A common theme of dietary guideline recommendations is to eat more wholegrain foods at the expense of highly refined grains. These recommendations arose from the result of accumulating evidence that has linked wholegrain foods to reduced risks of type 2 diabetes and heart disease.
People who eat the recommended amount of wholegrain foods are less likely to be overweight. The higher nutrient value and fibre content of wholegrains over refined grains can help to control appetite, improve glycaemic (blood glucose) control and insulin sensitivity, and beneficially alter gut microbiota.
Controlled trials where people switch to eating more wholegrain foods do not always show a benefit on body weight. The difficulty in doing such studies comes from how problematic it can be in isolating the effects of wholegrains from eating a healthier overall diet.
A new study has strictly controlled diet quality while keeping body weight constant to see if metabolic effects of wholegrain foods could be detected.
Researchers calculated the specific energy needs of 81 men and women aged between 40 and 65. The first two weeks had everyone eating the same types of food to set a baseline for energy needs to maintain body weight. For the next six weeks, each person was randomly allocated to eat either a wholegrain or refined grain diet.
Two clear benefits were identified in the wholegrain diet. Eating wholegrain foods caused a greater faecal output, meaning less of the potential calories in food were being absorbed and instead were lost through the stool.
The other change was that resting metabolic rate rose in those eating wholegrains. Combining these two favourable energetic effects would mean a deficit of around 420 kilojoules (100 Calories) per day, which is no small number when spread over months and years.
Raising metabolic rate and stool energy excretion, combined with a benefit of fibre on appetite, builds a stronger rationale for recommending a switch to more wholegrain foods in assisting weight loss.
A downside of the work was the short duration of the trial and the use of a very controlled diet which may not translate to free living food choices.
Eating more wholegrains in place of highly refined grains could be an important part of healthy eating and keeping weight in check.