Difficulties in measuring habitual food intake following gastric bypass surgery has severely undermined efforts to address key questions regarding subsequent weight loss. However, a recent study published in The Journal of Nutrition suggests that the decline in energy intake post-surgery can largely be attributed to eating the same foods as those eaten pre-surgery but in smaller amounts, as reported by M Barbara E Livingstone (Ulster University) and co-authors. According to the research team, these findings challenge prevailing views about the dynamics of food intake following weight loss surgery. 

Gastric bypass surgery is one of the most effective treatments for obesity. Yet, the mechanisms underlying sustained weight loss following surgery are complex and poorly understood. To bridge this knowledge gap, changes in 24-hour energy intake, food preferences, and associated eating behaviors in patients were evaluated and compared with time-matched weight-stable control participants. To ensure the highest degree of sensitivity and accuracy over outcome variables (total energy intake, relative energy intake from fat and sugar, food preferences, eating behaviors, and body composition), all measurements were made under fully controlled residential conditions.

Participants were studied on 3 occasions, at baseline (1 month pre-surgery) and at 3- and 12-months post-surgery.  At each time point, participants completed a 36-hour stay at a fully residential human intervention study unit that consisted of bedroom suits and communal living and dining areas.  To ensure that food and beverage choices were compatible with usual food intake, participants completed a food choice questionnaire.  Food choices were used to design personalized menu of foods based on a 6-macronutrient mix paradigm.  Each participant was allowed 24-hour unlimited access to the same personalized menu of foods throughout each study visit. 

Explicit (conscious) and implicit (subconscious) measures of food reward were determined by presenting participants with images food items that were either high/low fat and sweet/savory. Participants rated the foods based on how pleasant the food would taste (explicit measure) and by which food (high fat compared with low fat foods and sweet foods paired with savory foods) they would most want to eat now (implicit measure).

Among participants serving as controls, there was an increase in relative fat intake at 3 months, but no other changes were observed in food intake or body composition. At 12 months post-surgery, patients lost on average 27.7 pounds of initial body weight. The decline in energy intake at 3 months post-surgery was followed by a partial rebound at 12 months, but at both times, dietary energy density and relative macronutrient intake remained constant. The decline in energy intake was due to eating the same foods as consumed pre-surgery and by decreasing the portion size, but not the number of eating occasions. Although patients reported a diminished explicit liking for sweet foods at 3 months post-surgery and a lower desire to consume them at both 3- and 12-months post-surgery, intake of high-sugar foods was maintained.

Collectively, study findings suggest that post-operative eating behavior may be predictive of longer-term weight change and merits further investigation.  Expressed changes in preference for high-sugar foods did not manifest in decreased consumption and the partial rebound in energy intake at 12 months was attributed to eating the same pre-surgery foods but in smaller amounts.


M Barbara E Livingstone, Tamsyn Redpath, Fathimath Naseer, Adele Boyd, Melanie Martin, Graham Finlayson, Alex D Miras, Zsolt Bodnar, David Kerrigan, Dimitri J Pournaras, Carel W le Roux, Alan C Spector, Ruth K Price, Food Intake Following Gastric Bypass Surgery: Patients Eat Less but Do Not Eat Differently, The Journal of Nutrition, Volume 152, Issue 11, November 2022, Pages 2319–2332, https://doi.org/10.1093/jn/nxac164.

Images via canva.com.