Sunday, January 22, 2012

DGA 2011 - Grains

2.3 Grain (cereal) foods (mostly wholegrain)


Key nutrients in wholegrain foods include carbohydrate (starch), protein, dietary fibre, B group vitamins, vitamin E, iron, zinc, magnesium and phosphorus. Other protective components are fermentable carbohydrates, oligosaccharides, flavonoids, phenolics, phytoestrogens, lignans, protease inhibitors, saponins and selenium [36, 37].

Wholegrains aren’t as nutrient dense as the guidelines make them out to be.  As a group they aren’t a great source of B vitamins, having no B12, inadequate riboflavin and folate [1], the biotin in grains and their form of vitamin B6, pyridoxine glucoside, have poor bioavailability relative to animal-based foods [2].  Pellagra is caused by niacin deficiency and associated with high intakes of corn, yet corn has sufficient niacin on paper, which suggests the niacin in corn at least has poor bioavailability, perhaps from dietary lectins in corn damaging the intestinal microvilli [2].  Wholegrains generally have insufficient vitamin E and all have insufficient selenium except for wheat and rye (which also depends on the soil) [1].  The minerals that wholegrains appear to be rich in on paper (iron, zinc, magnesium and phosphorus) have their bioavailability reduced by high concentrations of phytic acid [3] [4] [5].

The recommended amount of protein to reduce chronic disease risk is 15-25% of total calories [6].  Wholegrains are very average sources of protein.  They are roughly 15% protein by calories [1] (the lower limit) and they have many factors which compromise the protein quality.  Grains have an unbalanced amino acid profile being low in the essential amino acid lysine and high in proline and glutamine.  There are a family of storage proteins in grains called prolamines (gliadin, zein, etc), named because they are rich in proline and glutamine.  Prolamines are difficult to digest and therefore can cause allergic reactions in people with a genetic predisposition, intestinal permeability and a poorly regulated immune system.

Speaking of intestinal permeability, gluten is a peptide in gliadin and increases intestinal permeability by stimulating the release of zonulin (which loosens the tight junctions) in both coeliacs and non-coeliacs [7] [8].  Intestinal permeability causes poor nutrient absorption, inflammation and can lead to autoimmune disease [2] [7] [8].  Saponins increase intestinal permeability [9] and tend to be found in the pseudo-grains like chia, amaranth, quinoa and buckwheat.  Another thing that increases intestinal permeability is dietary lectins, especially those in wheat and corn.  Lectins increase intestinal permeability by damaging villi and shortening microvilli.  Lectins can over arouse the immune system, setting the scene for autoimmunity [10].  Wheat germ agglutinin and corn lectin can also transport bacteria throughout the bloodstream as they can bind to glucosamine, a glycoprotein found in enterocytes and bacterial cell walls [11].  WGA has a binding affinity for insulin receptors, which can lead to excessive insulin release and an increased risk of cancer [12].

Finally these difficult to digest and problematic prolamines and lectins are made even more resistant to the digestive process by protease inhibitors and phytic acid by blocking the action of the digestive enzymes protease, pepsin and trypsin [2].  With the protein in wholegrains being so poorly bioavailable and such a poor quality it is likely people would be compelled to overeat calories and gain some weight on the grain-based western diet in order to satisfy protein needs [13].  Wholegrains are not a good source of protein.

The oligosaccharides likely refers to the inulin (a fructan) in wheat.  Inulin is a poorly absorbed sugar that can be fermented by pathogenic bacteria, leading to gut dysbiosis and small intestinal bacterial overgrowth [14].  This too can lead to intestinal permeability and release endotoxins such as lipopolysaccharides into the bloodstream [15].  Lignans are phytoestrogens and the subject of phytoestrogens is covered in response to the previous section, although the quantities of lignans in grains shouldn’t be as bad as the isoflavones in soy.

Research and Recommendations

Research supporting wholegrain consumption may be misleading.  Clinical trials may include wholegrains as part of an overall diet and lifestyle intervention or by comparing a group eating wholegrains to a group eating refined grains.  It’s not surprising that the wholegrain group has better health outcomes, there is little doubt that wholegrains are healthier than refined grains, but unfortunately all these studies show is that either the overall intervention works or that wholegrains are healthier than refined grains.  Epidemiological studies may find similar outcomes, that people who eat wholegrains tend to be healthier, which is what one would expect from the clinical trials when they replaced refined grains with wholegrains.  Epidemiological studies may also be confounded by health conscious people being more likely to eat wholegrains in response to previous dietary guidelines.  The question though is not whether wholegrains are healthier than refined grains, but instead are wholegrains healthy in their own right?  Does adding of wholegrains to our diets improve our health?  Or are they cheap source of calories, a mediocre food, potentially problematic and something we may as well be without?  These are the questions that need to be answered.

Even if those questions have not been answered, the dietary guidelines should at least be consistent with the conclusions of the studies it cites.  The dietary guidelines recommend six servings of mostly wholegrain cereals per day, yet this is more than what the studies suggest is ideal.

“The protective effect was noted with between 1–3 serves per day of wholegrain foods (predominantly oats).”

“The evidence supports three serves per day of wholegrain foods conferring between 21-42% reduction in risk of type 2 diabetes.”

“There is evidence of a probable association between consumption of 3–5 serves per day of grain (cereal) foods (mainly wholegrain) and reduced risk of weight gain”

“There is recent evidence suggesting that consumption of 1-3 serves of cereals high in dietary fibre per day is associated with reduced risk of colorectal cancer in adults”

Above are the studies on which the dietary guidelines have found support for wholegrain consumption.  The number of servings are 1-3, 3, 3-5 and 1-3.  That averages out at roughly 3 serves per day.  However, the dietary guidelines recommend 6 serves of grains per day, which is above all the ranges and double the average that find a reduced risk of disease.  If the dietary guidelines wish to be consistent with the research it cites, the recommended number of serves of grains per day should be 3 serves of wholegrains and no serves of refined grains.

The guidelines are currently recommending six serves, but to make most of them wholegrain.  ‘Most’ does not mean ‘all’, in other words refined grains are getting a free pass, one could even say that refined grains are being recommended in these guidelines, alongside and equal to proper food like fruit and meat.  None of the research cited found any evidence of refined grains improving health or suggested their consumption.  Refined grains are low in almost all micronutrients, except the ones they may be fortified with.  If much of the nutrient density comes from fortification how is that different from eating junk food then taking a supplement.  The dietary guidelines are supposed to be recommending consumption of whole foods.  I don’t consider refined or enriched grains a whole food.

“these Guidelines make recommendations based only on whole foods”

Not only do the dietary guidelines give refined grains a free pass, but they may also end up in wholegrain foods.  The definition of wholegrain foods is for it to contain only 25% wholegrain.  That means up to 75% of a wholegrain product could be made from refined grains.

“In this review, the most commonly used definition was found to be that of Jacobs et al. (1998) [235] who defined wholegrain foods as those containing 25% or more of wholegrains”

In an attempt to eat healthy, people may buy ‘wholegrain’ products with 50% wholegrains (I’m being generous).  They then treat themselves to 2 serves of refined grains for their efforts.  They think refined grains can’t be that bad if the guidelines aren’t explicitly saying not to eat them.  Not like saturated fat.  (Never mind that the excess carbohydrate from the grains will be converted to palmitic acid (16:0).  Or that SFA are negatively associated with LDL oxidation, atherosclerosis and not associated with CVD).  Anyway our health conscious person eats 2 serves of whole grains, 4 serves of refined grains and thinks they are eating healthily.  That has to change.


In this section the dietary guidelines have lowered their standards.  They are recommending excessive consumption of cereal grains, a food group with mediocre nutrition and potential health problems due to antinutrients such as their potent lectins and gluten.  Most of the scientific evidence simply suggests wholegrains are healthier than refined grains and interventions that include wholegrains are successful.  The dietary guidelines recommend six servings of grains (mostly wholegrain), despite the cited studies only recommending three serves of wholegrains and no refined grains.  The guidelines should not be giving a free pass to refined grains.  Instead such a nutrient poor food group, responsible for no good health outcomes (and presumably negative ones), should be considered an extra.

If the guidelines want this food group to maintain six servings, then what should happen is for starchy vegetables, mature legumes, nuts and seeds to be removed from their other groups and placed into the group with wholegrains, which could now be called ‘starches and seeds’.  These foods can be grouped together as they have a similar nutritional profile.

Instead of recommending: eat six serves of grain (cereal) foods (mostly wholegrain).  What should be recommended instead is to: eat three serves of wholegrains, or: six serves of a combination of starchy vegetables, wholegrains, mature legumes, nuts and/or seeds.

No comments:

Post a Comment