Fiber directly improves insulin sensitivityiStock
A number of studies have found that eating more dietary fiber for a period of weeks or months is linked to a reduction in biomarkers for insulin resistance. This may be due in part to dietary fiber’s anti-inflammatory effects—high-fiber diets have been associated with reduced blood levels of C-reactive protein, a marker for systemic inflammation—and also to the fact that the short-chain fatty acids that fiber produces when it ferments in the intestinal tract tend to inhibit the breakdown of the body’s fat stores into free fatty acids. This breakdown of fat stores appears to play a major role in creating insulin resistance in the skeletal muscles.
Fiber slows the release of glucose into the bloodstreamiStock
Soluble fiber’s general effect of slowing down the digestive process means that the carbohydrates we eat take longer to be broken down into glucose. As a result, the release of glucose into the blood after eating tends to occur more slowly over a longer period of time following a high-fiber meal. This means that glucose doesn’t rise to as high a peak after eating, putting less stress on the glucose metabolism process.
Fiber signals the liver to manufacture less glucoseiStock
The same fermentation process that signals the body to become more responsive to insulin also suppresses glucose production in the liver—countering the liver’s glucose overproduction that occurs as the result of insulin resistance.
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Fiber makes you feel more full so it’s easier to eat lessiStock
A number of studies have found that people who eat diets high in fiber feel more full after eating and also feel less hungry between meals. For starters, dietary fiber is simply bulkier than other nutrients. This causes the stomach to become more distended when you eat fiber, which sends appetite-suppressing signals to the brain. Soluble fiber also slows down the passage of food through the digestive tract, causing nutrients to be absorbed more slowly, which has been linked to an increase in digestion-related sensations of satiety. There is also evidence that the need to chew high-fiber foods more thoroughly than other food types contributes to a feeling of being full. Finally, fiber also appears to act directly on cells in the intestinal wall to trigger a hormonal response that may contribute to feelings of satiety.
In addition, foods high in fiber are generally lower in calories, period. Because research shows that we judge how much to eat based on the actual volume of food we consume, this effect should also tend to reduce the amount of calories you take in.
Dietary fiber alters your gut bacteria so that it consumes more caloriesiStock
A high-fiber diet alters the makeup of the gut microbiome (the many billions of bacteria and other microbes that populate the intestinal tract) in a way that causes these microbes to consume more calories from the food that you eat, again allowing fewer calories to pass into the body.
A high-fiber diet makes it easier to maintain a healthy weightiStock
The fact that a diet high in fiber results in increased satiety and an altered intestinal microbiome both suggest that a high-fiber diet can help prevent excess body fat. A number of studies have confirmed that the more fiber people eat, the lower their body weight and body fat tends to be. In addition, several short-term studies of overweight people on high-fiber diets have found that these diets tend to result in moderate weight loss. Losing even a relatively small amount of weight will improve insulin sensitivity and reduce type 2 diabetes risk.
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