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Should you worry about blood sugar spikes if you don't have diabetes?

Blood Sugar Spikes After Eating Without Diabetes

Reviewed · 6 sources · By Anthony Falcone

The short answer: A rise in blood sugar after a meal is normal. In 153 healthy, non-obese people wearing a glucose monitor, glucose stayed between 70 and 140 mg/dL (3.9–7.8 mmol/L) for 96% of the day and went above 140 for a median of about 30 minutes a day. Short, light walking breaks during long sitting lowered post-meal glucose by about 17% on average in one-day trials, and a dip below your usual level 2–3 hours after eating went with more hunger later.1,6,4

Before you start

  • This guide is for adults without diabetes. If you have diabetes or prediabetes, are pregnant, or take medicine that lowers blood sugar, your targets and what to do about them are for your doctor or diabetes team to set. Nothing here is advice about medication.
  • See a doctor rather than a glucose app if you have constant thirst, pass a lot of urine, lose weight without trying, or feel shaky, sweaty or confused a few hours after meals. A blood test, not a consumer glucose monitor, is how diabetes and prediabetes are diagnosed.2
  • In a Stanford study, some people whose standard blood tests were normal still rose above 140 mg/dL after a meal. If your readings worry you, take them to your doctor instead of changing your diet on your own.2
  • 96% of the day spent between 70 and 140 mg/dL (3.9–7.8 mmol/L) by 153 healthy, non-obese people wearing a glucose monitor (median)1
  • 30 min a day above 140 mg/dL in the same healthy people (median, 2.1% of the time)1
  • 80% of people who ate a standard bowl of cornflakes and milk in a Stanford monitor study went above 140 mg/dL2
  • 46,898 meals logged by 800 people with glucose monitors: the same meal gave very different rises in different people3
  • +312 kcal eaten over the next 24 hours by people with the biggest glucose dips 2–3 hours after breakfast, compared with the smallest dips (observational, 1,070 adults)4
  • 17% average drop in post-meal glucose when short, light walking breaks interrupted sitting, across 7 one-day trials6

What's a normal blood sugar after eating if you don't have diabetes?

The best reference we found comes from 12 US centres that put a blinded glucose monitor (Dexcom G6) on 153 healthy people aged 7 to 80 who were not obese, for up to 10 days. Average glucose was 98 to 99 mg/dL (5.4 to 5.5 mmol/L) in every age group except people over 60, whose average was 104 mg/dL (5.8 mmol/L).1

Glucose stayed between 70 and 140 mg/dL (3.9 to 7.8 mmol/L) for a median of 96% of the day. It went above 140 mg/dL for a median of 2.1% of the time, about 30 minutes a day, and below 70 mg/dL for 1.1%, about 15 minutes a day. So short rises after meals, and even short trips above 140, are part of a normal day.1

For comparison, the diagnostic thresholds doctors use are based on lab tests, not monitors: a fasting glucose of 100–125 mg/dL, or 140–199 mg/dL two hours into a 75 g glucose drink test, counts as prediabetes; 126 mg/dL fasting or 200 mg/dL at two hours counts as diabetes. A monitor reading above 140 after a meal is not the same thing as a diagnosis.2

Why the same meal spikes one person and not another

In one study, 800 people wore glucose monitors for a week and logged 46,898 meals. Their rises after identical meals varied a lot from person to person, so the authors concluded that one-size-fits-all food rules may be of limited use for blood sugar. A computer model that combined blood tests, diet, body measurements, activity and gut bacteria predicted each person's response, and held up in a second group of 100 people. We could read only the summary of this paper.3

A Stanford study put monitors on 57 people without a prior diabetes diagnosis for 2 to 4 weeks; screening found 5 with type 2 diabetes and 14 with prediabetes. In 30 of them who ate three standard breakfasts, 16 people whose standard tests were normal went above 140 mg/dL, or even above 200 mg/dL, after one or more of the meals.2

Blood sugar spikes and crashes: does the dip make you hungry?

The PREDICT 1 study followed 1,070 healthy adults in the UK and US with glucose monitors as they ate 8,624 standard breakfasts and then 71,715 meals of their own choice. What best predicted later hunger was not the height of the rise in the first 2 hours, but how far glucose dipped below the person's usual pre-meal level 2 to 3 hours after eating.4

Compared with the quarter of people with the smallest dips, the quarter with the biggest dips reported 9% more hunger 2 to 3 hours after breakfast, ate their next meal 24 minutes sooner, ate 75 kcal more in hours 3 to 4, and 312 kcal more over 24 hours. The largest dips followed the meal with the largest rise, a glucose drink. When the same person ate the same meal twice, a bigger dip still went with eating sooner and eating more, though more weakly.4

These are correlations, and small ones (0.14 to 0.27 in size for the main results), so the dip is one of many things that decide when and how much we eat. The dip was not linked with how alert people felt.4

How to reduce blood sugar spikes after eating: walk, don't sit

A meta-analysis pooled 7 randomised crossover trials in which adults, mostly overweight or with obesity, spent a day in the lab and ate meals while either sitting the whole time, standing up regularly, or taking short light walks. Most trials used breaks of 2 minutes every 20 minutes or 5 minutes every 30 minutes.6

Light walking breaks lowered post-meal glucose by about 17% on average compared with sitting (from about 3% to 56% across trials), and also lowered insulin. Standing breaks helped less, about 10% on average, and walking beat standing. Neither changed blood pressure. The trials could not show whether the length or frequency of the breaks matters.6

What's on the plate matters, but less predictably than you'd think

In the Stanford study, cornflakes with milk (low in fibre, high in sugar) pushed 80% of the people who ate it above 140 mg/dL. Responses to a peanut butter sandwich and a protein bar varied more from person to person, and the sandwich, with more fibre, fat and protein, more often gave a low or moderate response. The link with fibre fell just short of statistical significance (p = 0.06).2

In a blinded randomised trial within the same study, diets chosen for each person by the prediction model led to lower post-meal rises. That fits the large person-to-person differences, but it also means general food lists can only take you so far.3

Continuous glucose monitor for non-diabetics: is it worth it?

Monitors are consistent enough to compare meals. In 394 healthy adults who wore two monitors at once, two of the same brand differed by a median of 3.7% in the size of the 2-hour rise after standard meals, and two different brands by 12.5%. Both pairs mostly ranked a person's meals in the same order.5

So compare your own meals on one brand of monitor, not your numbers against someone else's device. An earlier, smaller study of 16 healthy adults wearing two monitors found meal rankings that disagreed a lot between devices.5

What none of the studies in this guide tested is whether flattening your post-meal rises improves long-term health if you don't have diabetes. They describe what's normal, how people differ and what lowers the rise on the day; that is useful, but it is not the same as a health benefit.1,2,3,4,5,6

What to do with this

  • Don't panic at a rise after a meal: healthy people spent a median of 96% of the day between 70 and 140 mg/dL and about 30 minutes a day above 140.1
  • After a meal, break up sitting with short, easy walks, for example 2 minutes every 20 minutes or 5 minutes every 30, as in the trials.6
  • If you want a steadier breakfast, swap a low-fibre, sugary cereal for something with more fibre, fat and protein: cornflakes with milk sent 80% of eaters above 140 mg/dL.2
  • If you're hungry again 2 to 3 hours after a meal, that meal may be worth a look: bigger glucose dips at that time went with more hunger and more eating later.4
  • If you try a glucose monitor, compare meals on the same brand and look at patterns, not single readings.5

How sure is this?

  • None of these studies tested whether lowering post-meal spikes improves long-term health in people without diabetes. They measured glucose, hunger and eating over days, not disease.1,2,3,4,5,6
  • The hunger study was funded in part by the company Zoe, and several authors of both PREDICT 1 papers work or have worked for Zoe or consult for it. The hunger study is observational, its correlations are small, and the paper was corrected after publication.4,5
  • The reference ranges come from one monitor model in 153 non-obese people, children included, and we could read only the paper's summary; a correction to the paper has been published that we could not read. The 800-person personalised-nutrition study we also know only from its summary.1,3
  • The Stanford study was small (57 people, 30 in the meal tests) and included people with diabetes and prediabetes found at screening.2
  • The walking trials lasted one day in a lab, kept people seated for hours in a way few of us do, and mostly included adults who were overweight or had obesity. The authors note possible publication bias.6

Common questions

Is it normal for blood sugar to spike after eating?

Yes. Healthy people wearing glucose monitors spent a median of 96% of the day between 70 and 140 mg/dL, and about 30 minutes a day above 140.1

What is a normal blood sugar level after eating for non-diabetics?

On a monitor, mostly between 70 and 140 mg/dL (3.9–7.8 mmol/L), with average glucose of 98 to 99 mg/dL in healthy people under 60 and 104 mg/dL over 60. Diagnosis uses lab tests: 140–199 mg/dL two hours into a glucose drink test counts as prediabetes.1,2

Why do I get hungry 2 to 3 hours after eating?

One reason may be a glucose dip. In 1,070 healthy adults, people whose glucose fell furthest below their usual level 2 to 3 hours after breakfast felt hungrier, ate sooner and ate 312 kcal more over the day than people with the smallest dips.4

Does walking after eating lower blood sugar?

In one-day trials, yes: short light walks every 20 to 30 minutes during long sitting lowered post-meal glucose by about 17% on average compared with sitting, more than standing breaks did.6

Should non-diabetics wear a continuous glucose monitor?

It's optional. Monitors are consistent enough to compare your own meals on one brand, but no study here shows that acting on the readings improves long-term health if you don't have diabetes.5,1

Sources

  1. Shah VN, DuBose SN, Li Z, Beck RW, Peters AL, Weinstock RS, Kruger D, Tansey M, Sparling D, Woerner S, Vendrame F, Bergenstal R, Tamborlane WV, Watson SE, Sherr J. Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study. The Journal of Clinical Endocrinology & Metabolism, 2019. Official reference values. doi.org/10.1210/jc.2018-02763
  2. Hall H, Perelman D, Breschi A, Limcaoco P, Kellogg R, McLaughlin T, Snyder M. Glucotypes reveal new patterns of glucose dysregulation. PLOS Biology, 2018. Case series. doi.org/10.1371/journal.pbio.2005143
  3. Zeevi D, Korem T, Zmora N, Israeli D, Rothschild D, Weinberger A, et al. Personalized nutrition by prediction of glycemic responses. Cell, 2015. Randomised trial. doi.org/10.1016/j.cell.2015.11.001
  4. Wyatt P, Berry SE, Finlayson G, O'Driscoll R, Hadjigeorgiou G, Drew DA, Al Khatib H, Nguyen LH, Linenberg I, Chan AT, Spector TD, Franks PW, Wolf J, Blundell J, Valdes AM. Postprandial glycaemic dips predict appetite and energy intake in healthy individuals. Nature Metabolism, 2021. Survey / forum study. doi.org/10.1038/s42255-021-00383-x
  5. Merino J, Linenberg I, Bermingham KM, Ganesh S, Bakker E, Delahanty LM, et al. Validity of continuous glucose monitoring for categorizing glycemic responses to diet: implications for use in personalized nutrition. The American Journal of Clinical Nutrition, 2022. Case series. doi.org/10.1093/ajcn/nqac026
  6. Buffey AJ, Herring MP, Langley CK, Donnelly AE, Carson BP. The acute effects of interrupting prolonged sitting time in adults with standing and light-intensity walking on biomarkers of cardiometabolic health in adults: a systematic review and meta-analysis. Sports Medicine, 2022. Meta-analysis. doi.org/10.1007/s40279-022-01649-4

The Nutrition Timing Protocol puts timing in its place: total intake decides most of your results. It covers spreading protein over the day, eating before and after training, morning versus evening eating and front-loading calories to tame evening hunger, plus simple habits for steadier blood sugar such as a short walk after meals, with example days you can copy and 15 peer-reviewed references. Nutrition Timing Protocol

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