My heart rate is always elevated after I eat hovering around 100 or so resting and 120-130 on exertion for an hour or so after I eat. I guess it has been doing it so long I don't pay it much mind. I also tend to get most of my pvcs/pacs after I eat as well so like itdood said, I think the vagus nerve is being stimulated and sending signals to the heart causing it to act up. So how fast is your heart beating? Do you feel faint? The other issue you may want to check out might be hyperthyroidism. It can cause a fast heart rate and weight loss. If you haven't had it checked you might want to go to your GP to be tested. Take care, I am sure whatever it is, is nothing to worry too much over.
It might not be a particular food. Our body will naturally send a signal to the heart through nerves to speed up when we eat. This is to help us digest the food and to absorb it. It's a way of getting more blood to the intestines to help those muscles and to also absorb the nutrients.
There's a bunch of different things that could be going on. It might be your own anxiety about it, contemplating that it's going to happen. Or, your heart is speeding up more than normal for various reasons. Or, there might be some sort of pressure in your belly pressing these nerve branches that go to your heart. You see, the same nerves that go to you GI tract also go to your heart, so people notice that when they have GI distress they also get weird heart issues too. Or, there might be something wrong with your biochemistry.
You might want to try some high calorie drinks like Ensure, it might be easier to digest. See your doctor and have it looked into.
I had something very similar, I was checked out by a cardiologist. They ruled out any problems, I just had to live with it. Eventually it did get better.
Start by going to your general practitioner and have an EKG done and a blood work. Then go from there.