Keto and Intermittent Fasting: A Beginner's How-To Guide
Keto changes what you eat. Intermittent fasting changes when you eat. Put them together and you get one of the most talked-about routines in nutrition right now. But is combining keto and intermittent fasting a smart move for a beginner, and how do you actually start without feeling exhausted and starving? This guide explains how each approach works, why people pair them, a simple step-by-step plan for starting, what you can drink while fasting, and who should skip it.
What is intermittent fasting?
Mayo Clinic describes intermittent fasting as a pattern of eating based on time limits (Mayo Clinic). Instead of focusing on specific foods, you eat during a set window and fast outside it. The most common styles are:
- Time-restricted eating: you eat within a daily window and fast for the rest of the day. The popular 16:8 method means 16 hours of fasting and an 8-hour eating window (for example, noon to 8 p.m.). Shorter fasts of 12 to 14 hours are a gentler start.
- 5:2 fasting: eating normally five days a week and eating very little on two non-consecutive days.
- Alternate-day fasting: fasting or eating a small amount of food every other day. This is the most demanding option and is rarely the best place to begin.
Keto in 60 seconds
A ketogenic diet is a very low-carb, high-fat way of eating. Harvard's Nutrition Source explains that it typically keeps carbohydrates under 50 grams a day, sometimes as low as 20 grams, with most calories coming from fat (Harvard Nutrition Source). With so few carbs available, the body starts producing ketones from fat for fuel. If you are new to keto, start with our keto food list for beginners, and read What Is BHB? to understand what ketones are.
Why people combine keto and intermittent fasting
The two approaches share a common thread. A 2019 review in the New England Journal of Medicine describes "metabolic switching": after several hours without food, the body shifts from relying mainly on glucose to using fat and ketones for energy (de Cabo & Mattson, NEJM 2019, PubMed). Keto encourages that same shift through food choices, so many people see the two as natural partners.
There are practical reasons too:
- Fewer meals to plan. Two keto meals in an 8-hour window can be simpler than three meals plus snacks.
- Filling food. Many people find protein- and fat-rich keto meals satisfying, which can make a fasting window easier to stick to.
- Structure. A clear eating window reduces late-night grazing.
Be realistic about the evidence, though. Mayo Clinic notes that intermittent fasting may improve some short-term measures such as weight, blood sugar and blood pressure, but long-term effects are still unclear, and some studies find simply eating fewer calories works just as well. Mayo also notes some evidence linking a 16:8 schedule to higher heart disease risk compared with other time-restricted patterns, which is one more reason to discuss your plan with your doctor. Combining keto and fasting is a tool, not a magic switch.
How to start intermittent fasting on keto: a step-by-step plan
The most common beginner mistake is starting keto and a long fast on the same day. Go one step at a time.
- Weeks 1–2: get comfortable with keto first. Eat three keto meals a day, drink plenty of water and let your body adjust. The first days of low-carb eating can bring headaches and fatigue; our keto flu guide explains how to handle them.
- Week 3: start with a 12:12 schedule. Finish dinner by 7 p.m. and eat breakfast at 7 a.m. Most of those 12 hours happen while you sleep.
- Week 4: stretch to 14:10. Push breakfast back an hour or two, or have an earlier dinner.
- Then try 16:8 if it feels good. A common pattern is eating between noon and 8 p.m., with two keto meals and an optional snack.
- Listen to your body. If you feel dizzy, shaky or unwell, eat something and shorten your fast. Fasting should never feel like punishment.
Sample 16:8 keto schedule
| Time | What to do | Example |
|---|---|---|
| 7 a.m. – 12 p.m. | Fasting window | Water, black coffee, plain tea |
| 12 p.m. | First meal | Eggs with spinach, avocado and cheese |
| 3–4 p.m. | Optional snack | A handful of almonds or olives |
| 7 p.m. | Last meal | Salmon, roasted broccoli, olive oil |
| 8 p.m. – noon | Fasting window (mostly sleep) | Water, herbal tea |
What can you drink while fasting on keto?
During the fasting window, stick to drinks with no or almost no calories:
- Water (still or sparkling): the most important one. Keto and fasting can both increase fluid loss.
- Black coffee without sugar or milk.
- Plain green, black or herbal tea, unsweetened.
Cream, milk, sugar, juice, smoothies and "bulletproof" coffee with butter or oil all contain calories, so most fasting plans count them as breaking the fast. Save them for your eating window.
Keto intermittent fasting tips for beginners
- Make your meals count. With fewer meals, include protein and plenty of non-starchy vegetables so you still get fiber, vitamins and minerals.
- Don't overeat to "make up" for fasting. Eat normal, satisfying portions.
- Mind your electrolytes. Salt your food to taste and include potassium- and magnesium-rich foods such as avocado, leafy greens and nuts.
- Time supplements with food. Gummies contain some calories, and many capsules are best taken with a meal. Follow the label and take them inside your eating window.
- Be flexible. Social dinners, travel or a hard workout are good reasons to adjust your window. Consistency over weeks matters more than a perfect day.
Is it safe to do keto and intermittent fasting?
For many healthy adults it can be, but it is not for everyone. Mayo Clinic lists possible side effects of intermittent fasting such as tiredness, dizziness, headaches, mood swings and constipation, and advises that it is not appropriate for people with an eating disorder, people who are pregnant or breastfeeding, or those at high risk of bone loss and falls. It can also affect blood sugar in people with diabetes.
Talk to your doctor before starting if you have diabetes, heart disease, kidney disease, low blood pressure, take any medication (especially for blood sugar or blood pressure), or are under 18.
Key takeaways
- Keto controls what you eat; intermittent fasting controls when you eat.
- Both encourage the body's shift from glucose toward fat and ketones for fuel.
- Start keto first, then ease in: 12:12 → 14:10 → 16:8.
- During the fast: water, black coffee and plain tea only.
- Fill your eating window with protein, non-starchy vegetables and healthy fats, and take supplements with meals.
- Not suitable for everyone; check with your doctor first.
Frequently asked questions
Can you do keto and intermittent fasting at the same time?
Yes, many people do. The easiest way is to get used to keto first for a week or two, then gradually shorten your eating window, starting with 12 hours of fasting overnight.
What is the best intermittent fasting schedule for keto beginners?
A 12:12 or 14:10 schedule is a gentle starting point. Once that feels comfortable, many people move to 16:8, such as eating between noon and 8 p.m.
Does black coffee break a fast?
Plain black coffee has almost no calories, so most intermittent fasting plans allow it. Adding cream, milk, sugar or butter adds calories and is usually counted as breaking the fast.
Should I take keto supplements while fasting?
It's generally best to take them during your eating window, with food, and exactly as the label directs. Keto gummies in particular contain some calories, so they fit better with a meal.
Who should not try intermittent fasting?
According to Mayo Clinic, people with an eating disorder, people who are pregnant or breastfeeding, and people at high risk of bone loss and falls should avoid it. Anyone with diabetes or other health conditions should speak with a doctor first.
Supporting your keto routine
Food and good habits come first. If you also like to include a keto supplement in your routine, these are two popular options in our store. Take them with a meal inside your eating window, follow the directions on the label, and check with your doctor if you are unsure.
- Keto Strong Pills – a BHB ketone capsule formula designed to complement a ketogenic lifestyle. Multi-bottle packs are in the Keto Strong collection.
- LifeStyle Keto Pills – a daily keto capsule, made in the USA in an FDA-registered facility.
Prefer a different form? Our guide Gummies vs Capsules vs Liquid Drops compares the options. Every order ships free anywhere in the USA, and Subscribe & Save gives you 10% off with monthly delivery.
The bottom line
Keto and intermittent fasting can work well together because both encourage your body to use fat and ketones for energy, and a set eating window can make keto meals simpler to plan. Start slowly, keep your fasting drinks plain, fill your meals with real food, and stop if you feel unwell. Most importantly, talk with your healthcare provider so the plan fits your health and lifestyle.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.*