Regarding Blood Sugar Level. Excercise.

My Father was suffering from Pain in legs last year. So we Consulted our Physician. He suggested to go for a sugar test. We had blood sugar PP done. The result came 227. But our doctor told my father to reduce potato intake and limit sugar intake and gave a diet chart for controlling sugar. He told to again go for PP test after 15 days. We again had it. This time result came out to be 124. He said it is normal now. He asked to get it checked every month and follow diet chart strictly. No medicine was prescribed. We went for test almost every month and readings of PP test came as follows. 1.124 2.120 3. 136 4.151 Now today again he went for PP test and result is 178. So does he needs medicine now or upto 180 its considered okk. My doctor said that upto 180 after 2 hours of meal is ok. So please confirm whether 178 is high or its normal which could be controlled through diet and excercise.