Health Benefits of Fibre and Whole Grains

Reduces mortality risk

In both developed and developing countries, cardiovascular diseases (CVD) and cancer are major causes of mortality. A recent meta-analysis (meta-analysis provide the highest level of evidence) showed that a greater intake of both-total whole grains and specific whole-grain foods, was significantly associated with a lower risk of all-cause mortality, mortality from cardiovascular disease and risk of mortality from total cancers. An increase of 3 servings total whole grains was associated with a 17% lower risk of mortality from all causes, a 25% lower risk of mortality from CVD, and a 10% reduced risk of total-cancer mortality.¹

A study among a large US population (367,442 participants) followed through a period of 14 years, found that increased consumption of whole grains or cereal fibre was significantly associated with reduce risk of all-cause mortality and death from CVD, cancer, diabetes, respiratory disease, infections, and other causes. As compared with individuals with the lowest intake of whole grains, those with the highest intake had a 17% lower risk of all-cause mortality and 11 to 48% lower risk of disease-specific mortality. The study specifically examined the association of the whole grain component, namely dietary fibre intake on mortality. As compared with individuals with the lowest intake of cereal fibre, those in the highest intake group had a 19% lower risk of all-cause mortality and 15 to 34% lower risk of disease-specific mortality. The results suggested that the protective effects of whole grains may be due, at least in the main part, to its cereal fibre component.²

Wu H. et al (2015) in a study conducted with 2 large cohorts of US men and women suggested that higher whole grain consumption, with or without added bran or germ, can lower total and CVD mortality. In addition, the bran portion of the whole grain foods, as well as bran added to foods, was significantly associated with a lower CVD mortality. These findings were consistent with previous studies, Nurses’ Health Study (NHS) and Health Professionals Follow-Up study (HPFS) which also suggested that the bran component, but not germ, was significantly associated with reduced risk of diabetes, hypertension, Coronary Heart Disease (CHD) or CVD mortality among those with diabetes, after mutual adjustments of bran and germ.

The proposed mechanisms for these observed significant associations could be attributed to the nutrients and phytochemicals present in the bran portion of the whole grain.³ Bran is a rich source of fibre, B-group vitamins, vitamin E, magnesium and phytochemicals.

Reduces CVD risk

It was seen that consumption of whole grain diets lowers LDL cholesterol and total cholesterol in apparently healthy adults when compared to non-whole grain control diets. The effect varied with the type of whole grain consumed and was augmented by simultaneous calorie restriction.⁴ Earlier studies have shown that the use of statins was associated with healthier lipoprotein profiles when combined with higher whole grain intake (>16g) relative to lower whole grain intake.⁵

A 6 week intervention trial on healthy adults who were low whole grain consumers (not more than 1 serving of whole grain or whole grain products/day) showed that the consumption of whole grain products resulted in a significant reduction in total, LDL and non-HDL cholesterol.⁶ The lipid lowering effect in this study appeared to be due to the fibre content of the whole grain rather than due to beta glucan, an established cholesterol lowering agent found in oats.

In a study among overweight and obese adults it was seen that the improvement in diastolic blood pressure was >3 fold greater when they consumed a whole grain compared to a refined grain diets thus, lowering the risk for ischemic heart disease, stroke and other vascular diseases. It seems likely that diets enriched with whole grains may be linked to hypertension and CVD through an anti-inflammatory-related mechanism.⁷

Reduces risk for type 2 diabetes

A recent review of studies on the effect of whole grain consumption on metabolic parameters showed that the consumption of whole grain foods is able to improve acutely the postprandial glucose and insulin homeostasis compared to similar refined foods in healthy subjects.⁸

Chanson-Rolle et al report on an inverse relationship between whole grain consumption and the occurrence of type 2 diabetes up to an intake of whole grain ingredients of approximately 50 g/d.

Their model of data analysis suggests an overall absolute reduction of 0.3% in risk of type 2 diabetes for each 10g of whole grain consumed daily.⁹

Several plausible explanations have been put forth for the whole grain’s mechanism of action in potentially reducing the incidence of type 2 diabetes.

1. The insoluble fibre of whole grains would delay gastric emptying and decrease the rate of glucose absorption¹⁰
2. Chromium and Magnesium in whole grains help maintain normal glucose and insulin metabolism¹⁰
3.  Fermentation of fibre from whole grains in the large intestine produces short chain fatty acids (SCFAs) which improve glucose homeostasis and insulin sensitivity⁸
4.  Prevention of oxidative damage to pancreatic cells that produce insulin because of the antioxidants in whole grains⁸

Reduces risk for cancer

The protective role of whole grains against cancer risk is biologically plausible through several mechanism – lowering of adiposity, impact on sex hormone levels, protective effects of antioxidants and the health benefits of their dietary fibre content¹¹. However, there is scientific evidence for the protective effect of whole grain consumption against only certain types of cancer such as head and neck^11, renal cell carcinoma¹¹, breast cancer¹² and gastrointestinal cancers.^11,13 Further studies using newer biomarkers are required in order to draw broader and more firm conclusions.

Reduces risk for obesity

Whole grains promote satiety because of their fibre content, promote insulin function that reduces lipogenesis and fat storage and whole grain consumption is often accompanied by a healthier life style.¹⁰  While epidemiological studies have consistently found an inverse association between whole grain intake and Body Mass Index (BMI), adiposity and weight grain, the collective evidence based on clinical trials have not been conclusive. A recent study found newer mechanistic insights that explain the epidemiological findings namely positive effects on Resting Metabolic Rate (RMR), increased energy excretion in stools and improved post prandial glucose response when whole grains were substituted for refined grains in the diets of men and post-menopausal women aged 40-65 years.¹⁴ Studies also found small but measurable improvements in body fat distribution (decreased visceral fat) with an energy restricted diet based on whole grains.¹⁵

Whole grains and gut health

The fibre from whole grains such as wheat is mostly insoluble and is known to increase tool bulk, reduce transit time, and make fecal elimination easier and quicker. In this way, consumption of insoluble fibre rich whole grains can regulate bowel functions to promote the wellbeing of healthy people and can function as a remedy to alleviate several gastrointestinal diseases such as peptic ulcers and cancer.¹⁶

Whole grains also contain several microbiota accessible substrates such as resistant starch and non-starch polysaccharides such as β-glucan and arabinoxylans, that resist digestion in the upper gastrointestinal tract, making them an important fuel for the gut microbiota. Microbial metabolites such as SCFAs, phenolic metabolites and secondary bile acids play a key role in the intersection between diet and metabolic health by regulating appetite, energy homeostasis, lipid and glucose metabolism, inflammatory status, oxidant stress and activation of the immune system.¹⁷

Lawson C, et al.¹⁸, found significant improvements in digestive health, digestive comfort and general psychological wellbeing in habitual low-fibre consumers during the 2-week intervention period. The study participants were fed one bowl of ready-to-eat breakfast cereal containing at least 5.4 g fibre (of which 70% is wheat bran fibre) for 2 weeks duration. The physiological mechanism of action for the effect of wheat bran fibre on stool bulking and frequency is well-recognized, and relates to water absorption. The inability to digest cellulose and wheat bran fibre morphology. However, the mechanism of action for the secondary benefits to psychological wellbeing, reported in the study, has not been established adequately.¹⁸

Whole grains and fibre-related but not synonymous

Historically increasing whole grain intake was recommended because they make an important contribution to dietary fibre intake. However, it is important to note that whole grain does not always equate with high fibre¹⁹ and the focus in dietary guidance on increasing whole grains intake has not improved levels of fibre consumption.¹⁴ This is because different whole grains, such as wheat, barley, brown rice, and corn, vary widely in their fibre content.

Thus, public health messages may need to be modified to consider the source of the whole grain and the amount of fibre delivered by the whole-grain products. The American Heart Association (AHA) 2020 Goals classified grain products as whole grains if the ratio of total carbohydrate to fibre, each in grams per serving, was less than or equal to 10:1, which is approximately the ratio of carbohydrate to fibre in whole wheat flour.²⁰ A variety of grain food choices, including whole grains, enriched grains, bran-based grain foods, and other grain-based foods with fibre along with encouraging consumption of fruits, vegetables and legumes may help close the fibre gap.¹⁴ The USDA in their 2015-2020 dietary guidelines for Americans states that ,”those who consume all of their grains as whole grains should include some grains, such as some whole-grain ready-to-eat breakfast cereals, that have been fortified with folic acid”, keeping in mind the need for folic acid fortification especially for pregnant women.²¹

Recommendations for fibre and whole grains

Recommendations to increase consumptions of whole grain is global and guidelines are provided by Australia, Canada, Chile, China, Colombia, Denmark, France, Germany, Greece, Iceland, India, Latvia, Mexico, Oman, Singapore, Switzerland, the United Kingdom, and the United States.¹⁹ Specific recommendations, however, are either primary (that is specific for whole grain) or secondary (made in order to achieve another (primary) target, for example, dietary fibre intake).²² According to the 2015-2020 U.S guidelines, the recommended amount of grains in a 2000 kcal diet is 6oz equivalents (1oz equivalent is 1yg) and at least one half of this amount must be in the form of whole grain. The Dietary guidelines for Indians recommends increasing the consumption of whole grains, legumes, nuts, fruits and vegetables to maintain body weight and body composition.²³ The Indian Council for Medical Research (ICMR) recommends a daily intake of 40 g of total dietary fibre.²⁴

Wheat bran: the best fibre for promotion regularity

Wheat bran is a very rich source of insoluble fibre (arabinoxylans, cellulose and beta glucans) along with vitamins, minerals and antioxidants. It regulates gastro intestinal physiology and health by delaying gastric emptying and increasing fecal bulk. The effect of wheat bran on increasing fecel bulk is greater than other grains such as oats or vegetables and fruits.²⁵ Wheat bran is considered as the “gold standard” when it comes to fecal bulking and promoting regularity since no other fibre or laxative has been shown to be as effective.²⁶

Consumption of wheat bran has protective effect against diseases such as cardiovascular, obesity, and gastrointestinal disorders such as constipation, diverticulosis and colorectal cancer.²⁵

European Food Safety Authority (EFSA) has an approved health claim on wheat bran which states – “Wheat bran fibre contributes to an increase in faecal bulk and reduction in intestinal transit time”.²⁷