Food waste has a great impact on food and nutrition security, the environment, and global, regional as well as national economies. However, little is known about the associated nutrient loss embedded in wasted foods, especially in developing countries, with Lebanon being a case in point. The present paper uses data gathered from a survey of 250 households conducted in Beirut, Lebanon, in which respondents filled 7-day food waste diaries in order to investigate the drivers of food waste generation at the household level and its dietary content. The results show that food waste is approximately 0.2 kg per capita per day in urban Lebanon. This wasted food contains on average 451.2 kcal, 37.5 g carbohydrates, 14.9 g protein, 2.9 g dietary fiber, 2.4 μg vitamin D, 165.2 mg calcium and 343.2 mg potassium. Furthermore, a Tobit analysis of the socio-demographic and behavioral drivers of food waste generation was conducted. This analysis shows that being the sole homeowner, spending more on food, having a larger number of household members, being ready to eat everything prepared, and tending not to buy special offers, significantly increases household food waste generation, at least in terms of physical weight. This is the first study conducted in Lebanon and the Middle East aiming at investigating food waste, and the associated nutrient loss as well as the drivers of food waste generation at the household level. This work could help provide evidence for policymakers to address both food and nutrition security issues in Lebanon.