The phrase ‘Japanese Paradox’ has been used frequently in recent decades. It is a label that denotes the fascinating ability of Japanese persons to maintain slender builds despite substantial volumes of white rice consumption.
Most often this phrase is uttered by health-conscious westerners who appreciate the concept of glycemic response to food while possessing an awareness of its repercussions in the picture of health.
Ethnicities other than Japanese lack this enviable genetic endowment to withstand the harmful effects that one would expect from LOTS of simple carbohydrates. Right?
Wrong. The Japanese paradox is actually fallacious. Or, at least, a misnomer that is only partially paradoxical.
While Japan boasts impressively low levels of obesity compared to other developed countries (5% vs. 35% in the USA), the prevalence of Type II Diabetes Mellitus (T2DM) only differs marginally by a few percentage points. This underlines how metabolic disease as seen with T2DM is preceded by risk factors independent of BMI.
Instead, recent research emerging from Japanese scientists has magnified lifestyle and diet composition as even more influential in the development of these preventable diseases.
Approximately 30% of daily energy intake is derived from white rice for the average Japanese person and it remains a fixture at most meals. Bread and pasta consumption is on the rise, in parallel with other westernised convenience foods, but traditional diet staples aren’t usurped easily nor quickly – white rice will continue to constitute the base of most Japanese dishes.
A systematic review conducted by Nanri et al. (2010) demonstrated that, paradoxically, higher quartiles of white rice consumers had significantly lower BMIs, were more physically active, and worked more strenuous exercise throughout the week. But this same portion of participants were at significantly greater risk of T2DM, despite being superficially healthy.
Body habitus is not an accurate predictor of health markers. Japanese persons are typically slight in build with little subcutaneous fat because of a lifestyle that gives rise to an imbalance between energy intake and energy expenditure; large volumes of incidental activity, smaller portion sizes when eating, and pre-occupation with work.
Visceral fat accumulation, on the other hand, is sensitive to other factors that include psychological stress, sleep duration and quality, and the quality (more so than quantity) of food intake.
The females who consumed 3 or more servings of rice in this large study were susceptible to T2DM irrespective of physical activity level, while physically active males meeting exercise guidelines appeared to negate the detrimental metabolic repercussions of frequent white rice consumption.
As such, the connection between white rice intake and Japanese males’ incidence of T2DM is somewhat equivocal, though regular exercise seems instrumental in preserving insulin sensitivity and thus staving off metabolic disease.
A Chinese study corroborates the above findings to a large extent; women who consumed ≥300 g rice/d had a 1.8-fold greater risk of developing T2DM than women who consumed <200 g rice/d.
What about brown rice?
This grain is unanimously considered the healthier alternative to its white counterpart, but most would agree that it lacks the same palatability polished white rice is renowned for. ‘Genmai’ (brown rice in Japanese) is thus an unpopular choice.
It follows that adherence to a research study in which Japanese participants are subject to extended periods of eating conventional brown rice would pose an issue. So Nakayama et al. (2017) instead administered glutinous brown rice (GBR), a variety similar in texture to sushi rice but dissimilar in glycemic effect, to a Japanese group with T2DM for 8 weeks.
Though GBR isn’t as complex a carbohydrate as long-grain basmati brown rice, the diabetic biomarkers of glycated haemoglobin (HbA1c) and post-prandial blood glucose levels were significantly better in this group when compared to the white rice group.
Terashima et al. (2016) even discovered that a single day of GBR consumption in place of white rice noticeably improved blood markers related to diabetes. GBR may stimulate GLP-1 secretion secondary to an increase of short-chain fatty acids produced from dietary fibre by the gut microbial flora. Magnesium, γ-oryzanol (sourced from the bran of GBR) and insoluble fibre are stripped in the process of transforming brown rice to white rice, and all of these compounds exert positive effects on our glycemic stability.
In light of these findings, and with adherence to any dietary intervention being the linchpin in its success, GBR may be a tastier yet still effective alternative to grainier brown rice.
It would be remiss not to mention several confounding factors that may compound the negative effects of eating white rice. Individuals consuming significantly high amounts of white rice also tend to eat less fat, protein and fibre at the same meal; all of which are known to slow gastric emptying rate and blunt the post-prandial blood glucose spike that we see when sugar is consumed in isolation.
Additional confounders noted in this field of Japanese research include:
- Extensive smoking in Japan, a habit that can impair βcell function and thus glucose metabolism
- 10 hours per day of work appears to be the threshold beyond which metabolic syndrome risk is increased significantly (Kobayashi, 2012)
- Eating speed is positively correlated with greater waist circumference, lower HDL cholesterol, poorer fasting blood glucose levels, hypertension, and ultimately metabolic syndrome (Yamaji, 2018; Nagahama et al., 2014). Observationally, the speed of eating in Tokyo amongst ‘salary men’ is rapid. I have acculturated effortlessly in this regard.
Wrapping things up, white rice isn’t inherently unhealthy but its consumption does necessitate several considerations. Besides serving as a dense source of tasty and simple carbohydrates, it doesn’t provide us with any micronutrients, nor fibre, nor protein. It is therefore a food that doesn’t readily satiate but rather predisposes to overeating while eliciting a hefty blood glucose spike.
The research elucidated in this article has more than likely encouraged a number of readers to exercise some restraint with white rice where possible, but be aware of the confounding factors mentioned above.
Of particular salience is that the Japanese persons in the higher quartiles of white rice consumption ultimately ate little else with their rice to dampen its metabolic impact, and their overall diet lacked an adequate proportion of both protein and fat.
I enjoy white rice as much as the rest of you and, well, living in Japan makes for a difficult time if one is to completely eschew it. Not to mention foregoing sushi trains – no thanks. In saying this, the health-conscious individual understands that white rice probably shouldn’t be consumed at every meal.
Mitigating the metabolic damage chronic white rice intake may induce involves:
- Eating it with generous doses of protein, fat and fibre
- Preceding or succeeding its consumption with somewhat intense physical activity where possible
- Consciously chewing your food (rather than inhaling it like Kobayashi)
- Food sequence
By this last point I mean it is sensible to consume the other macronutrients (protein, fibre, fat) prior to the carbohydrates. In Japan, a set meal typically involves eating foods separate from one another as opposed to one big bolus. I prefer the latter, though, so will usually serve myself the more satiating foods first before topping with white rice.
Discounting that “occasional” (in other words, daily) rice ball, or acquiescing to that rice-heavy dish your friends are eating can be too easy, especially when there appears to be no superficial or immediate health consequences. *I’m still in my 20s with a great metabolism, and I’m not overweight so I can afford it!*
But the surge in preventable metabolic disease in Japan and other developed countries is very real, and living with T2DM is not easy. These morbidities often develop insidiously without obvious notice, making them even more dangerous. They are preventable though, so abandoning a reactive mentality in favour of proactivity is crucial. Be conscientious with your food choices.
Kobayashi, T., Suzuki, E., Takao, S., & Doi, H. (2012). Long working hours and metabolic syndrome among Japanese men: a cross-sectional study. BMC Public Health, 12(1), 395. doi:10.1186/1471-2458-12-395
Mizoue, T., Yamaji, T., Tabata, S., Yamaguchi, K., Ogawa, S., Mineshita, M., & Kono, S. (2006). Dietary patterns and glucose tolerance abnormalities in Japanese men. The Journal of nutrition, 136(5), 1352-1358.
Morimoto, N., Kasuga, C., Tanaka, A., Kamachi, K., Ai, M., Urayama, K. Y., & Tanaka, A. (2018). Association between dietary fibre: carbohydrate intake ratio and insulin resistance in Japanese adults without type 2 diabetes. British Journal of Nutrition, 119(6), 620-628.
Nakayama, T., Nagai, Y., Uehara, Y., Nakamura, Y., Ishii, S., Kato, H., & Tanaka, Y. (2017). Eating glutinous brown rice twice a day for 8 weeks improves glycemic control in Japanese patients with diabetes mellitus. Nutrition & diabetes, 7(5), e273.
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