【A Roughly 10-Fold Gap】Comparing Obesity Rates in Japan and America, the Health Risks of Different Diets, and What to Watch Out For

“Why are there so many more people in Japan who aren’t overweight compared with Americans?”

If you’ve ever traveled abroad, you may have wondered the same thing.

In fact, the gap in obesity rates between Japan and America is shockingly large.

And that gap is deeply tied to differences in diet, food culture, and eating habits.

In this article, I’ll compare obesity rate data from Japan and the U.S. and explain why Japanese food has protected people’s health, along with the reality that this advantage has been crumbling in recent years.

And finally, I’ll introduce fasting as the most powerful health habit for people in modern Japan to adopt.

What Is the Obesity Rate, Anyway? How Japan and America Define “Obesity” Differently

Before comparing obesity rates, it helps to first know “what counts as obesity,” which makes the meaning of the numbers much easier to understand.

What Is BMI, the Standard Measure for Obesity?

BMI is a measure of body size calculated by dividing your weight (kg) by the square of your height (m).

For example, for someone who is 170 cm (5 ft 7 in) tall and weighs 72 kg (159 lb), it’s 72 ÷ (1.7 × 1.7), or about 25.

BMI is a rough number for your body’s “size as seen from the outside,” and it’s widely used in health checkups and elsewhere.

In Japan, a BMI of 22, which is statistically associated with the lowest likelihood of illness, is used as the guideline for “standard body weight”.

For someone 170 cm tall, the standard body weight works out to about 64 kg (141 lb).

If you calculate your own BMI once, the numbers in this article will feel more personal and easier to relate to.

WHO and Japan Draw the Line for “Obesity” Differently

Under the international standard of the WHO (World Health Organization), a BMI of 25 or higher is “overweight,” and a BMI of 30 or higher is “obese.”

Under the Japan Society for the Study of Obesity’s standard, on the other hand, you’re classified as “obese” once your BMI reaches 25.

Japan’s standard is stricter probably because Japanese people are thought to be more likely than Westerners to develop diseases like diabetes at lower body weights.

That’s why international comparisons often use “BMI 30 or higher,” which makes Japan’s numbers look extremely low.

The “What’s Inside” Problem That BMI Can’t Show

BMI is a handy yardstick, but it can’t tell muscle from fat.

To put it another way, it tells you how big a house looks from the outside, but not how much stuff (visceral fat) is crammed inside.

The reason Japan’s metabolic syndrome checkups measure waist circumference at the level of the navel is likely to check this “inside.”

People whose weight is normal but whose waistline is large may be carrying more risk than the numbers suggest.

Don’t feel reassured just by the number on the scale; pay attention to everyday changes too, like which hole you use on your belt or how tight your pants feel.

Whether you can notice these small signs early is likely the key for Japanese people to manage obesity well.

Obesity Rate Data for Japan and America: The Shocking Gap in Numbers

International Comparison of Obesity Rates

According to the latest WHO data (2022), adult obesity rates (BMI 30 or higher) are as follows.

While the obesity rate in America is about 42%, Japan’s is just 4 to 5%.

That’s roughly a 10-fold difference.

This number isn’t simply a difference in body shape.

Obesity is one of the biggest factors raising the risk of many chronic diseases, including diabetes, heart disease, cancer, and dementia.

Things to Keep in Mind When Looking at the Numbers

Obesity rates vary slightly depending on the year of the survey and whether height and weight were actually measured or self-reported.

That’s why the exact numbers may differ from source to source, such as “about 40% in America” or “about 4% in Japan.”

But no matter which survey you look at, the trend that “America has many times more people with obesity than Japan” doesn’t change.

What matters more than the exact numbers is understanding where this big gap comes from.

Looking at Overweight (BMI 25 or Higher), Japan Can’t Relax Either

Looking at “obesity” defined as BMI 30 or higher, Japan’s level is low, but looking at “overweight” defined as BMI 25 or higher, about 30% of people fall into that category.

Research has also shown that compared with Westerners, Japanese people tend to build up visceral fat more easily at the same BMI (visceral-fat-type obesity).

The reality is that there are many cases of people who don’t look overweight but have metabolic problems.

You can’t flatly say, “Japanese people are safe because the obesity rate is low.”

The Gap in Obesity Rates Leads to a Gap in How Much Illness There Is

The more people with obesity a country has, the more people tend to suffer from weight-related conditions such as diabetes, heart disease, and knee or back pain.

As illness increases, so do the costs of doctor visits and medication, along with the number of days people miss work.

In other words, the obesity rate isn’t a matter of appearance; it’s like a “health thermometer” that reflects how long and how well the people of that country can live.

Knowing the gap between Japan and the U.S. can also give you clues for thinking about your own future health.

Why Is America So Overweight? The Fundamental Differences in Food Culture

American Food Culture: Ultra-Processed Foods, Huge Portions, and All-Day Grazing

To sum up the American diet in a word, it’s “mass consumption of ultra-processed foods.”

In particular, “all-day grazing (the habit of always eating something)” creates a state in which insulin is secreted nonstop and fat storage never stops.

This is likely a breeding ground for obesity and diabetes.

Rapidly Rising Type 2 Diabetes and Heart Disease in America

High obesity rates are directly linked to an increase in chronic diseases.

In America, about 11% of adults have type 2 diabetes, and another roughly 35% are said to have prediabetes.

Heart disease is the leading cause of death in America, and much of it is closely tied to eating habits, obesity, and lack of exercise.

It’s also said that annual healthcare spending exceeds 3 trillion dollars, and about 80% of it goes toward chronic diseases caused by eating habits.

Car Culture and a “Life Without Walking”

In America, many areas are car-dependent, and it’s normal to drive even for shopping in the neighborhood.

In Japan, by contrast, many people commute by train or bus and walk to the station.

These daily “little walks” may look like a small difference, but accumulated over years, they create a big difference in the energy you burn.

The combination of eating a lot and moving little is what’s fueling obesity in America.

An Environment Where “Cheap, Big, and Sweet” Food Is Easy to Get

In America, it’s said that high-calorie foods like sugary drinks and fried foods are cheaper and easier to get than vegetables and fruit.

People with less money or time are more likely to rely on convenient, cheap, high-calorie foods.

In other words, obesity in America isn’t just about individual weakness of will; it’s also an environmental problem in which “the most fattening options are the easiest to reach for”.

Why Japanese Food Has Protected People’s Health: The Scientific Strengths of the Traditional Diet

5 Health Characteristics of Traditional Japanese Food

Behind Japan’s ability to remain one of the world’s top countries for longevity with a low obesity rate are the characteristics of traditional Japanese food.

What deserves special attention are the habits of “hara hachi bu” and “leaving time between meals.”

This is close to what modern science would call a “mini fast,” and it moderately suppresses insulin secretion and keeps the body in fat-burning mode.

Ichiju-Sansai Is “a System That Naturally Creates Balance”

Ichiju-sansai (one soup, three dishes: rice, a soup, and three side dishes) is a meal format that makes it easy to cover staple foods, main dishes, and side dishes.

Because a variety of dishes are served a little at a time in small bowls and plates, it’s hard to overeat any one dish.

If you start with miso soup or vegetable dishes, fiber enters your stomach first, and your blood sugar rises more gently.

In a sense, ichiju-sansai is a way of eating with a “hard-to-overeat format” built in from the start, even without any special knowledge.

Protein Centered on Fish and Soy

In the American diet, beef and processed meats tend to be the main sources of protein.

In contrast, in the traditional Japanese diet, fish and soy (grilled fish, simmered fish, tofu, natto, miso, and so on) were the core of protein intake.

Fish oil and soy are thought to be gentler on the blood vessels and heart than fat from meat.

Even the small difference of “what takes center stage as your protein source” likely grew into a difference in health over the long years.

The Link Between Longevity in Okinawa and Fasting-Like Eating Habits

In the food culture of Okinawa, once known for the longest life expectancy in the world, the teaching of “hara hachi bu” (eat until you’re 80% full) was deeply rooted.

Eating small amounts and creating plenty of hunger time between meals: this is a habit very close to the idea behind intermittent fasting.

For more on the relationship between fasting and longevity, also check out Autophagy and the Anti-Aging Effects of 16-Hour Fasting.

The Crisis of a “Westernized Diet” Facing Modern Japan

A Rapidly Westernizing Diet

From the postwar years through the period of rapid economic growth, the Japanese diet rapidly became Westernized.

The spread of fast food chains, convenience store meals becoming part of everyday life, and mass consumption of processed foods. Because of these, Japanese eating habits have begun to drift far from traditional Japanese food.

In fact, the number of people with type 2 diabetes in Japan has roughly tripled over the past 30 years, and a link with the Westernization of the diet has been pointed out.

“Three Meals a Day Plus Snacks” Leads to Excess Insulin Secretion

Many people in Japan today live a lifestyle of “eating three full meals a day and snacking too.”

But with these eating habits, insulin is secreted intermittently all day long, keeping the body constantly in a “state where it easily stores fat.”

Without enough hunger time between meals, your body loses its chances to burn fat.

For more on the relationship between insulin and obesity, also read Scientific Data on How 16-Hour Fasting Improves Blood Pressure and Blood Sugar.

The Younger the Generation, the Bigger the Impact: Digitalization and Changes in Eating

The spread of social media, the rise of delivery services, and an abundance of convenience-store sweets: today’s younger generations in Japan are growing up in a food environment completely different from that of the postwar generation.

Working late into the night and grabbing dinner at a convenience store.

Snacking while looking at their phones.

As these habits pile up, the reality of modern Japan is that it’s easy to end up “hidden obese” (slim on the outside but carrying a lot of visceral fat).

We’ve likely entered an era in which the sense of security that “I’m Japanese, so I’ll be fine” no longer holds.

Changes Spreading to Children’s Eating Habits Too

The effects of a Westernized diet extend not only to adults but to children as well.

When kids get used to sugary juice, packaged snacks, and fast food from an early age, their taste buds tend to develop to find strong or sweet flavors “delicious.”

It’s said that the taste preferences and eating habits formed in childhood tend to continue into adulthood.

Gathering around the same table as a family and serving miso soup and vegetable dishes as a matter of course is the most accessible way to prevent obesity in the next generation.

Check Whether You’ve Slipped into an “American-Style” Diet

The more of the following items apply to you, the more it’s a sign that you’re moving toward an American-style diet even while living in Japan.

Even if many of these apply to you, there’s no need to feel down.

If you start bringing things back one at a time from wherever you notice, you can regain the strengths of Japanese food.

Frequently Asked Questions About the Obesity Rate Gap Between Japan and America

Creating “Time Without Eating” Is Modern People’s Most Powerful Weapon for Protecting Their Health

The gap in obesity rates between Japan and America comes not only from differences in what people eat, but from differences in eating habits as a whole: “when, how much, and how often” people eat.

Traditional Japanese food included “natural fasting-like elements,” but with the modern Westernization of the diet, those benefits are fading.

That’s exactly why it’s important now to deliberately “create time without eating.”

Intermittent fasting can be seen as a way to practice, as a scientific method, the wisdom of traditional Japanese eating habits that modern people are losing.

Specifically, just sticking to simple rules (don’t eat after 8 p.m., and have only water or coffee in the morning until lunch) starts to flip on the fat-burning switch inside your body.

It’s the complete opposite of an American-style culture of ultra-processed foods and all-day grazing.

Even without changing what you eat, simply creating “time without eating” lets you recreate Japan’s traditional hara hachi bu culture in modern life.

What matters isn’t making American food culture the villain, but remembering the “wisdom of not overeating” that Japanese people originally had.

Methods for creating “time without eating,” like 16-hour fasting, could be described as a way to make that wisdom easier to adopt in today’s busy lifestyles.

Japanese-Style Eating Changes You Can Make Starting Today

Along with creating time without eating, try shifting what you eat a little closer to the Japanese style when you do eat.

You don’t have to give up convenience stores or fast food entirely; just being mindful of “what to add and what to cut back on” can change what’s in your meals.

These are all tricks that need no special tools or money, and that Japanese people of the past did as a matter of course.

You don’t need to change everything at once, so pick one that seems doable and start by keeping it up for a week.

For the specific changes your body can go through with fasting, also check out The Changes You Can Feel in Your Body After 2 Weeks of 16-Hour Fasting.

Start with 16-hour fasting.

Read The Complete Guide to Intermittent Fasting, and you can start today.

If you’d like to make fasting easier to keep up, another option is to use a supplement that supports fasting.

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