Author : Felix, Angelina DR

Summary : Type 2 diabetes mellitus (T2DM) is one of the four leading public health
problems in the world. The risk for the disease is governed by a complex
interplay of genetic and multiple lifestyle influences, of which diet is a major
modifiable risk factor. In recent years, the effects of rice consumption on
T2DM has been the subject of heightened interests.

Rice (Oryza sativa L.) exists in different types and forms around the
world, and metabolic effects vary according to varietal differences. With the
general aim of contributing knowledge on the role of rice in T2DM, this
dissertation was thus conducted. The research was designed to determine the
effects of rice grain components on selected biomarkers associated with
T2DM, and to understand how the relationships may relate to T2DM risk
prevention and management. The dissertation focused on Philippine rice to
represent the indica rice subspecies. Indica rice are cultivated in tropical
countries which have the highest projected increase in diabetes prevalence by
2030. Also, to the best of knowledge, the metabolic effects of indica rice are
less studied compared to japonica rice that are cultivated in Japan and Korea.

The Philippines is rich in traditional and modern rice varieties. Filipinos
have general preference for moderately tender cooked rice, typified by the
popular rice variety, IR64. However, consumer preferences varied across
ecosystems (Chapter IlI). Rice consumers in the upland and saline ecosystems
had preferences for slightly harder cooked rice texture (18-25% apparent amylose content [AC] with intermediate gelatinization temperature [GT]), while those from cool-elevated ecosystems preferred the softer and sticky rice with <18%AC and low GT.

AC- the linear fraction of starch, is the main factor affecting cooked rice
texture, and consumer preference. It is also cited as the most important
source of variation in post-prandial glucose response (GR) from rice. In
Chapter IV, the effects ofAC on GR from milled rice was determined. Seven
milled Philippine rice varieties with different AC were cooked with adjusted
water-rice ratio to have similar cooked rice hardness (to address effects of
cooking method and GT). The rice samples were subjected to glycemic index
(GI) determination in healthy Filipino volunteers who were given a serving
of the food containing 50 g of available carbohydrate. Results showed GR to
be lowest for the variety with highest apparent AC (PSB Rc10), and highest
for the low-AC rice (Sinandomeng). There were significant differences in the
incremental area under the curve (IAVC) of GR among high-, intermediateand
low-AC rice varieties. GR was in close association with GI (r = 0.99;
p<0.01), and AC was negatively correlated with GI (r=-0.65; p<0.05).

The association of milled rice AC to GI was validated in a follow-up study
(Chapter V). In this study, it was also found that rice protein content can
affect GI. Improved Malagkit Sung song which has a 9%crude protein content
in the previous trial had a GI of63±2 (medium), while at the current 6%crude
protein content its GI was recorded at 94±5 (high). The higher protein content
that was covering the starch granules may have prevented rapid hydrolysis of the endosperm starch.

In Chapter V as well, dietary fiber (DF) was shown to affect GL
Unpolished rice or brown rice (BR) had lower GI than its milled counterpart.
Among the four AC types, the decrease in GI from milled rice to BR was
greatest for waxy rice (0-2% AC), and low-AC rice (10-17% AC), both with
high GI (::::70). Intermediate (17-22%)-AC IR64 with medium (56-69) GI
showed lesser drop, but high-AC PSB Rc10 (» 22% AC) had no significant
decrease. GI was again highest for waxy (0-2% AC) rice and lowest for high-
AC rice for both rice forms, but the decrease in GI with increasing AC was
lower for BR than for milled rice. In the previous study (Chapter IV), the
association of apparent AC with GI was more pronounced in the combined
effect of AC and DF on GI (r= -0.71; p<0.05).

GR and GI of black and red colored unpolished rice in comparison with
BR, were also determined (Chapter VI). Results found black and red rice to
have similar GR, which were comparable with that of the BR. GI was
classified as medium for all samples (GI= 63±4, 59±4, and 59±5, for the black,
red and BR, respectively), despite significant differences in total phenolic and
anthocyanin contents. The study suggests that phenolic and anthocyanin
contents in Philippine rice do not influence GR.

Aside from its direct effect on GR, rice can also be linked to T2DM via
its effects on satiety and food intake. Very few studies however, investigate
rice satiety. Hence, the satiating capacity of milled and brown rice of different
AC types, and of colored rice were evaluated. In all trials, the estimation of satiety was done in conjunction with GI measurement. Satiety quotient (SQ)
and/or satiety index (SI) were computed based on VAS, and was used as index
of short-term satiety, together with 2-h post-meal cooked rice intake. There
was no difference in the SQ between black and red colored rice, and between
colored rice and BR (Chapter vn. Short-term satiety was also similar across
the seven milled rice samples, and satiety was found to be independent of
both AC and GI (Chapter VII). On the other hand, a tendency for BR to be
more satiating than milled rice was observed in Chapter VIII. Both SQ and
SI tended to be higher in BR than milled rice, regardless of AC type. SI was
also found to have strong positive correlation with DF content. Contrary to
hypothesis, however, the higher SQ and SI for brown rice was not translated
into lower subsequent food intake after 2-h, and common cooked rice intake
was not affected by DF content. The satiety of BR using a longer time span
(4-h post meal or at lunch time) was then pursued using a different set of
human volunteers (Chapter m. BR remained to be perceived as more filling
and suppresses hunger better than milled rice. However, the difference in
adjusted satiety scores at ~4 h post meal between milled rice and BR, was
only significant for the high-AC variety. Mean post meal cooked rice intake
also remained similar across rice AC types and rice forms, but intake based
on dry weight decreased with increasing AC. Further estimation of energy
intakes at post meal and within 24-h indicated that energy intake was
independent of rice DF content, but was negatively associated with rice AC.

Hyperlipidemia, which is also prevalent worldwide, is associated with
risk of T2DM. Non-alcoholic fatty liver disease (NAFLD) is being linked with
the development and progression of T2DM, including related complications.
Polyphenols notably anthocyanin were suggested to prevent cellular damage
in hepatocytes associated with NAFLD through different mechanisms of
action. In Chapter X of this dissertation, the effect of the rice powder extract
(RPE) from an unpolished Philippine black rice variety and BR on hepatic
lipid accumulation was compared. The extracts were prepared out of cooked,
freeze- dried samples, and were tested using obese and diabetic mice model
(KKAy). The study found that RPE from black rice (BL) and BR improves
hepatic lipid accumulation via peroxisomal fatty acid oxidation. A
histochemical analysis also revealed that BL and BR RPE feeding
ameliorated triacylglycerol (TG) accumulation in the liver. To elucidate the
mechanism underlying the improvement in hepatic TG accumulation, gene
expression was evaluated using real-time peR. The mRNA expression levels
of acyJ-CoA oxidase (AO.x), a rate-limiting enzyme of peroxisomal fatty acid
oxidation, were significantly higher in the BL and BR groups than in the
control-K group. RPE showed peroxisome proliferator activated receptor a
(PPARa) agonistic activity which did not differ between BL and BR RPE
despite a higher anthocyanin content in black RPE. It is likely that another
compound has PPARa agonistic activity in RPE or that RPE contains
compounds that modify the activity, and further study was recommended.

This dissertation revealed that grain components of Philippine rice
affect biomarkers associated with T2DM. AC was the most important
property that modulate T2DM metabolic response. AC was inversely
associated with GR and post-meal cooked rice intake, and rice varieties with
at least intermediate-AC is suggested for the prevention and management of
T2DM in populations where indics rice is the staple food, such as the
Philippines. Revisiting the breeding objectives in the Philippine rice varietal
development program, is recommended, in reference to the increasing
preference for softer cooked rice among Filipinos. Switching from milled rice
to BR can also contribute to T2DM risk reduction, through the combined
effect of dietary fiber with AC in lowering GR and GI. Effects of DF from rice
to satiety and food intake are yet to be established, with full account of other
factors such as cognitive cues and eating behaviors. Nonetheless, the
perceived better satiating potential of BR than milled rice may provide
opportunities to maximize promotion of BR as a functional food, if taken as
entry point for nutrition education and as part of a holistic dietary
intervention under the national diabetes prevention and control plan.

The dissertation also showed that protein content can lower GR and GI
of indics rice. More importantly, in vitro and in vivo experiments
demonstrated that RPE from black unpolished rice and BR, have PPARa
agonistic activities, and can improve hepatic TG accumulation. These are new
findings and are worthy of further investigations.