Keto vs Intermittent Fasting: Which One, or Both?

Quick answer: Keto changes what you eat; intermittent fasting changes when you eat. They aren't rivals, and you don't need fasting to make keto work. KetoDick treats fasting as an optional add-on for people who are already settled into keto, not something for month one, and he warns that chasing fast results with long fasts can tip into disordered eating (videos Ewo-C_Cc4hU, 7Aixw4uRksI).

On this page

• Side by side
• Why they overlap
• Why not both from day one
• If you want to add fasting
• What the research says
• KetoDick's take
• When to involve your doctor
• Key takeaways
• Related

Side by side

Why they overlap

Fasting is ketogenic. Go without food long enough and your body does exactly what keto does, only harder: after weeks of fasting, ketones replace glucose as the brain's main fuel (Owen et al., 1967). A long review of starvation describes the same shift from glucose to fat and liver ketones, sparing body protein as it goes (Cahill, 2006).

That's why the two get mentioned together. Keto gets you to a fat-burning state while you still eat; fasting gets there by not eating. Once you're on keto and hunger has settled, skipping a meal is a lot less dramatic than it used to be.

Why not both from day one

Month one on keto is already a lot. KetoDick's rule is that if you're in month one you shouldn't be restricting calories at all: glycogen is draining, insulin is still high, you'll feel flat and hungry, and the job is learning labels and recipes (video 7Aixw4uRksI). Stack a fasting schedule on top and you're restricting twice while your body is still learning to run on fat.

He's also no fan of long fasts aimed at dropping weight quickly, or of short-term goals in general (video xyEZL0HuejI). His reason runs back to his business work: problems that took years to build take years to fix (video xyEZL0HuejI).

If you want to add fasting

1. Get through month one first. Count carbs, hit protein, eat fat to fullness, and wait for hunger to drop (video 7Aixw4uRksI).
2. Check you're in the weight-loss phase. That's when hunger self-regulates and some people add 16/8 or 5:2 (video NUJNFG6lLWw).
3. Cut fat, keep protein and fibre. When fat comes down in the weight-loss phase and some people try fasting, he says protein and fibre stay (video 7Aixw4uRksI).
4. Do the protein arithmetic. For adults over 65, the PROT-AGE group recommends 1.0–1.2 g/kg a day and 25–30 g per meal (Bauer et al., 2013); a review of weight management links about 1.2–1.6 g/kg a day and 25–30 g per meal with better appetite and weight outcomes (Leidy et al., 2015). A 70 kg (154 lb) woman at 1.2 g/kg needs 84 g a day. Over three meals that's 28 g each; squeeze it into two and it's 42 g each.
5. Stop if it turns into a contest. If you're fasting longer to keep up with someone's posted results, that's the warning sign he names (video 7Aixw4uRksI).

What the research says

• Prolonged fasting shifts the brain to ketones as its main fuel (Owen et al., 1967), part of a broader starvation shift to fat and ketones that spares body protein (Cahill, 2006).
• For exercising people, the ISSN suggests 20–40 g of protein per dose every 3–4 hours (Jäger et al., 2017). A tight eating window makes that spacing harder to hit.
• Older adults are advised 25–30 g of protein per meal (Bauer et al., 2013).

What this site's evidence pages don't contain is a trial of intermittent fasting for weight loss, or one comparing keto with and without fasting. KetoDick says research leans toward fewer eating hours (video xyEZL0HuejI), but there's no paper on the evidence pages to back or test that, so take it as his read.

KetoDick's take

He mentions fasting as something some people add once settled in, never as a requirement: intermittent schedules such as 5:2 or 16/8 in the weight-loss phase (video NUJNFG6lLWw), or "a one or two day fast after they're settled in", from the video (video Ewo-C_Cc4hU).

On breakfast specifically, he says the research leans toward fewer eating hours, but the dawn effect, the early-morning blood-sugar rise, varies from person to person (video xyEZL0HuejI). So he doesn't hand out one rule for when to eat.

His sharpest point is the warning. Some people, chasing the results they see posted, flirt with anorexia, and anyone planning deliberate restriction should include their doctor (video 7Aixw4uRksI). So what you do is use fasting as a tool if it feels easy, and drop it the moment it feels like punishment.

When to involve your doctor

• Diabetes medication. Fasting and carb cutting both lower blood sugar. In the Virta clinic study, the low-carb group used less diabetes medication as HbA1c fell (Hallberg et al., 2018). Doses need adjusting with your doctor before you add fasting, not after a low.
• Eating-disorder history. He says anyone with an eating disorder should involve a therapist and a doctor (video xyEZL0HuejI). Fasting schedules are a structured form of not eating; if that's ever been a problem for you, skip them unless your care team agrees.
• Pregnancy or breastfeeding. This isn't the time to experiment with fasting; talk to whoever is looking after your pregnancy.

Key takeaways

• Keto changes what you eat; intermittent fasting changes when.
• You don't need fasting for keto to work.
• Month one: no fasting, no restriction. Learn the food and let hunger settle.
• If you add fasting later, cut fat and keep protein and fibre; check your protein per meal.
• Long fasts for quick results, and fasting as a contest, are where it goes wrong.

Related

• Guide: Fat loss · Hunger · Month one · Protein for older adults · Eating disorders
• Blog: Does lazy keto work? · Always hungry on keto? · How much protein per meal · Clean eating and orthorexia · Why am I not hungry on keto?
• Videos: Eating too much fat on keto · Common beginner questions · Setting realistic goals · Still hungry on keto?