Robert O Young has argued in a series of UK and US best-sellers that a series of potentially deadly diseases can be beaten by anyone who gets their pH right: their balance between acids and alkalines.
His theory is that, according to his website, pH Miracle Living, "cancer is unequivocally not a disease, but a symptom" of excessive acid in the body. Its treatment, he reckons, like other conditions such as diabetes and obesity, should be to eat high-alkaline foods, such as the three-to-six avocados Mr Young consumes a day.
Doctors do not agree. "This is biological nonsense," said Cancer Research UK.
"True, cancer cells can't live in an overly alkaline environment, but neither can any of the other cells in your body.
"There's no good evidence to prove that diet can manipulate whole body pH, or that it has an impact on cancer."
Mr Young's books, including his latest, Reverse Cancer Now, are on sale in the UK. The Herald understands British authorities are looking at some of his merchandise. A spokesman for the district attorney in San Diego said: "Customs in the UK is one of the law enforcement agencies we've been working with during the investigation of this case."
Mr Young's website features video testimonials from people who claim to have reversed cancer while on his regimen.
He also sells a range of products, such as water ionizers that can cost more than $2,000. His "Young pHorever" range of dietary supplements,such as fruit and vegetable powder, retail at $38 for half a pound and come in a bottle with a smiling picture of Mr Young and his wife Shelley, co-author of some of his work.
Mr Young's patients have been in the news before. Kim Tinkham, a breast cancer sufferer, appeared on the US chat show Oprah saying she believed she could beat the disease using alternative methods, including the power of positive thinking outlined in US best-selling book The Secret.
Ms Tinkham turned to Mr Young, whose alkalising treat-ment, she said, made her feel better in a week.
Ms Tinkham died, three years after being diagnosed.