Evidence suggest that high protein diets are able to elicit weight loss in humans. The exact reason for the weight loss effect of protein is not fully understood, but may relate to alterations in satiety due to stimulation of gut hormones or reductions in the glycaemic effects of food due to slower gastric transit times. That high protein diets are consistently reported to switch off appetite is interesting because it suggests that ingestion of sufficient protein may be a primary driver of appetite. Protein is of particular importance to animals because it provides essential amino acids that are required for growth, development and metabolic regulation. Animals can regulate protein intake to ensure adequate quantities of essential amino acids, and reductions is protein and a subsequent decrease intake of essential amino acids may trigger increased feeding behaviour in an attempt to maintain normal circulatory levels.
That lower protein intakes may trigger compensatory feeding behaviour in humans in order to maintain pools of essential amino acid has been investigated by researchers1 in a random cross-over design study. Thirty seven healthy subjects were fed isoenergetic diets that contains either 2 or 0.5g per kg bodyweight per day for 14 days. Following this loading phase, there was a 2.5 day period when subjects could eat ad libitum amount of food, and this intake was recorded. During the ad libitum phase, protein intake was 13% higher in the low protein group compared to the high protein group (253g versus 225g). However, total energy intake did not differ between the two treatments. A satiety questionnaire during the ad libitum phase showed an increased preference for savoury and high protein foods, when following the low protein diet, compared to when following the high protein diet.
These results suggest that periods of low protein intake are accompanied by compensatory periods of higher protein intakes in humans. This might reflect the needs of the individual to maintain pools of essential amino acids in order to promote normal metabolic function. Compensatory feeding mechanisms to maintain protein intake have been reported in animals previously, but this is the first time that such mechanisms have been demonstrated in humans, and the first time that sensory changes in food preference have been reported following protein depletion. The fact that energy intake remained similar between the high and the low protein groups, in combination with the sensory changes, suggests that this compensatory feeding period may not cause weight gain. However, the short-tern nature of this study does not exclude this possibility. Compensatory feeding behaviour in the absence of protein availability may trigger consumption of non-protein foods and cause weight gain.
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