A comparison of the acute effect of whey and a plant-based protein supplement on postprandial metabolism and appetite

Time-restricted eating (TRE) has emerged as a promising strategy for weight loss and supporting metabolic health (1) , yet limiting opportunities to eat may compromise overall nutritional adequacy of the diet and pose a barrier to long-term adherence (2)(3) . Allowing consumption of certain foods outside the eating window, while maintaining the benefits of TRE, may help overcome such issues. Protein intake promotes diet-induced thermogenesis and insulin and satiety hormones secretion, affecting postprandial energy expenditure (EE), appetite and glycaemia (4) . The extent to which protein from different sources may disrupt fasting is unclear, as the existing literature focuses on comparing a limited range of proteins as part of mixed meals, resulting in a lack of insight into their metabolic effects when ingested on their own. The present study aims to compare the acute effects of 20g of a plant-based v animal-based protein supplement on postprandial metabolism, appetite and subsequent energy intake. Fifteen healthy adults (mean ± SD age: 26±4.4y) completed three study visits in randomised single blind crossover study design. After an overnight fast, participants consumed one of three test drinks: 20g whey or plant protein supplement (mix of pea, brown rice and pumpkin seed protein) prepared with water only, or an equivalent volume of water (control). Blood metabolites, insulin and GLP -1 were measured at baseline and over three hours postprandial alongside EE, substrate utilisation, and subjective appetite. Intake from an ad libitum lunch meal was used to access the effect of each supplement on subsequent energy intake. There was a significant main effect of condition and time on plasma ketones and NEFA (p<0.05). Postprandial ketones were significantly lower after whey compared to control at T90 (p=0.014) and T120 (p=0.025). There was no significant difference in ketone levels between plant protein and control or between the two proteins. Postprandial NEFA were significantly lower after whey at T30 (p=0.003), T60 (p<0.0001), T90 (p<0.0001), and T120 (p=0.003), and after plant protein at T30 (p=0.049), T60 (p<0.0001) and T90 (p<0.0001) compared to control. NEFA levels were significantly higher after plant protein compared to whey at T30 (p=0.031) and T60 (p=0.008). Subjective feelings of hunger were significantly lower at T60 after whey (p=0.002) and plant protein (p=0.018) compared to control, but there was no significant difference between the two proteins. Consuming protein may disrupt fasting through eliciting a transient reduction in ketones and NEFA, and this was more pronounced after eating whey protein. However, both protein sources were effective in reducing feelings of hunger one hour after intake which may be helpful in the context of reducing hunger experienced during TRE. Analysis of postprandial glucose, insulin, GLP-1 and EE will further elucidate the effects of protein on fasted metabolism.