"Ayurveda states there are 3 ways to cure disease. Food, herbs and poisons."
That, of course, is wrong. There are additional way to cure a disease. Unless of course that you're using "poison" as a catch-all term to mean anything which isn't food or herbs, in which case it it's a rather useless redefinition to mean simply 'neither food nor herb.'
For example, radiation therapy for cancer is neither a food nor herb, so by definition you place it into "poison", even though it doesn't act like any chemical poison. There's a certain logic to that assignment - radiation treatment is not something an otherwise healthy person would do - but it's a treatment that no traditional Ayurveda practitioner ever considered.
UVB exposure (ie, sunlight or phototherapy) can be an effective treatment for some people who are vitamin B deficient because of malabsorption syndromes (like Cystic fibrosis and short bowel syndrome) which prevent them from absorbing vitamin D through their diet.
Since UVB can cure a disease but is neither a food nor an herb, it must be a poison, right? But UVB is something that healthy people get all the time, so it wouldn't normally be considered a poison. In fact, it could be removed completely, so long as there were other source of vitamin B. Still, you might say that UVB is a food instead of a poison. The problem there is that too much exposure to UVB increases the risk of cancer. Is it both a food and a poison?
Oxygen therapy is useful as part of many treatments, including aborting cluster headache attacks. Perhaps oxygen is also a food? Bu too much oxygen leads to oxygen toxicity. So it is definitely a poison, right? Interesting that we require poison in order to breath.
The issue is, as Nursie stressed, that "the dose makes the poison". Paracelsus said that almost 500 years ago, and it's still true. Even in Ayurvedic assignments of different treatments.
Ayurveda says that nutmeg is an herb, right? It's used as a medicine because of its sedative properties. But eat 10 or so of the seeds and there's a good chance you will die. So, an herb can also be a poison?
Obviously then the three categories are not that distinct. I would argue that they are blurry enough as to be unusable. Life is not so simple as to classify treatments into three distinct groups.
And I don't know what you mean by "Modern [medicine] ... has very little information on how to cure through food." Beriberi, rickets, scurvy, pellagra, kwashiorkor, Korsakoff's syndrome, and Wernicke's encephalopathy are just some of the diseases which modern medicine has cured through food. For several thousand years, beriberi was endemic in Asia, because polished white rice was a staple food.
What is the Ayurveda treatment for handle that disease, and was it developed before or after modern medical researchers identified that it was nutrition deficiency? (Hint: it was after.)
(PS: ultrasonic waves are used to break up kidney stones. That's cure for a disease, no? Are ultrasonic waves food, herb, or poison?)