Eating sweet potato to prevent cancers, diabetes

The tubers have become diet, while the leaves
are often used as animal feed. But
researchers have found that extract of the
leaves and tubers of white sweet potatoes
could be used to prevent and treat cancers
and diabetes.
SWEET potatoes may provide the next novel
drugs for cancer and diabetes. Recent study
by Japanese researchers published in
Journal of Agriculture, Food and Chemistry
indicates that the growth of human cancer
cells can be successfully suppressed with
sweet potato extracts.
A previous study had demonstrated that the
phytochemicals in sweet potato have
significant antioxidant and anticancer
activities. The antioxidant activity was
directly related to the total amount of
phenolics and flavonoids in the extracts.
Researchers suggest that the additive roles
of phytochemicals may contribute to its
ability in inhibiting tumor cell proliferation
in vitro.
Also, researchers from Austria, Italy and
Switzerland have demonstrated the
tolerability, efficacy, and mode of action an
extract of white sweet potatoes on
metabolic control in type 2 diabetic patients.
The researchers suggest that despite its
“ sweet” name, sweet potato may stabilize
blood sugars and lower insulin resistance.
Other studies have shown that the flavone
extracted from sweet potato leaf could
control blood sugar and modulate the
metabolism of glucose and blood lipid, and
decrease outputs of lipid peroxidation and
scavenge the free radicals in non-insulin
dependent diabetic rats.
India researchers have demonstrated the
cytotoxic and antioxidant activities of
sweet potato. The study published in the
International Journal of Pharmacy and
Pharmaceutical Sciences concluded: “On the
basis of the above results it can be
concluded that he ethanolic extract possess
significant anticancer and antioxidant
activities studied by in vitro models. The
presence of flavonoids and related phyto-
constituents may be responsible for the
activity. Further investigations are required
to find active component of the extract and
to confirm the mechanism of action. Further
studies warranted, for isolation of the
constituents responsible for the activity and
also to explore the exact mechanism of
action of the activity.”
Commonly called sweet potato, Ipomoea
batatas belongs to the plant family
Convolvulaceae. In Nigeria, it is called edia-
makara in Anaang, dankai in Berom, iyan-
ebo in Edo, bia mbakara in Efik, ba-fadamee
in Hausa, ediam-umani in Ibibio, ji-bekee or
nduku in Ibo, beke buru in Ijo-Izon, dangali
in Kanuri, dangura in Mambila, duku in
Nupe, atsaka in Tiv, imitata or ole-oyinbo in
Urhobo, anamo or odukun in Yoruba.
According to the Useful Plants of West
Tropical Africa by H. M. Burkill, the tubers
have been used for distillation to ‘tumbo
spirit’ in Nigeria. Vitamins are well
represented, particularly the yellow-fleshed
cultivars. The plant is usually a three to four
months crop, but some cultivars run to six
months. Little medicinal use is made of the
tubers. They are used in frictions on the
skin in Cote D ’Ivoire to prevent loss of
pigmentation. A purgative tisane is made
from the root with leaves of Cassia
occidentalis (Leguminosae:
Caesalpinioideae) and the bark of Bridelia
ferruginea (Euphorbiaceae) in Congo.
Bactericidal and fungicidal substances have
been isolated from the tuber and the haulm.
The young leaves are commonly eaten by
man, and leafy stems are fed to stock. They
are a good source of vitamins and minerals
especially calcium and especially in the
purple-leafed forms. They are anti-diabetic
and anti-scorbutic.
In Senegal poultices for abscesses are made
of the leaves. The leaf-sap is used on burns
in Cote D ’Ivoire, the pounded leaves are
made into an enema given to avert
miscarriage, and leaves are applied in
topical frictions to relieve intercostal pain
and in mouth-wash and gum-massage for
toothache. Toxic substances have been
reported and excessive ingestion is known
to cause diarrhoea, and even death. Some
alkaloid has been recorded in the stems and
leaves and in the roots.
The Japanese study is titled “Growth
suppression of human cancer cells by
polyphenolics from sweet potato (Ipomoea
batatas L.) leaves. ”
R. Kurata, M. Adachi, O. Yamakawa, and M.
Yoshimoto of the Department of Upland
Farming Research, National Agricultural
Research Center for Kyushu Okinawa
Region, Yokoichi, Miyakonojo, Miyazaki,
Japan found that sweet potato leaves
(Ipomoea batatas L.) contain a high content
of polyphenolics that consist of caffeic acid,
chlorogenic acid, 3,4-di-O-caffeoylquinic
acid, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-
caffeoylquinic acid, and 3,4,5-tri-O-
caffeoylquinic acid.
They wrote: “We investigated the
suppression of the proliferation of selected
human cancer cells by phenolic compounds
isolated from sweet potato leaf. The human
cancer cells used in this research included a
stomach cancer (Kato III), a colon cancer
(DLD-1), and a promyelocytic leukemia cell
(HL-60). Caffeic acid and di- and
tricaffeoylquinic acids dose-dependently
depressed cancer cell proliferation, and the
difference in sensitivity between
caffeoylquinic acid derivatives and each
kind of cancer cell was observed.
“Specifically, 3,4,5-tri-O-caffeoylquinic acid
effectively depressed the growth of three
kinds of cancer cells, and caffeic acid had an
exceptionally higher effect against HL-60
cells than other di- and tricaffeoylquinic
acids. In attempting to clarify the
mechanism of growth suppression with the
addition of the apoptotic inhibitor N-
ethylmaleimide, we observed that the
nuclear granulation in 3,4,5-tri-O-
caffeoylquinic acid-treated HL-60 cells
suggested apoptosis induction. This effect
was confirmed by DNA fragmentation, an
increase of caspase-3 activity, and
expression of c-Jun. Growth suppression of
HL-60 cells by 3,4,5-tri-O-caffeoylquinic acid
was determined to be the result of
apoptotic death of the cells. These results
indicate that 3,4,5-tri-O-caffeoylquinic acid
may have potential for cancer prevention.”
According to the study by Bernhard Ludvik
of the Department of Medicine III, Division
of Endocrinology and Metabolism,
University of Vienna, Vienna, Austria;
Beatrice Neuffer of Via Livio 14, Chiasso,
Switzerland; and Giovanni Pacini of the
Metabolic Unit, Institute of Biomedical
Engineering, ISIB, National Research Council,
CNR, Padova, Italy, a total of 61 type 2
diabetic patients treated by diet were given
4 gram of extracts of white sweet potato
called Caiapo once daily for 12 weeks. Each
subject underwent a 75-g oral glucose
tolerance test (OGTT) at baseline and after
one, two, and three months to assess two-
hour glucose levels. Additionally, fasting
blood glucose, HbA1c, total cholesterol, and
triglyceride levels were measured.
After treatment with Caiapo, HbA1c
decreased significantly, whereas it
remained unchanged in subjects given
placebo. Fasting blood glucose levels
decreased in the Caiapo group and did not
change in the placebo group. A decrease in
body weight was observed in both the
placebo group and in the Caiapo group,
probably due to a better- controlled lifestyle.
In the Caiapo group, body weight was
related to the improvement in glucose
control. Two-hour glucose levels were
significantly decreased in the Caiapo group
compared with the placebo group. Mean
cholesterol at the end of the treatment was
significantly lower in the Caiapo group than
in the placebo group. No significant
changes in triglyceride levels or blood
pressure were observed, and Caiapo was
well tolerated without significant adverse
effects.
The researchers concluded: “This study
confirms the beneficial effects of Caiapo on
plasma glucose as well as cholesterol levels
in patients with type 2 diabetes. For the first
time, the long-term efficacy of Caiapo on
glucose control was demonstrated by the
observed decrease in HbA1c. Thus, the
neutraceutical Caiapo seems to be a useful
agent in the treatment of type 2 diabetes. ”
Phytochemical analysis sweet potato leaves
showed that they are very nutritious when
compared to vegetables such as cassava
leaves, amaranth, mushrooms, taro, and
pumpkin leaves. Sweet potatoes are
reportedly good source of vitamins A, B and
C, iron, calcium and phosphorus.
High in complex carbohydrates and dietary
fibre; deficient in protein.
An invention made from the extracts of leaf
and stems of sweet potato has been shown
to have qi and spleen invigorating effects,
cooling the blood and stopping bleeding.
Such a composition has the potential of use
for ITP (idiopathic thrombocytopenic
purpura), radiotherapy- and chemotherapy-
induced thrombocytopenia.
A 2006 study of commonly consumed roots
crops in the Philippines (Kamote, Ipomoea
batata; ubi, purple yam, Dioscorea alata;
cassava, Manihot esculenta; taro or gabi,
Colocasia esculenta; carrot, Daucus carota;
yacon (Smallanthus sonchifolius) showed
them to be rich sources of phenolic
compounds with antioxidant acitivity,
highest in sweet potato, followed by taro,
potato, purple yam and lowest in the carrot
Other results suggest the total phenolic
content was positively correlated with
radical scavenging activities of the sweet
potato leaves. Purple sweet potato
anthocyanins have antioxidative activity in
vivo as well as in vitro.
Another study has identified new
chitinolytic enzymes in sweet potato leaves.
Chitinases catalyze the hydrolysis of chitin,
the main structural component of fungal
walls and arthropod integuments. Studies
suggest it has other functions and has been
proposed to play a role in the defense
against pathogens. Chitinases are also
useful in the production of biomedical and
biotech products; used in the production of
chitooligosaccharides, glucosamines and
GlcNAc. Other applications are found in
mosquito control and pathogenic plant
fungi control.