Forget everything you know about what's making us fat.
We hear a lot about Americans being fast food-addicted couch potatoes, and while that does play a role in the nation's expanding waist lines, a new study concludes it's not the driving force behind the obesity epidemic.
Instead all Americans -- no matter what income level they have and no matter what neighborhood they live in -- are getting bigger because food is cheaper than ever before, the study authors say. Simply put, we're spending less of our total budget on food so we're buying more.
The study, published in the June edition of the journal CA Cancer, found that people in 1930 spent about a fourth of their disposable income on food. Today food takes up about a tenth of our disposable income. Food is also easier to prepare and easier to purchase than it was in 1930.
That means Americans aren't just eating more high-calorie food, they are eating more of a variety of foods. Consequently, Americans have consumed, on average, about 20% more calories since the 1970s.
Lead study authors Roland Sturm and An Ruopeng hope it will lay to rest some myths about obesity.
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"If you look at the data over time, you actually see a slight increase in exercise. And Americans have more access to fruits and vegetables," said Roland Sturm who is a senior economist at the RAND Corporation. "It's not Southern hospitality that is driving this trend, nor is it income or education. Really nothing protects us from this challenge of obesity."
On average, Americans have been getting fatter since at least the 1950s, maybe even longer. While the data isn't perfect, experts looking at health records for men between the ages of 40 and 49 see a steady increase in body mass index since 1900.
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Obesity isn't only a problem for people who want to wear bikinis to the beach. Excess body fat can raise a person's risk for heart disease, cancer, diabetes, stroke and chronic illnesses.
"What this article reinforces is that we need to continue our research to find what combination of strategies will be most effective long term in helping all of us live healthier lives," said Colleen Doyle, director of nutrition and physical activity for the American Cancer Society.