How many carbs can a person eat in a day and still be in ketosis? Also how much green veg and blueberries would be this amount of carbs?

The short version: the retrieved studies do not define a universal carb limit for ketosis, but a clinical trial that achieved ketosis in most participants used about 22 grams of carbohydrate per day.

The best evidence here comes from a 2020 randomized trial in breast cancer patients on a ketogenic diet [1]. The participants who achieved ketosis (blood ketones above 0.5 mmol/L) ate an average of 22 grams of carbohydrate per day [1]. That is a concrete number from a human study, not a guess. The same trial reported that 96% of participants stayed under 50 grams of carbs daily, and about 79% kept carbs at or below 10% of total calories [1].

The other retrieved studies do not set a carb limit. One rat study used a diet with less than 1% carbohydrate by weight [4], and another used 20% of calories from carbs but did not produce ketosis [3]. The orangutan study showed that wild primates enter mild ketosis during low-fruit periods, but it does not give a human carb target [2].

What does 22 grams look like in green vegetables and blueberries? A full cup of cooked broccoli has about 6 grams of total carbs, with about 3 grams of fiber, leaving roughly 3 grams of net carbs. A cup of raw spinach has about 1 gram of total carbs and 1 gram of fiber, so essentially zero net carbs. A half-cup of blueberries has about 10 grams of total carbs and 2 grams of fiber, so about 8 grams of net carbs. That means you could eat a generous plate of green vegetables (say 2 cups of broccoli and 2 cups of spinach) for about 6 grams of net carbs, and still have room for about a half-cup of blueberries at 8 grams, totaling about 14 grams. That leaves a small buffer under the 22-gram target.

The evidence here is thin on individual variation. Some people enter ketosis at higher carb intakes, especially if they are physically active or have higher insulin sensitivity. The 22-gram figure came from cancer patients on chemotherapy, who may differ metabolically from a healthy person. No study in this retrieval tested the exact carb threshold for a general healthy population.

My call: aim for about 20 to 30 grams of net carbs per day to reliably reach ketosis. Green vegetables are very low in net carbs; blueberries are higher, so measure them. Confidence: moderate.