More Evidence That a High-Fiber Diet Can Curb Type 2 Diabetes

High-Fiber Diet

Story at-a-glance -

  • People who ate more than 26 grams of fiber a day had an 18 percent lower risk of developing type 2 diabetes than those who ate 19 grams a day or less
  • Fiber may benefit diabetes by altering hormonal signals, slowing down nutrient absorption or altering fermentation in the large intestine, along with promoting feelings of satiety and weight loss
  • The majority of your fiber should come from vegetables, not grains

By Dr. Mercola

In the US, nearly 80 million people, or one in four has some form of diabetes or pre-diabetes. One in two people with diabetes do not know they have it,1 which increases the odds of developing complications, which can be deadly.

Leading a healthy lifestyle is one of the best strategies to prevent, and treat, type 2 diabetes, and even more specifically, eating a high-fiber diet is emerging as a key strategy you can use to lower your risk.

More Than 26 Grams of Fiber a Day May Lower Your Diabetes Risk

US dietary guidelines call for adults to consume 20-30 grams of fiber per day. I believe an ideal amount for most adults is around 50 grams per 1,000 calories consumed. Most people, however, get only half that, or less.

In a recent study conducted by researchers at the Imperial College London, those who had the highest intake of fiber (more than 26 grams a day) had an 18 percent lower risk of developing type 2 diabetes than those with the lowest intake (less than 19 grams a day).2

The fiber may benefit diabetes by altering hormonal signals, slowing down nutrient absorption or altering fermentation in the large intestine, along with promoting feelings of satiety.3

Eating a high-fiber diet is also associated with weight loss, and the researchers believe this may, in turn, lower diabetes risk. In fact, when the researchers accounted for participants' BMI, the benefits of a high-fiber diet disappeared, which suggests the benefit is largely due to fiber's role in maintaining a healthy weight.

That being said, the study's author noted other mechanisms are also likely at play when it comes to fiber's role in preventing type 2 diabetes:4

"…for instance improving control of blood sugar and decreasing insulin peaks after meals, and increasing the body's sensitivity to insulin."

How Does a High-Fiber Diet Protect Against Obesity and Diabetes?

One way that a high-fiber diet may be protective against obesity and diabetes has to do with your intestinal bacteria's ability to ferment fibers.

More specifically, when you eat foods high in fermentable fibers, such as cabbage, beans, and other vegetables, the bacteria in your intestines ferments them into butyrate and propionate, which are short-chain fatty acids (SCFAs) involved in sugar production. As reported by Medical News Today:5

"The researchers explain that glucose has certain elements that are detected by nerves located in the vein that collects blood from the intestine - known as the portal wall. A nerve signal is then transmitted to the brain.

The brain then activates a series of defenses against diabetes and obesity in response to the signal. The defenses include increased satiety, increased energy expenditure during periods of rest and less glucose production from the liver."

In an animal study, mice fed a diet rich in fibers gained less weight and had protection against diabetes, unlike mice fed a diet without fiber supplementation.6 When mice engineered to not produce glucose were used in the study, they gained weight and developed diabetes even when fed a high-fiber diet. Medical News Today continued:7

"These findings suggest that it is the glucose-producing activity of the intestines as a result of propionate and butyrate, and intestinal bacteria, that cause fermentable fibers to protect against obesity and diabetes."

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Which Type of Fiber Is Best for Diabetes?

The featured study found that while cereal and vegetable fiber lowered diabetes risk by 19 percent and 16 percent, respectively, fruit fiber had no such beneficial effect. I would caution you against relying on cereal or other grains as your source of fiber, however, as whole-grain breads, cereal, pasta, and other forms of grains have non-fiber carbohydrates (sugar and starch) in addition to the fiber.

While the fiber will not raise your blood sugar levels because it is not broken down by your body, grains will raise your insulin and leptin levels, which is a major driver of most chronic diseases, including type 2 diabetes. Carbohydrates that are not fiber will be quickly metabolized into sugar, and it makes little sense to eat large amounts of sugar if you're seeking to lower your risk of diabetes.

Sugars and grains (complex carbs) raise your blood sugar. When this happens, insulin is released to direct the extra energy into storage. A small amount is stored as a starch called glycogen, but the majority is stored as your main energy supply—fat.

Insulin's major role is not to lower your blood sugar, but rather to store the extra energy for future times of need. Insulin's effect of lowering your blood sugar is merely a "side effect" of this energy storage process.

If you consume loads of sugars and grains, your blood sugar spikes will lead to increased insulin, which leads to increased fat storage. The extra fat then produces more leptin, a hormone that tells your brain when to eat, how much to eat, and most importantly, when to stop eating.

The problem arises when your leptin levels become chronically elevated. At this point, you become leptin resistant—your body can no longer "hear" the hormonal signals telling your brain you're full and should stop eating.

As your fat stores increase, your weight goes up, and insulin resistance sets in. Now your body has become "deaf" to the signals from both hormones (leptin and insulin), and disease often follows, one of which is diabetes.

Just as with insulin, the only known way to reestablish proper leptin signaling is through proper diet, including the right type of fiber, which is primarily that from vegetables.

High Intake of Soluble Fiber Improves Type 2 Diabetes

A separate study also revealed that consuming a high-fiber diet (in this case 50 grams a day) resulted in benefits to type 2 diabetes. The high-fiber diet improved control of blood sugar levels, decreased excess insulin levels and lowered lipid concentrations in patients with type 2 diabetes.8

Soluble fiber, like that found in cucumbers, blueberries, beans, and nuts, was found to be particularly beneficial for type 2 diabetes. Soluble fiber dissolves into a gel-like texture, helping to slow down your digestion.

This helps you to feel full longer and is one reason why fiber may help with weight control. Soluble fiber may also help to slow your body's breakdown of carbohydrates and the absorption of sugar, helping with blood sugar control.

Insoluble fiber, found in foods like dark green leafy vegetables, green beans, celery, and carrots, does not dissolve at all and helps add bulk to your stool. This helps food to move through your digestive tract more quickly for healthy elimination.

Many whole foods, especially fruits and vegetables, naturally contain both soluble and insoluble fiber. If your diet could use more fiber, resist the urge to fortify it with whole grains.

A simple "rule" to remember is simply to get most of your fiber in the form of vegetables, not grains, and focus on eating more vegetables, nuts, and seeds. The following whole foods, for example, contain high levels of soluble and insoluble fiber.

Chia seeds Berries Vegetables such as broccoli and Brussels sprouts
Root vegetables and tubers, including onions and sweet potatoes Almonds Psyllium seed husk, flax, and chia seeds
Green beans Cauliflower Beans

Prebiotics: Another Way Certain Types of Fiber May Benefit Diabetes

Certain types of fiber are prebiotics, which help nourish beneficial bacteria in your gut. These beneficial bacteria in turn assist with digestion and absorption of your food, and play a significant role in your immune function. Inulin, a prebiotic fiber found in onions, leeks, and garlic (among many other foods), has also shown particular promise for type 2 diabetes.

Women with type 2 diabetes who consumed 10 grams of inulin a day for two months had improvements in glycemic control and antioxidant levels.9 It's thought that inulin may work to improve diabetes by positively modifying gut microflora or due to a direct antioxidant effect.

Prolonged exposure to excess insulin causes oxidative stress, which is thought to play a key role in type 2 diabetes and its complications. Inulin may help to counteract this with its antioxidant effects. Unprocessed whole foods (and as mentioned particularly onions and garlic), are among the best prebiotics, so if you're eating right, you should be getting plenty in your diet. Psyllium seed husk is also a prebiotic.

A High-Fiber Diet Is Beneficial Even if You Don't Have Diabetes

A high-fiber diet can help reduce your risk of premature death from any cause, likely because it helps to reduce your risk of a number of chronic diseases. This includes type 2 diabetes, heart disease, stroke, and cancer. Research also shows it can help heart patients live longer.

Studies have also linked a high-fiber diet to beneficial reductions in cholesterol and blood pressure, improved insulin sensitivity, and reduced inflammation—all of which can influence your mortality risk. One meta-analysis evaluating the impact of a high-fiber diet on mortality pooled data from 17 different studies tracking nearly 1 million Europeans and Americans.10 As reported by Scientific American:11

"Yang's team divided participants into five groups based on their daily fiber intake. Those in the top fifth, who ate the greatest amount of fiber daily, were 16 percent less likely to die than those in the bottom fifth, who consumed the least amount of fiber. In addition, eight studies showed a 10 percent drop in risk for any cause of death with each 10-gram per day increase in fiber intake."

Another study produced similar results. Every 10-gram increase of fiber intake was associated with a 15 percent lower risk of mortality, and those who ate the most fiber had a 25 percent reduced risk of dying from any cause within the next nine years compared to those whose fiber intake was lacking.12 Research published in 2013 also found that for every seven grams more fiber you consume on a daily basis, your stroke risk is decreased by seven percent.13 This equates to increasing your consumption of fruits and vegetables by about two additional portions per day, a manageable amount.

What Else Can Help You Overcome or Prevent Type 2 Diabetes?

Type 2 diabetes involves loss of insulin and leptin sensitivity, which is easily preventable, and nearly 100 percent reversible without drugs, by addressing your diet and other lifestyle habits, such as exercise, sleep, and intermittent fasting. I suggest taking a lifestyle inventory to see where you might have room for improvement and implementing the steps below. Also, make sure to monitor your fasting insulin level. This is every bit as important as monitoring your fasting blood sugar. You'll want your fasting insulin level to be between 2 and 4.

The higher your level, the greater your insulin resistance and the more aggressive you need to be in your treatment plan, especially when it comes to altering your diet.

  • Swap out processed foods, all forms of sugar—particularly fructose—as well as all grains, for whole, fresh food. A primary reason for the failure of conventional diabetes treatment over the last 50 years has to do with seriously flawed dietary recommendations. Fructose, grains, and other sugar-forming starchy carbohydrates are largely responsible for your body's adverse insulin reactions, and all sugars and grains—even "healthy" organic whole grains—need to be drastically reduced.
  • If you're insulin/leptin resistant, have diabetes, high blood pressure, heart disease, or are overweight, you'd be wise to limit your total fructose intake to 15 grams per day until your insulin/leptin resistance has resolved. For all others, I recommend limiting your daily fructose consumption to 25 grams or less to maintain optimal health. The easiest way to accomplish this is by swapping processed foods for whole, ideally organic foods. This means cooking from scratch with fresh ingredients.

    Processed foods are the main source of all the primary culprits, including high fructose corn syrup and other sugars, processed grains, trans fats, artificial sweeteners, and other synthetic additives that may aggravate metabolic dysfunction. Besides fructose, synthetic trans fat increases your risk for diabetes by interfering with your insulin receptors.14 Since you're cutting out a lot of energy (carbs) from your diet when you reduce sugars and grains, you need to replace them with something. The ideal replacement is a combination of:

    • Low-to-moderate amount of high-quality protein. Substantial amounts of protein can be found in meat, fish, eggs, dairy products, legumes, and nuts. When selecting animal-based protein, be sure to opt for organically raised, grass-fed or pastured meats, eggs, and dairy, to avoid potential health complications caused by genetically engineered animal feed and pesticides.
    • Most Americans eat far too much protein, so be mindful of the amount! I believe it is the rare person who really needs more than one-half gram of protein per pound of lean body mass. Those that are aggressively exercising or competing and pregnant women should have about 25 percent more, but most people rarely need more than 40-70 grams of protein a day.

      To determine your lean body mass, find out your percent body fat and subtract from 100. This means that if you have 20 percent body fat, you have 80 percent lean body mass. Just multiply that by your current weight to get your lean body mass in pounds or kilos. To determine whether you're getting too much protein, simply calculate your lean body mass as described above, then write down everything you're eating for a few days, and calculate the amount of daily protein from all sources.

      Again, you're aiming for one-half gram of protein per pound of lean body mass, which would place most people in the range of 40 to 70 grams of protein per day. If you're currently averaging a lot more than that, adjust downward accordingly.

    • As much high-quality healthy fat as you want (saturated and monounsaturated). For optimal health, most people need upwards of 50-85 percent of their daily calories in the form of healthy fats. Good sources include coconut and coconut oil, avocados, butter, nuts, and animal fats. (Remember, fat is high in calories while being small in terms of volume. So when you look at your plate, the largest portion would be vegetables.)
    • As many non-starchy vegetables as you want
  • Exercise regularly and intensely. Studies have shown that exercise, even without weight loss, increases insulin sensitivity.15 High intensity interval training (HIIT), which is a central component of my Peak Fitness program, has been shown to improve insulin sensitivity by as much as 24 percent in just four weeks.
  • Improve your omega-3 to omega-6 ratio. Today's Western diet has far too many processed and damaged omega-6 fats, and is far too little omega-3 fats. The main sources of omega-6 fats are corn, soy, canola, safflower, peanut, and sunflower oil (the first two of which are typically genetically engineered as well, which further complicates matters). Our bodies evolved for an optimal 1:1 ratio of omega-6 to omega-3. However, our ratio has deteriorated to between 20:1 and 50:1 in favor of omega-6. This lopsided ratio has seriously adverse health consequences.
  • To remedy this, reduce your consumption of vegetable oils (this means not cooking with them, and avoiding processed foods), and increase your intake of animal-based omega-3, such as krill oil. Vegetable-based omega-3 is also found in flaxseed oil and walnut oil, and it's good to include these in your diet as well. Just know they cannot take the place of animal-based omega-3s.

  • Maintain optimal vitamin D levels year-round. Evidence strongly supports the notion that vitamin D is highly beneficial for type 2 diabetes. The ideal way to optimize your vitamin D level is by getting regular sun exposure or by using a high-quality tanning bed. As a last resort, consider oral supplementation with regular vitamin D monitoring to confirm that you are taking enough vitamin D to get your blood levels into the therapeutic range of 50-70 ng/ml. Also please note that if you take supplemental vitamin D, you create an increased demand for vitamin K2.
  • Get adequate high-quality sleep every night. Insufficient sleep appears to raise stress and blood sugar, encouraging insulin and leptin resistance and weight gain. In one 10-year long study of 70,000 diabetes-free women, researchers found that women who slept less than five hours or more than nine hours each night were 34 percent more likely to develop diabetes symptoms than women who slept seven to eight hours each night.16 If you are having problems with your sleep, try the suggestions in my article "33 Secrets to a Good Night's Sleep."
  • Maintain a healthy body weight. If you incorporate the diet and lifestyle changes suggested above you will greatly improve your insulin and leptin sensitivity, and a healthy body weight will follow in time. Determining your ideal body weight depends on a variety of factors, including frame size, age, general activity level, and genetics. As a general guideline, you might find a hip-to-waist size index chart helpful.
  • This is far better than BMI for evaluating whether or not you may have a weight problem, as BMI fails to factor in both how muscular you are, and your intra-abdominal fat mass (the dangerous visceral fat that accumulates around your inner organs), which is a potent indicator of leptin sensitivity and associated health problems.

  • Incorporate intermittent fasting. If you have carefully followed the diet and exercise guidelines and still aren't making sufficient progress with your weight or overall health, I strongly recommend incorporating intermittent fasting. This effectively mimics the eating habits of our ancestors, who did not have access to grocery stores or food around the clock.
  • They would cycle through periods of feast and famine, and modern research shows this cycling produces a number of biochemical benefits, including improved insulin/leptin sensitivity, lowered triglycerides and other biomarkers for health, and weight loss. Keep up your intermittent fasting schedule until your insulin/leptin resistance improves (or your weight, blood pressure, cholesterol ratios, or diabetes normalizes). After that, you only need to do it "as needed" to maintain your healthy state.

  • Optimize your gut health. Your gut is a living ecosystem, full of both good bacteria and bad. Multiple studies have shown that obese people have different intestinal bacteria than lean people. The healthier your microflora, the stronger your immune system will be and the better your body will function overall. Fortunately, optimizing your gut flora is relatively easy. You can reseed your body with good bacteria by regularly eating fermented foods (like natto, raw organic cheese, miso, and cultured vegetables).
  • Consume adequate amounts of magnesium. Magnesium plays a key role in preventing insulin dysregulation and type 2 diabetes -- yet 80 percent of Americans are likely magnesium deficient. One study found those with the highest magnesium intake reduced their risk of metabolic problems by 71 percent.17 The best source of magnesium is whole, organic foods, especially dark green leafy vegetables; other good sources include seaweed, dried pumpkin seeds, unsweetened cocoa, flaxseed, almond butter, and whey, but it can be difficult to get enough from diet alone.
  • Of the many forms of magnesium supplements available today, a newer form called magnesium threonate shows particular promise due to its ability to penetrate cell membranes.