From a non-American's perspective, I think part of the mistrust comes from Americans have been through high-profile lies perpetrated by government agencies.

For example, a more recent one in the last few decades is the Food Pyramid/MyPlate that was/is promoted by the US government's agriculture department. This has led to Americans in the late '70s/early '80s to start a war on saturated fat and cholesterol, and the rapid adoption of carbohydrates in the average diet. What has happened in the decades following is a rapid increase in metabolic diseases such as cardiovascular disease, diabetes, and mental illnesses — all of which were rare in human history prior to the '70s. While I'm glad Americans are waking up to the realisation of the mass brainwashing of what constitutes "healthy" food, I'm still upset that — due to the influence of America on the global stage — my own country has followed suit in adopting the US's dietary guidelines to the detriment of our own health.