Fasted training raises your fat burning during the session and can improve your insulin sensitivity. It does not automatically mean you lose more fat, because that depends on your total energy balance over the day. For your blood values, the timing of your test matters most.
I find fasted training useful but oversold. Burning more fat during a session is different from losing more fat.
Do you burn more fat training fasted?
During the training itself you burn more fat fasted than after a meal. A meta-analysis confirmed that aerobic exercise in the fasted state raises fat burning during the session compared with training after eating (Vieira, 2016). Whether you therefore lose more fat over the whole day is another question.
Fat burning during an hour of cardio says little about your fat mass over weeks.
What does fasted training do to your blood sugar and insulin?
Fasted training can favourably influence your glucose tolerance and insulin sensitivity. In a controlled study, training in the fasted state improved glucose tolerance during a fat-rich diet, with more GLUT4 in the muscle (Van Proeyen, 2010). That fits the idea that fasted training makes your muscle more metabolically flexible.
| What | Effect of fasted training |
|---|---|
| Fat burning during session | Higher than training after eating |
| Fat loss over the week | Depends on total energy balance |
| Insulin sensitivity | Can improve |
| Heavy strength performance | Can be slightly lower without fuel |
Why the timing of your blood test matters
A blood test measures your values at that moment, so fasted or fed makes a difference. For fasting glucose and fasting insulin you really need to be fasted, otherwise your values are not comparable. A workout shortly before your draw can also temporarily affect your glucose.
The HOMA-IR calculation from fasting glucose and insulin only holds up with a true fasted measurement (Matthews, 1985). More on this in fasting insulin and HOMA-IR.
Who is fasted training useful for?
Fasted training fits calm cardio and metabolic goals well, less so heavy strength sessions. For a hard workout or a PR attempt, fuel beforehand can help your performance. So choose based on your goal, not on a trend.
To track your sugar handling, compose a panel through our custom blood test. Also read the overview measuring metabolic health and what poor sleep does to your hormones.
My advice: use fasted training as a tool, not a belief. Always measure your blood sugar and insulin truly fasted, and discuss abnormal values with your GP.
References
- Vieira AF, Costa RR, Macedo RCO, et al. Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis. British Journal of Nutrition. 2016. PMID: 27609363.
- Van Proeyen K, Szlufcik K, Nielens H, et al. Training in the fasted state improves glucose tolerance during fat-rich diet. The Journal of Physiology. 2010. PMID: 20837645.
- Matthews DR, Hosker JP, Rudenski AS, et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia. 1985. PMID: 3899825.
Disclaimer
Elk bloedtestresultaat bevat een professionele beoordeling door een BIG-geregistreerde arts. Dit artikel geeft algemene informatie en is geen vervanging voor medisch advies. Een bloedtest is een hulpmiddel om beter geïnformeerd het gesprek met je huisarts in te gaan, geen diagnose op zichzelf. Bespreek voor behandelbeslissingen je resultaten met je huisarts.
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Enhanced Health
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