In the middle ages, wild celery was used as a medicinal plant to treat anxiety, insomnia, rheumatism, gout and arthritis. Luckily for us, in the 15th century a sweeter, more tender variety was developed, providing the perfect crisp and tasty, low calorie snack. Celery is a good source of potassium, helping to control blood pressure and counteract the negative effects of too much salt in the diet. It also contains dietary fibre, which helps to keep your digestive system healthy.