To perform the various activities the human body requires energy. This energy is got from food. The food that we eat is finally broken down to glucose also called sugar (carbohydrates breakdown product), amino acids (protein breakdown product) and fatty acids (fats breakdown product). This Blood Glucose is absorbed by the intestines in to the blood. It goes to the liver and all the other organs of the body .Insulin secreted by the beta cells of pancreas also enter the blood stream. Insulin carries the Blood Glucose or Blood Sugar inside the cells in different parts of the body. Inside the cells through a complex process the glucose is broken down and energy is released or stored. This energy carries out all the functions of the human body .hence glucose (commonly known as sugar) provides the source of energy for carrying out bodily functions.
Common sugar we use is sucrose. It is a disaccharide or two glucose molecules joined together. So blood sugar is not sucrose but glucose. When we eat sugar the sucrose is broken down to two molecules of glucose. This glucose is absorbed in the blood stream. All sources of carbohydrates (rice, cereals, salads, vegetables etc) are finally broken down in the body to form glucose for energy. These are called complex carbohydrates and they get slowly broken down in to glucose molecules and hence lead to mild increases in blood sugars in a diabetic.
Pulses, eggs, meat and fish have predominantly proteins and little carbohydrate. So they do not increase blood sugars greatly. Oil, ghee, butter, cheese are pure fats and hence does not increase blood sugars. However they are high calorie and hence lead to increase in weight and cholesterol and complications.
So blood sugar is same as blood glucose. Different food items will increase blood glucose to different extent. This ability to increase blood glucose is called the glycemic index of a particular food.Glycemic index of glucose is 100. All other food substance have less than 100 glycemic index .sweets, chocolates, ice creams have high glycemic index and hence will increase blood sugar rapidly. Salads, pulses, green veggies and meat and eggs have low glycemic index and will increase sugars slowly and marginally.
Hence the basis of diet in diabetes involves consuming low calorie and low glycemic index foods .These foods will not suddenly increase blood sugars and allow the body and medications time to act and gradually decrease blood sugar levels.