<Introduction>
In Japan, since around 2015, the low-carb diet－we call "Locabo" based on the English term "a low-carb"－has been catching on among many people. Japan is traditionally a rice-eating culture, but after World War II, more and more people preferred bread and noodles, and with increasingly westernized diets, many feel that we are gaining weight as well. 

This time, I’d like to introduce the Locabo diet in Japan, which is believed to be effective not only for losing weight but also for lowering abnormal blood sugar levels and other lifestyle diseases.

<My stance: I will approach the issues of obesity and blood sugar abnormalities separately.>

Generally, experts advocating for carbohydrate restriction seem to believe that the cause of obesity lies not in excessive caloric intake but in carbohydrates (sugars) that elevate blood sugar levels and stimulate insulin (*1) secretion (the carbohydrate-insulin model).

Additionally, it is believed that prolonged insulin resistance or decreased insulin secretion capacity, can lead to abnormal glucose metabolism, ultimately resulting in the development of lifestyle-related diseases such as diabetes. 

In other words, both obesity and symptoms like blood sugar abnormalities are thought to be part of a series of events centered around insulin. However, I believe that obesity is caused by different mechanisms related to carbohydrates, so I would like to explain them separately. 

(*1) Insulin is a hormone that lowers the level of glucose in the blood. It's released into the blood by the pancreas　when the glucose level goes up. Insulin helps glucose enter the body's cells, where it can be used for energy or stored for future use.

"In Japan, the phrase “carbohydrate restriction diet” has been generally used, but the word “restriction” has a somewhat negative image. Therefore, we had to use some different words. We came up with the new word “Locabo” after the English phrase “low-carb” and then it spread throughout Japan. 

Locabo is not strict but rather a loose carbohydrate restriction. By definition, the diet tries to keep the carbohydrate intake amount per day to around seventy to one hundred and thirty grams in total, by taking twenty to forty grams per meal, three times a day and also a dessert or sweets up to ten grams. 

The leading advocate for promoting low-carb diets in Japan is Dr. Satoru Yamada, and summarizing his thoughts, we get the following points: 
    

(1) When blood sugar levels rise due to meals, insulin is secreted from the pancreas. Excessive insulin secretion may potentially lead to weight gain. Japanese individuals have a weaker ability to secrete insulin compared to Westerners, and many people experience blood sugar abnormalities even if they are not overweight. More than half of those who develop typeⅡdiabetes have a BMI less than twenty-five.

(2) The higher the frequency of insulin secretion and the higher the upper limit of blood sugar levels, the greater the burden on the pancreas. Over time, this burden can lead to impaired insulin secretion and the onset of diabetes. Additionally, sharp fluctuations in blood sugar levels may potentially contribute to aging, cell cancerization, cognitive disorders (Alzheimer's), and an increased risk of developing cardiovascular diseases.

(4) The belief that reducing fat intake is essential for health has been unquestionably accepted in Japan for a long time. However, various data from the twenty-first century has revealed that even if one reduces fat consumption, it may not lead to improvements in blood lipid levels or prevent heart disease and obesity.

While trans fats should be avoided, there is no need to unnecessarily restrict other types of fats. As for the intake of animal fat (saturated fat), such as those found in meat, studies indicate that, when limited to the Japanese population, there is no association with the incidence of myocardial infarction or stroke (data from 2013).

(5) Even with reduced carbohydrate intake, the brain can utilize ketones (produced from fatty acids) as an energy source. In cases of extreme carbohydrate restriction, an accumulation of ketones in the body can lead to a shift in blood acidity, potentially causing a condition known as ketoacidosis. Given the associated risks, it is advisable not to engage in extreme carbohydrate restriction.

(6) Very few individuals can sustain strict caloric limits or a low-fat diet over the long term. A more lenient approach to carbohydrate restriction is easier to adhere to since it doesn't require constant caloric monitoring, and it often yields more favorable results compared to other dietary approaches. It is important to broaden the options for individuals, exploring which dietary approach suits them best.
      

According to the National Health and Nutrition Survey, per capita daily intake of carbohydrates has been consistently decreasing for over sixty years. The daily intake of energy, too, increased until the early 1970’s, but has been on a declining trend since then.

Nevertheless, in recent years, the number of diabetics and latent diabetics with abnormal blood sugar levels continues to rise. 

For more detailed data on this trend and other factors I can think of other than carbohydrate intake, please refer to the following article. 

【Related article】Diabetes is Increasing Despite Decreased Carbohydrate Intake
    

In terms of controlling blood sugar levels, I believe a moderately low-carb diet can be effective. However, what about the issue of obesity?

According to Gary Taubes, the author of "Why We Get Fat," the debate over whether "overeating calories" or "carbohydrates" are the cause of weight gain has been ongoing since the early 1800’s. The reason behind this is that with a low-carb diet, individuals were able to lose weight without worrying about the quantity of other calorie sources such as meat and fats.

This contradicted the calorie theory and faced strong opposition from experts who staunchly believed in it and considered fats harmful to the heart[1], but now it is said that recent intervention studies have demonstrated the significant weight loss effects of a low-carb diet[2], solidifying its position in the field.

Experts who advocate for a low-carb diet seem to believe in the carbohydrate-insulin model, suggesting that carbohydrates cause weight gain by raising blood sugar levels and promoting insulin secretion. According to this model, it is deemed acceptable to consume proteins and fats that do not stimulate insulin secretion, as long as carbohydrates are reduced, in order to compensate for calories. However, I find this explanation to be insufficient.

Therefore, as a countermeasure, we must do the opposite in order to lose weight; not only to reduce carbohydrates to a certain extent but also to increase the intake of foods that take longer to digest (proteins, fats, dairy products, etc.) and foods rich in fiber, so that undigested food will remain abundant in the intestines. (In this regard, the concept of  glycemic index [GI] and glycemic load [GL]  is very important.) 

Additionally, even if insulin is considered to promote fat storage, I do not believe it is the fundamental cause of obesity.

Some people who advocate a low-carb diet say, "As long as you adjust your insulin secretion, you can eat anything without worrying about calories, even fatty foods, cheese, and meat. And since that's how you lost weight, it was the carbohydrates, not the caloric intake, that was the reason." I don’t think this explanation is correct.
    

In recent years, as the global rise in obesity becomes a significant concern, I believe that for those who tend to gain weight, easily digestible refined carbohydrates are undeniably central factors contributing to weight gain. 

However, not everyone gains weight because they eat carbohydrates; factors such as the type of carbohydrates (those with a high GI value), unbalanced diets, and irregular eating habits (such as skipping breakfast or late-night meals) are also associated with the issue.

For instance, focusing solely on caloric and/or carbohydrate "intake," might make it seem like skipping breakfast or opting for simple meals like cup noodles, "snack bread and rice balls," or fast food for lunch is a reasonable choice. It may even appear that not eating vegetables could be somewhat helpful in reducing a few carbs or calories. 

While I cannot provide data, to the best of my knowledge, there has been a significant decline in the "quality of meals" among temporary laborers in factories and workplaces, and low-income individuals in Japan in recent years.

When trying to cut down on food expenses, carbohydrates are the cheapest source of calories available, offering a temporary sense of satisfaction. 

<References>
[1] Gary Taubes. Why We Get Fat. New York: Anchor books, 2011, Pages 159-160.
[2] Jason Fung. The Obesity Code. Greystone books, 2016, Page 100.

(1) and (2) are summarized from the contents of "Diabetes is Increasing Despite Decreased Carbohydrate Intake."　

(1) The number of diabetes patients in Japan has been steadily increasing since the estimated count began in 1997, rising from 6.9 million to reach 10 million in 2016. Including pre-diabetics with blood sugar abnormalities, the total exceeds 20 million in 2016 (approximately one in six people). Compared to Western populations, Japanese people have a weaker ability to secrete insulin, and over half of those who develop typeⅡdiabetes have a BMI lower than 25.

(2) In Japan, there has been a decreasing trend in caloric and carbohydrate intake for over fifty years. At least in the context of Japan, the rise in obesity, diabetes, and blood sugar abnormalities cannot be solely explained by the amount of caloric and carbohydrate intake alone. Factors such as high glycemic index (GI) foods, sugars, unbalanced diets, and irregular lifestyles including not eating breakfast, may be related to this increase.

(3) Focusing solely on caloric and/or carbohydrate intake might make it seem reasonable to skip breakfast, opt for quick and easy meals like instant noodles or fast food for lunch, and even consider eliminating vegetables.
However, a low-quality diet skewed towards easily digestible carbohydrates and repeated bouts of hunger, may not only increase the risk of developing health issues such as blood sugar abnormalities but also contribute to obesity. 

(4) My stance is that the recent increase in (A) the risk of obesity and (B) the prevalence of blood sugar abnormalities is due to the different properties of carbohydrates.

As for (B), the major influence is how a diet containing carbohydrates raises blood glucose levels and its relationship with insulin. In contrast, (A) is associated with easily digestible carbohydrates diluting the food (nutrients) consumed and, under certain conditions, leading to intestinal starvation.

In short, in my theoretical framework, the fundamental issue with obesity is that one’s 'set-point' for body weight goes up through intestinal starvation, and carbohydrates indirectly affect that.

(5) Reducing carbohydrate intake is not the only important factor in decreasing the risk of obesity and blood sugar abnormalities. It is also important to consume low-GI grains, incorporate foods from other food groups (such as meat, fish, vegetables, nuts, dairy, seaweed, etc.) in the diet, and maintain a regular eating schedule (e.g. three meals a day).

All of these practices contribute to slowing down digestion, moderating the speed of absorption, and helping to keep blood glucose levels stable. The concepts of "second meal effect" and "resistant starch" are also important in this regard. 

In terms of weight loss, it is crucial to have undigested food consistently remaining in the intestines by consuming more foods that take longer to digest (e.g. proteins, fats) and more fibrous foods.
This approach helps reduce the sensation of hunger, leading to a gradual decrease in absorption rates. Therefore, controlling hunger is, in fact, the key for achieving successful weight loss, in my opinion.

(6) I believe that simple carbohydrates like sugar are significantly related to blood sugar abnormalities. However, the cause of inducing intestinal starvation lies in complex carbohydrates (polysaccharides) such as starch and wheat flour, and not in simple sugars.