Keto made easy

Spend Your Carbs on Vegetables: Fiber, Net Carbs and Why Exactly 20 Grams?

2017-08-01

In this video

A 20-minute live video from my day 35, built around one phrase: spend your carbs wisely.

Watching this in 2026

This is the video where I first pushed back on "exactly 20," and I'd stand by the push. The 20-gram line often gets treated as a law of physics. I read it as a study protocol, a fixed number so researchers are all testing the same thing (video 1vyxuWlxT5M). That's a fair reading of why tidy numbers show up in diet research.

I also said something here I should have said more often: I was quoting male numbers to a mostly female audience. If you're a woman, especially a smaller one, my glycogen and calorie figures run high for you.

The claim worth unpacking: how much fibre, and does keto get enough?

I said keto poops come from too little fibre and a gut that's changing. The fibre research has a lot to say about both.

How much. The US reference intake is 14 g per 1,000 kcal: 25 g a day for women 19 to 50 and 21 g a day for women 51 and over (National Academies, 2005). In the large meta-analysis by Reynolds et al., 2019, the highest fibre intakes were linked with 15–30% lower all-cause and cardiovascular mortality, and the largest reductions came at 25–29 g a day.

That's the part keto makes hard. On a 20 g total-carb diet, even if every gram were fibre, you'd be short. That's the honest case for "spend your carbs on vegetables," and for going over 20 if it's fibre doing it.

The gut. I said glucose-dependent bacteria die off on keto. The research doesn't use those words, but it does find the shift. In Ang et al., 2020, a ketogenic diet changed the human gut microbiome, including lower bifidobacteria. In mice fed no fibre at all, gut bacteria started breaking down the gut's protective mucus layer (Desai et al., 2016). That's a mouse study, but it's a good reason not to run a fibre-free keto for months.

Soluble fibre. I said it partly digests. The evidence collected here doesn't measure its blood-sugar effect, but it does show soluble fibre does something useful: 2–10 g a day gave small, significant drops in total and LDL cholesterol across 67 trials (Brown et al., 1999).

The line to update: labels and net carbs

I said US labels only list total dietary fibre, so net carbs are an estimate. The estimate part still stands. No major body defines "net carbs," and the FDA's dietary-fiber Q&A counts dietary fiber inside total carbohydrate without using the term at all. How to read a label anyway is in net vs total carbs.

I also repeated that carrots have a higher glycemic index than a Snickers bar. No evidence page here covers that, and glycemic index ignores portion size anyway. See glycemic index vs glycemic load.

Then vs now

Who should check with a doctor

If you have diabetes and take medication, a deliberate 50 to 100 g "nutrient loading" day changes your blood sugar; plan it with your doctor. If loose stools or constipation last more than a few weeks, or come with blood or pain, that's a doctor visit, not a fibre experiment.

Key points