In recent years, chronic diseases, such as high blood pressure, diabetes, heart attack, and cancer, have increased around the world. Obesity is a common factor that makes individuals susceptible to these diseases. One reason for excessive weight gain is the frequent consumption of fast food. This study examined the impact that fast food has on obesity by analyzing the influence of peer pressure on fast food consumption and the role that exercise plays in weight gain. Two mathematical models were proposed to study each factor separately. The models demonstrated the dynamics of individuals transitioning from one weight class to another according to their body mass index (BMI). The models were governed by systems of nonlinear ordinary differential equations. A qualitative approach for analyzing the systems was utilized, and the numerical simulations supported the qualitative results. The results of this study may contribute to the development of strategies for controlling obesity. In particular, the models showed the importance of resisting peer pressure that drives individuals to eat fast food meals, as well as maximizing the role that quitters can play in convincing obese individuals to stop consuming fast food meals. In addition to the two previous strategies, the research revealed that physical activity has a significant role in reducing weight.

近年来，高血压，糖尿病，心脏病和癌症等慢性疾病在全球范围内呈上升趋势。肥胖是使个体易患这些疾病的常见因素。体重过度增加的原因之一是经常食用快餐。这项研究通过分析同伴压力对快餐消费的影响以及运动在增重中的作用，研究了快餐对肥胖的影响。提出了两个数学模型来分别研究每个因素。这些模型展示了根据体重指数（BMI）从一个体重类别过渡到另一个体重类别的个体的动态。这些模型由非线性常微分方程组控制。采用了定性方法来分析系统，数值模拟证明了定性结果。这项研究的结果可能有助于控制肥胖的策略。尤其是，这些模型显示了抵制驱使同伴施加压力的个人的重要性，这些同伴迫使个人吃快餐，并最大程度地发挥戒烟者在说服肥胖的个体停止食用快餐方面的作用。除了上述两种策略外，研究还表明体育锻炼在减轻体重方面也起着重要作用。并最大程度地提高戒烟者在说服肥胖者停止食用快餐方面的作用。除了上述两种策略外，研究还表明体育锻炼在减轻体重方面也起着重要作用。并最大程度地提高戒烟者在说服肥胖者停止食用快餐方面的作用。除了上述两种策略外，研究还表明体育锻炼在减轻体重方面也起着重要作用。