In a study comparing the impact of a high-protein total diet replacement (HP-TDR) to that of a control diet (CON), a typical North American diet, researchers led by Camila Oliveira, a doctoral student at the University of Alberta, reported that a HP-TDR led to higher total energy expenditure (EE), increased fat oxidation and negative fat balance. These results suggest that a HP-TDR may promote fat loss compared with a conventional isocaloric diet. The findings, ‘A High-Protein Total Diet Replacement Increases Energy Expenditure and Leads to Negative Fat Balance in Healthy, Normal-Weight Adults’, were published in The American Journal of Clinical Nutrition.
"Considering the prevalence of obesity worldwide and its impact on health, it's not surprising nutritional strategies such as total diet replacements and high-protein diets are becoming increasingly popular as weight management strategies; however, research around these topics has not kept pace with their growth in popularity," commented Oliveira.
According to the World Health Organization, obesity has nearly tripled worldwide since 1975. In 2016, for example, more than 1.9 billion adults were categorized as overweight. Of these, more than 650 million had obesity. Because obesity is associated with a higher incidence of diabetes, cardiovascular disease and some cancers, the rise in its incidence has led to a global public health emergency.
Total diet replacements, nutritionally complete formula foods designed to replace the whole diet for a set period of time, have become increasingly popular strategies to combat obesity. Another popular weight management strategy are high-protein diets, which have been shown to promote weight loss and weight maintenance by increasing our sense of fullness, energy expenditure, and ability to maintain or increase fat-free mass. Taken together, the combination of a total diet replacement with a high-protein diet may be a promising strategy for weight management. In fact, several high-protein total diet replacement products are widely available to consumers. The question is do they work?
In order to conduct their experiment, the authors recruited a group of healthy, normal-weight adults between the ages of 18 and 35 via advertisements placed on notice boards at the University of Alberta, Canada. Subjects were then randomly assigned into one of two groups: one group was fed the high-protein total diet replacement, which consisted of 35% carbohydrate, 40% protein and 25% fat. The second group, the control group, was fed a diet with the same number of calories, but consisting of 55% carbohydrate, 15% protein, and 30% fat, a typical North American dietary pattern. Participants received the prescribed diets for a 32-hour period while inside a metabolic chamber.
In total, 43 healthy, normal-weight adults (19 females and 24 males) were included. Compared with the CON diet, the HP-TDR produced higher total energy expenditure [(EE) 81 ± 82 kcal/d, p<0.001], protein and fat oxidation rates (38 ± 34 g/d, P <0.001; 8 ± 20 g/d, p=0.013, respectively) and a lower carbohydrate oxidation rate (–38 ± 43 g/d, p<0.001). In addition, a HP-TDR led to decreased energy (–112 ± 85 kcal/d; p<0.001), fat (–22 ± 20 g/d; P <0.001) and carbohydrate balances (–69 ± 44 g/d; p<0.001) and increased protein balance (90 ± 32 g/d; p<0.001).
The results of the study provide further evidence that a diet with a higher proportion of protein might lead to an increase in energy expenditure and fat oxidation compared to a diet consisting of the same number of calories, but with a lower proportion of protein as well as a higher proportion of carbohydrate or fat.
"Although these results are restricted to a specific population of healthy, normal-weight adults, they can help nutrition scientists and healthcare providers better understand the real physiological effects of a high-protein total diet replacement in humans,” said Dr Carla Prado, Professor, University of Alberta and the study's principal investigator. “In our opinion, it is imperative to first understand the physiological impact of a high-protein total diet replacement in a healthy population group so that the effects are better translated in individuals with obesity and its related comorbidities."
In summary, the results of this study suggest that high-protein total diet replacements may be a promising nutritional strategy to combat rising rates of obesity.
“Future studies are needed to better understand the long-term effects of this dietary intervention on the physiology of both healthy and diseased population groups,” added lead author Oliveira.