In June 1950, Holiday magazine called Pennington’s diet a “believe it or not diet development” and “an eat-all-you-want reducing diet.” Two years later, Pennington discussed his diet at a small obesity symposium hosted by the Harvard department of nutrition and chaired by Mark Hegsted. “Many of us feel that Dr. Pennington may be on the right track in the practical treatment of obesity,” Hegsted said afterward. “His high percentage of favorable results is impressive and calls for more extensive and for impartial comparative trials by others”—although, Hegsted concluded, “any method of [obesity] treatment other than caloric restriction still requires study by all methods that can be brought to bear on the problem.”

The Harvard symposium led to the publication of Pennington’s presentation in The New England Journal of Medicine, and this, along with the Vogue article, prompted the competing medical journals to address it. In a scathing editorial called “Freak Diets!” The Journal of the American Medical Association (JAMA) took the position that calorie restriction was the only legitimate way to induce weight loss, and that what Hegsted had called “impartial comparative trials by others” were not necessary. “The proposed high-fat diet will probably add unduly to the patient’s weight and thus, in addition to the other harmful effects of obesity, increase the hazard of atherosclerosis,” wrote JAMA. In Britain, The Lancet wrote, “A low calorie intake is the best way to restore the composition of the body to normal, and this is most easily arranged by eliminating fat from the diet.” If Pennington’s diet worked, according to The Lancet, it did so only because “any monotonous diet leads to a loss of weight.”

Clinicians—doctors who actually treated obese patients—pushed back against the experts. After The Lancet’s editorial, local clinicians wrote that the diet was successful in “a surprisingly large proportion of cases,” as one Devonport physician put it. “Results so far certainly seem to support the work of Pennington which you rather lightly dismiss.” “Pennington’s idea of cutting out the carbohydrate but allowing plenty of protein and fat works excellently…,” wrote the prominent British endocrinologist Raymond Greene, “and allows of a higher caloric intake than a proportionate reduction of protein, fat and carbohydrate…. The diet need not be monotonous. Many patients come to prefer it.” By early 1954, The Lancet’s editors were backpedaling, just as they had with Banting a century earlier. “Pennington has hardly proved his case,” the journal argued, but it accepted the possibility that his diet worked, and perhaps not through the usual method of restricting calories.