New year, new diet?

Wholegrains, legumes and refined grains in weight loss...

If you are gearing up for a healthy summer eating plan and are not sure what to include, consider the results of some new research that has just been published. Over one hundred people participated in an 18 month weight loss trial with advice to either follow a control diet based on the National Heart Foundation of New Zealand guidelines, or a diet that emphasised wholegrains and legumes.

The first 6 months involved 2-weekly counselling sessions, cooking classes, supermarket tours, and recipe ideas, in the following 12 months participants had monthly contact with the investigators. Participants in the (very healthy) control group were instructed to follow the guidelines published by the National Heart Foundation of New Zealand which included recommendations to eat at least 3 servings of vegetables and 2 serving of fruit, at least 6 servings of breads and cereals (where 1 serve is equivalent to 1 slice of bread),at least 2 servings of reduced fat milk and milk products, 1-2 small servings of protein-rich foods (meat, poultry, fish, seafood and legumes) and 1-2 tablespoons of monounsaturated or polyunsaturated fats and oil products and a small amount of nuts and seeds. The intervention group was given similar advice, except they were specifically instructed to consume 2 servings of legumes as a substitute for 2 serving of breads and cereals, and all other breads and cereals were to be wholegrain.

Key foods were provided to the participants for the first 6 months of the study to encourage consumption of the ‘suitable foods’ for their group. For example, participants assigned to the control group received cornflakes, cans of fruits and veggies white bread and cereals with a medium to high glycaemic index. The intervention group received rolled oats and rye, canned legumes, wholegrain and rye bread. Providing key foods seems to have played a role in the participant’s weight loss, as after 6 months when less support was provided many people re-gained some of the weight they had lost.

Data from weighed food records showed that most people in the intervention group complied reasonably well with the substitution of legumes into their diet, with the median legume intake over the first 6 months almost reaching the advised 2 serves/day. This declined to just under 1 serve/day in the last 6 months of the study. Wholegrain intake remained stable in the intervention group over the 18 months at around 1.5 serves/day. Wholegrain intake was slightly higher in the intervention vs the control group at 2 and 6 months, but no different at 12 months, therefore, it is likely that poor compliance after 6 months could have diminished the difference between diets.

The great thing about this study for the participants is that both groups lost a significant amount of weight – approximately 7kg at 6months, and 5kg at 18 months, compared to their weight when they started the weight loss program. Due to the overall similar decrease in energy intake and similar weight loss in both groups it is more difficult to see differences between the two interventions. Overall, there was a small difference in wholegrain intakes between both groups and significantly noticeable differences between legume intakes. Both groups decreased blood pressure, triglycerides and glycaemic load resulting in significant weight loss in both intervention groups, but there was no significant difference between the groups. Despite a small difference in the glycaemic index (GI) between the two diets, there was no relationship of GI to weight loss, consistent with other trials. The group that ate more wholegrains and legumes had a significantly lower waist circumference by 2.8cm after 18 months of the weight loss program. This group also had a lower Total cholesterol and a lower LDL cholesterol at the end of the study.

From a practical perspective, 81% of people stuck out the complete 18 months of the weight loss program, giving a good indication that people were willing to incorporate wholegrains and legumes in their diet over this period. Overall, all participants found the diets easy to follow and did not report any decrease in dietary satisfaction. The researchers concluded that their data provides strong evidence in support of national guidelines for healthy eating that recommend the inclusion of wholegrains and legumes in the diet. This research also shows that although wholegrain foods are a better choice, core refined grain foods such as white bread, white pasta, and white rice can be included as part of a successful weight loss program.

Venn BJ et al, 2010. The effect of increasing consumption of pulses and wholegrains in obese people – a randomised controlled trial. JACN