Of the developed nations, Australia is one of the most overweight, with more than 60% of adults and one in four children overweight or obese. The prevalence of overweight and obesity in Australia has been steadily increasing during the past 30 years and if the current trends continue unabated, it is estimated that nearly three-quarters of the

 Australian population will be overweight or obese by 2025. While evidence suggests that rates of overweight and obesity may be reaching a plateau in children, the prevalence in Australia is still higher than is desirable.

It is well recognised that a diet high in wholegrain cereals and legumes promotes good health. The weight of evidence available from research shows it can also help maintain a healthy weight. Two reviews of epidemiological and intervention studies have both concluded that there is an association between cereal intake (particularly wholegrain) and reduced risk of weight gain or being overweight.

A meta-analysis of 11 prospective cohort studies on the relationship between wholegrain consumption and body weight reported a mean reduction of 0.63 Body Mass Index (BMI) units between the highest (≥3 serves a day) and lowest intakes of wholegrain foods.

The second review of 41 cross-sectional, cohort and intervention studies concluded that there is good evidence that a diet high in wholegrains:

• is associated with a lower BMI, waist circumference and risk of being overweight;
• can help reduce weight gain; and
• can assist in weight loss as part of an energy controlled diet.

There is no evidence that changing from refined to wholegrain foods without energy restriction will lead to weight loss, but a study of cereal foods (at least five serves a day) in a hypocaloric diet led to significantly greater reduction of abdominal body fat with wholegrain compared to refined grain cereals.

In a prospective cohort of over 27,000 men (from the Health Professionals Follow-up Study), a high wholegrain intake was found to be inversely associated with long term weight gain. It was estimated that for every 40g a day increment in wholegrain intake from all foods, weight gain was reduced by an average of 0.49kg during the eight year follow-up, with the associations persisting after accounting for changes in added bran or fibre intakes.

The protective role of wholegrains in weight management is further supported by three recent studies:

• A cross-sectional study of participants aged 60-80 years in a US clinical trial found that fat mass, percent body fat and trunk fat mass were inversely associated with wholegrain intake using DEXA (Dual energy x-ray absorptiometry).
• A sub-analysis of a Netherlands cohort study examining 4,237 adults aged 55-60 years for a five year period, using logistic regression, demonstrated that the risk of being obese as compared to normal weight was 10% lower for each additional gram of wholegrain consumption. In women, this risk was 4% lower.
• A hypocaloric clinical trial in overweight adults, found that including three serves of oat-based wholegrain foods per day reduced their waist circumference significantly more than control subjects consuming the same levels of energy a day.

A word on low-carbohydrate diets:

There is no evidence that low carbohydrate diets that restrict grain foods offer long term advantages for sustained weight loss. In fact, the scientific literature supports findings from the National Weight Control Registry, which shows that regular breakfast consumption and eating a low-fat, high carbohydrate diet are some of the behaviours of successful weight-loss maintainers.

In recent evidence-based practice guidelines, the Australian National Health & Medical Research Council (NH&MRC) cautions against the use of low carbohydrate diets and has concluded that a low-fat diet with increased activity is still the best approach for weight management.

Put simply, the weight of the scientific evidence supports current dietary recommendations to enjoy a wide variety of grain-based foods, particularly wholegrains, as part of a healthy diet in the pursuit to achieve and maintain a healthy weight.

Suggested Mechanisms

Fibre: It is believed that the higher fibre content of diets rich in wholegrains is one of the main mechanisms through which they help control body weight. Dietary fibre can assist weight control in the following ways:

• higher fibre wholegrain foods are typically less energy dense than refined foods;
• the bulking properties of dietary fibre promote satiety;
• high fibre wholegrain foods typically (but not always) have a lower glycaemic index (GI), which slows the rate of starch digestion leading to lower blood glucose and insulin levels after a meal; and
• fibre increases chewing, which increases saliva and gastric juice production. This expands the stomach and helps to satisfy the appetite sooner.

Metabolic Effects: In the Health Professionals Followup Study, associations between wholegrain intake and reduced weight gain were attenuated after adjustments were made for micronutrients like magnesium, and they persisted even after bran and fibre intakes were accounted for, implying additional metabolic effects beyond the effect of the fibre content.83 This suggests there are additional components in wholegrains that may contribute to metabolic alterations which favour long-term weight management.81

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