[12] In 2002, Gundry began transitioning from Clinical Professor of Cardiothoracic Surgery at Loma Linda University School of Medicine to private practice by starting The International Heart & Lung Institute in Palm Springs, California.

[15][16] While not an accredited dietitian, Gundry's advice focused on heart health and followed conventional wisdom of Western diets such as drinking a glass of red wine per day, increasing intake of plants and nuts, reducing simple carbohydrates, and consuming fish and grass-fed meats.

In 2022, he authored Unlocking the Keto Code which promotes a lectin-free ketogenic diet consisting of goat and sheep dairy products, fermented foods, grass-fed beef, shellfish, olive oil, and red wine.

[9][7][27][6] T. Colin Campbell, a biochemist and advocate for plant-based diets, states that The Plant Paradox contains numerous unsupported claims, and refutes that it makes a "convincing argument that lectins as a class are hazardous.

[27] Harriet Hall of Science-Based Medicine has noted that Gundry's alleged evidence for the benefits of a lectin-free diet is anecdotal and meaningless as there are no studies with control groups in the medical literature to support his claims.

He also commented that the book makes an unusual claim that consumption of fruit leads to obesity and weight gain which is not supported by any evidence and is contradicted by cohort and experimental studies which show an inverse association.

[1] Kratz concluded that "while the diet recommended in The Plant Paradox probably has general health benefits for people who can stick with it, it’s not clear whether avoiding common dietary lectins is beneficial".

The American Heart Association issued an expression of concern, warning that the abstract may not be reliable and that, among other problems, there were "no statistical analyses for significance provided, and the author is not clear that only anecdotal data was used”.