Despite of modest gains in the fight against the obesity epidemic in recent years, health experts still don’t seem to have a definite answer to what exactly causes weight problems on such a large scale, not only here in the United States but, progressively, around the world.

A new study published in CA – A Cancer Journal for Clinicians examined an array of potentially contributing factors such as changing eating and lifestyle habits, larger portion sizes, availability and affordability of food, to mention just a few.

The latter – availability and affordability – seemingly stand out among possible culprits, according to this study.

Not only are we eating more highly caloric foods, we eat more of all types of food, mainly because food has become much cheaper, nearly ubiquitous, and more convenient to prepare, said Dr. Roland Sturm, an economist at RAND Corporation, a non-profit organization that specializes in public policy research, in a press release that came with the study.

In cooperation with his fellow-researcher, Dr. Ruopeng An, a professor at the Department of Kinesiology and Public Health of the University of Illinois at Urbana-Champaign, Dr. Sturm investigated what percentage of their income average Americans spend on food today, and found that it is proportionally much less than their parents and grandparents had to.

Food in America is cheaper now than it has ever been in history, the researchers concluded. In the 1930s, most people spent about one-quarter of their income on food. In the 1950s, it dropped to one-fifth. Today, it is around one-tenth.

“Not only has the cost of food dropped, but it has become even more available,” wrote Dr. An in the press release. “So a smaller share of Americans’ disposable income now buys many more calories,” he added.

The argument that greater availability and lower prices help increase consumption is certainly valid. Yet, does that really explain why so many people can’t stop eating to the point where they get seriously ill?

I think the picture is much bigger.

The fact is that not all foods are equal. The cheapest items often have the least nutritional value – like processed meals and snacks that are typically high in calories as well as fat, sugar, and salt content. The healthiest kind, on the other hand, like fresh produce, lean protein sources, and whole grains, are not only out of reach financially for low-income families, they are not even always available where they live – in so-called food-deserts.

Besides economic constraints, lack of awareness and education in health matters also plays a role. The public is quite confused about which diet and lifestyle guidelines to follow, considering the oftentimes contradictory messages people are given.

Having cheap and abundant food available by itself should not automatically lead to unhealthy consumption, as the study seems to suggest. As consumers, we are ceaselessly bombarded with food advertisements, prodding us to eat far more than our bodies can possibly need.

In addition, government policies that subsidize large-scale production of commodities like corn and sugar, but give nothing to fresh produce farmers, may keep prices down for some (mostly processed) foods but also contribute indirectly to our public health crisis.

To improve the current situation, the research duo agrees that changing our existing food environment has to be part of the equation. Appealing to personal responsibility alone will not do. Influencing pricing for unhealthy foods through taxation may be one way. But while they don’t reject outright certain forms of intervention through policy changes, they don’t believe those to be effective enough.

Unfortunately, as long as we cannot agree on the causes of the obesity crisis, real solutions will remain elusive as well.

Timi Gustafson R.D. is a registered dietitian, newspaper columnist, blogger and author of the book “The Healthy Diner – How to Eat Right and Still Have Fun”®, which is available on her blog and at amazon.com.  For more articles on nutrition, health and lifestyle, visit her blog, “Food and Health with Timi Gustafson R.D.” (www.timigustafson.com).