Mere smell of food may make you fat

Mere smell of food may make you fat

A mouse's sense of smell might be a contributing factor in its weight gain and loss.

When a mouse can't smell its food, it thinks it has eaten more than it has, triggering more energy use.

The team also found that mice with a boosted sense of smell - super-smellers - got even fatter on a high-fat diet than did mice with normal smell. Losing the ability to smell also caused a different group of already-obese mice to lose weight, the researchers reveal today in Cell Metabolism.

But before you consider turning this information into a new weight-loss concept, beware: it's unclear whether humans would arrive at the same results as the mice. Once food is secured, the body feels free to burn it. They did so by studying both lean and fat mice, whose olfactory sensory nerves had been temporarily destroyed. The mice turned their beige fat cells - the subcutaneous fat storage cells that accumulate around our thighs and midriffs - into brown fat cells, which burn fatty acids to produce heat.

Under these stressful conditions, the body energizes itself by triggering a release of catecholamines, or adrenaline, 'which is known to turn on this brown-fat-burning program, ' says Professor Dillin. In the group on the high-fat diet, however, the mice that couldn't smell weighed 16% less than animals that could, which became obese.

On the negative side, the loss of smell was accompanied by a large increase in levels of the hormone noradrenaline, which is a stress response tied to the sympathetic nervous system.

"That would be unbelievable", Dillin noted. This suppressed the mice's sense of smell.

The reverse is true for mice engineered to be "super-smellers".

Instead, the researchers determined, they stayed svelte because they burned more calories, especially in their brown fat.

At the end of the tests, these latter had mostly doubled their initial weight.

"It's one of the most interesting discoveries to come out of my lab", author Andrew Dillin exclaimed. Then they fed the animals either a normal diet or one made up of fatty foods - at least among mice - that generally lead to obesity. These mice lost only fat weight, with no effect on muscle, organ or bone mass.

The work was supported by the Howard Hughes Medical Institute, the Glenn Center for Research on Aging and the American Diabetes Association.