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Regardless of how many carbohydrates you eat, there’s one thing you need to know about them: quality matters. This fact was recently demonstrated by a research article published in The Lancet. The authors of this study performed a systematic review and meta-analysis to combine the findings from multiple studies on carbohydrate quality. They compared carb quality with risk of non-communicable diseases. The authors combined a total of 243 studies with a total of 4,635 participants, which makes for a very credible and powerful result.

The findings showed that dietary fiber is the most potent aspect of carbohydrate quality; the highest fiber consumers showed a 15 to 30 percent decrease in their risk of all-cause and cardiovascular mortality, type 2 diabetes, and colorectal cancer. Fiber was also associated with decreased risk of breast cancer, and with lower body weight, blood pressure, and total cholesterol.

The amount of fiber needed to achieve these health protections? Just 25 to 29 grams per day. That’s the daily recommendation for women and less than the recommendation of 36 grams for men. The authors did note, however, that more fiber may provide further benefit.

Unfortunately, Americans average just half of that protective dose; modern, processed diets are very low in fiber. Those who follow low-carbohydrate or ketogenic diets are also at risk for low fiber intake, although 25 grams per day of fiber is quite achievable on a ketogenic diet when care is taken to reach those numbers.

Although the results weren’t as great as those for fiber, whole grains were also found to have a protective effect when compared to refined grains. This makes sense, since whole grains have more fiber. It’s worth noting, however, that sufficient fiber intake is easily attainable on a grain-free diet, so this study should not be interpreted to mean that whole grains are necessary for health.

Glycemic index was also analyzed, and there was no association found between it and health outcomes. Glycemic load is a more helpful way to express the blood sugar-rising effects of a food, but it was not analyzed in this study.

These findings make sense from an ancestral perspective. Most ancestral populations consume a large amount of fiber. Of course, they don’t consume whole-grain sandwiches or waffles. Instead, they eat a high variety of unrefined plant foods, mostly fruits and vegetables.

Further, fiber has many demonstrated effects. It feeds the microbiome in a way that can be protective against obesity and insulin resistance. Fiber also binds cholesterol and carries it out of the body. It also reduces constipation and, in turn, colorectal cancer risk. Finally, it improves satiety, thus facilitating appropriate energy intake.

Fortunately, getting enough fiber is possible on a low-carb diet, or even on a ketogenic diet. If you follow a low-carb diet, some high-fiber foods that can fit include avocados, berries, leafy greens, cruciferous vegetables, and nuts. Use a food tracker website or app to check whether your daily fiber intake meets the minimum of 25 grams per day and adjust accordingly.

Of note, this paper did not include studies where fiber supplements were used. So, there’s no evidence here that they’re an acceptable substitute. Real food is always the best bet.