Does walking effectively help?

Before I try to concieve, I'd like to get a bit more fit and healthy (ensure the best possible pregancy!) My SO and I have been drinking much more water, and eating better foods in better portions.
​I am not heavily overweight, but i do have about 2-3 inches of back fat, and a muffin top that it about 1.5 inches. I want to start walking about a mile every weekday (its on my way, so convienient) and i have family members that are skeptical that it will really change anything. They say the only way is to jog/run because it increases my heart rate.
Is this really true? I'd like some helpful advice. Thanks!