- Type 2 diabetes is caused by decreased insulin secretion and insulin resistance, and Japanese people are also prone to developing it (based on data from the International Diabetes Federation and the Ministry of Health, Labour and Welfare).
- The ketogenic diet, which is low in carbohydrates and high in fats, can lead to short-term weight loss and improvements in blood sugar levels and HbA1c. However, its long-term safety remains uncertain.
- People taking medication (especially insulin or SU drugs) are at risk of hypoglycemia and need to adjust their medication in consultation with their doctor.
- It is important to monitor cardiovascular risk, kidney function, and lipid abnormalities, while ensuring a good intake of quality fats, sufficient vegetables, and hydration.
Introduction: Is the Ketogenic Diet “Good” or “Bad” for Type 2 Diabetes?
Diabetes is on the rise worldwide, and the International Diabetes Federation (IDF) reports that the number of people with diabetes runs into the hundreds of millions. In Japan as well, surveys by the Ministry of Health, Labour and Welfare show that when including those at risk of diabetes, the numbers are considerable, with type 2 diabetes accounting for 95% of cases. Amid this, we’ve been hearing more and more stories like, “My blood sugar dropped on the ketogenic diet,” or “I was able to reduce my medication.” Our team has also reviewed the information firsthand and compiled the benefits and cautions in an easy-to-understand way.
Basic Knowledge of Type 2 Diabetes: Why Are Japanese People Also Prone to It?
Insulin Secretion and Insulin Resistance
Type 2 diabetes is a condition where blood sugar control is disrupted due to insulin resistance—when insulin doesn’t work effectively—and a decrease in insulin secretion. Compared to Western populations, Japanese people may not show obvious obesity but tend to have a reduced ability of the pancreas to secrete insulin, which can lead to high blood sugar relatively early on. That’s why paying attention to diet and lifestyle habits is so important.
How the Ketogenic Diet Is Said to “Work”
Reducing the burden on blood sugar and insulin through carbohydrate restriction
A ketogenic diet typically consists of about 75% of total energy from fats, 20% from proteins, and less than 5% from carbohydrates. By keeping carbohydrate intake low, the rise in blood sugar after meals and the accompanying insulin secretion are suppressed, reducing the burden on the pancreas and making it easier to improve insulin resistance. Additionally, when the body enters a state of ketosis, it uses fat as its primary energy source, leading to weight loss, which also contributes to better blood sugar control.
Effectiveness in Clinical Practice
Short-term clinical trials have reported that ketogenic and strict low-carbohydrate diets are effective in improving body weight, fasting blood glucose, and HbA1c levels. In the clinical reports we reviewed, there were cases showing significant improvements in patients with type 2 diabetes accompanied by obesity. However, most observations lasted only about 6 to 12 months, and there is limited evidence regarding long-term (several years) safety and sustained effectiveness.
Calorie Restriction vs. Ketogenic Diet: Which Is Better?
What Research Shows
Traditionally, calorie restriction has been the main focus, but a Spanish study (by Goday et al.) reported that a low-calorie ketogenic diet group had advantages over a conventional low-calorie diet group in terms of weight loss and improved blood sugar control. Additionally, the American Diabetes Association (ADA) includes low-carbohydrate diets as one option within personalized nutrition therapy. However, there is still no definitive conclusion on which method is best for everyone.
How to Choose in Practice
The key points are whether you can maintain it consistently and whether it can be done safely. Since losing weight itself can improve blood sugar levels, calorie management is effective for many people. The ketogenic diet may efficiently lower both weight and blood sugar in a short period, but the quality of fats, nutritional balance, and medical supervision are essential. In cases we've seen around us, there were instances where people drastically reduced carbohydrates on their own and ended up feeling unwell, which made us realize the importance of consulting with a specialist.
Precautions for Diabetic Patients When Following a Ketogenic Diet
Drug Interactions and the Risk of Hypoglycemia
For those undergoing insulin therapy or using sulfonylureas (SU drugs), significantly reducing carbohydrate intake can increase the risk of hypoglycemia. Medication doses will need to be reduced or adjusted, so always coordinate closely with your primary doctor. It is dangerous to stop medication on your own without medical guidance.
Ketoacidosis, kidney function, and lipid management
The ketogenic diet is generally not recommended for people with type 1 diabetes due to the high risk of ketoacidosis. Even in type 2 diabetes, it is important to be cautious of dehydration, electrolyte imbalances, and impacts on kidney function. Since excessive intake of saturated fats may raise LDL cholesterol levels, we recommend focusing on unsaturated fats such as olive oil and fish oils.
Tips for Practice
- Create a plan together with your doctor and registered dietitian (including medication adjustments).
- Regularly monitor blood glucose, HbA1c, lipid levels, and kidney function.
- Ensure adequate intake of fluids and electrolytes, along with plenty of vegetables and dietary fiber.
- Be mindful of alcohol, processed foods, and high salt intake.
- Avoid drastically cutting carbohydrates on your own—especially if you have an existing medical condition.
Summary
The ketogenic diet can be an effective short-term method for improving blood sugar levels and promoting weight loss in people with type 2 diabetes, but it’s not suitable for everyone. Those who are on medication, have impaired kidney function, or have type 1 diabetes need to be especially cautious. As we organized this information, we got the impression that while the diet can be effective, managing the risks is essential. If you’re interested, please consult your primary doctor or a specialized dietitian first to proceed safely.
Disclaimer: The information in this article is for general informational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional before making any health-related decisions.