Abstract
Higher protein meals increase satiety and the thermic effect of feeding (TEF) in acute settings, but it is unclear whether these effects remain after a person becomes acclimated to energy restriction or a given protein intake. This study assessed the effects of predominant protein source (omnivorous, beef/pork vs. lacto-ovo vegetarian, soy/legume) and quantity (10%, 20%, or 30% of energy from protein) on appetite, energy expenditure, and cardio-metabolic indices during energy restriction (ER) in overweight and obese adults. Subjects were randomly assigned to one protein source and then consumed diets with different quantities of protein (4 weeks each) in a randomized crossover manner. Perceived appetite ratings (free-living and in-lab), TEF, and fasting cardio-metabolic indices were assessed at the end of each 4-week period. Protein source and quantity did not affect TEF, hunger, or desire to eat, other than a modestly higher daily composite fullness rating with 30% vs. 10% protein diet (p = 0.03). While the 20% and 30% protein diets reduced cholesterol, triacylglycerol, and APO-B vs. 10% protein (p < 0.05), protein source did not affect cardio-metabolic indices. In conclusion, diets varying in protein quantity with either beef/pork or soy/legume as the predominant source have minimal effects on appetite control, energy expenditure and cardio-metabolic risk factors during ER-induced weight loss.
Highlights
An energy deficit is required for overweight and obese adults to lose weight, and research shows that reducing energy intake and retaining fasting and postprandial resting energy expenditure both support this outcome [1]
The subjects did not become acclimated to an energy deficit state or to the protein content of the meals/diets they would habitually consume while dieting
Limited research exists on the impact of dietary protein quantity on postprandial and daily appetitive responses from subjects acclimated to the energy and protein contents of the diets, with inconsistent findings and methodologies used to measure perceived appetite [3,9,10,11,12]
Summary
An energy deficit is required for overweight and obese adults to lose weight, and research shows that reducing energy intake and retaining fasting and postprandial resting energy expenditure both support this outcome [1]. Since protein is generally recognized as the most satiety-inducing macronutrient [5] and some acute and short-term feeding studies support that higher protein intake increases satiety and reduces energy intake at the meal [6,7], adults who are dieting may be encouraged to consume high-protein diets. Most of these acute and short-term protein feeding studies were conducted using subjects who were consuming their usual self-chosen, energy balanced diets prior to the testing days. Limited research exists on the impact of dietary protein quantity on postprandial and daily appetitive responses from subjects acclimated to the energy and protein contents of the diets, with inconsistent findings and methodologies used to measure perceived appetite [3,9,10,11,12]
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