I've been riding regularly since July. I've lost 35 lbs. and am regularly doing 100-120 miles a week on the three to four days I have time to ride. I decided to do a metric century and had a miserable ride.
I tried eating prior to my ride to have a little more energy. I hadn't done anything that long for at least 10 years. I ate a bowl of shredded wheat in Silk with a banana around 7 am. I was going to leave at 8 but saw the weather and that the wind was going to pick up and so I left at about 7:15 am. During the first hour and a half of my ride I couldn't give any effort without my heart rate going way high. I putted along a 14 mph on the flats and my heart rate was 145. After the hour and a half were up, I rode a little better and my heart rate went down into the 130 range but I was still only going 15-16 mph (still on level ground). After another hour, I finally was able to get up to speed and cruised along at 18 mph and my heart rate stayed about 130. After doing that for awhile I started getting tired and so I stopped and ate an Energy Bar and tried to ride again and felt like my legs were absolutely out of gas. I did make the ride but felt like crap most of the time.
I ate pasta the night before and slept fairly well. What gives? After the ride, I also had very little appetite.
There are certain "rules" for how much time the average person needs to wait after eating to begin a strenuous activity. The more you eat and the more fat and protein, the longer you have to wait. The times run in hours. You'll find them in various cycling publications. You didn't wait long enough for that particular meal at that particular time.
Another possibility is soy. I react poorly to soy and can't use it. Makes some sense as I'm of Euro ancestry and not Asian.
A better strategy would have been to eat a couple of hours before the m century and snack periodically on an energy bar (like eat a quarter of it at a time) and gels.
eat a big meal the night before a big ride. Have a good breakfast, and let it settle for an hour. Use the first hour to build to cruising speed. You want to start as slow as a mule. Baby yourseself until you get warmed up, then turn up the speed gradually. After an hour, you wll be dying to let it loose, and you'll be ready.