DFAC Pro Bodybuilder, PhD Nutritional Scientist – Andrew Chappell
Perhaps one of the most controversial subjects in the field of nutrition is the consumption of cereal grains. Despite more than 6 decades of research that demonstrates their numerous benefits, cereal grains have taken a bit of a ‘kicking’ from the fitness industry over the past 25 years, which has led to confusion and misunderstanding regarding whether we should be consuming them as part of a healthy diet. Therefore, in this article, we are going to look at some of the scientific evidence which demonstrates the many health benefits we gain from cereal grains and provide some evidence-based guidelines on how much we should be consuming.
The Backlash Against Wholegrains
The backlash against the consumption of wholegrains that has been apparent over the last couple of decades within the fitness industry and some elements of the media seems to be due to the rise of various dietary movements which have cast doubt on the role and importance of carbohydrate in our diet. It probably started with the Atkins diet, where all carbohydrates were bad for us, regardless of the sources. Then we had the Low Glycaemic Index (GI) movement. This suggested that carbohydrates were good for us, but we just had to avoid the fast-digesting ones. As nutritional scientist I always liked this approach, as it helped to move people away from processed grains onto wholegrains. However, it still suffered from anomalies. For example, ice cream and chocolate can be low GI foods but are not the healthiest sources of carbohydrate. After low GI, we had the rise of the Paleolithic or Paleo’ diet. Protein and fat from animal sources were once again key elements of this dietary regime. Carbohydrates were allowed, but only if you could forage them. So, things like berries and tubers (e.g., potatoes) were allowed but cereal grains were off the menu once again. The great irony of the Paleo diet, of course, is that modern civilisation itself was more or less created off the back of cereal grain cultivation 12,000 years ago and our ancestors have been eating grains for at least 50,000 years or more. As Neolithic hunter gathers were nomadic, their diets would have been different throughout the world and would consist of whatever food would have been available in their environment. Beef from feed lot cattle wouldn’t have been on the menu, and as to the health benefits of a Paelo diet, well the average life expectancy of a caeman was just 29 years. The latest dietary movement is gluten-free. This strictly excludes gluten, which is a mixture of proteins found in cereals such as wheat, barley, rye, and oats. Gluten-free has become popular since it was recognised that gluten can trigger serious health problems or other insensitivities in certain individuals, but does mean that we should all avoid gluten containing cereals?
Beneficial Effects Associated with Wholegrain Cereals
Diets rich in whole grain cereals have long been considered beneficial for good health (Bingham 1990). This is supported by data from various studies which suggest that the fibre component of wholegrain cereals may play an important role in the prevention of cardiovascular disease (CVD), type II diabetes mellitus (T2D), colorectal cancer (CRC), obesity and metabolic syndrome, (the medical term for a combination of diabetes, high blood pressure and obesity) (Bingham et al. 2003, Mozaffarian et al. 2003, He et al. 2010, Murphy et al. 2012, Buil- Cho et al. 2014).
These diseases place a great burden on society, not just in terms of ill-health and premature death, but also financially and socially. Consequently, their prevention and management are major public health issues. For example, CVD is currently the leading cause of mortality in West, while CRC currently ranks as one of the leading causes of cancer related deaths worldwide (Rosemond et al. 2008, Hotchkiss 2011 Siegel et al. 2014).
Wholegrain Cereals and Cardiovascular Disease
An analysis of much of the current evidence regarding fibre intake and cardiovascular disease (CVD) identified that for every 7 g / day of fibre consumed, CVD risk was reduced by 9 %; insoluble and soluble fibre, wholegrain and fruit fibre were all associated with a reduced risk of CVD (Threapleton et al. 2013). One of the problems of observational research is that it is often limited by confounding factors. These are factors, which, although not directly addressed in the study, can still affect its outcome thereby confusing the result. For example, people who consume diets rich in wholegrains, fruit and vegetables are typically more concerned about their health. They also tend to exercise more, consume less trans and saturated fats, maintain a healthier body weight, eat less processed meats, suffer from fewer co morbidities, drink less alcohol, smoke less and come from higher socioeconomic backgrounds. All of which can influence an individual’s risk of developing CVD. However, even when these factors have been allowed for, the beneficial effects of fibre still persist.
How do Wholegrain Cereals Protect against Cardiovascular Disease?
The common oat (Avena sativa) and barley groat (Hordeum vulgare) are a rich source of a dietary fibre referred to as β-glucan (BG) (Redaelli et al. 2013, Anderson et al. 2008).
Numerous mechanisms have been proposed by which BGs may reduce CVD risk. These can be classified as either direct or indirect. Direct mechanisms include a reduction in blood pressure, LDL cholesterol, inflammatory markers and the development of blood clots, while suggested indirect mechanisms include reducing obesity, satiety, fasting glucose levels or the interactions with healthy gut bacteria (Pereira and Pins 2000; Cummins and Tiwari 2012; Tang 2013).
One of the mechanisms by which wholegrains protect against CVD is through the binding of cholesterol by β-glucan (BG). It is widely acknowledged that BGs have LDL cholesterol lowering properties with several endorsed health claims including The European Food Safety Authority (EFSA) and the Food and Drug Administration (FDA). The EFSA claim acknowledges that “oat beta-glucan at doses of at least 3g/d have shown a statistically significant decrease in LDL-cholesterol concentrations, and that there was strong evidence supporting the biological plausibility of the effect”.
The mechanism by which BGs lower cholesterol is due to an increased excretion of bile acids and perhaps the inhibition of cholesterol synthesis. Human trials conducted by Kirby et al. (1981) and Anderson et al. (1984) established that subjects who consumed a diet high in oat bran increased bile acid excretion and significantly reduced LDL cholesterol. Subsequent in vitro trials have since identified that oat BGs are extremely viscous and capable of binding and trapping bile acids (Sayer et al. 2011; Kim & White 2012).
Figure 1 provides an explanation of the interaction between cholesterol and bile acid metabolism for the interested reader.
Wholegrains Dietary Fibre and Colorectal Cancer
The precise cause of colorectal cancer (CRC) is currently unknown. However, the consensus of scientific opinion suggests that diet may play a role in its development. Diets high in red and processed meat and low in dietary fibre from wholegrains increase colon cells’ exposure to carcinogenic compounds while reducing their exposure to potentially beneficial substances (Bingham 1990).
Prolonged exposure to these compounds over a lifetime may increase the risk of developing colonic polyps which can progress to cancerous tumours (Bingham 1990). Like cardiovascular disease, a lack of physical activity, obesity, smoking, type 2 diabetes, and alcohol consumption are also thought to contribute to the development of CRC (Huxley et al. 2013).
The gut microbiome, i.e., the microorganisms, bacteria, viruses, protozoa, and fungi present in the gut, is explicitly linked to diet and fibre intake. Specific microbes such as Faecalibacterium prausnitzii, which degrade fibre, may exude anti-inflammatory properties and short chain fatty acid metabolites that provide some protection against the disease (Sokol et al. 2008, Cao et al. 2014).
The European Prospective Investigation into Cancer and Nutrition (EPIC), the largest and most comprehensive observational study to date studying the effects of wholegrains on CRC risk, noted that those individuals who consumed a diet high in fibre had a reduced risk of developing large bowel cancer (Bingham et al. 2003). More specifically, those who consumed fibre from the highest quintile (32g per day) versus the lowest intake group (13g per day) were 0.58 (CI: 0.41 –to 0.85) less likely to develop large bowel cancer after a ten year follow up. In an update of the EPIC study, Murphy et al. (2012) identified that once confounders were adjusted for (i.e., smoking, physical activity, sex, age, BMI, education, hormone replacement therapy, and intake of red and processed meat) fibre was still associated with a reduced risk of colon cancer.
Few studies have been performed to assess if oat consumption rather than wholegrains per se may reduce cancer risk and overall mortality.
How do Wholegrain Cereals Protect against Colorectal Cancer?
Numerous mechanisms have been proposed by which wholegrains and dietary fibre are thought to play a role in the prevention of CRC. Indigestible insoluble carbohydrates are associated with laxation, increasing faecal wet weight and the speeding up of intestinal transit (Bingham 1990). This helps to reduce the exposure of the cells of the colon to potentially cancer producing compounds (Russell et al. 2011).
Wholegrains contain vitamins, minerals and phenolic compounds which can act as antioxidants in comparison to refined grains. Antioxidant compounds such as tocopherol and ferulic acid may inhibit the development of carcinogenic substances (Wattenberg 1985). Soluble fibre is fermented by the colonic microbiome and the short chain fatty acids produced decrease colonic pH, reducing the solubility of secondary bile acids. These secondary bile acids are believed to increase the risk of CRC (Ridon et al. 2006). Conversely, high protein, low carbohydrate, low fibre diets may be detrimental to colonic health as the exposure of cells of the colon to these carcinogenic compounds is increased (Russell et al. 2011). The point at which the consumption of carbohydrates or dietary fibre attenuates the influence of such a diet is currently unknown.
Wholegrains and Coeliac Disease
Coeliac disease is an auto immune disorder. It is not an allergy or food intolerance. This means that the body’s immune system mistakenly attacks and destroys healthy body tissue. In the case of Coeliac disease, it is caused by an adverse reaction to gluten. This results in damage to the lining of the gut which inhibits the body’s ability to absorb nutrients.
Coeliac disease can cause a range of symptoms, including diarrhoea, abdominal pain and bloating, and is associated with anaemia and osteoporosis. It is thought to effect around 1% of the population worldwide. There is currently no cure. Consequently, Coeliacs have to adhere to a strict gluten free diet, which can be extremely challenging as it requires the avoidance of foods containing wheat, barley or rye. Just how challenging this can be, becomes apparent when you consider that many everyday foods contain gluten, e.g., pasta, most types of bread, cakes, breakfast cereals, certain types of sauces and some ready meals. The incorporation of other wholegrains into the diet such as oats could be a viable alternative for Coeliacs. However, contamination can occur during harvesting and storage (Comino et al. 2011, Koerner et al. 2011, Richman 2012).
Beyond Coeliac disease, non – Coeliac gluten sensitivity may be far more prevalent within the Western population as a whole, but there are issues surrounding diagnosis, especially when self-diagnosis is concerned. Readers should be aware that there are several molecules similar to gluten (e.g., A1 and A2 beta – caseins found within milk), which cause similar symptoms such as abdominal pain, bloating and diarrhoea in certain individuals, making diagnosis difficult. Food intolerances affect between 6 and 8% of the Western population, and typically include fish, shellfish, nuts, milk and eggs. Therefore, those who suffer from conditions such as irritable bowel syndrome should exercise caution before eliminating whole grains from their diets, given the beneficial health effects associated with them. Readers of pervious articles will also be aware of the hygiene hypothesis (Shredded Beef – The Gut Microbiome: the next frontier) and the potential problems associated with limiting food groups and how this might affect immune system tolerance.
How Much Wholegrain Should We Consume?
Current recommendations from the Food Standards Agency’s ‘Eatwell Guide’ (Figure 2) suggest that our diets should contain approximately 30 % starch from wholegrain sources, with up to 60 % coming from fibrous cereals, fruit and vegetables. The recommendations provided by the Eat Well Guide can be easily incorporated into the athlete’s diet using a macronutrient split of carbohydrate 40 – 60 %, fat 20 – 30%, protein 10 – 20%. Wholegrains can also make a meaningful contribution towards our protein intake.
The FSA Eatwell Guide should be the basis of your dietary plan.
Conclusion
It seems that those who choose to follow fad diets and go against the grain – pun intended – choose to ignore the huge body of scientific evidence accumulated over the past 60 years, which demonstrates the considerable range of benefits a diet rich in wholegrain can provide. The question remains for the dieting athlete will you choose to wholegrain or not to wholegrain? That is the question.
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