Ask a Dietitian: Can You Combine Intermittent Fasting with a Vegetarian Diet?

The Question

I want to do intermittent fasting and eat vegetarian at the same time — will I fall short on nutrition?

The Dietitian's Answer

The two can be combined, but it raises the bar for meal planning. Intermittent fasting (such as a 16:8 time-restricted eating window) already shortens your daily eating window. If you're also vegetarian, you need to fit enough protein, iron, calcium, and other key nutrients into that limited window — and it's easy to fall short simply because there isn't enough time, or you can't physically eat enough.

Points That Need Special Attention

• Prioritize nutrient-dense foods within your eating window (soy products, nuts and seeds, whole grains), leaving less room for low-nutrient-density foods to eat into your limited time
• Watch whether total calorie intake is adequate — avoid letting the double constraint of fasting plus vegetarianism push your calories too low for too long
• Nutrients that are easy to fall short on, like B12, iron, and calcium, need proactive planning — don't let fasting cause you to miss supplement timing
• Stay well hydrated during the fasting period; unsweetened weak tea or black coffee in moderation is fine, but don't substitute sugary drinks for plain water

Who Shouldn't Try This Casually

Pregnant or breastfeeding women, teenagers, people with a history of eating disorders, and people with digestive conditions shouldn't attempt intermittent fasting combined with strict vegetarianism without professional guidance — stacking these two dietary restrictions places heavier demands on nutrition and overall physical condition. It's best to have a dietitian assess whether this approach suits you individually, rather than trying it on your own.