What are the common challenges of 16/8 fasting?

If you are not seeing the progress you expect with a 16-hour fast with an 8-hour eating window (16:8), it may be due to consuming too many calories during your eating window, choosing highly processed foods, or not getting enough physical activity. Evaluating your overall dietary pattern and food choices can help. A 2025 systematic review found that intermittent fasting strategies show comparable outcomes to continuous energy restriction for body weight management ( 1 ).

What happens after 16 hours of fasting?

After approximately 16 hours of fasting, your body may shift to using stored energy sources as glycogen levels deplete. This metabolic shift — sometimes referred to as the transition to fat oxidation — is one of the reasons people practice extended fasting windows. The degree and timing of this shift can vary depending on individual factors such as activity level and prior dietary patterns.

Can I drink coffee and milk during intermittent fasting? Does milk in coffee break intermittent fasting?

You can drink black coffee during your fasting window without breaking your fast. However, adding milk will break your fast. Milk contains calories and macronutrients — including protein and carbohydrates — that initiate the digestive process and interrupt the fasted state. If you are fasting to support autophagy or maintain a strict fasted state, it is best to stick to plain black coffee or water during the fasting window.

What not to do in intermittent fasting?

The most common mistakes include eating during the fasting window, not staying hydrated, overeating during the eating window, and failing to prioritize nutrient-dense foods. See the dedicated section above for a full breakdown. This article is for informational purposes only and does not constitute medical advice. Intermittent fasting may not be suitable for everyone. Always consult a qualified healthcare provider before making changes to your dietary routine.