Why do many high-fiber foods still have a high GI value ?

foods high in fiber
high in fiber foods

What is Glycemic Index ?

Carbohydrate is an essential part of our diets, but not all carbohydrate foods are equal. The glycemic index (GI) was first developed by Jenkins and colleagues 2) and the Glycemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels 3). Carbohydrates with a low GI value (55 or less) are more slowly digested, absorbed and metabolised and cause a lower and slower rise in blood glucose and, therefore usually, insulin levels.

Research shows that both the amount and the type of carbohydrate in food affect blood glucose levels. Studies also show that the total amount of carbohydrate in food, in general, is a stronger predictor of blood glucose response than the GI.

The glycemic index or GI ranks carbohydrates according to their effect on blood glucose levels. The lower the GI, the slower the rise in blood glucose levels will be when the food is consumed. The effect may differ from person to person.

The GI index runs from 0–100 and usually uses glucose, which has a GI of 100, as the reference. Slowly absorbed carbohydrates have a low GI rating (55 or below), and include most fruits and vegetables, milk, some wholegrain cereals and bread, pulses and basmati rice. GI numbers are to be used as a guide only as individual foods do not have the same response in all people with diabetes.

  • Low GI foods are foods with a GI less than 55.
  • Intermediate GI foods are foods with a GI between 55 and 70.
  • High GI foods are foods with a GI greater than 70.

Below are examples of foods based on their GI.

Low GI Foods (55 or less)

  • 100% stone-ground whole wheat or pumpernickel bread
  • Oatmeal (rolled or steel-cut), oat bran, muesli
  • Pasta, converted rice, barley, bulgar
  • Sweet potato, corn, yam, lima/butter beans, peas, legumes and lentils
  • Most fruits, non-starchy vegetables and carrots

Not all low-GI foods are healthy choices – chocolate, for example, has a low-GI because of its fat content, which slows down the absorption of carbohydrate.

Medium GI (56-69)

  • Whole wheat, rye and pita bread
  • Quick oats
  • Brown, wild or basmati rice, couscous

High GI (70 or more)

  • White bread or bagel
  • Corn flakes, puffed rice, bran flakes, instant oatmeal
  • Shortgrain white rice, rice pasta, macaroni and cheese from mix
  • Russet potato, pumpkin
  • Pretzels, rice cakes, popcorn, saltine crackers
  • melons and pineapple

Table 1. The average GI of 62 common foods derived from multiple studies by different laboratories 4)

High-carbohydrate foodsBreakfast cerealsFruit and fruit productsVegetables
White wheat bread*75 ± 2Cornflakes81 ± 6Apple, raw36 ± 2Potato, boiled78 ± 4
Whole wheat/whole meal bread74 ± 2Wheat flake biscuits69 ± 2Orange, raw43 ± 3Potato, instant mash87 ± 3
Specialty grain bread53 ± 2Porridge, rolled oats55 ± 2Banana, raw51 ± 3Potato, french fries63 ± 5
Unleavened wheat bread70 ± 5Instant oat porridge79 ± 3Pineapple, raw59 ± 8Carrots, boiled39 ± 4
Wheat roti62 ± 3Rice porridge/congee78 ± 9Mango, raw51 ± 5Sweet potato, boiled63 ± 6
Chapatti52 ± 4Millet porridge67 ± 5Watermelon, raw76 ± 4Pumpkin, boiled64 ± 7
Corn tortilla46 ± 4Muesli57 ± 2Dates, raw42 ± 4Plantain/green banana55 ± 6
White rice, boiled*73 ± 4Peaches, canned43 ± 5Taro, boiled53 ± 2
Brown rice, boiled68 ± 4Strawberry jam/jelly49 ± 3Vegetable soup48 ± 5
Barley28 ± 2Apple juice41 ± 2
Sweet corn52 ± 5Orange juice50 ± 2
Spaghetti, white49 ± 2
Spaghetti, whole meal48 ± 5
Rice noodles53 ± 7
Udon noodles55 ± 7
Couscous65 ± 4
Dairy products and alternativesLegumesSnack productsSugars
Milk, full fat39 ± 3Chickpeas28 ± 9Chocolate40 ± 3Fructose15 ± 4
Milk, skim37 ± 4Kidney beans24 ± 4Popcorn65 ± 5Sucrose65 ± 4
Ice cream51 ± 3Lentils32 ± 5Potato crisps56 ± 3Glucose103 ± 3
Yogurt, fruit41 ± 2Soya beans16 ± 1Soft drink/soda59 ± 3Honey61 ± 3
Soy milk34 ± 4Rice crackers/crisps87 ± 2
Rice milk86 ± 7
*Low-GI varieties were also identified.
Average of all available data.

Note: The GI should not be used in isolation; the energy density and macronutrient profile of foods should also be considered 5).

The amount of carbohydrate you eat has a bigger effect on blood glucose levels than GI alone.

The GI value relates to the food eaten on its own and in practice we usually eat foods in combination as meals. Bread, for example is usually eaten with butter or margarine, and potatoes could be eaten with meat and vegetables. Therefore relying solely on the glycemic index of foods could result in eating unbalanced and un-healthy diets high in fat, salt and saturated fats.

An additional problem is that GI compares the glycaemic effect of an amount of food containing 50g of carbohydrate, but in real life we eat different amounts of food containing different amounts of carbohydrate.

The recommendation is to eat more low and intermediate GI foods, not to exclude high GI foods. By choosing the low glycaemic index foods and thus the minimally processed foods, people can lose more weight, feel fuller longer, and remain healthier.

The GI is only a small part of the healthy eating plan for people with diabetes. For people with diabetes, meal planning with the GI involves choosing foods that have a low or medium GI. If eating a food with a high GI, you can combine it with low GI foods to help balance the meal.

Carbohydrates are an essential nutrient. You need carbs as they break down into glucose in your body providing the

– main fuel for your brains and nervous systems,
– preferred source of fuel for most organs and your muscles during exercise.

Consuming good quality carbohydrates aka Low GI ones help to facilitate the management of diabetes, weight loss and weight loss management and reducing the risk of developing type 2 diabetes, diabetes complications and other chronic lifestyle diseases.  In fact a low GI diet provides health benefits for everybody across all stages of life.

What can affect the Glycemic Index of Foods

Fat and fiber tend to lower the GI of a food. As a general rule, the more cooked or processed a food, the higher the GI; however, this is not always true.

Below are a few specific examples of other factors that can affect the GI of a food:

  • Ripeness and storage time — the more ripe a fruit or vegetable is, the higher the GI.
  • Processing — juice has a higher GI than whole fruit; mashed potato has a higher GI than a whole baked potato, stone ground whole wheat bread has a lower GI than whole wheat bread.
  • Cooking methods — how long a food is cooked (al dente pasta has a lower GI than soft-cooked pasta), frying, boiling and baking.
  • Fibre: wholegrains and high-fibre foods act as a physical barrier that slows down the absorption of carbohydrate. This is not the same as ‘wholemeal’, where, even though the whole of the grain is included, it has been ground up instead of left whole. For example, some mixed grain breads that include wholegrains have a lower GI than wholemeal or white bread.
  • Fat lowers the GI of a food. For example, chocolate has a medium GI because of it’s fat content, and crisps will actually have a lower GI than potatoes cooked without fat.
  • Protein lowers the GI of food. Milk and other diary products have a low GI because they are high in protein and contain fat.
  • Variety — converted long-grain white rice has a lower GI than brown rice but short-grain white rice has a higher GI than brown rice.

Starchy foods with a low GI are digested and absorbed more slowly than foods with a high GI. Some factors that influence glycemic properties of foods are listed in Table 2.

TABLE 2 Food factors influencing glycemic responses

Amount of carbohydrate

Nature of the monosaccharide components
Glucose
Fructose
Galactose
Nature of the starch
Amylose
Amylopectin
Starch-nutrient interaction
Resistant starch
Cooking/food processing
Degree of starch gelatinization
Particle size
Food form
Cellular structure
Other food components
Fat and protein
Dietary fibre
Antinutrients
Organic acids

(Source 6))

What are High in Fiber Foods

Dietary fiber, also known as roughage or bulk, is the part of a plant that the body doesn’t absorb during digestion. Fibre is the part of food that is not digested in the small intestine. Dietary fibre moves largely unchanged into the large intestine or colon where it is fermented by friendly bacteria that live there. The scientific community define dietary fibre as intrinsic plant cell wall polysaccharides of vegetables, fruits and whole-grains, the health benefits of which have been clearly established, rather than synthetic, isolated or purified oligosaccharides and polysaccharides with diverse, and in some cases unique, physiological effects 7). The American Association of Cereal Chemists 8), define “dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plants substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation” 9). The World Health Organization (WHO) and Food and Agriculture Organization (FAO) agree with the American Association of Cereal Chemists International (AACCI) definition but with a slight variation. They state “Dietary fibre means carbohydrate polymers1 with ten or more monomeric units, which are not hydrolysed by the endogenous enzymes in the small intestine of humans and belong to the following categories: that dietary fiber is a polysaccharide with ten or more monomeric units which is not hydrolyzed by endogenous hormones in the small intestine” 10).

Generally speaking, dietary fiber is the edible parts of plants or similar carbohydrates, that are resistant to digestion and absorption in the small intestine. Dietary fiber can be separated into many different fractions. Recent research has begun to isolate these components and determine if increasing their levels in a diet is beneficial to human health. These fractions include arabinoxylan, inulin, pectin, bran, cellulose, β-glucan and resistant starch. The study of these components may give us a better understanding of how and why dietary fiber may decrease the risk for certain diseases 11).

It was considered that the recommended intakes of fruit, vegetables, legumes and regular consumption of whole-grain cereals from Dietary Guidelines for Americans would provide adequate intakes of total dietary fibre 12). Low intakes of dietary fiber are due to low intakes of vegetables, fruits, and whole grains 13).

Dietary fiber and whole grains contain a unique blend of bioactive components including resistant starches, vitamins, minerals, phytochemicals and antioxidants. As a result, research regarding their potential health benefits has received considerable attention in the last several decades. Epidemiological and clinical studies demonstrate that consumption of dietary fiber and whole grain intake is inversely related to obesity 14), type two diabetes 15), cancer 16) and cardiovascular disease 17).

  • Eating fibre and wholegrain foods is linked to a lower risk of obesity, type 2 diabetes and heart disease, and may also reduce the risk of bowel cancer.
  • Eating high fibre foods can also help prevent constipation – this in turn can help to prevent haemorrhoids.
  • Because high fibre foods are filling they may also make it easier to stay at a healthy weight.
  • Foods high in fibre are generally good sources of vitamins and minerals, as well as other important nutrients.

The Food and Drug Administration (FDA) has approved two health claims for dietary fiber. The first claim states that, along with a decreased consumption of fats (<30% of calories), an increased consumption of dietary fiber from fruits, vegetables and whole grains may reduce some types of cancer 18). “Increased consumption” is defined as six or more one ounce equivalents, with three ounces derived from whole grains. A one ounce equivalent would be consistent with one slice of bread, ½ cup oatmeal or rice, or five to seven crackers. The second FDA claim supporting health benefits of dietary fiber states that diets low in saturated fat (<10% of calories) and cholesterol and high in fruits, vegetables and whole grain, have a decreased risk of leading to coronary heart disease 19). For most, an increased consumption of dietary fiber is considered to be approximately 25 to 35 g/d, of which 6 g are soluble fiber.

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 20). 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 21). A related Harvard study of female nurses produced quite similar findings 22).

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 23), 24).

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 25), 26), 27). 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 28) and the European Prospective Investigation Into Cancer and Nutrition–Potsdam, have shown similar results.

Recent studies support this inverse relationship between dietary fiber and the development of several types of cancers including colorectal, small intestine, oral, larynx and breast 29), 30), 31). Although most studies agree with these findings, the mechanisms responsible are still unclear. Several modes of actions however have been proposed. First, dietary fiber resists digestion in the small intestine, thereby allowing it to enter the large intestine where it is fermented to produce short chain fatty acids, which have anti-carcinogenic properties 32). Second, since dietary fiber increases fecal bulking and viscosity, there is less contact time between potential carcinogens and mucosal cells. Third, dietary fiber increases the binding between bile acids and carcinogens. Fourth, increased intake of dietary fiber yield increased levels of antioxidants. Fifth, dietary fiber may increase the amount of estrogen excreted in the feces due to an inhibition of estrogen absorption in the intestines 33). Obviously, many studies support the inverse relationship of dietary fiber and the risk for coronary heart disease. However, more recent studies found interesting data illustrating that for every 10 g of additional fiber added to a diet the mortality risk of coronary heart disease decreased by 17–35% 34), 35). Risk factors for CHD include hypercholesterolemia, hypertension, obesity and type two diabetes. It is speculated that the control and treatment of these risk factors underlie the mechanisms behind dietary fiber and coronary heart disease prevention. First, soluble fibers have been shown to increase the rate of bile excretion therefore reducing serum total and LDL “bad” cholesterol 36). Second, short chain fatty acid production, specifically propionate, has been shown to inhibit cholesterol synthesis 37). Third, dietary fiber demonstrates the ability to regulate energy intake thus enhancing weight loss or maintenance of a healthier body weight. Fourth, either through glycemic control or reduced energy intake, dietary fiber has been shown to lower the risk for type two diabetes. Fifth, dietary fiber has been shown to decrease pro-inflammatory cytokines such as interleukin-18 which may have an effect on plaque stability 38). Sixth, increasing dietary fiber intake has been show to decrease circulating levels of C-Reactive protein, a marker of inflammation and a predictor for coronary heart disease 39).

Fiber is found only in plant foods like whole-grain breads and cereals, beans and peas and other vegetables and fruits. Because there are different types of fiber in foods, choose a variety of foods daily. Eating a variety of fiber-containing plant foods is important for proper bowel function, can reduce symptoms of chronic constipation, diverticular disease, and hemorrhoids, and may lower the risk for heart disease and some cancers. However, some of the health benefits associated with a high-fiber diet may come from other components present in these foods, not just from fiber itself. For this reason, fiber is best obtained from foods rather than supplements.

Dietary fiber can be separated into many different fractions. Recent research has begun to isolate these components and determine if increasing their levels in a diet is beneficial to human health. These fractions include arabinoxylan, inulin, pectin, bran, cellulose, β-glucan and resistant starch. The study of these components may give us a better understanding of how and why dietary fiber may decrease the risk for certain diseases 40).

Types of Dietary Fiber

Many people think that if a food is rich in fibre it will automatically be low GI, but that’s not the case at all. To begin with, there’s not just one type of dietary fibre – there are many different kinds and is typically divided into three main categories: soluble fibre, insoluble fibre and resistant starch. In addition, processing makes a big difference to fibre’s digestibility.

Table 3. Components of dietary fiber according to the American Association of Cereal Chemists 41).

Non Starch Polysaccharides and Oligosaccharides
Cellulose
Hemicellulose
Arabinoxylans
Arabinogalactans
Polyfructoses
Inulin
Oligofructans
Galacto-oligosaccharides
Gums
Mucilages
Pectins
Analagous carbohydrates
Indigestible dextrins
Resistant maltodextrins
Resistant potato dextrins
Synthesized carbohydrates compounds
Polydextrose
Methyl cellulose
Hydroxypropylmethyl cellulose
Resistant starches
Lignin substances associated with the NSP and lignin complex
Waxes
Phytate
Cutin
Saponins
Suberin
Tannin

(Source: American Association of Cereal Chemists 42)).

There are 3 types of fibre 43) – soluble fibre, insoluble fibre and resistant starch – and they are found in different foods. Because they have different health benefits, it’s important to include all 3 in your diet.

1)Soluble fiber. This type of fiber dissolves in water to form a gel-like material. It’s found in oats, legumes (split peas, dried beans such as red kidney beans, baked beans and lentils), nuts, seeds, apples, citrus fruits, carrots, barley, psyllium, vegetables and seeds. Foods high in these fibres can help you feel full. Some soluble fibres in fruit, oats, barley and psyllium can reduce the amount of cholesterol absorbed from the small intestine. This can help to lower blood cholesterol levels, although it is more important to eat a diet low in saturated fat. They also help reduce constipation by speeding up the time it takes for faeces to pass through the body. Soluble fibre can also help stabilise blood glucose levels in people with diabetes.

Soluble dietary fiber has been associated with lower postprandial glucose levels and increased insulin sensitivity in diabetic and healthy subjects; these effects were generally attributed to the viscous and/or gelling properties of soluble fiber 44). Soluble dietary fiber exerts physiological effects on the stomach and small intestine that modulate postprandial glycemic responses, including delaying gastric emptying 45), which accounts for ~35% of the variance in peak glucose concentrations following the ingestion of oral glucose 46), modulating gastrointestinal myoelectrical activity and delaying small bowel transit 47), 48), reducing glucose diffusion through the unstirred water layer 49), and reducing the accessibility of α-amylase to its substrates due to the increased viscosity of gut contents 50). Notably, the increased viscosity and gel-forming properties of soluble fiber are predominantly responsible for its glycemic effect, since the hypoglycemic effect can be reversed by the hydrolysis of guar gum or following ultra-high heating and homogenization 51). In addition, the intestinal absorption of carbohydrates was prolonged by soluble dietary fiber, which was partially due to altered incretin levels, including increased glucagon-like peptide 1 levels 52). In experimental clamp studies, soluble dietary fiber also influenced peripheral glucose uptake mechanisms 53), 54), including increasing skeletal muscle expression of the insulin-responsive glucose transporter type 4 (GLUT-4), which enhances skeletal muscle uptake, augments insulin sensitivity and normalizes blood glucose 55). In humans, various fatty acids stimulate the expression of peroxisome proliferator-activated receptor-γ, which increases adipocyte GLUT-4 levels 56).

A more recent study to find out the health benefits of soluble fiber on type 2 diabetes 57). A total of 117 patients with type 2 diabetes between the ages of 40 and 70 were assessed. Patients were randomly assigned to one of two groups, and administered extra soluble dietary fiber (10 or 20 g/day), or to a control group (0 g/day) for one month. The 20 g/day soluble dietary fiber group exhibited significantly improved fasting blood glucose and low-density (LDL) lipoprotein “bad cholesterol” levels, as well as a significantly improved insulin resistance index. In addition, 10 and 20 g/day soluble dietary fiber significantly improved the waist and hip circumferences and levels of triglycerides and apolipoprotein A. The results of the present study suggested that increased and regular consumption of soluble dietary fiber led to significant improvements in blood glucose levels, insulin resistance and metabolic profiles 58).

2) Insoluble fiber. Insoluble fibre is a type of fibre that doesn’t dissolve in water. It’s found in high fibre breads and cereals, the outer skins of fruit and vegetables, and in nuts and seeds. Because insoluble fibre absorbs water, it helps to soften the contents of the bowel, contributing to keep the bowels regular. This type of fiber promotes the movement of material through your digestive system and increases stool bulk, so it can be of benefit to those who struggle with constipation or irregular stools. Whole-wheat flour, wheat bran, nuts, beans and vegetables, such as cauliflower, green beans and potatoes, are good sources of insoluble fiber.

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 59).

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 60).

3) Resistant starch. While most starch is digested in the upper part of the gut, resistant starch resists digestion in the small intestine and so goes all the way to the large intestine. Once in the large intestine, friendly bacteria ferment resistant starch. This process produces substances (gasses) that help to keep the lining of the bowel healthy. Resistant starch is starch that is not easily absorbed. Different ways of cooking can create different amounts of resistant starch. For example, resistant starch is found in slightly undercooked (‘al dente’) pasta, cooked but cooled potatoes (including potato salad), cooked and cooled grains like rice, quinoa, barley and buckwheat, under-ripe bananas, beans, lentils and a product called Hi-maize used in some breads and breakfast cereals. Freekeh, a Middle Eastern grain available in some supermarkets, is another good source. In general, foods that are less highly processed contain more resistant starch. An important benefit of resistant starch is that it ferments, which produces substances that help to keep the lining of the bowel healthy.

How much fiber do you need ?

American women are recommended to eat 25g of dietary fibre per day and men 30g per day. Most Americans eat less than this. Getting sufficient fibre isn’t just about adding unprocessed wheat bran to breakfast cereal – it’s important to include different types of fibre from a variety of plant foods.

To get enough fibre every day, the U.S. Department of Health and Human Services 61) recommends that an individual eats:

  • at least 4 serves of wholegrain or wholemeal foods every day (or ensure about half of your daily serves of breads and cereals are wholegrain or wholemeal varieties)
  • at least 2 serves of fruit daily
  • 5 serves of vegetables daily including legumes (also known as ‘pulses’)
  • wholefoods rather than dietary fibre supplements as the benefits of fibre from food may be from the combination of nutrients in food working together.

Table 4. Below is an example of how an adult may meet their daily dietary fibre requirements:

FoodFibre Content
3/4 cup whole grain breakfast cereal4.5g
2 slices wholemeal bread4.5g
1 apple (with skin) and 1 orange5.5g
2 cups mixed raw vegetables10g
1/4 cup legumes eg. baked beans3g
Total27.5g
(Source 62)).
daily fiber requirement

Note: Daily recommended fiber intake are highlighted in pink. (Source: U.S. Department of Health and Human Services and U.S. Department of Agriculture: Dietary Guidelines for Americans 2015-2020 63)).

Tips for including more fibre in your diet

  • Know which packaged foods are high in fibre by reading the nutrient panel on the pack. A food with at least 4g fibre per serve is a good source; food with at least 7g fibre per serve is an excellent source.
  • Enjoy wholegrain, wholemeal or mixed grain toast instead of white.
  • Use wholegrain pasta instead of white pasta.
  • Try brown rice or quinoa instead of white rice with casseroles or curries.
  • Use wholemeal flour to thicken sauces, gravies and stews.
  • Try wholegrain or wholemeal crisp breads with toppings such as creamed corn or salsa dip.

Foods High in Fiber

It is now known that diets rich in fiber are generally low in saturated fat and many national authorities including the U.S. Department of Health and Human Services and U.S. Department of Agriculture in their Dietary Guidelines for Americans 64) recommended you eat whole grains, vegetables, and fruits as parts of healthy diet and greater consumption of grain products to control weight 65). Whole grains may have beneficial effects on weight control through promoting satiety 66), 67), 68). Healthy eating patterns include whole grains and limit the intake of refined grains and products made with refined grains, especially those high in saturated fats, added sugars, and/or sodium, such as cookies, cakes, and some snack foods. The grains food group includes grains as single foods (e.g., rice, oatmeal, and popcorn), as well as products that include grains as an ingredient (e.g., breads, cereals,
crackers, and pasta). Grains are either whole or refined. Whole grains (e.g., brown rice, quinoa, and oats) contain the entire kernel, including the endosperm, bran, and germ. Refined grains differ from whole grains in that the grains have been processed to remove the bran and germ, which removes dietary fiber, iron, and other nutrients. The recommended amount of grains in the Healthy U.S.-Style Eating Pattern at the 2,000-calorie level is 6 ounce-equivalents per day. At least half of this amount should be whole grains 69). The intake of whole grains may also slow starch digestion or absorption, which leads to relatively lower insulin and glucose responses that favor the oxidation and lipolysis of fat rather than its storage 70), 71), 72). They are emphasized in the Dietary Guidelines for Americans because they provide vitamins, minerals, complex carbohydrates (starch and dietary fiber), and other substances that are important for good health. They are also generally low in fat, depending on how they are prepared and what is added to them at the table.  However, most grain products consumed in the United States are highly refined 73), 74). Refined-grain products have a higher starch content but a lower fiber content (ie, greater energy density) than do whole grains. Concentrations of vitamins, minerals, essential fatty acids, and phytochemicals that are important in carbohydrate metabolism are also lower in refined grains 75).

Indirect evidence from both epidemiologic and short-term experimental studies suggests a beneficial role of a high-fiber diet in weight control 76), 77), 78). Most Americans of all ages eat fewer than the recommended number of servings of grain products, vegetables, and fruits, even though consumption of these foods is associated with a substantially lower risk for many chronic diseases, including certain types of cancer 79).

Dietary fiber is widely prescribed 80), either alone or in combination with lipid-lowering therapies, to reduce cholesterol levels 81). The exact mechanism by which soluble fiber lowers serum levels of low-density lipoprotein (LDL) and cholesterol is not completely understood; however, it has been suggested that soluble fiber may interfere with lipid and/or bile acid metabolism 82). A reasonable increase in dietary fiber intake (20–35 g/day) is recommended by the American Diabetes Association based on the effects of soluble fiber on plasma levels of cholesterol 83). Recent epidemiological findings have suggested that there is an association between high dietary fiber intake and a reduced risk of developing diabetes and coronary heart disease 84), 85). In particular, soluble dietary fiber has been shown to reduce insulin resistance in female non-diabetic patients 86).

A more recent study to find out the health benefits of soluble fiber on type 2 diabetes 87). A total of 117 patients with type 2 diabetes between the ages of 40 and 70 were assessed. Patients were randomly assigned to one of two groups, and administered extra soluble dietary fiber (10 or 20 g/day), or to a control group (0 g/day) for one month. The 20 g/day soluble dietary fiber group exhibited significantly improved fasting blood glucose and low-density (LDL) lipoprotein “bad cholesterol” levels, as well as a significantly improved insulin resistance index. In addition, 10 and 20 g/day soluble dietary fiber significantly improved the waist and hip circumferences and levels of triglycerides and apolipoprotein A. The results of the present study suggested that increased and regular consumption of soluble dietary fiber led to significant improvements in blood glucose levels, insulin resistance and metabolic profiles 88).

Whole grains

Whole grains are an important source of dietary fiber and other nutrients 89). Whole grains are a source of nutrients, such as dietary fiber, iron, zinc, manganese, folate, magnesium, copper, thiamin, niacin, vitamin B6, phosphorus, selenium, riboflavin, and vitamin A 90) 91). Healthful diets rich in dietary fiber have been shown to have a number of beneficial effects, including decreasing risk of coronary heart disease and promoting regularity. Some examples of whole-grain products could include whole wheat bread, whole wheat cereal, and brown rice.

Whole grains are just that whole. Nothing has been added or taken away by processing. When whole grains are processed, some of the dietary fiber and other important nutrients are removed. A processed grain is called a refined grain. Most refined grains are enriched, a process that adds back iron and four B vitamins (thiamin, riboflavin, niacin, and folic acid) 92). Because of this process, the term “enriched grains” is often used to describe these refined grains. These are called enriched grains. White rice and white bread are enriched grain products. If you read the packaging for these foods, you will see the word “enriched.” Some enriched grain foods have extra nutrients added. These are called fortified grains. Many ready-to-eat cereals are fortified. At least half of the grains you eat should be whole-grain; other grains should be fortified or enriched 93).

The following are some examples of how whole grains could be listed:

  • whole wheat
  • wild rice
  • quinoa
  • brown rice
  • whole oats/oatmeal
  • buckwheat
  • sorghum
  • whole rye
  • whole-grain corn
  • bulgur (cracked wheat)
  • popcorn
  • whole-grain barley
  • millet
  • triticale
foods that are high in fiberhigh fiber foods listhigh fiber foods list high fiber foods list high fiber foods listhigh fiber foods list

Note: Foods fiber content are highlighted in pink. (Source: U.S. Department of Health and Human Services and U.S. Department of Agriculture: Dietary Guidelines for Americans 2015-2020 94)).

References   [ + ]

Sign up to get VIP access to eBooks and valuable health tips for FREE!>>> Subcribe now