Kerala doesn't have a restaurant culture. People eat with their families at home or are too poor to eat in what we would call restaurants. When I first visited in 1970, I recall the food being very spicy and served on banana leaves. Kerala has been developed into a major tourist destination since then and there are a lot more hotels and restaurants catering to the needs of both domestic and international tourists.
Getting into the native foods of the places I visit are part of why I live travel so much. And the food of South India is very, very different from the food of North India, the food people in the States and Europe are usually talking about when they mention "Indian food." And the food in South India is different from region to region. In Kerala, the Malayalam cuisine is obviously based on the local ingredients-- coconuts, spices (cardamom, chili, tumeric, coriander, cloves, ginger, cinnamon, pepper, cumin, etc), fish, rice, fruits and vegetables...
The tourist guide books for Kerala all celebrate the restaurants in the luxury hotels. With no real restaurant culture, they've long been the places where you could get hygienic and good-tasting food. But not remotely Keralan food. The Keralan food served in the 5-star hotel restaurants is made for elderly Brits and German-- very nearly tasteless. To say the spice factor is cut back to a minimum is a joke. Top rated restaurants in Ft. Kochi (Cochin) are expensive and attempt to be as European-friendly as they can. Fodor, for example, recommends The History at the exclusive hotel, Brunton Boatyard. It wasn't bad-- not at all-- but it was completely forgettable, uninteresting and way over-priced. We ate there on our first night. After that we asked everyone where we could find the best authentic Keralan cooking. There was a consensus and we found the Pavilion at the modest Abad Hotel in Chullickal, a one dollar tuk-tuk ride from Ft. Kochi. We ate there half a dozen times, and not because it was so shockingly inexpensive. We ate there so often because the food was absolutely delicious-- and because they didn't tone it down just because we're white.
Neither of us even had so much as a loose movement the whole time we were in Kerala. The food was healthy, clean, delicious and nutritious. As long as I'm bringing up body functions, there is one thing I want to mention. This is the "cool" and "dry" season-- relatively-- but it never drops below 90 degrees and it's so humid that nothing gets dry. So we're drinking water all the time. And sweating out out. I've rarely consumed as much water but rarely pissed as infrequently. It all gets sweated out. It's essential that if you visit Kerala you drink a lot of water-- a lot more than usual.