Pandemics and lockdowns may be associated with unpremeditated consequences, such as bodyweight changes, isolation, as well as sedentarity. Reports have been published on malnutrition among patients suffering from COVID-19. This study aimed to highlight the short-term effects of the lockdown on the nutritional health of elderly people living at home and benefiting from home care services, yet without any COVID-19 pathology. In 50 subjects displaying weight, body mass index, and MNA score stability two months earlier, we observed significant alterations in these parameters following the lockdown. Thus, malnutrition rose from 28–34% to 58%. Furthermore, trigger factors for malnutrition changed, with social isolation accounting for 64% of the confinement’s deleterious effects among the elderly. In conclusion, despite the elderly being not directly affected by SARS-CoV2, the nutritional status of elderly subjects living at home with no or only mild autonomy loss was greatly and rapidly affected by the lockdown. Moreover, the main trigger factors for malnutrition were essentially related to social isolation and depressive syndromes. Knowing the impact of confinement on the elderly’s health, these results may help further modulate ongoing public health interventions in case of future lockdowns.