Updated December 16, 2014.
Green beans, string beans, snap beans -- they are all the same thing, and they have a lot to offer us in the way of nutrition for a very low amount of carbohydrate. (Yellow string beans aren't quite as nutritious as the green type.)

Carbohydrate and Fiber Counts for Raw Green Beans

• ½ cup green beans (or about 10 4" beans): 2 grams effective (net) carbohydrate plus 2 grams fiber and 17 calories
• ¼ lb (4 oz) green beans: 4 grams effective (net) carbohydrate plus 2 grams fiber and 35 calories

Glycemic Index for Green Beans

As with most non-starchy vegetables, there is no scientific study of the glycemic index of green beans.
More Information about the Glycemic Index

Estimated Glycemic Load of Green Beans

• ½ cup green beans (or about 10 4" beans): 1
• ¼ lb (4 oz) green beans: 3
  

More Information About the Glycemic Load

Health Benefits of Green Beans

Green beans are a very good source of fiber. They are an excellent source of Vitamin C, a very good source of Vitamin K and Vitamin A and a good source of folate and manganese. They also contain fair amounts of many other nutrients including potassium, iron, beta-carotene, lutein and B vitamins.

Low-Carb Recipes with Green Beans

• Green Bean Casserole with Onion Topping
  
  
• Garlic Green Beans with Pine Nuts
  
  
• Chicken (or Turkey) Pot Pie
  
  
• Easy Thai Coconut Chicken Curry
  
  

More Information About Green Beans at Calorie Count.
More Carb Profiles:

• Fruits
  
  
• Vegetables
  
  
• Nuts and Seeds
  
  
• Grains and Legumes
  
  
• Milk, Cream, Soy Milk, etc.

<sub>Sources:

Leroux, MarcusFoster-Powell, Kaye, Holt, Susanna and Brand-Miller, Janette. "International table of glycemic index and glycemic load values: 2002." American Journal of Clinical Nutrition. Vol. 76, No. 1, 5-56, (2002).

USDA National Nutrient Database for Standard Reference, Release 20.</sub>