smoothie with 2 cups of raw spinach ingests 1312 mg of oxalates or over five times the level of what Holmes considers a high-oxalate diet, just in the spinach consumption alone and over 26 times the amount of oxalates in a low oxalate diet (50 mg per day)4. The estimated human production of oxalates is 40 mg per day3. On a green smoothie diet with two cups of spinach, the diet in normal humans contains 33 times the endogenous human production of oxalates just based on the spinach alone.

All of Lodi’s assertions about the benefits of a vegetarian diet are meaningless since there is no single vegetarian diet; there are as many vegetarian diets as there are vegetarians.

4 – Inaccuracy about the availability of calcium and magnesium in spinach.
Lodi states that “every plant, green and otherwise (including spinach) has abundant magnesium and calcium and potassium”. Unfortunately, none of the calcium and magnesium in spinach or other high oxalate plants is bioavailable since it is strongly bound to oxalates. Furthermore, the average oxalate value of spinach is 7.5 times its calcium content, making spinach a very poor choice for someone to maintain adequate calcium stores5. According to Kohmani, who added a good deal of spinach, similar to the diet of a person ingesting a daily green smoothie or a large daily spinach salad, to the diet of rats to determine its effects5:

“If to a diet of meat, peas, carrots and sweet potatoes, relatively low in calcium but permitting good though not maximum growth and bone formation, spinach is added to the extent of about 8% to supply 60% of the calcium, a high percentage of deaths occurs among rats fed between the age of 21 and 90 days. Reproduction is impossible. The bones are extremely low in calcium, tooth structure is disorganized and dentine poorly calcified. Spinach not only supplies no available calcium but renders unavailable considerable of that of the other foods. Considerable of the oxalate appears in the urine, much more in the feces.”

5 – Lodi argues that his patients haven’t complained about kidney stones while drinking a lot of green smoothies so oxalates must not be problematic.
Lodi’s contention that his patients on a high oxalate diet don’t have kidney stones is anecdotal. He presents no data from active chart review of his patients to determine if questions about kidney stones were ever asked. Furthermore, it is doubtful that his patients would have even have connected their diet with their kidney stones. I have had numerous seminars on the connection between oxalates and kidney stones and it is common to get feedback from the audience members that they had kidney stones shortly after starting either a diet including a spinach green smoothie or a large spinach salad on a regular basis. Since these comments were not even solicited, it is likely that even a larger number of individuals may have experienced kidney stones but were shy to voice their experiences. A neurologist friend attributes his recent severely-disabling stroke to the dietary changes encouraged by his wife that placed him on a daily green spinach smoothie for a considerable time.

Furthermore, Lodi seems to think that a lack of kidney stones indicates a lack of oxalate problems. However, oxalates may form in virtually every organ of the body including the eyes, vulva, lymph nodes, liver, testes, skin, bones, gums, thyroid gland, heart, arteries, and muscles6-7. Oxalates may occur in these other organs without appearing in the urinary tract at all and in individuals without genetic hyperoxalurias7. Oxalates have been implicated in heart disease7, stroke, vulvodynia, and autism8-10. Women of child-bearing age need to be especially careful of the spinach green smoothie diet because of the autism oxalate connection and the negative effects of spinach containing oxalates on fertility5. Prisoners in the state prisons in Illinois were encouraged by the Weston-Price Nutrition Foundation to file a lawsuit against the state because of their deteriorating health due to a high amount of soy protein in the prison diet11. Soy protein is tied with spinach as the highest oxalate foods4. Oxalates are especially toxic to the endothelial cells of the arteries, leading to atherosclerosis12. Oxalate crystals are concentrated in the atherosclerotic lesions7. Such lesions have commonly been overlooked by the use of stains of atherosclerotic lesions that make the oxalate crystals difficult to visualize. The relatives of people consuming the green smoothie diet would only know of their loved ones’ oxalate deposits throughout their organs on the day of their autopsies which employed pathological examinations that can detect oxalates.

Primary genetic hyperoxaluria is not the major cause of kidney stones in adults since 80% of individuals died of this disorder before age 20 and it is so rare that it could not possibly be the cause of most cases of oxalate kidney stones13. However, a genetic polymorphism present in up to 20% of Caucasian groups called P11L codes for a protein with three times less activity of alanine: glyoxylate aminotransferase (AGT) than the predominant normal activity polymorphism, leading to excessive endogenous production of oxalates14. This substantial group of individuals would be even more susceptible to the harm of a high oxalate diet. Kidney stones were rampant in the United Kingdom during the World Wars when rhubarb, another high oxalate food, was recommended as a substitute for other low oxalate but unavailable vegetables13.

In summary, those who do not care for their health can eat or drink whatever they want. But they should realize that their diets are fad-based and/or based on quasi-religious (“feasts” as part of the “awakening” according to Lodi) reasons, not based on hard scientific evidence. Furthermore, they should be aware that their diet may kill them15. The green smoothie fad will go down in medical history with the AMA journal allowing cigarette advertising with physician endorsements and the use of mercury-containing teething powder for babies as one of the greatest health follies in a considerable time.


  1. Lodi, T. Green smoothie bliss: Was Popeye secretly on dialysis?  Townsend Letter for Doctors. Dec 2015 pgs 28-39
  2. Shaw, W.  The Green Smoothie Health Fad: This Road to Health Hell is Paved with Toxic   Oxalate Crystals.  Townsend Letter for Doctors. Jan 2015 Available online at:
  3. Holmes RP, Goodman HO, and Assimos DG. Contribution of dietary oxalate to urinary oxalate excretion. Kidney International, Vol. 59 (2001), pp. 270–276
  4. Harvard T.H. Chan School of Public Health Nutrition Department’s File Download Site on oxalates in the diet. Accessed December 1,2015
  5. Kohmani,EF. Oxalic acid in foods and its fate in the diet. Journal of Nutrition 18(3):233-246,1939
  6. Jessica N. Lange, Kyle D.Wood, John Knight, Dean G. Assimos, and Ross P. Holmes. Glyoxal Formation and Its Role in Endogenous Oxalate Synthesis. Advances in Urology Volume 2012, Article ID 819202, 5 pages doi:10.1155/2012/819202
  7. G.A. Fishbein, R. G. Micheletti, J. S. Currier, E. Singer, and M. C. Fishbein, Atherosclerotic oxalosis in coronary arteries, Cardiovascular Pathology, vol. 17, no. 2, pp. 117–123, 2008.
  8. Giuseppe Di Pasquale, , Mariangela Ribani, Alvaro Andreoli, , Gian Angelo Zampa, and Giuseppe Pinelli,  Cardioembolic Stroke in Primary Oxalosis With Cardiac Involvement. Stroke 1989, 20:1403-1406
  9. Solomons CC, Melmed MH, Heitler SM.Calcium citrate for vulvar vestibulitis. A case report. J Reprod Med. 1991 Dec;36(12):879-82.
  10. Konstantynowicz J, Porowski T, Zoch-Zwierz W, Wasilewska J, Kadziela-Olech H, Kulak W, Owens SC, Piotrowska-Jastrzebska J, Kaczmarski M. A potential pathogenic role of oxalate in autism. Eur J Paediatr Neurol. 2012 Sep;16(5):485-91.
  11. Monica Eng, Chicago Tribune reporter. Soy in Illinois prison diets prompts lawsuit over health effects. December 21, 2009. Accessed December 2,2015
  12. RI Levin, PW Kantoff and EA Jaffe Uremic levels of oxalic acid suppress replication and migration of human endothelial cells. Arterioscler Thromb Vasc Biol 1990, 10:198-207
  13. A. J. Chaplin Histopathological occurrence and characterization of calcium oxalate: a review. J. Clin. Path., 1977, 30, 800-811
  14. Michael J. Lumb and Christopher J. Danpure.  Functional Synergism between the Most Common Polymorphism in Human Alanine:Glyoxylate Aminotransferase and Four of the Most Common Disease-causing Mutations.  Journal of Biological Chemistry Vol. 275, No. 46, November 17, pp. 36415–36422, 2000
  15. Sanz P, Reig R: Clinical and pathological findings in fatal plant oxalosis. Am J Forensic Med Pathol 13:342–345, 1992
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About the Author

William Shaw, PhD

William Shaw, PhD, is board certified in the fields of clinical chemistry and toxicology by the American Board of Clinical Chemistry. Before he founded The Great Plains Laboratory, Inc., Dr. Shaw worked for the Centers for Disease Control and Prevention (CDC), Children’s Mercy Hospital, University of Missouri at Kansas City School of Medicine, and Smith Kline Laboratories.