Their role in weight management
The World Health Organisation recognises that healthy weight maintenance is a large challenge, as is overcoming obesity. Despite the public health significance of obesity and the promotion of various weight loss diets, there is no scientifically agreed optimal diet for its prevention and treatment, and opinions differ about the role of nutrients such as dietary fats and carbohydrates in the cause. Research does show, however, that diets including wholegrains and fibre can help to reduce the risk of being overweight.
'Wholegrain’ foods contain intact and /or milled grains where the grain components - bran (fibre-rich outer layer), endosperm (middle starch and protein layer) and germ (nutrient rich inner core) - are present in the same proportion as in the original grain.
Wholegrains are important sources of carbohydrate, protein, dietary fibre, minerals, vitamins and other bioactive components such as antioxidants. The many benefits of wholegrains are well documented, in particular their association with protection against chronic diseases (heart disease, diabetes and some cancers). They have also been shown to have role in long term weight control.
There is good evidence from scientific studies that a diet high in wholegrains is associated with a lower body mass index (BMI), waist circumference and risk of being overweight.
A study of over 27,000 men showed high wholegrain intake to be inversely associated with long term weight gain. For every 40g of wholegrains eaten daily, weight gain was reduced by an average of 0.49kg.
Another study found a higher intake of wholegrain or high fibre foods to be associated with a 49% lower risk of becoming obese over a 12 year period. Plant based foods and dietary fibre were shown to be protective against excess bodyweight in a large, ethnically diverse research population.
The higher fibre content of diets rich in wholegrains is believed to be one of the means by which they help control body weight. Research shows that increased dietary fibre promotes satiety due to its bulk and low energy density, with hormonal responses leading to reduced hunger and reduced energy intake. The high-fibre content of most wholegrain foods is believed to help in preventing weight gain by increasing appetite control. It does this by delaying carbohydrate absorption, hence promoting the feeling of fullness.
Increasing dietary fibre intake by an additional 14g per day has been shown to result in a 10% decrease in energy intake and a weight loss of over 1.9 kg over 4 months. The effects of dietary fibre were more striking in obese individuals. The authors of this US study concluded that increasing dietary fibre intake from the current average of 15g to 25-30g per day, would be beneficial and may help reduce the prevalence of obesity.
In addition to fibre there are also additional components in wholegrains that contribute to metabolic changes, favouring long term weight management.
The National Health and Medical Research Council recommend a dietary fibre intake of 25-30g per day for adults and 14-18g per day for children above one year of age.
There is currently no official recommendation for wholegrain intake in Australia, but based on the scientific evidence, Go Grains Health & Nutrition recommends 48g of wholegrains a day is an achievable, evidence based target intake.
Wholegrain content of some foods
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NHMRC. Nutrient Reference Values for Australia and New Zealand. Executive Summary. 2006.