If a substance can be bad for people with one set of genes, but harmless or beneficial for people with different genes, it’s easier to see why studies that lump everyone together can be unclear or misleading. In one way, today’s cutting-edge nutritional research is pointing back toward older truths, said Ray Rodriguez, who heads UC Davis’ nutritional genomics center and who organized the weekend conference. “People don’t always respond the same way to the same diet. I think our ancestors knew that, our grandmothers knew that, but experts assumed we really all did respond the same,” Rodriguez said. One of his favorite examples is a low-fat diet. Most people with high cholesterol see it drop when they consume less fat. But a smaller group, roughly 30 percent, see it increase instead. Other examples are certain to come tumbling out as academic researchers, pharmaceutical companies and the food industry keep exploring what our bodies do with foods we eat.