Modulation of Protein Status in Humans Leads to Preference for Increased Portions

IntroductionProtein together with energy is an essential component of the diet. Implicit control of protein consumption is a key element of food decision‐making and behavior in humans. However, it is unclear which food characteristics, especially sensory, are the determinants of food choices guiding to adequate protein intake. A low‐protein diet is known to induce unconscious search for foods containing protein. By comparing food preferences of human subjects under a low‐protein diet to preferences of the same subjects subjected to a balanced diet, this study aimed at identifying implicit determinants of protein level in common foods.Materials and Methods23 healthy volunteers (13 women) 18 to 35 years old, non‐overweight (BMI between 18 and 25 kg/m2) followed two successive dietary interventions in a randomized crossover design during which they consumed either a diet containing 0.5g of protein/kg body weight/day, or 1.4g protein/kg/day. Both diets were iso‐energetic and variations in protein content were compensated by variations in both carbohydrates and fats. Experimental diets lasted 4 days each and were separated by a 10‐day wash‐out period during which participants were instructed to go back to their normal diet. At the beginning and at the end of each experimental diet period participants completed an on‐screen task during which they choose the preferred food from two food photographs. Foods present on photographs differed in protein content, portion size, or sensory qualities. A total of 153 pairs was used. Based on this task, preference scores for each food was estimated using the Bradley‐Terry method for analysis of paired comparisons. Effect of subjects' protein status on preference scores and its interaction with food sensory and nutritional characteristics was then evaluated.ResultsPreference analysis showed a significant effect of subjects' protein status on food preference scores (p=0.0047). A significant interaction was found between protein status and portion size (p=0.0002), a low‐protein diet resulting in a preference for larger portions. Other food characteristics such as protein content of foods and their sweet or salty taste, did not appear to affect preferences in a situation of low protein status (p=0.11 and p=0.14, respectively).ConclusionThis study showed an alteration of food preferences induced by a low‐protein diet, observed after 4‐day dietary intervention. Subjects following a low‐protein diet appear to prefer larger food portions that could be interpreted as an attempt to restore protein balance.Support or Funding InformationThe study was funded by a grant from French Nutrition Society