In a keto fast, you combine a low-carb, high-fat ketogenic diet with periods of intermittent fasting—for example, you may eat keto within an 8-hour window and then fast for 16 hours.
Some early research suggests that pairing these approaches may support faster ketone production, reduce cravings, and improve metabolic control. However, long-term studies are limited.
By cutting carbs and limiting your eating window, your body may shift more quickly from burning glucose to burning fat and producing ketones (chemicals your body makes when it uses fat for energy).
When you only eat during certain times as part of intermittent fasting, your body spends less time processing new foods and relies more on other sources of long-term energy, such as fats.
So when you pair fasting with a ketogenic diet, you may burn stored fat more quickly.
Both keto and intermittent fasting have been shown to help lower blood sugar and decrease insulin resistance. Several research studies have shown that the ketogenic diet can help reduce hemoglobin A1c (HbA1c, a measure of your blood sugar over several months) and body weight compared to standard diets.
Like keto, intermittent fasting may also help improve your blood sugar and weight to some degree. Combining a keto diet and fasting may help stabilize energy levels and reduce insulin spikes more in some people.
Many people report less hunger and a more stable appetite when they follow a keto fast.
The production of ketones may suppress hunger signals, and limiting eating windows may lower overall calorie (energy) intake. A review of intermittent-fasting protocols found changes in how your stomach sends signals related to eating and regulating your appetite when your meals are time-restricted.
While this change may make dieting easier, it may also increase the risk of overeating during the eating window or neglecting nutrient-dense foods.
While a keto fast diet plan may offer benefits, combining two restrictive approaches may also come with risks.
Cutting carbs and fasting can lead to decreased levels of essential nutrients—and less frequent meals can mean fewer opportunities to take in vitamins and minerals.
Another research review found that ketogenic diets may increase the risk of micronutrient deficiencies and reduced muscle mass, especially after six months.
To help offset, manage, or prevent these risks, it’s important to monitor any lab results, stay hydrated, and include whole-food sources of important nutrients.
Following an intermittent fasting eating pattern while on a ketogenic diet may give your results a boost. Eating in restricted windows can help you produce ketones more quickly, leading to the benefits of a ketogenic diet.
If you’re generally healthy, combining keto with fasting may make sense to try under a doctor’s guidance—but it’s not for everyone. For example, a keto fast may not be a safe option for people who:
- Are pregnant or breastfeeding
- Have type 1 diabetes, kidney disease, or liver disease
- Have an eating disorder
- Take certain medications
- Drink alcohol
For anyone, it’s important to discuss the risks and benefits of this type of eating plan with a doctor before beginning.
Here’s how to get started safely:
- Begin slowly: Try starting with a standard keto diet for one to two weeks, then introduce a mild time-restricted eating window, such as 12 eating hours and 12 fasting hours.
- Snack smart: In your eating window, prioritize high-quality fats, moderate protein, and non-starchy vegetables. Skip highly processed foods.
- Stay hydrated and replenish electrolytes: Aim for two to three liters of water daily and include foods with sodium, such as broth, avocado, and nuts and seeds.
- Adjust your fasting window gradually: Move to an 8-hour eating and 16-hour fast only if you feel good and your electrolytes are at healthy levels.
- Monitor and adjust: Track energy levels and mood, and get blood work done if your doctor recommends it.
A few days of eating in a keto fast may look something like this:
Day 1 (Eating window 12 p.m.–8 p.m.):
- Lunch: Spinach salad with grilled salmon, olive oil, and walnuts
- Snack: Celery sticks with almond butter
- Dinner: Zucchini noodles with pesto and chicken thighs
Day 2 (Eating window 11 a.m.–7 p.m.):
- Breakfast: Scrambled eggs with spinach and avocado
- Lunch: Shrimp and broccoli stir-fry in coconut oil
- Snack: Olives and cheese
- Dinner: Pork chops with cauliflower mash
Day 3 (Eating window 1 p.m.–9 p.m.):
- Lunch: Mixed greens, feta cheese, cucumber, olive oil, and olives
- Snack: Mixed raw nuts
- Dinner: Beef steak with roasted Brussels sprouts and butter
