None listed
Conditions
Brief summary
Protein intake has remained relatively stable through the development of the obesity epidemic, yet total energy intake has risen. The protein leverage hypothesis (PLH) proposes that a separate and dominant appetite for protein drives excess energy intake when dietary protein is diluted by fat and carbohydrate. The PLH has been shown in various other species, including non-human primates where excess total energy intake occurs when the percent protein of the diet decreases. Experimental and population-level data also suggest the same may be true in humans (meta-analysis included in the current manuscript). Experimental verification of the protein leverage hypothesis is lacking because it is difficult to separate the role of protein from confounding influences on intake associated with concurrent changes in dietary fat and carbohydrate. The unequivocal test for the PLH is to develop protocols that disguise macronutrient composition of foods offered to subjects under ad libitum feeding conditions. We have recently developed these protocols and in the current study report experiments in which they were applied to confirm the PLH in humans. Here we show that reducing dietary protein by 5% whilst controlling palatability, availability, variety and sensory aspects of the diet resulted in subjects increasing total energy intake by 12%, and this increase was mainly due to increased intake of foods available between meals. We therefore confirm the PLH in humans and show that any change in the nutritional environment that dilutes dietary protein with carbohydrate and fat will promote increased energy intake. Our findings provide a new understanding of a major global health problem, and have considerable implications for the management of obesity.
Interventions
Each participant attended three 4-day periods of in-house dietary manipulation. Participants were given ad libitum access to diets containing 10%, 15% and 25% protein over the three 4day periods. Carbohydrate was adjusted to be 60, 55 and 45% energy and dietary fat was kept constant at 30%. Food intake was measured by recording the weight of the food before and after serving, to the nearest gram. Energy intake was calculated using the nutritional information for each recipe. The trial was a rand
Each participant attended three 4-day periods of in-house dietary manipulation. Participants were given ad libitum access to diets containing 10%, 15% and 25% protein over the three 4day periods. Carbohydrate was adjusted to be 60, 55 and 45% energy and dietary fat was kept constant at 30%. Food intake was measured by recording the weight of the food before and after serving, to the nearest gram. Energy intake was calculated using the nutritional information for each recipe. The trial was a randomised crossover-trial, each participant completed each of the three 4-day interventions with at least a one week washout period between interventions.
Sponsors
The University of Sydney
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Prevention
Masking
Blinded (masking used) (Subject)
Eligibility
Sex/Gender
All
Age
18 Years to 65 Years
Healthy volunteers
Yes
Inclusion criteria
Lean, healthy male and female participants.
Exclusion criteria
Exclusion criteria included diabetes, high blood pressure, gastrointestinal problems, asthma, eczema or hay fever, chronic medical conditions, anaemia, allergies or strong dislikes to any study foods, smoking, following a weight reducing diet within the 3 months prior to the screening interview, pregnancy and breastfeeding, a history of eating disorders or irregular eating habits. Vegetarian and vegans were excluded to aid in preparation of the intervention foods.
Outcome results
None listed