ORIGINAL ARTICLE Effects of food form on appetite and energy intake in lean and obese young adults DM Mourao 1 , J Bressan 2 , WW Campbell 1 and RD Mattes 1 1 Department of Foods and Nutrition, Purdue University, West Lafayette, IN, USA and 2 Universidade Federal de Vicosa, Vicosa, Brazil Objective: To investigate the independent effect of food form on appetite and energy intake in lean and obese adults using high carbohydrate, fat or protein food stimuli. Design: Crossover dietary challenge with matched beverage and solid food forms: high carbohydrate (watermelon and watermelon juice); high protein (cheese and milk); high fat (coconut meat and coconut milk). Subjects: A total of 120 lean (18–23 kg/m 2 ; N ¼ 60) and obese (30–35 kg/m 2 ; N ¼ 60) adults (18–50 years old) with stable body weight. Forty different participants (N ¼ 20 lean and 20 obese) were tested with each of the food systems. Measurements: Appetitive sensations, food palatability and dietary intake. Results: Regardless of the predominant energy source, the beverage food form elicited a weaker compensatory dietary response than the matched solid food form. Thus, total daily energy intake was significantly higher by 12.4, 19 and 15% on days the beverage forms of the high-carbohydrate, -fat and -protein foods were ingested, respectively. This was due more to a weak effect on satiety than satiation. The obese participants had higher energy intake at the lunch, including the beverage high- protein load, but overall differences between lean and obese participants were small and not systematic. Conclusion: Food rheology exerts an independent effect on energy intake. Dietary compensation for beverages is weaker than for solid food forms of comparable nutrient content. Thus, they pose a greater risk for promoting positive energy balance. International Journal of Obesity (2007) 31, 1688–1695; doi:10.1038/sj.ijo.0803667; published online 19 June 2007 Keywords: viscosity; beverage; energy intake; appetite; feeding; human Introduction Accumulating evidence indicates that energy-yielding bev- erages evoke weaker appetitive and compensatory dietary responses than energy-matched food challenges in solid form. 1–7 Further, there is increasing documentation of a positive association between beverage consumption and body weight or body mass index (BMI). 4,8–13 The mechan- isms by which beverages and solid food forms elicit differential appetitive and dietary responses are not known. Studies comparing responses to different beverage and solid foods (for example, fruit juice vs cheese and crackers, 14 or soda vs cookies 15 ) have yielded mixed findings. To isolate the independent effect of food rheology on appetitive and dietary responses, it is essential to hold other attributes constant. One study applied this approach to contrast responses to a solid casserole and soup, 16 but responses to soups and beverages differ markedly – soup has higher satiety value. 17,18 An aim of this study was to contrast appetitive and acute compensatory dietary responses to solid foods and beverages closely matched on all but rheological properties. Macronutrient-specific effects on satiety and satiation are well documented. 19–21 Most, although not all, studies of these effects employed solid food vehicles. Less is known about the existence or magnitude of differential influences in beverages. Some findings suggest that they may not hold. 22,23 While there may be differences in nutrient composition and energy density among beverages that mitigate viewing all beverages similarly, from an energy balance perspective, distinctions may not be valid. The principal source of energy from beverages in the US diet over the past two decades has derived from carbohydrate, 24 but there is increasing popularity of beverages with different primary energy sources (for example, specialty coffees with high fat content and performance enhancing beverages containing high protein concentrations). Whether, and to what extent, these items pose a particular challenge to energy balance requires assessment. A second aim of this Received 11 December 2006; revised 7 April 2007; accepted 8 May 2007; published online 19 June 2007 Correspondence: Dr RD Mattes, Professor of Foods and Nutrition, Department of Foods and Nutrition, Purdue University, 212 Stone Hall, 700 W State Street, West Lafayette, IN 47907-2059, USA. E-mail: mattes@purdue.edu International Journal of Obesity (2007) 31, 1688–1695 & 2007 Nature Publishing Group All rights reserved 0307-0565/07 $30.00 www.nature.com/ijo