Might it be the miso? The millions of kilos of fish? The copious green tea? We’ll never know, because no one’s bothered to study it conclusively. If it isn’t clearly the what of the Japanese diet, then maybe the country’s incredible health and longevity is caused by what isn’t in the Japanese diet, and the traditional Japanese diet is suspiciously lacking in saturated fat.
The lipid hypothesis, or the idea that eating fat increases your risk of heart disease and weight gain, sounds plausible enough, and the Japanese have the low rates of cardiovascular related deaths to tentatively agree. Unfortunately, the causal link has never been established in an experiment. It’s been refuted many times; study after study shows the amount of fat the Japanese eat has negligible effect on their heart health. Neither does American fat consumption for that matter. We eat less fat than ever, no joke, and our rates of heart disease haven’t subsided much in forty years. In fact, they’ve actually increased. Thank goodness we keep funding these trials, because no one seems to actually read them. If they did, we’d all realise the lipid hypothesis is even more questionable than the ingredients in baloney, begging the all-important question: if saturated fat isn’t to blame, what is?
Meet the cowboys. Considered nutrition renegades of the day,* the loudest critics of the lipid hypothesis speak of sugar as if it cheated us in poker and warn us pasta and potatoes will foul our chaste reputation. America’s love of simple sugars isn’t just responsible for heart disease, they claim, but all diseases of civilisation, as well as a whole host of other metabolic syndrome precursors to the state of health that lets our kids die before we do. These folks, who, prior to 1960, would have been voices lost in the common convention of the day, have a very different explanation. How much fat we eat, the argument goes, isn’t causing heart disease and obesity. The problem is our carbohydrate intake, specifically the insulin response caused by eating too many carbohydrates. After all, insulin is the single hormone responsible for the internal stimuli that regulate fat storage. By extension, the theory goes, Americans and their ultra-high carbohydrate consumption (and ultra-low insulin sensitivity) are obese because we have too much insulin floating around. It also might explain why America is less healthy since we started eating less fat, because to curb our saturated fat intake, we eat more sugars than ever. Hello, 72-oz electric blue slushie, please proceed directly to my ass. In short, what we eat tells our bodies to store more fat.
If too much insulin is the cause, and eating to control its production the cure, the Japanese offer up a paradox. They eat rice and a lot of it.** And they eat the most refined version of rice they can get. Polished white rice may lack the anti-nutrients present in wheat or legumes, but rice is no lightweight on the glycemic index. With a score of 58, just half a cup of cooked rice packs 100g of carbs. You’d have to drink 25 glasses of wine or eat 3 bananas to get the same insulin response, and the Japanese eat at least half a cup of the stuff with every meal. If hyperactive insulin production really is to blame for obesity and aging, how can the Japanese eat so much insulin producing rice and still resist those ill effects?
Is it in their genes? Ridiculous though it might be, those lucky Sino-genes are the next logical explanation for why Japanese people ripen so gracefully and keep for so long. The country is overwhelmingly homogenous, and the population’s near entire lactose intolerance is proof enough their gene pool is different from our own vaguely European chromosomes. Does that mean genes are responsible for Japan’s fabulous health track record and insulin-defying body chemistry?
Nope. Environmental factors are the predominant cause. The Japanese weren’t always at the top of the charts, so to speak. In fact, post-war, Japanese life expectancy was embarrassingly low. As the economy picked up, so did life expectancy, quickly actually, too quickly for the difference to be purely genetic. One decade the Japanese are doomed to early death, the next the same generation is apparently never going to die. Take members of that generation out of Japan and their life expectancies drop too. Numerous Japanese-American transplants share the same disease and obesity statistics as the place they live, not the place they come from. Do some digging and you’ll find a handful of studies following native Japanese who move to America and the like and get just as fat, old, and sick as the rest of us. This phenomenon, experienced firsthand, was the impetus for Naomi Moriyama’s lifestyle change and subsequent book supposedly spilling the beans on Japan’s longevity secrets. The same is true of all my American mates who moved to Japan fearing they would never find trousers big enough and consequently lost enough weight to fit into Japanese sizes. It would seem the cause is nurture, not nature.
What we have here is a stalemate. The Japanese aren’t immune to heart disease and premature death because they eat less saturated fat. They also aren’t immune to heart disease and premature death because they eat fewer carbohydrates. Their genes are not a mitigating factor. It is possible that the victor is neither fat nor carbohydrates, but some third element like shiso. I suppose it’s also possible that several elements working in conjunction are creating an effect individually they could not. These are possible, but given the data, not probable. More likely, the health of the Japanese can be attributed to something other than their diet.
In other words, while Moriyama’s recipe for longevity might create the right environment for success, it’s equally likely her observations focus on the part of Japanese food culture that has little impact on longterm health. The distinction is important, not just because of false attribution, but because it could help us solve our own health problems. Asking why the Japanese live so long is a loaded question. The most common explanations — they eat less food, they eat less saturated fat, they have blessed genes — are also the causes America attributes to obesity. If they can’t definitively explain Japanese health, it seems unrealistic to expect these to also explain America’s poor health. What’s left is a series of wilder-sounding hypotheses relating to things like food combining or the convergence of strange meridians precisely over the island nation. These, while possible explanations, are even harder to scientifically test, begging the mother of all questions: how do we know what is cause and what is correlation? And if we want to replicate the stunning health of the Japanese, what are we supposed to eat?
*In Hilde Bruch’s era, that insulin-driving carbs were to blame was conventional wisdom, not the Atkins-like alternative hypothesis it is today.
**So do the Koreans, Taiwanese, mainland Chinese, and dozens of other Pacific rim nations. No point in looking at them though; while many of these populations might be healthier than Americans, no other Asian population exhibits the kind of centenarian-producing health patterns the Japanese do, suggesting the presence of rice is not the missing key.
