Low-Carb Foods (Grams of Fiber per 100g):

Strawberries -- 2.0 (32 kcal)
Spinach (raw) -- 2.2 (23 kcal)
Broccoli (raw) -- 2.6 (34 kcal)
Atkins Bread -- 14.3 (250 kcal)
Keto Ketatoes Mix -- 25.2 (378 kcal)

Hi-Carb Foods (Grams of Fiber per 100g):

Baked Potato -- 2.2 (75 kcal)
White Bread -- 2.4 (266 kcal)
Corn Flakes -- 2.5 (373 kcal)
Whole Wheat Bread -- 6.9 (246 kcal)
Raisin Bran Cereal -- 9.0 (311 kcal)
All Bran Cereal [w. Added Fiber] -- 50.0 (192 kcal)

For the most part...Hi-Carb foods which are higher in Fiber tend to also be high in Calories. For example, Plain Baked Potato and Spinach boast the same Fiber content...But, the Spinach has < 1/3 the Calories of the Potatoes. It gets even worse when you compare Broccoli and Cereals such as Corn Flakes. Boasting near identical Fiber contents, we find that Cereal also boasts over 10x the Calories of Broccoli.

For a more accurate comparison, let's compare 2,000 kcal worth of each of the foods --

Low-Carb Foods (Grams of Fiber per 2,000 kcal):

Strawberries -- 125.0
Spinach (raw) -- 191.3
Broccoli (raw) -- 152.9
Atkins Bread -- 114.4
Keto Ketatoes Mix -- 133.3

Hi-Carb Foods (Grams of Fiber per 2,000 kcal):

Baked Potato -- 58.7
White Bread -- 18.0
Corn Flakes -- 13.4
Whole Wheat Bread -- 56.1
Raisin Bran Cereal -- 57.9
All Bran Cereal [w. Added Fiber] -- 520.8

The only Hi-Carb food on that list to reach, much less beat any of the Low-Carb foods in Fiber Content vs. Calories is ALL BRAN CEREAL WITH ADDED FIBER. How many Low-Fat/Hi-Carb dieters do you know that eat lots of ALL BRAN Cereal. Nope, most of them are eating Regular Cereals such as Corn Flakes...which are so high in Calories compared to their Fiber content that it would be PHYSICALLY IMPOSSIBLE to achieve the 25 - 38g suggested there and stay within a standard 2,000 kcal Diet. In fact to obtain even the minimum 25g from Regular Cereals as exampled by Corn Flakes, one would need to consume 3731 Calories. Assuming that person's Maintnance Calories are 2,300...which would result in a weight gain of 2.86 pounds per week or 149 pounds per year. That doesn't sound very healthy.

By comparison, to obtain your 25g of Fiber from the LC Food with the worst ratio (an amazingly high 114.4) one need only consume 481 Calories. If the maintance Calories are the same, that person can get their full Daily Value of Fiber and have over 1,800 Calories to spare.