Researchers followed over 113,000 Korean adults for about 9 years to understand how much carbohydrates people should eat. They found something interesting: people who ate very low amounts of carbohydrates (less than 55% of their daily calories) had higher risks of dying from all causes and heart disease compared to those eating a moderate amount (55-65% of calories). However, eating more carbohydrates than this didn’t provide extra benefits. The study suggests that for populations eating traditionally high-carbohydrate diets, there’s a “sweet spot” where moderate carbohydrate intake appears healthiest.

The Quick Take

  • What they studied: How much carbohydrates people eat affects their chances of dying from any cause, cancer, or heart disease
  • Who participated: 113,043 Korean adults aged 40-69 years with no major health conditions at the start, followed for an average of 9.2 years
  • Key finding: People eating less than 55% of their daily calories from carbohydrates had 50% higher risk of dying from any cause and 3 times higher risk of dying from heart disease, compared to those eating 55-65% from carbohydrates
  • What it means for you: If you eat a traditional diet with plenty of carbohydrates, cutting carbs too drastically may increase health risks. A moderate carbohydrate intake appears safer than very low intake, though this finding applies mainly to populations eating high-carb diets traditionally.

The Research Details

This was a large, long-term observational study called a cohort study. Researchers recruited 113,043 Korean adults aged 40-69 and tracked their health for about 9 years. At the beginning, participants filled out detailed questionnaires about what they ate, including how many carbohydrates, proteins, and fats they consumed. Researchers then followed these people over time and recorded who got sick or died, and from what causes.

The researchers used a statistical method called Cox regression to analyze the data. This method helps them understand whether the amount of carbohydrates people ate was connected to their risk of dying. They looked at three types of death: all causes combined, cancer specifically, and heart disease specifically. They also examined what happened when people replaced carbohydrates with different types of fat (saturated, unsaturated, and polyunsaturated).

The study was conducted in South Korea, where people traditionally eat diets with higher amounts of carbohydrates compared to Western countries. This is important because the findings may apply differently to populations with different eating patterns.

This research approach is valuable because it follows real people in their everyday lives rather than testing them in a laboratory. The large number of participants (over 113,000) and long follow-up period (9+ years) make the results more reliable. By studying a population that traditionally eats high-carbohydrate diets, researchers could see what happens when people vary their carbohydrate intake within a realistic range for their culture.

Strengths: Very large sample size, long follow-up period, detailed dietary assessment using a validated questionnaire, and careful statistical analysis. The study adjusted for many other factors that affect health (age, exercise, smoking, etc.). Limitations: This is an observational study, so it shows associations but cannot prove that carbohydrate intake directly causes differences in mortality. People who eat very low carbohydrates might differ in other ways that affect health. The study was conducted in Korea, so results may not apply equally to other populations with different traditional diets.

What the Results Show

The main finding was a “reverse J-shaped” relationship between carbohydrate intake and death risk. This means that very low carbohydrate intake (less than 55% of daily calories) was associated with higher death risk, but eating more carbohydrates didn’t continue to lower the risk—it stayed about the same. Specifically, people eating less than 55% of calories from carbohydrates had a 50% higher risk of dying from any cause compared to those eating 55-65% from carbohydrates.

For heart disease deaths specifically, the difference was even more dramatic. People eating less than 55% of calories from carbohydrates had 3 times higher risk of dying from heart disease compared to the 55-65% group. This was a statistically significant finding, meaning it’s unlikely to be due to chance.

Interestingly, eating more carbohydrates than 65% of daily calories didn’t provide additional protection. People eating 65-70%, 70-75%, 75-80%, or even 80% or more of calories from carbohydrates all had similar death risks to the 55-65% group. This suggests there’s a “sweet spot” rather than a “more is better” pattern.

These findings held true whether people replaced carbohydrates with saturated fat, monounsaturated fat, or polyunsaturated fat. The type of fat didn’t change the pattern.

The researchers also looked at carbohydrate quality—whether the carbohydrates came from foods that raise blood sugar quickly or slowly. Surprisingly, they found no clear connection between carbohydrate quality and death risk from any cause. This suggests that for this population, the amount of carbohydrates mattered more than the type. Cancer mortality showed no significant association with carbohydrate intake at any level, meaning carbohydrate intake didn’t appear to affect cancer death risk in this study.

Previous research on carbohydrate intake and health has been mixed, especially in Western populations where low-carbohydrate diets are more common. This study adds important information by focusing on a population eating traditionally high-carbohydrate diets. The finding that very low carbohydrate intake increases health risks is consistent with some previous studies but contradicts the idea that lower carbohydrate intake is always healthier. The study suggests that the “optimal” amount of carbohydrates may depend on what a population traditionally eats.

This study has several important limitations. First, it’s observational, meaning researchers watched what people ate and what happened to them, but couldn’t control all the factors that might affect the results. People who eat very low carbohydrates might differ in other important ways (exercise habits, overall diet quality, health status) that could explain the higher death risk. Second, the study was conducted in Korea, where traditional diets are high in carbohydrates, so these findings may not apply to Western populations eating lower-carbohydrate diets. Third, dietary intake was measured only at the beginning of the study, so researchers didn’t know if people’s eating habits changed over the 9+ years of follow-up. Finally, while the study included over 113,000 people, the number of deaths in some carbohydrate intake groups was relatively small, which could affect the reliability of those specific findings.

The Bottom Line

For people eating traditional high-carbohydrate diets (like in East Asia): Aim for carbohydrates to make up 55-65% of your daily calories. This appears to be the safest range based on this research. Avoid dropping below 55% of calories from carbohydrates, as this was associated with increased health risks. Eating more than 65% from carbohydrates doesn’t appear to provide additional benefits, so there’s no need to maximize carbohydrate intake. The type of carbohydrate (high or low glycemic index) appears less important than the total amount. Confidence level: Moderate. This is a large, well-conducted study, but it’s observational and was done in one population.

These findings are most relevant to people in East Asian countries or those eating traditional high-carbohydrate diets. People following very low-carbohydrate diets (like keto diets) should be aware of these findings, though the study doesn’t directly test such extreme diets. People with heart disease or at high risk for heart disease should pay particular attention, as the heart disease risk increase was most pronounced. These findings may not apply to Western populations eating lower-carbohydrate diets traditionally. People with diabetes or other medical conditions should consult their doctor before making major dietary changes.

Health benefits or risks from carbohydrate intake changes would likely take months to years to become apparent. This study followed people for an average of 9.2 years, so the effects measured were long-term. Don’t expect immediate changes if you adjust your carbohydrate intake—think in terms of months and years for meaningful health impacts.

Want to Apply This Research?

  • Track your daily carbohydrate intake as a percentage of total calories for 2-4 weeks. Most nutrition apps can calculate this automatically. Aim to see if you’re in the 55-65% range and monitor how you feel, your energy levels, and any changes in weight or health markers.
  • If you’re currently eating less than 55% of calories from carbohydrates, gradually increase your carbohydrate intake by adding whole grains, fruits, or starchy vegetables to meals. If you’re above 65%, you don’t need to reduce further based on this research. Track your carbohydrate percentage weekly to ensure you’re moving toward the 55-65% range.
  • Set a monthly reminder to review your carbohydrate intake percentage. Track any changes in energy levels, digestion, weight, or how you feel overall. If you have access to health markers (blood pressure, cholesterol, blood sugar), monitor these every 3-6 months to see if adjusting carbohydrate intake affects them. Share this data with your doctor during annual check-ups.

This research describes associations observed in a Korean population eating high-carbohydrate diets and should not be interpreted as medical advice. The study cannot prove that carbohydrate intake directly causes changes in mortality risk. Individual nutritional needs vary based on age, health status, activity level, and medical conditions. Before making significant changes to your diet, especially if you have heart disease, diabetes, or other medical conditions, consult with your doctor or a registered dietitian. This information is for educational purposes and should not replace professional medical advice.