The Role of Wholegrains in Weight Management

With all the hype around low carb diets I was delighted to write this article about whether wholegrains have a role in helping us to maintain or reach a healthy weight; this was published in the December 2016/January 2017 edition of NHD Magazine (a PDF of the full published article is available at the end of this post).

 

Wholegrains are defined as the intact, ground, flaked or cracked kernel which remain after the removal of inedible parts of the grain (such as the hull and husk), with the starchy endosperm, nutrient-dense germ and high fibre-bran present in the same relative amounts as they exist in an intact kernel1-2. Wholegrains are fantastically nutritious and can contain up to 75% more nutrients than refined grains, specifically they provide starchy carbohydrate, fibre (mainly insoluble fibre but some also contain soluble fibre), protein, B vitamins, folic acid, Vitamin E, omega 3 fatty acid, gut friendly short-chain fatty acids and minerals such as iron, manganese, zinc, selenium and copper2-3.

Studies have linked a diet high in wholegrains with numerous health benefits, such as a 20% reduced risk of bowel cancer and a 30% reduction in the risk of type 2 diabetes, heart disease and stroke2-5. Wholegrains are also promoted to aid weight management; this article will explore the mechanisms and evidence related to this.

wholegrains1

Picture reference: The Whole Grains Council

 

Types of Wholegrains2,5
  • Wholewheat including spelt wheat, durum wheat, whole wheat flour, wheat flakes, bulgur wheat and buckwheat
  • Brown rice and wild rice
  • Whole barley including hull-less or naked barley but not pearled
  • Whole rye and rye flour
  • Oats, including hull-less or naked oats, rolled oats, oatmeal, oat flakes
  • Maize (corn)
  • Millets
  • Quinoa
  • ‘Ancient grains’ e.g. kamut, freekah

Potential Mechanisms of Wholegrains in Weight Management

Wholegrains are high in starchy carbohydrates and low in fat, therefore compared to high fat foods they have a relatively low calorie content (4kcal per gram of carbs versus 9kcal per g of fat)2; therefore displacing higher calorie food may be one reason as to why a diet high in wholegrains may be beneficial for weight management6

As wholegrains generally have a low glycaemic index (GI) they slowly release carbohydrate into the blood and stabilise blood glucose levels; this coupled with the high fibre content of wholegrains is thought to promote satiety, control appetite and reduce urges for snacking2.  Depending on the fibre composition, it has been suggested that the mechanisms for increasing satiety include: increased time and effort of chewing resulting in a slower eating rate, decreased gastric emptying, alteration of gut hormone secretion, slower energy and nutrient absorption and lower postprandial blood glucose and lipid levels6-7.

 

Evidence for Wholegrains and Weight Management

There is some observational evidence which suggests that diets high in wholegrains are associated with lower levels of obesity, for example “The Nurses’ Health Study”8 found that women who consumed a high intake of wholegrains consistently weighed less than those with lower wholegrain intakes; and those with the highest fibre intake had a 49% lower risk of extreme weight gain. A recent large cross sectional study from the US also found that “greater whole grain consumption [was] associated with better intakes of nutrients and healthier body weight in children and adults”9; and similar findings have been reported in the UK10.

In terms of interventional trials, an early study11 related to bread intake found that roughly 83% of subjects consumed more calories when white bread was provided compared to wholemeal bread, and similarly Howarth et al (2001)12 found that adding 14g of fibre per day to subject’s diets during a weight loss trial resulted in a 10% decrease in calorie intake and a weight loss of >1.9kg.

Although, when the current body of research was analysed by the Scientific Advisory Committee on Nutrition (SACN, 2015)5, they reported that there is insufficient evidence as to whether wholegrains have an effect on BMI, change in body weight, body fatness or fat distribution; and there was no effect identified between dietary fibre intake, GI or GL on energy intake or body weight change. However, based on limited evidence SACN did find that high intakes of wholegrains may decrease total energy intake, and an association was also found between high carbohydrate low fat diets and a lower BMI (for a more detailed summary of relevant information from this SACN report see table 2 in the attached PDF of the full printed article below). 

SACN acknowledge that the discrepancy between wholegrain classification in different countries presented as a limitation in examining the combined effect of wholegrains; for example in Sweden and Denmark wholegrain products must contain 50% or more wholegrain ingredients on a dry matter basis, in the UK and US wholegrain products must contain 51% or more wholegrain ingredients on a wet weight basis, whereas in Germany wholegrain bread must contain 90% wholegrain ingredients5,13.

Although there are no specific UK guidelines for daily wholegrain intake, the Eatwell Guide and also the NICE Guidelines on “Obesity Prevention” (2006) recommend basing meals on starchy carbohydrates choosing “wholegrain versions where possible”14-15. Furthermore, the recent SACN report on “Carbohydrates and Health”5 advised that adults should consume at least 30g of fibre per day, and in order to reach this a significant daily intake of wholegrains is needed.

 

Advising on Wholegrain Intake

However, some countries have specific daily wholegrain recommendations for adults such as16-17:

Australia Women: 3-6 servings, men: 4.5-6 servings (age dependant).

1 serving =  1 slices of bread, ½ cup cooked rice/ pasta/noodles, ½ cup of porridge, ⅔ cup cereal flakes, ¼ cup of muesli, ¼ cup of flour, 3 crispbreads, 1 crumpet.

Canada At least three servings of whole grains from age 9 onwards.
Denmark At least 75g of wholegrains per day (based on a 2400kcal diet); therefore ~63g per day for a 2000kcal diet.
Sweden 75g of whole grain per 2400kcal diet; i.e. roughly 70g for most women and roughly 90g for most men.
United States Women: 3-6 servings, men: 3-8 servings (age dependant).

1 serving =  ½ cup cooked rice/bulgur/pasta/cooked cereal, 1 ounce dry pasta, rice or other dry grain, 1 slice bread, 1 small muffin (weighing one ounce).

The most recent National Diet and Nutrition Survey (NDNS) from 2012 – 201418 found that the average fibre intake for adults in the UK is below recommended levels at 13- 14g/day, which includes fibre found in wholegrains and also fruit and vegetables. Data from the previous NDNS (2008 – 2011)19 has been analysed specifically for wholegrain intake, which reported that the average daily wholegrain intake (dry weight) was low, at 20g per day for adults and 13g per day for children/teenagers, furthermore it was found that 18% of adults and 15% of children/teenagers did not consume any wholegrain foods.

Therefore it appears that on-going health promotion related to wholegrains is needed in the UK, such as advising the replacement of refined starchy carbohydrates with wholegrain versions. In order to maximise tolerance and minimise potential gut irritation it is important to increase wholegrain intake gradually, drink plenty of fluid and to be physically active for at least 150 minutes per week20. When reading food labels it is useful to highlight that “multigrain” does not indicate wholegrain (rather it means that means that the product contains more than one different type of grain)2, and fibre intake can be optimised by choosing “high fibre” varieties of wholegrain products which contain >6g of fibre per 100g21.

For more information on wholegrain types, portion sizes and ways to incorporate these into the diet see the “Wholegrain Foods and Ideas for Use” table on page 2 of the BDA food factsheet “Wholegrains”.

 

Conclusion

Wholegrains have numerous health protective qualities and in the UK we could benefit from increasing our daily intake. Specifically in relation to weight management a high wholegrain intake may help to reduce total calorie intake, and it is interesting that high carbohydrate low fat diets have recently been associated with a lower BMI; however more research is needed to clarify whether wholegrain intake has a direct effect on BMI, change in body weight, body fatness or fat distribution. 

 

References:

  1. Van der Kamp et al. (2014) The HEALTHGRAIN definition of ‘whole grain’. Food Nutr Res 58.
  2. BDA Food factsheet “Wholegrain” (https://www.bda.uk.com/foodfacts/wholegrains.pdf)
  3. Aune et al. (2016) Whole grain consumption and risk of cardiovascular disease, cancer, and all cause and cause specific mortality: systematic review and dose-response meta-analysis of prospective studies” (http://www.bmj.com/content/353/bmj.i2716?etoc)
  4. Aune et al. (2011) “Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies” (http://www.bmj.com/content/343/bmj.d6617)
  5. SACN (2015) “Carbohydrates and Health” (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/445503/SACN_Carbohydrates_and_Health.pdf)
  6. Slavin and Green (2007) “Dietary fibre and satiety” (http://onlinelibrary.wiley.com/doi/10.1111/j.1467-3010.2007.00603.x/full)
  7. Slavin (2005) “Dietary fiber and body weight” (http://www.ncbi.nlm.nih.gov/pubmed/15797686)
  8. Van Dam RM & Seidell JC (2007) Carbohydrate intake and obesity. European Journal of Clinical Nutrition 61 (Suppl. 1):75–99).
  9. Albertson et al. (2016) “Whole grain consumption trends and associations with body weight measures in the United States: results from the cross sectional National Health and Nutrition Examination Survey 2001-2012” (http://www.ncbi.nlm.nih.gov/pubmed/26801989)
  10. Dong et al. (2015) “Consumption Of Specific Foods And Beverages And Excess Weight Gain Among Children And Adolescents” (http://content.healthaffairs.org/content/34/11/1940.abstract)
  11. Grimes & Gordon (1978) “Satiety value of wholemeal and white bread” Lancet 17: 106.
  12. Howarth et al. (2001) “Dietary Fiber and Weight Regulation” (http://onlinelibrary.wiley.com/doi/10.1111/j.1753-4887.2001.tb07001.x/full)
  13. EFSA (2010) Scientific Opinion on the substantiation of a health claim related to whole grain (ID 831, 832, 833, 1126, 1268, 1269, 1270, 1271, 1431) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal 8, 1766.
  14. NICE (2006) “Obesity Prevention” (https://www.nice.org.uk/guidance/CG43?c=91500)
  15. FSA (2016) “The Eatwell Guide” (https://www.food.gov.uk/sites/default/files/finaleatwellguide23mar2016nothernireland23rd.pdf)
  16. The Wholegrain Council (accessed September 2016) (http://wholegrainscouncil.org/whole-grains-101/how-much-enough/whole-grain-guidelines-worldwide)
  17. Grain Foods and Legumes – An update on changes to the Australian Dietary Guidelines (2013) (http://www.glnc.org.au/wp-content/uploads/2011/04/GLN_102851_Factsheet-HEALTHCARE-PROF_02-WEB.pdf)
  18. PHE (2016) “National Diet and Nutrition Survey” (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/551352/NDNS_Y5_6_UK_Main_Text.pdf)
  19. Mann et al. (2015) “Low whole grain intake in the UK: results from the National Diet and Nutrition Survey rolling programme 2008–11” (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4462163/)
  20. British Nutrition Foundation “Dietary Fibre” (accessed September 2016) (https://www.nutrition.org.uk/healthyliving/basics/fibre.html)
  21. Regulation (EC) No 1924/2006 (http://eur-lex.europa.eu/legal-content/en/ALL/?uri=CELEX:32006R1924)

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