Can You Work Out While Fasting?

In 30 seconds

In small trials, strength training fasted or after eating gave similar strength and muscle results, and fasted cardio used more fat for fuel during the session, which is not the same as more fat loss over weeks. With insulin or some other diabetes medicines, exercising without eating can cause low blood sugar, so agree a plan with your diabetes team first.

• In four small studies, three at high risk of bias, fasted and fed strength training gave similar strength and muscle results.
• Fasted cardio uses more fat for fuel during the session, which does not show more fat loss over time.
• In one 12-week 16:8 trial, the time-restricted group lost slightly more lean mass than a three-meals group.
• With insulin or some other diabetes medicines, exercising while fasting can cause low blood sugar.

Should you train fasted or fed?

For strength, training fasted or after a meal made no clear difference in the few small studies that compared them. For cardio, fasted sessions change which fuel you use during the workout, but that short-term measure is not the same as greater fat loss.

A meta-analysis of four studies, three with a high risk of bias, found no significant differences between fasted and fed resistance training in fat-free mass, muscle growth or strength, while fasted sessions were associated with a larger reduction in fat mass with wide uncertainty.Source 11

A meta-analysis of 27 small studies with 273 participants found that aerobic exercise of up to 120 minutes produced higher fat oxidation during the session when performed fasted than after eating.Source 22

Will fasted training cost you muscle?

Adding an eating window to exercise lowered weight and fat mass modestly more, on average, than exercise with a usual diet. One 16:8 trial also found slightly more lean-mass loss in the time-restricted group. The NHS recommends regular strength work, though that trial did not test whether it prevents lean-mass loss. What to eat in the window is covered in what to eat during intermittent fasting, and fluids in hydration during intermittent fasting.

A meta-analysis of 19 small randomized trials with 568 adults found that time-restricted eating combined with exercise reduced body mass by about 1.9 kg and fat mass by about 1.5 kg more than exercise with a control diet, without extra benefit for fasting glucose or insulin.Source 33

In the 12-week TREAT trial of a noon-to-8 p.m. eating window, the time-restricted group lost slightly more appendicular lean mass than the group eating three structured meals a day, in the in-person subgroup of 50 participants.Source 44

NHS guidance recommends that adults do strengthening activities for all major muscle groups on at least 2 days a week and at least 150 minutes of moderate or 75 minutes of vigorous activity a week.Source 55

What does the evidence show?

The evidence comes from four small strength studies, three at high risk of bias, and from fuel measurements during single cardio sessions. Training fasted looked neither clearly better nor worse for strength and muscle in the adults studied, and no fat-loss advantage was shown.Source 11Source 22

Who should be careful training fasted?

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• Intermittent Fasting for Weight Loss: Realistic Results

  Intermittent fasting for weight loss shows modest average losses, about 4.6 kg more than control over 12 months, similar to daily calorie restriction.

• Electrolytes and Dehydration During Intermittent Fasting

  Do you need electrolytes during intermittent fasting? Not for an ordinary fast, per official sources. Learn the dehydration signs to watch and when to end a fast.

• What to Eat During Intermittent Fasting

  What to eat during intermittent fasting is ordinary food: vegetables, fruit, whole grains, pulses and protein, with fewer sugary drinks. Amounts count.

• What to Eat After You Break a Fast

  Here is how to break a fast: an ordinary meal of protein, vegetables and whole grains, eaten slowly. The window is not a licence to make up missed food.

Frequently asked questions

Is fasted cardio better for fat loss?

Fasted aerobic exercise uses more fat for fuel during the session, but that does not show more fat loss over weeks. A small meta-analysis linked fasted strength training with a larger drop in fat mass, but three of its four studies had a high risk of bias and the estimate was very uncertain.Source 22Source 11

Will working out while fasting make me lose muscle?

Fasted and fed strength training gave similar muscle results in small studies. In one 16:8 trial the time-restricted group lost slightly more lean mass than the comparison group. The NHS recommends strength work at least twice a week.Source 44Source 11Source 55

I take insulin. Can I exercise while fasting?

Only with a plan from your diabetes team. NHS guidance lists doing a lot of exercise without eating more carbohydrate or reducing your insulin dose, and missing or delaying meals, as causes of low blood sugar.Source 66

Sources

1. 1

   Resistance training performed in the fasted state compared to the fed state on body composition and strength in adults: A systematic review with meta-analysisAlexandra Ferreira Vieira et al. Elsevier BV, December 1, 2025.DOI: 10.1016/j.jbmt.2025.08.003 · PMID: 41316673Systematic review and meta-analysis

2. 2

   Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysisAlexandra Ferreira Vieira et al. Cambridge University Press (CUP), October 1, 2016.DOI: 10.1017/S0007114516003160 · PMID: 27609363Systematic review and meta-analysis

3. 3

   The Effect of Time-Restricted Eating Combined with Exercise on Body Composition and Metabolic Health: A Systematic Review and Meta-AnalysisZihan Dai et al. Elsevier BV, August 1, 2024.DOI: 10.1016/j.advnut.2024.100262 · PMID: 38897385Systematic review and meta-analysis

4. 4

   Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical TrialDylan A. Lowe et al. American Medical Association (AMA), November 1, 2020.DOI: 10.1001/jamainternmed.2020.4153 · PMID: 32986097Human randomized trial

5. 5

   Physical activity guidelines for adults aged 19 to 64NHS. NHS, May 22, 2024.Official guidance

6. 6

   Low blood sugar (hypoglycaemia)NHS. NHS, August 3, 2023.Official guidance

7. 7

   DehydrationNHS. NHS, May 1, 2026.Official guidance