Michael is one of 24 lean recruits in a preliminary experiment run by Celi and Chen. She spent two 12-hour overnights in a specialized room with precise temperature and airflow controls. During each session inside the chamber, she ate a diet of 50 percent carbohydrates, 30 percent fat and 20 percent protein — just enough, the scientists calculated, for her to maintain her weight — while they held the room temperature at 75 degrees for one session and 68 degrees for the other.
All the while, they measured her oxygen and carbon dioxide output. They calculated her body mass. She spent 10 minutes in an oval-shape, space-age-looking machine called a Bod-Pod, which computed the weight and volume of her fat composition. She swallowed a pill containing a sensor that traced her internal temperature, while patches placed on her skin gauged her external temperature. Her heart was constantly assessed, and every 30 minutes small amounts of fluids were collected from fat tissue around her belly to evaluate her metabolism. Blood and urine samples were also taken.
Another participant, Chris Nathasingh — 31 years old, 5-11 and 170 pounds — spent his 68-degree night with only a thin blanket to supplement his pajamas. He shivered and jumped in and out of bed to keep warm.
The next morning, he was exhausted but not very hungry. The second night, the temperature was adjusted to 75 degrees, and Nathasingh slept well. "I would not say that I was hungry or hungrier [after the second night], but I definitely could not wait to eat," he said. "Where sleep deprivation after the cold night made me only focus on sleep, the absence of such deprivation after the warm night made me focus on the next best thing: food."
Celi and Chen are optimistic about some early findings in the trial. The participants' energy expenditures went up when the room temperature was lowered. They plan to conduct a larger study, involving 180 volunteers, both lean and overweight.