Trans fats. Initially recommended as safe alternatives to saturated fat but turns out they’re absolutely horrible for you. It was known for a while but not acted on until the 1990s or so. They’re now being heavily regulated in the US as 0.5g or less per serving size. The WHO estimated in 2018 that trans fats cause roughly 500,000 deaths per year due to cardiovascular disease. Good news is now they’re much harder to get from foods that used to have a lot like margarine, peanut butter, or shortening as they have to contain less than a gram per serving.
Follow the money.
Different federal groups recommend things like lots of dairy - milk and processed cheese, tons of animal products, vegetable oils, grains as the basis and bulk of each meal, etc.
Public school nutrition guidelines through the CACFP are possibly the worst that I’ve personally dealt with. Tons of processed grains and milk. Tons of ground meat. Pizza counts as a complete meal because of tomato sauce. Applesauce and fruit cups instead of fresh fruit. Pretty poor excuse for the possibly healthiest meal some of these kids get each day.
The American heart association’s recommendations were bad last time I looked too but I can’t remember why off the top of my head.
Not exactly what you’re after, but rations for reservations led to much unhealthy eating for the indigenous people. Fry bread, I believe, is a result of the sugar, flour, lard that was ‘offered’ to replace ranging to hunt and collect familiar foods. You might be able to trace US Gov policies and actions all the way to indigenous diabetes rates in the US SW. I’ve read something about a specific tribe having some of the highest diabetes incidence on the planet. Tribe is the Pima. Most research papers seem old (around a decade in age), but here is a fresh graphic from the National Indian Council on Aging: https://www.nicoa.org/diabetes-still-highest-among-ai-an/
The extreme government incentivization of cheese. The huge surplus of it means they have to subsidize it to chain restaurants and they put it in absolutely everything. It’s basically just a good way to up the calories in just about everything.
Some of the worst nutrition advice has actually been the lack of it.Somehow ‘legal’ came to mean ‘not bad.’ So if a manufacturer could put it in food, it must be just fine to eat. This is, in fact, not the case. The FDA+CDC should’ve been clear from the get-go: just because they’ve allowed it in there doesn’t mean that food is healthy.
Wrong = Just the generic idea that everything that happens to grow, or is planted as a crop, or is raised as livestock in America just happens to be the things our government deems ‘healthy’ for Americans
9-11 servings of bread / grains a day and also the recommended dairy consumption. Eliminating gluten and dairy has made a huge difference in multiple ways. The government simply recommends whatever the lobbyists have paid them to.