What is the best time for women to fast?

Best Time for Women to Fast

For women, early time-restricted eating (eTRE) with an 8-hour eating window early in the day (e.g., 7:00 am to 3:00 pm) is the most effective fasting approach for weight loss and cardiometabolic health benefits. 1

Types of Fasting Approaches for Women

Early Time-Restricted Eating (eTRE)

• Restricts eating to an 8-hour window early in the day (e.g., 7:00 am to 3:00 pm)
• Most effective for weight loss (-2.3 kg compared to control groups) 1
• Improves diastolic blood pressure (-4 mm Hg) and mood 1
• Equivalent to reducing caloric intake by an additional 214 kcal/day 1

Standard Time-Restricted Eating (TRE)

• Later eating window (e.g., 12:00 pm to 8:00 pm)
• Less effective for weight loss (-0.94 kg) 2
• May lead to loss of lean muscle mass, particularly appendicular lean mass 2

Special Considerations for Women

Pregnancy

• Fasting during pregnancy is not recommended due to:
  • Increased risk of morbidity and mortality to fetus and mother 3
  • Pregnancy requires increased nutritional needs and consistent glucose levels
  • Pregnant women constitute a high-risk group requiring intensive care if they choose to fast 3

Post-Bariatric Surgery

• Complete fasting should be avoided for 12-18 months after bariatric surgery 3
• After this period, fasting may be permitted with proper hydration before fasting 3

Women with Diabetes

• Women with type 1 diabetes should be strongly advised not to fast due to high risk of severe hypoglycemia 3
• Women with type 2 diabetes who choose to fast should:
  • Ensure adequate fluid intake 3
  • Adjust medication timing (e.g., metformin 1,000 mg at sunset meal, 500 mg at predawn meal) 3
  • Monitor blood glucose more frequently 4

Implementing Fasting for Cardiovascular Health

Women seeking to improve cardiovascular health through fasting should:

1. Maintain ideal cardiovascular health parameters:

   • Total cholesterol <200 mg/dL (untreated)
   • BP <120/<80 mm Hg (untreated)
   • Fasting blood glucose <100 mg/dL (untreated)
   • BMI <25 kg/m² 3

2. Combine fasting with:

   • At least 150 min/week of moderate exercise or 75 min/week of vigorous exercise 3
   • Healthy DASH-like diet rich in fruits, vegetables, whole grains, and fish 3

Monitoring During Fasting

• For women with diabetes: monitor blood glucose 3+ times daily during fasting periods 4
• Target preprandial blood glucose: 90-130 mg/dL 4
• Target postprandial blood glucose: <180 mg/dL 4
• Watch for signs of hypoglycemia, especially in women with type 1 diabetes 3

Practical Implementation Tips

• Start with shorter fasting periods and gradually extend
• Stay well-hydrated during fasting periods
• Break fast with balanced meals containing protein, healthy fats, and complex carbohydrates
• Consider ASA classification when determining if fasting is appropriate:
  • ASA class I-III: Generally safe for fasting
  • ASA class IV-V: Fasting not recommended 3

Potential Benefits Beyond Weight Loss

• May improve reproductive health 5
• May prevent and ameliorate cancers common in middle-aged and elderly women 5
• May improve musculoskeletal disorders 5
• May enhance mood and mental health 1

The evidence suggests that early time-restricted eating provides superior benefits for women compared to other fasting approaches, particularly for weight management and cardiometabolic health. However, women should be cautious with fasting during pregnancy, after bariatric surgery, or if they have type 1 diabetes.