The association between nutritional status and gait speed remains unclear. This study described gait speed in older adults and quantified the association between overweight, obesity, undernutrition risk and gait speed. Gait speed as potential indicator of nutritional outcomes was also explored. A cross-sectional analysis was conducted in a population-based sample of 1,500 older adults ≥65 years old. Compared to "normal body mass index" women, odds ratio for a slow gait speed was approximately 2-fold higher in"overweight", 4-fold higher in "obese" and 6-fold higher in women at "undernutrition risk". "Undernutrition risk" category resulted from joining "undernutrition risk/undernutrition". For men, these associations were in the same direction, but the odds ratio estimates halved. In women, identified gait speed cut-offs were 0.87 m/s for "obesity" and 0.79 m/s for "undernutrition risk". In men, 0.94 m/s is the cut-off in which most older adults were correctly classified relative to "undernutrition risk". About half of Portuguese older adults presented a gait speed ≤0.8 m/s. Overweight, obesity and undernutrition risk were directly and increasingly associated with slow gait speed, but approximately twice as high in women compared to men. Gait speed revealed potential utility in marking nutritional problems, but further investigation is recommended.