Gaining weight is not simply a matter of counting calories, according to new research from Tel Aviv University Professor Amit Gefen.

What also matters is “mechanical stretching loads,” which is the weight people put on their body tissues when sitting or lying down. Gefen’s study is published in the “American Journal of Physiology.”

It shows that fat cells produce “more triglycerides, and at a faster rate, when exposed to static stretching,” he said.

Gefen first noticed that bed-ridden and wheelchair-bound people’s fat cells were invading muscles. This prompted him to study the effect of mechanical load on fat tissue.

In his experiment, he stimulated cells to produce lipid droplets. One group was placed in a cell-stretching device for prolonged periods of time and one group was not.

After just two weeks, the stretched cells developed “significantly more” and larger lipid droplets. When the cells reached maturity, the cells that were stretched produced fifty percent more fat than the cells that were not.

“Obesity is more than just an imbalance of calories,” said Gefen. He also commented that many people nowadays probably live too sedentary lifestyles.

Indeed, new research is shedding light on evidence that body weight is more than a matter of caloric intake.

Professor Robert Lustig of University of California, San Francisco, for example, claims that excessive calorie intake from sugar induces more weight gain than the same calorie intake from other sources (from grains, for example).

He blames increased sugar consumption for the rising rates of obesity in the U.S. in the last few decades. Among other detrimental effects, he claims sugar disrupts the body’s ability to regulate weigh gain and satiety.

In his viral lecture “Sugar: The Bitter Truth” (below), he cited a study that showed excessive sugar intake adversely affected peoples’ ability to lose weight through exercising.