The protein leverage hypothesis proposes that a genetic appetite for protein combined with a widespread decline in the ratio of protein to fat and carbohydrate in our diet is responsible for:

  1. Increased caloric intake and
  2. The resultant explosion in worldwide obesity.

In this study, researchers tested the protein leverage hypothesis in lean humans by disguising the macronutrient composition of foods offered to subjects under ad libitum feeding conditions. Energy intakes and hunger ratings were measured for 22 lean subjects studied over three 4-day periods of in-house dietary manipulation.

Subjects were restricted to fixed menus in random order comprising 28 foods designed to be similar in palatability, availability, variety and sensory quality and providing 10%, 15% or 25% energy as protein.  Nutrient and energy intake was calculated as the product of the amount of each food eaten and its composition.

Results

Lowering the percent protein of the diet from 15% to 10% resulted in higher total energy intake, predominantly from savoury-flavoured foods available between meals.

In contrast, increasing protein from 15% to 25% did not alter energy intake.

On the fourth day of the trial, however, there was a greater increase in the hunger score between 1–2 h after the 10% protein breakfast versus the 25% protein breakfast.

Conclusion

Lowering the protein content of your diet  promotes hunger and over-consumption of calories….enhancing the risk of obesity.