Fiber and blood sugar

Fibre and diabetes

Porridgeis a good source of fibre

Increasing the amount of fibre in your diet can help you manage your diabetes. It also helps keep your gut healthy and can reduce your bloodcholesterol, which lowers your risk of cardiovascular disease. If you are trying to maintain a healthy weight, it can also be beneficial.

The Scientific Advisory Committee on Nutrition (SACN), who looked at the role of fibre in maintaining good health, published these new recommendations in July 2015:

  • adults 16 years and over: 30g per day
  • 11-16 years: 25g per day
  • 5-11 years: 20g per day
  • 2-5 years: 15g per day

Currently, the average adult in the UK consumes only around 19g per day.

Here, we’ll help you identify foods that are high in fibre and simple ways you can increase your intake. Remember that you’ll also need to increase the amount youdrink. If you have diabetes, or are just managing your weight, the best options for drinks are water, no-calorie/low-calorie sugar-free drinks, unsweetened tea or coffee with milk.

What is fibre?

Dietary fibre is a type of carbohydrate that’s found in plant-based foods. It’s not absorbed or digested by the body, but plays an important role in maintaining good health. There are two types of dietary fibre – soluble and insoluble. Most foods contain both types, but are usually richer in one type than the other.

Soluble fibre

Found in oat, oat bran, linseeds, barley, fruit and vegetable, nuts, beans, pulses, soya and lentils.

Insoluble fibre

Good sources include: wholemeal bread, bran, wholegrain cereals, nuts, seeds and the skin of some fruit and vegetables.

Why is fibre important?

Having diabetes can increase your risk of cardiovascular disease. Evidence shows that increasing your intake of fibre, especially cereal and wholegrains, can help reduce the risk of cardio-metabolic diseases (this includes cardiovascular disease, insulin resistance and obesity) and colo-rectal cancer.

Higher intake of oat bran also leads to lower cholesterol levels and lower blood pressure.

Dietary fibre absorbs fluid and increases the bulk of waste matter, making your stools softer and easier to pass. Foods higher in soluble fibre have a particular role in reducing blood cholesterol. Increasing your dietary fibre can also help with managing your weight. These foods are filling and most are lower inglycaemic index(GI), which can help to control your appetite and have less of an effect on blood glucose levels.

How to increase your daily intake of fibre

To achieve the new SACN guidelines, we need to aim for at least five portions of fruit and vegetables a day. We need to try to base our meals around starchy carbohydrates, choosing wholegrain varieties, and include high-fibre snacks.

Here are some ideas, along with their fibre and carb content, to get you started:




Lunch or main meals



To increase your fibre intake even further, add salad or vegetables to your lunch or main meal.

High-fibre snacks

  • Plain oat cakes
  • Fruits
  • Nuts
  • Dried fruit
  • Yogurt with berries and pumpkin seeds

Keep an eye on the portion sizes when you are eating these snacks, especially if you are watching your weight.

Children and fibre

You can help your children to increase their fibre intake with the following ideas:

  • Offer fruits or a small portion of dried fruit as a snack.

  • Blitz vegetables in a tomato sauce and serve with pasta. Why not introduce them to wholewheat pasta? Perhaps start with a mixture of white and wholewheat.
  • Offer wholegrain cereals for breakfast, or even add some high-fibre, bran-based cereal to their favourite choices.
  • A smoothie made with milk and frozen berries as a snack or try frozen yogurt with berries as a sweet treat.

Shopping tips

You can compare theback of pack nutritional labelson pre-packed foods and choose the food with the higher amount of fibre. At times this information may not be available, but there are other ways of choosing foods high in dietary fibre:

  • Look for words such as ‘wholemeal’, ‘wholewheat’ and ‘wholegrain’ on labels.Wholegraincarbohydrates tend to be higher in fibre and lower in GI, which means they have less of an effect on your blood glucose levels.
  • Choose wholemeal, seeded or multi-grain bread – these are higher in fibre than white varieties. Brown bread is not as high in fibre as wholemeal.
  • Instead of white pasta or rice, choose the brown/wholewheat type.
  • Go forbeans, pulses and lentils – buy tinned to save on cooking time and add to casseroles, soups,

    salads and curries.

  • Choose oat-based, bran or wholegrain breakfast cereals.
  • Buy a selection of interesting and seasonal fruit and vegetables to help you aim for your five-a-day target.
  • Couscous and quinoa, which are wholegrains, are a great source of fibre.

Aiming for 30g a day may feel like a lot. As long as you try to increase your intake aiming to meet the recommendation slowly, you will be on the right path. Always speak to your healthcare professional before changing your diet.

How Fiber Helps Control High Blood Sugar

Are you filling up on fiber? If you have type 2 diabetes, you should be — including high-fiber foods in your diet is a healthy way to control high blood sugar. As an added bonus, you may be able to stay full longer on the correct portion sizes than you would if you were eating more refined foods. And eating lots of soluble fiber (the kind found in oatmeal, beans, and apples, among other foods) may help reduce dangerous visceral belly fat, according to a recent study.

“Fiber promotes good bowel health, lowers the risk of cancer and heart disease, and also controls your blood sugar in a certain way,” explains Amy Kranick, a registered dietitian and certified diabetes educator with the adult diabetes program at Vanderbilt University Medical Center in Nashville, Tenn.

When fiber is digested, your body handles it differently than the way in which refined carbohydrates, such as white flour, are digested. A portion of the fiber simply passes through your digestive system intact. This difference means that eating foods rich in fiber is less likely to cause a spike in high blood sugar.

“Fiber doesn’t require insulin , so it isn’t counted as part of your carbohydrates,” says Kranick. As a result, when you are reading labels and budgeting daily carbohydrates, you can subtract half the grams of dietary fiber from the total carbohydrate count.

At the same time, you should be keeping track of how much fiber you eat. Adults need at least 25 grams of fiber daily for best health outcomes, says Kranick.

Other Benefits of Fiber

Fiber may also help you manage your overall eating habits, says Kranick.

Here are some of the additional benefits of eating high-fiber foods:

  • Antioxidants. Many of the foods that contain fiber also contain antioxidants, which are generally good for your cells and your overall health. “The high-fiber items such as oats, the skin of fruits and potatoes, and beans are where the antioxidants are,” Kranick says.
  • Hunger control. Foods rich in fiber can help you feel full longer, staving off the hunger pangs that might lead to snacking on foods that will spike high blood sugar.
  • Portion control. Because fiber fills you up, it’s easier to stick to the proper portions. In contrast, refined foods that lack fiber tend to make you crave more — making it easier to eat in excess. “For some reason, it’s much easier to keep eating Reese’s Pieces than bowls of oatmeal,” says Kranick.

How to Add Fiber to a Diabetes Diet

Kranick acknowledges that making the switch to fiber can be a challenge for some people with type 2 diabetes.

“Patients who have type 2 diabetes come here because their diet tends to be high in calories and low in fiber,” she says. Shifting that balance to a diabetes diet with more fiber and fewer calories takes work — and time. But she points out, it can be accomplished with a little education in label reading and fiber food sources. Here’s what to do:

  • Read labels. You may be surprised by what you learn. For example, she says, a slice of whole-wheat bread with at least 3 grams of fiber is considered to be a fiber item. Use two to make a sandwich and add a small side salad or some fruit and you will be making a nice dent in your daily fiber goal. Remember to subtract the fiber grams from the total carbohydrates as you keep track of carbs. You want to look for:
    • 2.5 to 4.9 grams of fiber per serving for a good source of fiber
    • 5 grams or higher for a high-fiber serving
  • Know fiber foods. Here are some of the foods or ingredients you should look for:
    • Oats
    • Barley
    • Whole-grain breads, cereals, and pastas
    • Vegetables
    • Fruits
    • Brown rice
    • Nuts
    • Beans
    • Peas
    • Lentils
  • Avoid processed and refined foods. Kranick knows we are all pressed for time, but she warns that eating foods that are cheap, quick, and easy, or grabbing fast food on the go, means you are probably not going to get the fiber you need. Plan on adding some time to your food preparation habits, look for higher-fiber options like salads, or keep healthy snacks on hand — such as a handful of nuts, fresh fruit, or veggie slices and a healthy dip — to tide you over.
  • Go slow. If you are new to fiber, increase your intake slowly. Your body will need time to adjust.

With a little bit of effort you can add fiber to your diet — and improve your overall health while controlling high blood sugar.

Metabolic Effects of Dietary Fiber Consumption and Prevention of Diabetes


A high dietary fiber (DF) intake is emphasized in the recommendations of most diabetes and nutritional associations. It is accepted that viscous and gel-forming properties of soluble DF inhibit macronutrient absorption, reduce postprandial glucose response, and beneficially influence certain blood lipids. Colonic fermentation of naturally available high fiber foods can also be mainly attributed to soluble DF, whereas no difference between soluble and insoluble DF consumption on the regulation of body weight has been observed. However, in prospective cohort studies, it is primarily insoluble cereal DF and whole grains, and not soluble DF, that is consistently associated with reduced diabetes risk, suggesting that further, unknown mechanisms are likely to be involved. Recent research indicates that DF consumption contributes to a number of unexpected metabolic effects independent from changes in body weight, which include improvement of insulin sensitivity, modulation of the secretion of certain gut hormones, and effects on various metabolic and inflammatory markers that are associated with the metabolic syndrome. In this review, we briefly summarize novel findings from recent interventions and prospective cohort studies. We discuss concepts and potential mechanisms that might contribute to the further understanding of the involved processes.


Consumption of soluble dietary fiber (DF)2 reduces postprandial glucose responses after carbohydrate-rich meals, as well as lowering total and LDL cholesterol levels (1). These effects are likely explained the viscous and/or gel-forming properties of soluble DF, which thereby slow gastric emptying and macronutrient absorption from the gut. However, it is not soluble DF, but mainly the consumption of insoluble cereal DF and whole grains, that is consistently associated with reduced risk of type 2 diabetes in large prospective cohort studies (2,3). A number of recent studies give novel insights that might help establish a metabolic link between insoluble DF consumption and reduced diabetes risk. Potential candidates are improved insulin sensitivity and the modulation of inflammatory markers, as well as direct and indirect influences on the gut microbiota (Fig. 1).


Potential effects of DF consumption. Colonic fermentation with the production of SCFA can be observed with most types of DF to some extent, but it tends to be more pronounced with soluble DF in naturally available foods.


Potential effects of DF consumption. Colonic fermentation with the production of SCFA can be observed with most types of DF to some extent, but it tends to be more pronounced with soluble DF in naturally available foods.

Definition and types of DF

DF are highly complex substances that can be described as any nondigestible carbohydrates and lignins not degraded in the upper gut (4). Commonly, DF are classified according to their solubility in water, even though grading according to viscosity, gel-forming capabilities, or fermentation rate by the gut microbiota might be physiologically more relevant. Most DF is fermented to some degree. However, fermentation rates of DF widely vary, with soluble DF (i.e., pectin, inulin, and β-glucans) and insoluble resistant starch and oligosaccharides tending to be more readily fermented than cereal DF (i.e., cellulose and hemicelluloses) (5). Foods are assumed to be whole grains if all components of the kernel (i.e., bran, germ, and endosperm) are present in their natural proportions. Whole grain food products generally contain some 12% of total (mainly insoluble cereal) DF, and there is a strong correlation between whole grain and cereal DF intake (2). Some bran derived food products contain up to 25% of DF. Importantly, definition of whole grain both in cohort studies and on labels of commercially available cereal products typically does not require an intact kernel (3). In U.S. cohorts, whole grain and bran products from corn and wheat are the main sources of cereal DF. Main sources of soluble DF are fruits and vegetables (6) and, to a smaller extent, products from oat and barley that are rich in both insoluble DF and soluble β-glucans. It is, however, important to state that most naturally available high-fiber foods contain both soluble and insoluble fiber in varying amounts (6).

DF and risk of diabetes in prospective cohort studies

It is commonly assumed that beneficial effects of high fiber diets can mainly be attributed to viscous and/or gel-forming properties of soluble DF (1). Therefore, analyzing results from prospective cohort studies separately for foods high in “active” soluble DF and “inactive” insoluble DF should be expected to show stronger protective associations for soluble DF. However, this hypothesis is not supported by the available data. A recent meta-analysis that included 328,212 subjects showed no association with reduced diabetes risk both for fruit and vegetable (RR 1.04; 95% CI 0.94–1.15) DF intake (2). In contrast, a high intake of cereal DF was significantly associated with markedly reduced diabetes risk in most studies (RR 0.67; 95% CI 0.62–0.72) (2). Pooled data for 6 prospective cohort studies including 286,125 subjects indicate that a 2-serving-per-day increment in whole grain consumption might remarkably reduce diabetes risk by 21% (3). Interestingly, associations for consumption of the outer bran portion of the kernel, but not germ intake, were comparable to those of whole grain intake (3).

A causal relationship can not be stated, and estimation of food intake on the basis of semiquantitative FFQ is a known limitation (2). Moreover, even after statistical adjustment for potentially confounding factors, residual confounding by additional unmeasured or inaccurately measured factors can not be excluded. However, the consistency of the results clearly indicates that the consumption of insoluble cereal DF could play an important role in the prevention of diabetes.

Potential mechanisms

DF, satiety, and body weight.

Potential mechanisms that indicate DF consumption might alter diabetes risk include effects on satiety and body weight. A number of studies showed increased postmeal satiety or decreased subsequent hunger when subjects consumed high DF diets, both under conditions of fixed energy intake and when energy intake was consumed ad libitum (7). However, other studies reported no significant effects (7–10). Not all studies (11) showed an inverse association between postprandial glucose and insulin responses and satiety, and no clear conclusion can be drawn that low vs. high glycemic index meals are a key factor promoting satiety (12).

Most (7), but not all (13), observational studies showed an inverse, sometimes dose-dependent (14) relationship between DF consumption and body weight. Effects were moderate, with individuals in the highest quintile vs. lowest quintile of DF consumption gaining 3.6 kg less over a 10-y period (14). Several (7), but not all (9,15), relatively short-term interventions further indicate that moderate reductions of body weight can be achieved with high DF diets.

Generally, in human studies, no clear difference regarding weight gain has been shown between soluble and insoluble DF and fermentable and nonfermentable DF, or between foods naturally high in DF and fiber supplements (7). Therefore, reduced body weight in subjects consuming high DF diets is likely to contribute to reduced diabetes risk, but it cannot explain the observed stronger associations for insoluble DF.

DF and hormonal responses.

DF consumption affects the secretion of various gut hormones that may act as satiety factors (8,16–19). However, in many of the experiments in humans, hormonal changes were not linked to acute feelings of satiety. A guar gum DF supplement produced a heightened postprandial cholecystokinin response, but did not alter satiety ratings (16). Insoluble wheat DF-induced changes of orexigenic ghrelin and anorexigenic peptide YY (PYY) were not associated with acute changes in hunger and satiety (8) but may have affected satiety upon the consumption of a subsequent meal (8,20). Highly fermentable DF increase glucagon-like peptide 1 levels and may play a role in the regulation of postprandial satiety in diverse animal species. However, in humans, no fiber-induced changes of circulating glucagon-like peptide 1 levels have been observed (17,18,21), and ingestion of a fermentable (pectin, β-glucan) vs. a nonfermentable (methylcellulose) DF supplement was found to be less, rather than more, satiating (9). Glucose dependent insulinotropic polypeptide (GIP) is another incretin hormone that appears to be involved in the regulation of fat metabolism. Effects of DF consumption on circulating GIP yielded mixed results. Soluble DF reduced circulating GIP in diabetic humans (19), probably because of reduced carbohydrate absorption, whereas insoluble cereal DF consumption yielded accelerated responses of both biologically active GIP (17) and insulin (17,22) in healthy subjects. In a cross-sectional analysis, high intakes of cereal DF were positively associated with plasma adiponectin after adjusting for lifestyle factors and dietary glycemic load (23). Adiponectin may act as a peripheral starvation signal promoting the storage of triglycerides preferentially in adipose tissue (24). As a consequence, reduced triglyceride accumulation in the liver and in the skeletal muscle might convey improved systemic insulin sensitivity (25). In summary, various changes in circulating concentrations of gut and adipocyte derived hormones can be observed in humans that ingest a high DF diet. However, no obvious mechanism can be derived explaining stronger associations for insoluble DF with diabetes risk.

DF and insulin sensitivity.

An increased intake of total DF was inversely associated with markers of insulin resistance in several studies (26). Investigating different sorts of soluble and insoluble DF in randomized controlled intervention studies yielded mixed results. Consumption of wheat bran for 3 mo did not change fasting glucose and glycated hemoglobin (HbA1c) levels in diabetic subjects (27). High DF rye bread enhanced insulin secretion but did not appear to improve insulin sensitivity in postmenopausal women, as estimated with the frequently sampled intravenous-glucose-tolerance test (28). However, using a second meal test design, improved markers of insulin resistance have been reported after consumption of various other sorts of insoluble DF (17,18,20,29). When measuring insulin sensitivity using euglycemic-hyperinsulinemic clamps, consumption of insoluble DF increased whole body glucose disposal independent of changes in body weight in both short-term and more prolonged studies (21,30,31). Insulin resistant subjects are more likely to eventually develop diabetes. Therefore, improved insulin sensitivity could be a relevant factor contributing to reduced diabetes risk in subjects consuming diets high in insoluble DF.

DF and inflammation.

Recent studies show reductions of inflammatory markers in subjects consuming high DF diets (32). Interestingly, some sorts of DF have been reported to bind to specific receptors on immune cells, suggesting a direct immune–modulatory effect (5). Other potentially involved mechanisms might include weight loss when consuming high DF diets, as well as antihyperglycemic effects and effects on lipid oxidation (32). Both a diet high in total DF and consumption of a soluble DF supplement significantly decreased levels of the inflammatory marker C-reactive protein (33). Fermentation of soluble DF may also play a role due to potential antiinflammatory properties of butyrate (32). However, reductions in inflammatory markers have been reported to be comparable with both insoluble DF and more readily fermentable soluble DF (34).

Colonic fermentation and gut bacteria.

Short-chain fatty acids (SCFA) such as acetate, propionate, and butyrate are produced by bacterial fermentation of indigestible DF polysaccharides in the colon (1), with the proportion of different SCFA not being fixed, depending on the substrate and eventually on the gut microflora. Commonly, increased production of SCFA is assumed to be beneficial by reducing hepatic glucose output and improving lipid homeostasis (32). Further, G protein-coupled receptors (GPR)-41 and GPR43 function as direct targets of SCFA. An interesting finding was that oral administration of the GPR41 ligand propionate almost doubled plasma concentrations of anorexigenic leptin in mice, even though no effect on food intake was detected (35).

However, data not unequivocally indicate that fermentability of DF per se is a key factor contributing to reduced diabetes risk. Consumption of low fermentable cereal DF (corn and wheat) show stronger associations with reduced diabetes risk than more readily fermentable soluble DF from fruit and vegetables (2,3). When investigating effects of weakly fermentable insoluble cereal DF and highly fermentable resistant starch in a randomized controlled cross-over study in healthy women (17), markers of insulin sensitivity in a second meal test were improved to a similar extent with all DF, independent of the rate of colonic fermentation (Fig. 2). These experiments indicate that a dose-dependent relation between fermentability of DF and improved markers of insulin sensitivity was unlikely, even though the limited accuracy of the available methods to estimate colonic fermentation rates in humans must be considered (4). Further, SCFA might stimulate adipogenesis through GPR43 (35), and colonization of germ-free (gnotobiotic) mice with a prominent saccharolytic member of the normal human gut microbiota, together with the dominant human methane producing germ, resulted in markedly improved efficacy of colonic fermentation, associated with increased de novo lipogenesis and obesity in the host (36). However, it needs to be emphasized that nutritional habits and physiological effects of DF intake in rodents and humans largely differ, with rodents recovering energy from coprophagia (4). In humans, SCFA account for <10% of daily energy intake (37).


Effects of insoluble fiber on postprandial glucose handling in a second meal test. Postprandial serum insulin and plasma glucose responses upon the ingestion of control white bread in a second meal test, following the ingestion of 3 portions of control white bread the previous day, or white bread enriched with 31.5 g of the insoluble fraction of nonfermentable wheat DF, or white bread enriched with 31.8 g of the insoluble fraction of moderately fermentable oat DF (n = 14/group), or white bread enriched with 31.2 g of highly fermentable resistant starch (RS) (substudy, n = 9/group). Test breads were isoenergetic and macronutrient matched. Adapted from reference (17), with permission.


Effects of insoluble fiber on postprandial glucose handling in a second meal test. Postprandial serum insulin and plasma glucose responses upon the ingestion of control white bread in a second meal test, following the ingestion of 3 portions of control white bread the previous day, or white bread enriched with 31.5 g of the insoluble fraction of nonfermentable wheat DF, or white bread enriched with 31.8 g of the insoluble fraction of moderately fermentable oat DF (n = 14/group), or white bread enriched with 31.2 g of highly fermentable resistant starch (RS) (substudy, n = 9/group). Test breads were isoenergetic and macronutrient matched. Adapted from reference (17), with permission.

DF consumption might affect further factors linking the gut microbiota with obesity and insulin resistance. Obese subjects have a different composition of the gut microbiota than lean subjects, and changes toward the “lean microbiota” can be observed in obese subjects that lose weight . When transplanting the gut microbiota from obese mice or from lean mice to germ-free mice, the recipients of the “obese microbes” showed an increased gain of fat mass, even though energy intake was comparable (36). Interestingly, a high DF diet (oligofructose) reduced gram-negative bacterial content and body weight, whereas a high fat diet increased the proportion of a gram-negative bacterial lipopolysaccharides (LPS) containing microbiota in humans . Continuous subcutaneous infusion of LPS for 4 wk increased weight gain, liver fat, inflammatory markers, and markers of insulin resistance to a similar extent than a high-fat diet (38). These studies indicate that DF consumption could have the potential to influence the proportions of certain members of the gut flora, thus linking the concepts of bacterial colonization, inflammation, and insulin resistance.

Prospective cohort studies indicate that diets high in insoluble cereal DF and whole grains might reduce diabetes risk. In contrast, there is no strong support that soluble DF from fruits and vegetables play a key role in this context. Many of the proposed protective mechanisms of DF consumption are either shared by soluble and insoluble DF (moderate weight loss, low energy density, increased satiety, effects on inflammatory markers and gut hormones), or they are more likely to be relevant with soluble viscous DF consumption (hindering of macronutrient absorption, slowing of gastric emptying, reduced postprandial glucose responses, reduced total and LDL cholesterol, and colonic fermentation). Therefore, other unknown mechanisms appear to be involved in conveying reduced diabetes risk in subjects consuming diets high in insoluble cereal DF. A promising factor contributing to beneficial effects of insoluble DF consumption could be increased insulin sensitivity, even though mechanisms leading to this phenomenon need to be defined. Hypothetical mechanisms include a shift in the relation of gut microbiotic communities, as well as direct and indirect influences on yet unknown hormonal and molecular factors in the host that may be altered in subjects consuming high DF diets.

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  • DF

    dietary fiber

  • GIP

    glucose dependent insulinotropic polypeptide

  • GPR

    G protein-coupled receptors

  • LPS


  • RR

    relative risk for extreme quintiles

  • SCFA

    short-chain fatty acids


4 Manuscript received 15 October 2007. © 2008 American Society for Nutrition

By Dr. Robert Thompson


One major reason this doesn’t happen has to do with our diets. When you consume starch and refined sugar, these foods enter the bloodstream quickly, causing a sugar spike. Your body then produces the hormone insulin to drive that sugar from your bloodstream into cells. But over time, excessive levels of insulin can make your muscle cells lose sensitivity to the hormone, leading to type-2 diabetes and heart disease. Your fat cells are another story: They always remain sensitive. Insulin spikes lock fat into them, so you can’t use it for energy.

How do you break this cycle and get your body to work optimally again? Happily, you don’t need to go on an extreme diet. The first step is just to reduce the blood sugar spikes that produce sharp increases of insulin. The substance in our diet that’s most responsible for these surges is starch, namely, anything made from potatoes, rice, flour, corn, or other grains. (Think pasta, lasagna, white bread, doughnuts, cookies, and cakes.) You could cut out these foods entirely. But wouldn’t it be great if there were a way to solve the problem without completely eliminating these carbs?

It turns out there is. You can blunt the blood sugar-raising effects by taking advantage of natural substances in foods that slow carbohydrate digestion and entry into the bloodstream. No matter what kind of sugar blocker you use, your waistline (and health) will win in the end.

Sugar Blocker 1: Have a fatty snack 10 to 30 minutes before your meals

Reason: You remain fuller longer.

At the outlet of your stomach is a muscular ring, the pyloric valve. It regulates the speed at which food leaves your stomach and enters your small intestine. This valve is all that stands between the ziti in your stomach and a surge of glucose in your bloodstream. But you can send your pyloric valve a message to slow down.

Fat triggers a reflex that constricts the valve and slows digestion. As little as a teaspoon of fat, easily provided by a handful of nuts or a piece of cheese, will do the trick, provided you eat it before your meal.

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Sugar Blocker 2: Start your meal with a salad.

Reason: It soaks up starch and sugar.

Soluble fiber from the pulp of plants, such as beans, carrots, apples, and oranges, swells like a sponge in your intestines and traps starch and sugar in the niches between its molecules. Soluble means “dissolvable,” and indeed, soluble fiber eventually dissolves, releasing glucose. However, that takes time. The glucose it absorbs seeps into your bloodstream slowly, so your body needs less insulin to handle it. A good way to ensure that you get enough soluble fiber is to have a salad, preferably before, rather than after, you eat a starch.

Sugar Blocker 3: Have some vinegar.

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Reason: It slows the breakdown of starch into sugar.

The high acetic acid content in vinegar deactivates amylase, the enzyme that turns starch into sugar. (It doesn’t matter what kind of vinegar you use.) Because it acts on starch only, it has no effect on the absorption of refined sugar. In other words, it will help if you eat bread, but not candy. But there’s one more benefit: Vinegar also increases the body’s sensitivity to insulin.

You should consume vinegar at the start of your meal. Put it in salad dressing or sprinkle a couple of tablespoons on meat or vegetables. Vinegar brings out the flavor of food, as salt does.

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Sugar Blocker 4: Include protein with your meal.

Reason: You won’t secrete as much insulin.

Here’s a paradox: You want to blunt insulin spikes, but to do that, you need to start secreting insulin sooner rather than later. It’s like a fire department responding to a fire. The quicker the alarm goes off, the fewer firefighters will be needed to put out the blaze.

Even though protein contains no glucose, it triggers a “first-phase insulin response” that occurs so fast, it keeps your blood sugar from rising as high later and, reduces the total amount of insulin you need to handle a meal. So have meatballs with your spaghetti.

Sugar Blocker 5: Eat lightly cooked vegetables.

Reason: You digest them more slowly.

Both fruits and vegetables contain soluble fiber. As a rule, though, vegetables make better sugar blockers, because they have more fiber and less sugar.

But don’t cook your vegetables to mush. Boiling vegetables until they’re limp and soggy saturates the soluble fiber, filling it with water so it can’t absorb the sugar and starch you want it to. Also, crisp vegetables are chunkier when they reach your stomach, and larger food particles take longer to digest, so you’ll feel full longer. Another tip: Roasted vegetables like cauliflower can often serve as a delicious starch substitute.

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Sugar Blocker 6: Have a glass of wine with dinner.

Reason: Your liver won’t produce as much glucose.

Alcohol has unique sugar-blocking properties. Your liver normally converts some of the fat and protein in your blood to glucose, which adds to the glucose from the carbs you eat. But alcohol consumed with a meal temporarily halts your liver’s glucose production. A serving of any alcohol; beer, red or white wine, or a shot of hard liquor, will reduce the blood sugar load of a typical serving of starch by approximately 25 percent.

That doesn’t mean you should have several drinks (especially if you have diabetes, as multiple drinks can cause hypoglycemia). Not only does alcohol contain calories, but it also delays the sensation of fullness, so you tend to overeat and pile on calories. Be especially mindful about avoiding cocktails that are made with sweetened mixers, yet another source of sugar.

Sugar Blocker 7: Eat sweets for dessert only.

Reason: All of the above.

If you eat sweets on an empty stomach, there’s nothing to impede the sugar from racing directly into your bloodstream, no fat, no soluble fiber, no protein, no vinegar. But if you confine sweets to the end of the meal, you have all of the built-in protection the preceding rules provide. If you want to keep blood sugar on an even keel, avoid between-meal sweets at all costs, and when you do indulge, don’t eat more than you can hold in the cup of your hand. But a few bites of candy after a meal will have little effect on your blood sugar and insulin, and can be quite satisfying.

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Adapted from “The Sugar Blockers Diet: Eat Great, Lose Weight – A Doctor’s 3-Step Plan to Lose Weight, Lower Blood Sugar, and Beat Diabetes – While Eating the Carbs You Love,” by Rob Thompson, MD, with the editors of Prevention (Rodale, 2012). To buy the book, go to

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Fiber is a type of carbohydrate that the body can’t digest. Though most carbohydrates are broken down into sugar molecules, fiber cannot be broken down into sugar molecules, and instead it passes through the body undigested. Fiber helps regulate the body’s use of sugars, helping to keep hunger and blood sugar in check.

Children and adults need at least 20 to 30 grams of fiber per day for good health, but most Americans get only about 15 grams a day. Great sources are whole fruits and vegetables, whole grains, and beans.

Fiber comes in two varieties, both beneficial to health:

  • Soluble fiber, which dissolves in water, can help lower glucose levels as well as help lower blood cholesterol. Foods with soluble fiber include oatmeal, nuts, beans, lentils, apples and blueberries.
  • Insoluble fiber, which does not dissolve in water, can help food move through your digestive system, promoting regularity and helping prevent constipation. Foods with insoluble fibers include wheat, whole wheat bread, whole grain couscous, brown rice, legumes, carrots, cucumbers and tomatoes.

The best sources of fiber are whole grains, fresh fruits and vegetables, legumes, and nuts.

Some tips for increasing fiber intake:

  • Eat whole fruits instead of drinking fruit juices.
  • Replace white rice, bread, and pasta with brown rice and whole grain products.
  • For breakfast, choose cereals that have a whole grain as their first ingredient.
  • Snack on raw vegetables instead of chips, crackers, or chocolate bars.
  • Substitute beans or legumes for meat two to three times per week in chili and soups.

Fiber and disease

Fiber appears to reduce the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation. Despite these benefits, fiber probably has little, if any, effect on colon cancer risk.

Heart disease

High intake of dietary fiber has been linked to a lower risk of heart disease in a number of large studies that followed people for many years. (16) In a Harvard study of over 40,000 male health professionals, researchers found that a high total dietary fiber intake was linked to a 40 percent lower risk of coronary heart disease. (17) A related Harvard study of female nurses produced quite similar findings. (18)

Higher fiber intake has also been linked to a lower risk of metabolic syndrome, a combination of factors that increases the risk of developing heart disease and diabetes. These factors include high blood pressure, high insulin levels, excess weight (especially around the abdomen), high levels of triglycerides, and low levels of HDL (good) cholesterol. Several studies suggest that higher intake of fiber may offer protective benefits from this syndrome. (19,20)

Type 2 diabetes

Diets low in fiber and high in foods that cause sudden increases in blood sugar may increase the risk of developing type 2 Diabetes. Both Harvard studies—of female nurses and of male health professionals—found that this type of diet more than doubled the risk of type 2 diabetes when compared to a diet high in cereal fiber and low in high-glycemic-index foods. (21-23) A diet high in cereal fiber was linked to a lower risk of type 2 diabetes.

Other studies, such as the Black Women’s Health Study (24) and the European Prospective Investigation Into Cancer and Nutrition–Potsdam, have shown similar results.

Read about what you can do to help prevent type 2 diabetes.

Diverticular disease

Diverticulitis, an inflammation of the intestine, is one of the most common age-related disorders of the colon in Western society. Among male health professionals in a long-term follow-up study, eating dietary fiber, particularly insoluble fiber, was associated with about a 40 percent lower risk of diverticular disease. (25)

Fiber and constipation

Constipation is the most common gastrointestinal complaint in the United States, and consumption of fiber seems to relieve and prevent constipation.

The fiber in wheat bran and oat bran is considered more effective than fiber from fruits and vegetables. Experts recommend increasing fiber intake gradually rather than suddenly, and because fiber absorbs water, beverage intake should be increased as fiber intake increases.

Colon cancer

Studies have largely failed to show a link between fiber and colon cancer. One of these—a Harvard study that followed over 80,000 female nurses for 16 years—found that dietary fiber was not strongly associated with a reduced risk for either colon cancer or polyps (a precursor to colon cancer). (26)

Following the Scientific Trail: The Story on Fiber and Colon Cancer

Because science is such a dynamic process, you can never exactly tell where it is going to lead you. Conclusions that once seemed logical and fairly solid may be revised—or completely overturned—as more and better research is done on a particular topic. One example of this is the relationship between fiber and colon cancer.

Starting about 30 years ago, a high fiber intake was regularly recommended as one way to lower the risk for colon cancer. This recommendation was largely based on observations that countries with a high fiber intake tended to have rates of colon cancer lower than the rates found in countries with a low fiber intake.

But such descriptive studies don’t provide the most definitive information. While they are often good points to start a scientific journey, they only take a broad look at large groups of people. Descriptive studies generally can’t address all of the factors that might account for differences in rates of disease. Fiber intake could indeed have something to do with the differences in colon cancer rates, but those differences could also involve many other things that differ between countries, including other diet or lifestyle factors.

When studies that can take such things into account on an individual level began to look at the issue of fiber and colon cancer, the picture became much less clear. A number of case-control studies found that a high fiber intake was linked to a lower risk of colon cancer, but many did not. Given these wavering results—and because case-control studies are not an optimal way to assess food intake, relying as they do on participants’ recollections of what they ate in the past—more research using better methods was needed. In the meantime, many health professionals still regularly recommended a high fiber intake for people trying to lower their risk of colon cancer.

Not until the results of cohort studies came out did this recommendation begin to lose its backing. Because cohort studies observe a group of people over time, their findings are generally stronger than those of case-control studies, especially when it comes to something like diet and colon cancer. What most of these cohort studies found was that fiber intake had very little, if any, link with colon cancer.

Such findings were further bolstered by the results of randomized trials—types of studies that many consider the gold-standard of research. These studies took a group of people and randomly assigned individuals to one of two groups. One group was put on a high fiber diet, while the other group followed a lower fiber diet. After 3 to 4 years, the two groups were compared and no difference was found in rates of colon polyps—noncancerous growths that can turn into cancer. Of course, colon polyps are not cancer, but since it’s thought that all colon cancers start as polyps, it is strong evidence that fiber intake has no direct link with colon cancer.

In this case, the path of discovery led from widespread belief in a clear link between fiber and colon cancer to acceptance of the likelihood that there was no strong link between the two. As such, it’s an excellent example of how research can often develop. What may start as a clear connection based on findings from broad, descriptive studies can slowly unravel as more and better-quality research unveils the true nature of a relationship. However, keep in mind that a weak relationship is difficult to exclude altogether. Further studies might yet demonstrate a weak effect of fiber on colon cancer, although such a finding wouldn’t alter the conclusion that other means must be sought to prevent colon cancer.

Breast cancer

A large-scale 2016 study (27) led by researchers at Harvard T.H. Chan School of Public Health showed findings that higher fiber intake reduces breast cancer risk, suggesting that fiber intake during adolescence and early adulthood may be particularly important.

  • Women who eat more high-fiber foods during adolescence and young adulthood, including vegetables and fruit, may have significantly lower breast cancer risk than those who eat less dietary fiber when young.

16. Pereira MA, O’Reilly E, Augustsson K, et al. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Arch Intern Med. 2004;164:370-6.

19. McKeown NM, Meigs JB, Liu S, Wilson PW, Jacques PF. Whole-grain intake is favorably associated with metabolic risk factors for type 2 diabetes and cardiovascular disease in the Framingham Offspring Study. Am J Clin Nutr. 2002;76:390-8.

20. McKeown NM, Meigs JB, Liu S, Saltzman E, Wilson PW, Jacques PF. Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort. Diabetes Care. 2004;27:538-46.

22. Liu S, Willett WC, Stampfer MJ, et al. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr. 2000;71:1455-61.

23. Schulze MB, Liu S, Rimm EB, Manson JE, Willett WC, Hu FB. Glycemic index, glycemic load, and dietary fiber intake and incidence of type 2 diabetes in younger and middle-aged women. Am J Clin Nutr. 2004;80:348-56.

24. Krishnan S, Rosenberg L, Singer M, et al. Glycemic index, glycemic load, and cereal fiber intake and risk of type 2 diabetes in US black women. Arch Intern Med. 2007;167:2304-9.

25. Aldoori WH, Giovannucci EL, Rockett HR, Sampson L, Rimm EB, Willett WC. A prospective study of dietary fiber types and symptomatic diverticular disease in men. J Nutr. 1998;128:714-9.

26. Fuchs CS, Giovannucci EL, Colditz GA, et al. Dietary fiber and the risk of colorectal cancer and adenoma in women. N Engl J Med. 1999;340:169-76.

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