Blood Sugar Spikes and Energy Crashes: What the Research Shows
Metabolic Health · Research Review
It's 2:30 in the afternoon. Lunch was a sandwich, chips and a soda, and now your eyes are heavy, you can't focus, and you're already thinking about a snack. Most people call it a "sugar crash." The research says that's not just a figure of speech, and the fixes are simpler than most people expect.
The Short Version
→ Sugar doesn't give you a lasting lift. A meta-analysis of 31 studies found people felt more tired and less alert within an hour of eating it.1
→ People whose blood sugar dipped hardest a few hours after breakfast felt hungrier and ate about 312 more calories over the day.2
→ Eating vegetables and protein before carbs, and taking short walks after meals, both lower the post-meal rise.3,4,5
→ About 115 million U.S. adults have prediabetes, and most don't know it. A simple blood test can tell you where you stand.6,7
What a "crash" actually is
When you eat a meal heavy in fast-digesting carbs, blood sugar rises quickly. Your pancreas answers with insulin to move that sugar into your cells. In some people and after some meals, that response overshoots, and blood sugar drops below where it started a few hours later. That dip is the slump you feel.
Researchers in the PREDICT study tracked more than 1,000 healthy adults wearing glucose monitors across roughly 70,000 meals. The people with the biggest dips 2–4 hours after eating ("big dippers") reported 9% more hunger, ate their next meal about 30 minutes sooner, and ate about 75 more calories in the 3–4 hours after breakfast and about 312 more over the whole day than the "little dippers."2 This was a large observational study, so it shows a link, not proof of cause. But it fits what a lot of people already notice: a big spike in the morning often means a hungry, foggy afternoon.
The "sugar rush" is mostly a myth
A 2019 meta-analysis pooled 31 controlled studies with almost 1,300 adults. Sugar didn't improve mood at any point. Within an hour, people who had it felt more tired and less alert than people who didn't.1 If you reach for something sweet to get through the afternoon, the data suggest it's more likely to deepen the slump than fix it.
Order matters: eat the carbs last
In a small but well-known crossover study, 11 adults with type 2 diabetes ate the same meal on two different days. When they ate the vegetables and protein first and the carbohydrates afterward, their blood sugar was 29% lower at 30 minutes, 37% lower at one hour and 17% lower at two hours, with lower insulin too.3 The study was small and in people with diabetes, so the exact numbers won't carry over to everyone. But the idea is low-cost and easy: same food, different order. Fiber, protein and fat slow how quickly the carbs reach your bloodstream.
A short walk does a lot
Working muscles pull sugar out of the blood without needing much insulin. That's why movement after a meal is one of the most reliable tools in the research.
A 2022 meta-analysis in Sports Medicine looked at randomized crossover trials where people either sat for hours or broke up their sitting. Light walking breaks lowered post-meal blood sugar by about 17% on average compared with sitting straight through. Standing helped a little (about 10%), but walking did more.4
A 2025 meta-analysis of 17 trials in adults with obesity found the same pattern with "exercise snacks": brief bouts of walking, stair climbing or bodyweight squats spread through the day lowered the post-meal glucose and insulin response compared with uninterrupted sitting.5 You don't need a workout. Two to five minutes of easy walking after a meal, or every 30 minutes or so at a desk, is the kind of dose these studies used.
Sleep is part of blood sugar control
In a 2023 randomized crossover trial funded by the NIH, 38 healthy women cut their sleep by about 1.5 hours a night (to roughly 6 hours) for six weeks. Insulin resistance rose by nearly 15% overall and by more than 20% in postmenopausal women, and the change wasn't explained by weight gain.8 In plain English, the same breakfast takes more insulin to handle after a stretch of short nights. If your afternoons are rough, look at your nights too.
Don't panic over every spike
Wearable glucose monitors have made "spikes" a hot topic. Some context helps. In a 2019 study of 153 healthy people without diabetes wearing monitors, the typical person spent about 96% of the day between 70 and 140 mg/dL, with brief rises after meals.9 A short bump after a meal is normal. What matters more is the overall pattern: how high, how long, and whether your fasting numbers and A1c are creeping up over time.
Why it's worth knowing your numbers
The CDC estimates that 115.2 million U.S. adults have prediabetes.6 In the CDC's earlier national survey data, only about 1 in 5 adults with prediabetes had been told they had it.7 Prediabetes usually has no symptoms, though frequent energy crashes and constant hunger can be part of the picture.
The American Diabetes Association recommends that most adults be screened starting at age 35, and earlier for people with excess weight and other risk factors. Prediabetes is defined as an A1c of 5.7–6.4% or a fasting glucose of 100–125 mg/dL.10 Those are simple blood tests, and catching a rise early gives you the most room to change course with food, movement and sleep.
What you can do
→ Build meals around protein and vegetables, and eat those first. Save the bread, rice or dessert for the end of the meal.
→ Rethink the sweet afternoon fix. Swap the soda or candy for water and a protein-based snack.
→ Walk 2–10 minutes after meals, especially your biggest one. At a desk, get up and move every 30–60 minutes.
→ Protect your sleep. Aim for 7+ hours. Short nights make the next day's meals harder to handle.
→ Know your numbers. If you're 35 or older and haven't had an A1c or fasting glucose checked recently, ask your provider about it.
Energy crashes aren't a character flaw and you don't need a perfect diet to fix them. Small changes in what you eat first, whether you move after meals and how you sleep add up. If you want straight answers about your own numbers, that's a conversation worth having with a physician who will take the time.
Dr. Cody Belkoff, DO
Prime Body Solutions · Physician-Led Care · Liberty Lake, WA
Educational content only, not medical advice. Talk with your provider before changing your diet, exercise or medications, especially if you have diabetes or take medications that lower blood sugar.
References
- Mantantzis K, Schlaghecken F, Sünram-Lea SI, Maylor EA. Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood. Neurosci Biobehav Rev. 2019. doi:10.1016/j.neubiorev.2019.03.016
- Wyatt P, Berry SE, Finlayson G, et al. Postprandial glycaemic dips predict appetite and energy intake in healthy individuals. Nat Metab. 2021. (Observational cohort.) doi:10.1038/s42255-021-00383-x
- Shukla AP, Iliescu RG, Thomas CE, Aronne LJ. Food order has a significant impact on postprandial glucose and insulin levels. Diabetes Care. 2015. doi:10.2337/dc15-0429
- 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 Med. 2022;52(8):1765-1787. doi:10.1007/s40279-022-01649-4
- Chang Y, Wang H, Zhang X, Liu H. Acute effects of exercise snacks on postprandial glucose and insulin metabolism in adults with obesity: a systematic review and meta-analysis. Front Nutr. 2025;12. doi:10.3389/fnut.2025.1708301
- Centers for Disease Control and Prevention. Diabetes: At a Glance (National Diabetes Statistics). cdc.gov/diabetes/php/data-research
- Centers for Disease Control and Prevention. National Diabetes Statistics Report: Prevalence of Prediabetes Among Adults (NHANES 2017–March 2020). stacks.cdc.gov/view/cdc/148231
- Zuraikat FM, Laferrère B, Cheng B, et al. Chronic insufficient sleep in women impairs insulin sensitivity independent of adiposity changes: results of a randomized trial. Diabetes Care. 2023. doi:10.2337/dc23-1156
- Shah VN, DuBose SN, Li Z, et al. Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study. J Clin Endocrinol Metab. 2019. doi:10.1210/jc.2018-02763
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2025. Diabetes Care. 2025. doi:10.2337/dc25-S002
