Researchers followed nearly 10,000 Brazilian adults for 8 years to see how eating fewer carbohydrates affected their health. They found that people who ate low-carb diets had better insulin control and their pancreas didn’t have to work as hard, especially those without diabetes. Interestingly, people gained a small amount of weight, but their bodies became better at managing blood sugar. The study suggests that eating fewer carbs could be a helpful strategy for managing metabolic health in middle-aged and older adults, though personalized approaches work best for different people.

The Quick Take

  • What they studied: Whether eating a diet with fewer carbohydrates (less than 45% of daily calories) affects how well the body controls blood sugar and other heart health markers over 8 years
  • Who participated: 9,658 Brazilian adults, ages 35-74, some with type 2 diabetes and some without, tracked from 2008-2010 and again in 2017-2019
  • Key finding: People without diabetes who ate low-carb diets had lower insulin levels and better insulin sensitivity (their bodies used insulin more efficiently). People with diabetes also showed improved insulin control. However, both groups gained a small amount of weight.
  • What it means for you: Eating fewer carbohydrates may help your body use insulin more efficiently and reduce stress on your pancreas, which could benefit metabolic health. However, this approach works differently for different people, and weight changes should be monitored. Talk to your doctor before making major diet changes.

The Research Details

This was a long-term follow-up study that tracked real people’s eating habits and health over 8 years. Researchers didn’t tell people what to eat—instead, they asked participants about their food choices using detailed questionnaires at two time points (2008-2010 and 2017-2019). They then looked at how people’s health markers changed based on whether they naturally chose to eat fewer carbohydrates. The researchers used advanced statistical methods to account for other factors that might affect health, like exercise, smoking, age, and socioeconomic status.

The study divided participants into groups: those who never ate low-carb, those who started eating low-carb only at the second check-in, and those who consistently ate low-carb at both time points. This allowed researchers to see both immediate and long-term effects. They measured several important health markers including body weight, blood pressure, insulin levels, and insulin resistance (how well the body uses insulin).

The researchers used a special statistical technique called quantile regression, which is more sophisticated than standard analysis because it can show how the diet affects different groups of people differently, not just the average person.

This study design is valuable because it follows real people making their own food choices over a long period, rather than forcing people to follow a strict diet in a lab. This makes the results more relevant to everyday life. The 8-year timeframe is long enough to see lasting effects, and the large number of participants (nearly 10,000) makes the findings more reliable. By studying both people with and without diabetes, researchers could see whether low-carb diets work differently depending on someone’s health status.

Strengths: Large sample size, long follow-up period, diverse population, careful adjustment for other health factors, and use of validated food questionnaires. Limitations: The study relied on people’s memory of what they ate (self-reported), people weren’t randomly assigned to diets (they chose their own), and the study only included Brazilian adults so results may not apply equally to other populations. The modest weight gain observed could be due to measurement error or other lifestyle changes not captured in the study.

What the Results Show

Among people without diabetes, those who switched to a low-carb diet at the follow-up visit had noticeably lower insulin levels and better insulin sensitivity. Their pancreas also appeared to be working less hard (measured by a marker called HOMA-B). These improvements suggest their bodies became more efficient at managing blood sugar. People who consistently ate low-carb at both time points showed similar pancreatic improvements.

For people with diabetes, low-carb eating led to even more dramatic improvements in insulin sensitivity and lower insulin levels. This suggests the diet may be particularly helpful for those already struggling with blood sugar control. The improvements were larger in the diabetes group than in the non-diabetes group.

Across both groups, people gained a small amount of weight (about 0.3-0.5 pounds on average), which was unexpected. This modest weight gain occurred despite improved metabolic markers, suggesting that the quality of metabolic function improved even as weight slightly increased. Researchers note this could be due to changes in muscle mass or measurement variation rather than true fat gain.

Blood pressure changes were not significantly different between groups, suggesting low-carb diets don’t strongly affect blood pressure in this population. The study found that the benefits of low-carb eating appeared relatively quickly—people who only switched to low-carb at the second time point showed improvements similar to those who ate low-carb consistently. This suggests metabolic improvements can happen within a few years of dietary change.

These findings align with previous research showing that low-carb diets can improve insulin sensitivity in the short term. However, this is one of the longest studies examining these effects in a real-world setting. Previous studies often showed weight loss with low-carb diets, so the modest weight gain here is somewhat surprising and suggests that the relationship between low-carb eating and weight may be more complex than previously thought. The improvements in insulin function are consistent with what researchers expected based on how carbohydrates affect blood sugar.

The study has several important limitations. First, people reported their own food intake, which can be inaccurate—people may forget what they ate or underestimate portions. Second, researchers couldn’t prove that the low-carb diet caused the improvements; other lifestyle changes (like increased exercise) could have contributed. Third, the study only included Brazilian adults, mostly middle-aged and older, so results may not apply to younger people or other populations. Fourth, the study didn’t track exactly how much weight people gained or lost, only overall body mass index. Finally, people who chose to eat low-carb may have been different in other ways from those who didn’t, which could affect the results.

The Bottom Line

Moderate confidence: A low-carb diet (less than 45% of daily calories from carbs) may help improve how your body handles insulin and reduce stress on your pancreas, particularly if you have diabetes or are at risk for it. This could be a reasonable dietary strategy for middle-aged and older adults. However, the modest weight gain observed suggests monitoring your weight is important. Any major dietary change should be discussed with your doctor or a registered dietitian, especially if you take diabetes medications, as improved insulin sensitivity might require medication adjustments.

This research is most relevant to middle-aged and older adults (35-74 years old), particularly those with type 2 diabetes or prediabetes, or those concerned about metabolic health. People with normal blood sugar control may also benefit, though the improvements are less dramatic. This may be less relevant to younger adults, people with type 1 diabetes, or those with certain medical conditions. Pregnant women and people with a history of eating disorders should consult healthcare providers before making significant dietary changes.

Based on this study, improvements in insulin sensitivity and pancreatic function appear to develop within a few years of adopting a low-carb diet. Some improvements may occur sooner, but the study measured changes over 8 years, so patience is important. Weight changes may occur gradually and should be monitored regularly.

Want to Apply This Research?

  • Track daily carbohydrate intake as a percentage of total calories (aim for less than 45%) and monitor weight weekly. Also track fasting blood sugar if you have a home glucose monitor, or schedule regular blood work to measure insulin levels and HOMA-IR scores every 3-6 months.
  • Use the app to log meals and see your carbohydrate percentage in real-time. Set a daily carb target (around 45% of calories) and get notifications when approaching the limit. Create meal plans that emphasize proteins, healthy fats, and non-starchy vegetables while reducing bread, pasta, rice, and sugary foods.
  • Establish a baseline of current metabolic markers (insulin, blood sugar, weight) through your doctor. Check in monthly with weight and carb intake consistency. Every 3 months, review trends in the app and compare to previous periods. Every 6-12 months, get updated blood work to measure insulin levels and other metabolic markers to confirm improvements are occurring.

This research describes associations found in a study of Brazilian adults and should not be considered personal medical advice. Low-carbohydrate diets may affect diabetes medications, requiring dose adjustments—consult your doctor before making significant dietary changes, especially if you take insulin or other blood sugar medications. This study followed people’s natural food choices rather than testing a controlled diet, so individual results will vary. Pregnant women, people with a history of eating disorders, and those with certain medical conditions should discuss any major diet change with their healthcare provider. Always work with a registered dietitian or doctor to develop a personalized nutrition plan appropriate for your individual health status and goals.