Let me add on to rob_mtl's good answer.
Firstly, diabetes type 2 is a disease that seems to be reversible and curable by changing one's diet to have less carbohydrates and to be replaced with more fats and proteins. Please see this YouTube TED talk. Interestingly, the Buddha gave similar advice to King Pasenadi of Kosala 2500 years ago, in the Donapaka Sutta, at least with regard to reducing carbohydrate intake. Sometimes, Buddhist teachings can be very down-to-earth and practical.
A similar question to your's, was asked by householder Nakulapita to the Buddha in the Nakulapita Sutta:
I have heard that on one occasion the Blessed One was living among the
Bhaggas at Crocodile Haunt in the Bhesakala Grove at the Deer Park.
Then the householder Nakulapita went to the Blessed One and on
arrival, having bowed down to him, sat to one side. As he was sitting
there he said to the Blessed One, "Lord, I am a feeble old man, aged,
advanced in years, having come to the last stage of life. I am
afflicted in body & ailing with every moment. And it is only rarely
that I get to see the Blessed One & the monks who nourish the heart.
May the Blessed One teach me, may the Blessed One instruct me, for my
long-term benefit & happiness."
"So it is, householder. So it is. The body is afflicted, weak, &
encumbered. For who, looking after this body, would claim even a
moment of true health, except through sheer foolishness? So you should
train yourself: 'Even though I may be afflicted in body, my mind will
be unafflicted.' That is how you should train yourself."
Later, householder Nakulapita got more detailed advice from Ven. Sariputta the Arahant, elaborating the Buddha's advice:
Ven. Sariputta said: "Now, how is one afflicted in body & afflicted in
mind?
"There is the case where an uninstructed, run-of-the-mill person — who
has no regard for noble ones, is not well-versed or disciplined in
their Dhamma; who has no regard for men of integrity, is not
well-versed or disciplined in their Dhamma — assumes form (the body)
to be the self, or the self as possessing form, or form as in the
self, or the self as in form. He is seized with the idea that 'I am
form' or 'Form is mine.' As he is seized with these ideas, his form
changes & alters, and he falls into sorrow, lamentation, pain,
distress, & despair over its change & alteration.
"He assumes feeling to be the self, or the self as possessing feeling,
or feeling as in the self, or the self as in feeling. He is seized
with the idea that 'I am feeling' or 'Feeling is mine.' As he is
seized with these ideas, his feeling changes & alters, and he falls
into sorrow, lamentation, pain, distress, & despair over its change &
alteration.
"He assumes perception to be the self, or the self as possessing
perception, or perception as in the self, or the self as in
perception. He is seized with the idea that 'I am perception' or
'Perception is mine.' As he is seized with these ideas, his perception
changes & alters, and he falls into sorrow, lamentation, pain,
distress, & despair over its change & alteration.
"He assumes (mental) fabrications to be the self, or the self as
possessing fabrications, or fabrications as in the self, or the self
as in fabrications. He is seized with the idea that 'I am
fabrications' or 'Fabrications are mine.' As he is seized with these
ideas, his fabrications change & alter, and he falls into sorrow,
lamentation, pain, distress, & despair over their change & alteration.
"He assumes consciousness to be the self, or the self as possessing
consciousness, or consciousness as in the self, or the self as in
consciousness. He is seized with the idea that 'I am consciousness' or
'Consciousness is mine.' As he is seized with these ideas, his
consciousness changes & alters, and he falls into sorrow, lamentation,
pain, distress, & despair over its change & alteration.
"This, householder, is how one is afflicted in body and afflicted in
mind.
"And how is one afflicted in body but unafflicted in mind? There is
the case where a well-instructed disciple of the noble ones — who has
regard for noble ones, is well-versed & disciplined in their Dhamma;
who has regard for men of integrity, is well-versed & disciplined in
their Dhamma — does not assume form to be the self, or the self as
possessing form, or form as in the self, or the self as in form. He is
not seized with the idea that 'I am form' or 'Form is mine.' As he is
not seized with these ideas, his form changes & alters, but he does
not fall into sorrow, lamentation, pain, distress, or despair over its
change & alteration.
"He does not assume feeling to be the self...
"He does not assume perception to be the self...
"He does not assume fabrications to be the self...
"He does not assume consciousness to be the self, or the self as
possessing consciousness, or consciousness as in the self, or the self
as in consciousness. He is not seized with the idea that 'I am
consciousness' or 'Consciousness is mine.' As he is not seized with
these ideas, his consciousness changes & alters, but he does not fall
into sorrow, lamentation, pain, distress, or despair over its change &
alteration.
"This, householder, is how one is afflicted in body but unafflicted in
mind."
Another interesting parable is that of the salt crystal. From the Lonaphala Sutta:
"Suppose that a man were to drop a salt crystal into a small amount of
water in a cup. What do you think? Would the water in the cup become
salty because of the salt crystal, and unfit to drink?"
"Yes, lord. Why is that? There being only a small amount of water in
the cup, it would become salty because of the salt crystal, and unfit
to drink."
"Now suppose that a man were to drop a salt crystal into the River
Ganges. What do you think? Would the water in the River Ganges become
salty because of the salt crystal, and unfit to drink?"
"No, lord. Why is that? There being a great mass of water in the River
Ganges, it would not become salty because of the salt crystal or unfit
to drink."
"In the same way, there is the case where a trifling evil deed done by
one individual [the first] takes him to hell; and there is the case
where the very same sort of trifling deed done by the other individual
is experienced in the here & now, and for the most part barely appears
for a moment.
'Now, a trifling evil act done by what sort of individual takes him to
hell? There is the case where a certain individual is undeveloped in
the body, undeveloped in virtue, undeveloped in mind [i.e.,
painful feelings can invade the mind and stay there], undeveloped in
discernment: restricted, small-hearted, dwelling with suffering. A
trifling evil act done by this sort of individual takes him to hell.
'Now, a trifling evil act done by what sort of individual is
experienced in the here & now, and for the most part barely appears
for a moment? There is the case where a certain individual is
developed in the body, developed in virtue, developed in mind
[i.e., painful feelings cannot invade the mind and stay there],
developed in discernment: unrestricted, large-hearted, dwelling with
the immeasurable. A trifling evil act done by this sort of individual
is experienced in the here & now, and for the most part barely appears
for a moment.
For a detailed discussion, please read "Kamma and the Ending of Kamma", by Thanissaro Bhikkhu.