A fad diet is a trendy dietary pattern that promises quick and easy weight loss. It has become popular among people due to increasing obesity and social media. The aim of the study was to analyze the use of fad diets among office workers who spend most of the day sitting at a desk. The research design was cross-sectional in 152 office workers aged over 18 years. The survey consisted of 24 questions, and four sections. Pearson chi-square, Fisher's exact test and logistic regression analysis were used for data analysis. Of the 50 (32.89%) participants who tried a fad diet, the majority were female (86%). The ketogenic diet was more likely to follow a fad diet by participants (40%). The influence of person to person (50%) was commonly reported as a motivating factor for using fad diets by participants who tried them. In addition, the majority of participants (68%) who adhered fad diets reported that they achieved the desired result. Fad diet users and non-users differed by gender (p = .003), satisfaction with current weight (p <.000) and BMI (p= .021). The use of fad diets was positively correlated with some variables, including gender (p = .020), and satisfaction with current weight, body image (p = .006). In addition, when asked by 100 participants why they had not consulted qualified professionals, more than half (59%) replied: "I never thought about it.". Some participants described, "Because I did not know who and where to ask for advice" (27%), and "Because it's expensive" (7%). In summary, the ketogenic diet was the most common fad diet among office workers in Ulaanbaatar. Interpersonal influence was a motivating factor for participants to start the diet. A large percentage of respondents said they had never thought to ask a qualified person about fad diets.