Research
Hormonal
Pre-exercise carbohydrate ingestion (sugar) during the hour before exercise does not impair endurance performance and may improve it, despite causing transient hypoglycemia.
You can eat sugar 30-60 minutes before exercise without fear of 'crashing' or hurting your performance. While your blood sugar might dip slightly due to insulin, it doesn't seem to hurt you, and might even help. Focus on total carbohydrate intake rather than avoiding pre-exercise sugar.
GoodRefutesHIGH confidence
More importantly, in examining the studies which have measured endurance performance following sugar ingestion during the hour before exercise (Table 5), only one study has reported a negative effect... four studies have observed no significant effect... and three studies reported improvements in performance... Therefore, there is little support for the idea that sugar ingestion before exercise impairs performance.
Why this rating
Based on a review of multiple studies (Table 5) showing mixed but generally positive/neutral results.
Source
Timing and method of increased carbohydrate intake to cope with heavy training, competition and recovery
Edward F. Coyle · Journal of Sports Sciences · 1991
DOI 10.1080/02640419108729865
narrative_reviewCited 182×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Post-exercise muscle glycogen resynthesis plateaus at approximately 5-6% per hour (5-6 mmol kg-1 h-1) when consuming 50g of high-glycemic carbohydrate every 2 hours, and does not increase with higher doses (100g+).Good
- Glycogen loading (supercompensation) can be achieved practically by tapering training and consuming 500-600g of carbohydrates for 3 days prior to competition, avoiding the need for extreme carbohydrate restriction.Good
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This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →