A recent study published in the journal Nutrition, aimed to compare high protein and high fibre weight-loss diets in women with risk factors impacting the metabolic syndrome.
Many people who are overweight/obese have risk factors (cardiovascular disease, diabetes) associated with the metabolic syndrome. A diet high in protein (HP) was compared with a fibre-rich (HFib) (with minimally processed cereals and legumes) to determine whether high protein diets have the potential to confer greater benefits.
AdvertisementThe study involved dietary intervention for a period of eight weeks. Participants were randomly assigned to a high protein (HP) or a high fibre, high carbohydrate (HFib) energy-restricted diet. The macronutrient proportions were as follows:
• 30% of total energy (TE) derived from protein
• 40% TE from carbohydrate
• 20% TE from protein
• 50% TE from carbohydrate
• 35g or more dietary fiber daily with emphasis on whole grains and legumes
Total and saturated fat intakes were intended to be kept below 30% and 10% TE respectively. Energy intakes were designed to achieve weight loss of 0.5 - 1.0 kg per week.
Both groups were given material especially prepared for this study, including checklists, recipes and menu plans. Participants met nutritionists at randomization and every two weeks throughout the study to encourage dietary adherence. At these sessions, participants were weighed, daily food group checklists were reviewed, and strategies for maintaining adherence to the dietary advice was discussed. Participants were asked to maintain their usual levels of exercise for the duration of the study.
Our findings clearly show that both the high protein (HP) and the relatively high carbohydrate, high fibre (HFib) diets were associated with appreciable reductions in total body fat, waist circumference, truncal fat, blood pressure, fasting plasma glucose, total and LDL cholesterol, and triglyceride, insulin and an increase in insulin sensitivity. These favorable changes occurred without any loss of lean body mass.
However, given the aim of this study, the most important findings relate to the comparisons of the magnitude of the benefits observed with the two dietary prescriptions, the HP diet being associated with a significantly greater reduction in adiposity and diastolic blood pressure when compared with HFib.
Studies reported increased satiety in patients on high protein versus standard protein diets. But in this did not translate into more weight loss.
On the contrary, participants on HP diet reported greater hunger, more preoccupation with thoughts of food, and higher energy intakes, than participants on HFib. Yet, the former lost more weight. Although self-reported energy intakes are highly unreliable, it would appear that satiation was not a major factor explaining greater weight loss on the part of those on HP diet. The fact that dietary fibre is also associated with increased satiety and fullness may explain these observations.
Weight loss diets have often been associated with some loss of lean body mass, in addition to the reduction of fat mass. High protein diets have been associated with the retention of lean body mass (LBM) when compared with high carbohydrate diets even when there has been no difference in change in total body weight.
A meta-regression analysis of weight loss studies comparing low carbohydrate high protein diets with LFHC diets suggested that protein intakes greater than 1.05g/kg/d were associated with greater retention of fat free mass compared with lower protein intakes.
Findings also confirm the potential of high protein diets to facilitate LBM retention. The HP diet seems to provide no additional benefit, when compared to the HFib diet.
The study concluded that though a high protein diet might be the preferred prescription for weight reduction, a relatively high carbohydrate diet (diet that is rich in wholegrain cereals, legumes, intact fruits and vegetables and low in saturated fat) offers an alternative for those who choose not to increase protein intake as a result of cost or dietary preferences.
Lisa A Te Morenga, Megan T Levers, Sheila M Williams, Rachel C Brown and Jim Mann; 'Comparison of high protein and high fiber weight-loss diets in women with risk factors for the metabolic syndrome: a randomized trial', Nutrition, 2011.