Until recently, most Americans had never heard the term “seed oils,” even though they’ve likely cooked with and consumed them for decades. It’s the catchy description coined by internet influencers, wellness gurus and some politicians to refer to common cooking oils — think canola, soybean and corn oil — that have long been staples in many home kitchens. Those fiery critics refer to the top refined vegetable oils as “the hateful eight” and claim that they’re fueling inflammation and high rates of chronic diseases like obesity and diabetes. Robert F. Kennedy Jr., the new health secretary, has said Americans are...