They did several things to fatten and sicken Americans at an exponential pace over the last 50 years or so. 

1. Replaced raw/organic food with heavy pesticide-sprayed/GMO grown highly processed food

2. Established a food culture where Americans are trained to eat more than 2 or 3 times a day; many Americans currently have 5-6 feeding sessions per day

3. Established a food culture where the prominent use of seed oils and highly processed carbs replaced healthy fats for the body's daily energy.  [Your body actually runs FAR BETTER and more efficiently burning fat for it's fuel rather than sugary high-processed carbs]

4. Dumped a massive amount of chemicals into the US food supply; more than 700+ new chemicals were allowed into the food supply since just 2000, by the FDA

These 4 things in combination have resulted in a staggering national health crisis. 

Reversing the trend isn't hard; it's just going to take commitment.  You have to

1. Ditch the highly processed fake food for real food

2. While eating real food, do not eat more than 3 different times in one day; intermittent fasting is a big health boost

3. Get into a state where your daily carb consumption is so low, your body switches to fueling itself off of your bodyfat and the animal fat in your diet. 

4. In addition to avoiding the fake toxic food full of all of those 'generally recognized as safe' chemicals in them, take real steps to detoxify your body. 

You can make dramatic changes in a very short amount of time doing this.