Research appears to show that high protein, restricted energy diets are not superior to other diets.
In this time when we are so worried about COVID and infectious disease, we are ignoring the disease that is killing millions, and it’s a huge drain on the global economy. Obesity has become a global epidemic in the United States leading the way. The optimal dietary macronutrient composition to achieve weight loss is much debated and the research is very contradictory.
The good news is that a new study from New Zealand looks at this very question to find an answer. We know that cutting calories is one of the most effective dietary treatments for obesity and higher protein diets have been shown to promote weight loss. Many of these diets are low carbohydrate and high in fat. Some are also high in fat with no change in the protein. There is a multitude of lower carbohydrate diets. This research focuses on higher protein diets versus low carbohydrate.
It is not established whether the higher protein or the lower carbohydrate content may be the most important factor for successful weight loss. In this study, the researcher manipulated the macronutrient content of the low energy or lower calorie diet provides the opportunity to investigate these effects or each to see which is superior.
The purpose of the study was to investigate the effect of 8-week restricted-calorie diets which varied in protein and carbohydrate content on body weight loss, fat mass loss, lean mass loss, and satiety in a group of obese women. The obese but otherwise healthy female adults where they were randomized to one of four diet interventions but all completed an 8-week dietary intervention with similar caloric counts. Throughout the day, they were asked to consume three fixed meals.
The diets consumed were either normal protein and normal carbohydrate, high protein and normal carbohydrate, normal protein and high carbohydrate, high protein and low carbohydrate, or normal protein and low carbohydrate. The researchers used food and dietary records to determine compliance and assess energy and macronutrient intake at baseline, 4 weeks, and 8 weeks. Bodyweight was assessed at the same intervals. Body composition was measured by dual x-ray body scans at baseline and 8 weeks.
Forty-six females completed the study. A good level of dietary compliance to the dietary treatment was observed in all diet groups. The high protein diet groups significantly increased their protein intake from baseline and achieved a significantly greater protein intake than the normal protein diet groups. Bodyweight and body fat mass decreased significantly in all diet groups over 8 weeks. The mean weight loss ranged from 6 to 8 pounds and mean fat loss was between 2.9 to 4%. There was no difference in satiety among the diets either.
The problem with the data is that is failed to show any diet was superior. There was however no significant difference detected between the 4 diet groups over the 8-week calorie-restricted weight loss phase. Lean mass appears to be protected with only the high protein and Normal carbohydrate group seeing no loss in lean mass. This change was also not significant but it was a change.
Compliance is the key to weight loss. Any caloric restriction and result in weight loss. You need to pick a diet you can more readily comply with. In this study, those who were compliant lost a significant amount of body weight. No specific diet achieved a more significant weight loss outcome or changes in body composition. A higher-protein diet was equally beneficial in promoting weight loss and fat loss while preserving lean mass when compared with a lower-protein diet with the same carbohydrate content.
A higher-protein diet also did not promote satiety and limit caloric intake any better than a lower-protein diet with the same carbohydrate content. When protein was kept constant, a lower carbohydrate higher-fat diet was not superior at the loss of body weight and body fat loss along with the preservation of lean mass when compared with a higher carbohydrate lower-fat diet.
The bottom line: Compliance is the key to weight loss. In this study, none of the diets showed superiority at fat loss or satiety. Eight weeks is a rather short study, and longer studies with a greater sample size might show a more significant effect. I would take home the idea that compliance is key to weight or fat loss, and you must individualize your diet to ensure you comply.
- Y. Liu, “The effect of a higher-protein low energy diet on weight loss in obese women,” The University of Auckland, 2020 [Online]. Available: https://researchspace.auckland.ac.nz/handle/2292/50571