Researchers tracked blood sugar levels in over 500 healthy adults for a week using special monitors to see how different foods and meal times affected their glucose response. They found that meals with higher amounts of carbohydrates caused bigger blood sugar spikes, especially at lunch and dinner. The study also discovered that age, weight, sex, and existing blood sugar control all played a role in how much someone’s blood sugar rose after eating. These findings help explain why the same meal might affect different people’s blood sugar differently.

The Quick Take

  • What they studied: How different meals and meal times affect blood sugar levels in people without diabetes, and whether factors like age, weight, and sex make a difference.
  • Who participated: 514 healthy adults (average age 46 years, 64% women) from Spain who didn’t have diabetes. Researchers randomly selected them from health system records.
  • Key finding: Meals with more carbohydrates caused blood sugar to rise higher and stay elevated longer. Lunch and dinner caused bigger blood sugar spikes than breakfast. Older people, heavier people, and women tended to have higher blood sugar responses after eating.
  • What it means for you: If you’re concerned about blood sugar control, choosing meals with lower carbohydrate content—especially for lunch and dinner—may help keep your blood sugar more stable. However, this study only shows a connection, not that changing your diet will definitely improve your health.

The Research Details

This was a cross-sectional study, which means researchers took a snapshot of people at one point in time rather than following them over years. Between 2012 and 2015, researchers recruited 622 adults from a health center in Spain and gave them special glucose monitors (small devices that measure blood sugar continuously) to wear for 7 days. The monitors recorded blood sugar levels every few minutes, collecting over 1.3 million measurements total. During the same week, participants kept detailed food diaries so researchers could see exactly what they ate and when. The researchers then used statistical models to analyze whether the carbohydrate content of meals, meal timing, and personal characteristics like age and weight predicted how high blood sugar would rise after eating.

This research approach is valuable because it captures real-world eating patterns and blood sugar responses in everyday life, not in a controlled lab setting. By using continuous glucose monitors instead of just checking blood sugar once or twice, researchers got a much more complete picture of how blood sugar changes throughout the day. The large number of measurements (over 1.3 million) makes the findings more reliable and representative of what actually happens in people’s bodies.

The study was published in JAMA Network Open, a reputable medical journal. The researchers used objective measurements (continuous glucose monitors) rather than relying on people’s memory. However, because this is a cross-sectional study, it shows associations but cannot prove that one thing causes another. The study only included people without diabetes, so results may not apply to people with diabetes or prediabetes.

What the Results Show

The main finding was that meals with higher carbohydrate content caused blood sugar to rise higher. For every 10-unit increase in the carbohydrate load of a meal, blood sugar rose by about 1.3 mg/dL on average. While this might sound small, these increases add up over time and across many meals. Importantly, the timing of meals mattered significantly. Lunch and dinner caused much bigger and longer-lasting blood sugar spikes compared to breakfast. After lunch and dinner, blood sugar peaked around 70 minutes after eating, while after breakfast it peaked around 50 minutes. This suggests that the body may handle carbohydrates differently depending on the time of day and what else has been eaten earlier.

Age made a noticeable difference: for every 10 years of age, blood sugar response increased by about 2-3.5 mg/dL. This means older adults tend to have higher blood sugar spikes after meals. Weight also played a role, particularly after breakfast—heavier people had higher blood sugar responses. Interestingly, men had lower blood sugar levels than women in the hours after lunch and dinner, with differences up to 4.6 mg/dL. People with higher baseline blood sugar control (measured by HbA1c, a marker of long-term blood sugar) had more pronounced glucose spikes, suggesting their bodies were more reactive to carbohydrates.

This study confirms what previous research has suggested about carbohydrate content affecting blood sugar, but it provides more detailed information by using continuous monitoring in everyday settings. The finding that meal timing affects glucose response aligns with research on circadian rhythms and metabolism. The sex differences observed here add nuance to previous studies and suggest that personalized nutrition recommendations might need to account for biological sex.

This study only shows associations, not cause-and-effect relationships. Because it was cross-sectional (a snapshot in time), researchers couldn’t determine whether the factors they measured actually caused the blood sugar changes. The study only included people without diabetes, so the findings may not apply to people with diabetes or those at high risk. The participants were from Spain and may not represent other populations. Additionally, the study didn’t measure other important factors that affect blood sugar, like physical activity, stress, or sleep quality.

The Bottom Line

If you want to manage your blood sugar levels, consider choosing meals with lower carbohydrate content, particularly for lunch and dinner (moderate confidence). Eating breakfast may cause smaller blood sugar spikes than other meals (moderate confidence). These findings are most relevant for people concerned about metabolic health or those with family histories of diabetes. However, these are general patterns—individual responses vary significantly based on age, weight, sex, and other factors.

This research is most relevant for people interested in preventing type 2 diabetes, those with prediabetes, people managing their weight, and anyone concerned about long-term metabolic health. It’s particularly important for older adults and women, who showed larger blood sugar responses in this study. People already diagnosed with diabetes should consult their healthcare provider, as their responses may differ. Healthy young adults with normal weight may see less dramatic effects but could still benefit from the meal timing insights.

Changes in blood sugar response after dietary modifications typically become noticeable within days to weeks, though long-term health benefits (like reduced diabetes risk) take months to years to develop. Continuous glucose monitors can show individual responses within 7-14 days of dietary changes.

Want to Apply This Research?

  • Log the carbohydrate content of each meal and note the time of day (breakfast, lunch, dinner). If users have access to glucose monitoring, they can correlate specific meals with blood sugar responses. Track patterns over 2-4 weeks to identify personal triggers.
  • Users can set a goal to reduce carbohydrate content in lunch and dinner meals by 20-30% and track how they feel (energy levels, hunger, cravings) over two weeks. The app could suggest lower-carb alternatives for favorite meals and send reminders about meal timing.
  • Create a weekly summary showing average carbohydrate intake by meal time and correlate with energy levels or other health markers the user tracks. Set alerts if carbohydrate intake exceeds personalized targets, especially for lunch and dinner. Track changes in weight, energy, and overall wellbeing monthly to assess long-term impact.

This research shows associations between meal characteristics and blood sugar responses in healthy adults without diabetes. It does not prove that changing your diet will prevent disease or improve your health. If you have diabetes, prediabetes, or other metabolic conditions, consult your healthcare provider or registered dietitian before making significant dietary changes. Individual responses to foods vary greatly based on genetics, medications, activity level, and other factors. This information is educational and should not replace personalized medical advice.