Retropsective #171: “Dietary Protein and its Impact on Obesity”

“Dietary Protein and its Impact on Obesity” is the title of an essay in Diabetes in Control, a website for physicians that I monitor. It is yet another “take” on a study published in Obesity Reviews I reported on in Retrospective #170, “Your ‘instinctive appetite’ for protein’.” Medicalese notwithstanding, the takeaway was the same: “Analysis of percent protein in diet versus total energy intake showed that when a person’s diet was decreased from 20% protein to 10% protein, there was a significant increase in non-protein energy consumption and vice versa.”

“Age, study duration, and baseline BMI had no impact in dietary percent protein versus non-protein energy intake, but sex, however, did,” this analysis reported. “Men tended to have a higher dietary protein intake as compared to women.” This correlates with an early meta analysis I read years ago that reported that men averaged 16% dietary protein vs. 15% for women. Interestingly and I think very significantly, the Standard American Diet (SAD) recommends only 10% dietary protein (50g RDA of protein = 200kcal or 10% of a 2,000kcal daily intake for a woman, as illustrated on the Nutrition Facts panel on processed food packaging. A very low 10% recommendation for protein is problematic for me and ties in nicely with the hypothesis of this study, as I shall explain.

“The study also analyzed high protein intake, but diets with >20% protein did not show significant correlation to decline in energy consumption,” the Diabetes in Control piece reported. “According to the authors, maintaining proper proportions of macronutrients is…important not only for our muscles and cellular building blocks, but also to keep overall non-protein [carbohydrate and fat] energy intake down.

The “Practice Pearls” for this Diabetes in Control piece were as follows:

• Persons who maintain diets with 15-20% protein intake tend to intake less energy from carbohydrates and fats.
• Macronutrient energy intake should be calculated as a percentage of total diet; actual protein amount doesn't matter as much if it is diluted by the amount of carbohydrates and fats.
• Persons who fall in low socioeconomic status and women tend to eat less protein.

In the referenced research, “Protein leverage and energy intake,” the authors said, “Increased energy intakes are contributing to overweight and obesity. Growing evidence supports the role of protein appetite in driving excess intake when dietary protein is diluted. Understanding the interactions between dietary macronutrient balance and nutrient-specific appetite systems will be required for designing dietary interventions that work with, rather than against, basic regulatory physiology.”

“Percent dietary protein was negatively associated with total energy intake irrespective of whether carbohydrate or fat were the diluents of protein. The analysis strongly supports a role for protein leverage in lean, overweight and obese humans. A better appreciation of the targets and regulatory priorities for protein, carbohydrate and fat intake will inform the design of effective…weight loss diets, food labeling policies, food production systems and regulatory frameworks.”

So, the “protein leverage hypothesis” proffers that 1) increased energy intakes has contributed to overweight and obesity; 2) that protein as a macronutrient in the human diet has been diluted by either or both carbohydrates or fat by the excess intake of one or both; and 3) that the “protein appetite” is driving this excess intake of either or both carbohydrate and fat. The study concluded that the “right” amount of protein is 20%, and that this “protein leverage” applies to everyone.

Conclusion: “…when a person’s diet was decreased from 20% protein to 10% protein, there was a significant increase in non-protein energy consumption and vice versa.” Reminder: the “Standard American Diet” (see the Nutrition Facts panel) prescribes an RDA of 10% protein, 30% fat and 60% carbohydrate. Could it be that our government’s recommendations are what is making us fat? It is comforting to me that my target macronutrient distribution is 20% protein, 75% fat and 5% carbohydrate. What’s yours?