Keto made easy

Why Is the Keto Limit 20 Grams of Carbs?

Quick answer: 20 grams a day is a conservative starting line that gets almost everyone into ketosis, which is why it became the standard advice. It isn't a physical constant. A ketogenic diet is defined by its result, ketones in your blood, and the carb level that gets you there varies from person to person. Many people stay in ketosis at higher intakes, often quoted as up to about 50 g. Start low, then test.

In this article

What actually defines a ketogenic diet

Start with the definition, because the number hangs on it. KetoDick's version, which he repeats across years: a ketogenic diet is any mix of foods that keeps blood ketones in the nutritional-ketosis range (ffwBPoKxlDI). There aren't foods that are and aren't keto. There's the dose.

The mechanism is the reason carbs are the lever. Restricting carbs runs down your glucose and glycogen, insulin falls, stored fat becomes available, and the liver makes ketones (s_sNd1v8Low). The question "how many carbs?" really means "how low do my carbs need to be for my insulin to stay low enough for that to keep happening?" That answer belongs to your body, not to a forum.

Where 20 grams comes from

His reading is that 20 is a study protocol number. Researchers define a diet a certain way so that everybody in a trial eats the same thing and results can be compared: everyone on 20 g, not 23 and 27 and 18 (1vyxuWlxT5M). That's good science for a trial. It doesn't mean 21 g knocks you out.

It also works as advice because it's safe. If almost everyone is in ketosis at 20, then telling a stranger "20" will very rarely fail. That's why he calls it the colloquial recommendation: the usual definition is under 50 g a day, but some people need under 20, so 20 is what gets passed around (ffwBPoKxlDI).

Why one number can't fit everyone

His challenge to anyone who insists on exactly 20: show the science behind the same 20 grams for a six-foot man over 200 pounds who trains in combat sports, and for a five-foot woman who weighs 90 pounds. Not 23, not 18, not 25. He says he hasn't seen a study that tested ketosis at 50, 45 and 40 and found everyone lands at 20 (1vyxuWlxT5M).

The intuition behind his challenge is that carbs get burned, too: a bigger, more active body uses more fuel in a day, so it plausibly has more room before carbs pile up. That's reasoning, not a measured threshold. He makes a related point about glycogen, saying a man stores about 700 g and women should scale his figures down by 25 to 35 percent (1vyxuWlxT5M). Size, muscle, activity and how long you've been adapted all move the line.

20 versus 50: which should you use?

His number has changed with the audience and the year, and that's worth seeing plainly:

Video What he says
s_sNd1v8Low (2017) Under 20 g to start; some tolerate up to 50 g
ffwBPoKxlDI (2017) Usual definition under 50 g; 20 g is the common recommendation
cTGYIFOTPl8 (2017) The literature calls it LCHF or very low carb, under 50 g
1vyxuWlxT5M (2017) 25 g is fine if 5 g of it are bulk vegetables
xyEZL0HuejI (2017) Under 50 g "and nothing else matters", ideally 20
UygKGoP_BtA (2018) 50 g total carbs as the simple beginner rule, mostly green vegetables

The way to read that: 20 g is the strict, near-guaranteed version. 50 g total is the simpler version, and because it's total rather than net, it's partly a way to stop people gaming fibre on labels (see net vs total carbs). He also says you don't need to "hit" 20; if you only had 8 today, that's fine (Ewo-C_Cc4hU).

How to find your own number

  1. Start at 20 g, or 50 g total, for the first month. Pick one and keep it boring while you adapt.
  2. Spend the carbs on vegetables. Leafy greens are the best use of a small budget (1vyxuWlxT5M).
  3. Check that you're in ketosis. He says urine strips showing any colour, even trace, most of the time is enough early on, and that strips can stop showing after months as your body adapts (xyEZL0HuejI; see testing ketosis).
  4. After you're adapted, nudge up slowly. Add 5 g of carbs as vegetables for a week or two and check again.
  5. Stop at the level where you still feel the benefits. For most people that means steady energy and not being hungry all the time. If cravings come back, you've probably found your ceiling.

If your goal is weight loss rather than ketosis itself, the number matters less than you'd think; see do you have to be in ketosis to lose weight?

What the research says

The research pages don't contain a study that pins a single carbohydrate threshold for ketosis across different people. That's the gap he's pointing at.

What they do say: the American Diabetes Association's 2019 consensus report finds that cutting total carbohydrate has the most evidence for improving blood glucose, with low-carb patterns as one option among several (Evert et al., 2019). The NIH StatPearls clinical overview covers how a ketogenic diet is implemented and monitored, and how nutritional ketosis differs from diabetic ketoacidosis (Masood et al., StatPearls). Laffel's review covers ketone levels and blood and urine monitoring (Laffel, 1999), which is how you check your own threshold instead of trusting a forum's.

For weight, strict isn't obviously better than moderate. DIETFITS used a moderate low-carb arm, not a ketogenic one, and its 609 adults lost 6.0 kg in 12 months versus 5.3 kg on healthy low-fat, not a significant difference (Gardner et al., 2018). Across 13 trials of a year or more, very-low-carb ketogenic diets came out about 0.91 kg ahead of low-fat (Bueno et al., 2013).

KetoDick's take

He'd rather you spend 25 g on a big salad than 20 g on keto desserts (1vyxuWlxT5M). And if anyone gives you grief for being over 20, his advice is to ask them for their source (1vyxuWlxT5M).

One firm caution: if you take insulin or other diabetes medication, cutting carbs can drop your blood sugar quickly. He's described his own fasting glucose falling from near-diabetic to near-normal within about a month (xyEZL0HuejI). That's the point for many people, and it's also why your doctor needs to know before you drop to 20 g, so your dose can be adjusted.

Key takeaways