Investigators at Washington University School of Medicine in St. Louis have found that eating a low-calorie yet nutritionally balanced diet lowers concentrations of a thyroid hormone called triiodothyronine (T3), which controls the body's energy balance and cellular metabolism. The researchers also found that calorie restriction decreases the circulating concentration of a powerful inflammatory molecule called tumor necrosis factor alpha (TNF). They say the combination of lower T3 levels and reduced inflammation may slow the aging process by reducing the body's metabolic rate as well as oxidative damage to cells and tissues.
For the new study, researchers examined 28 subjects who had been eating a calorie restriction (CR) diet for an average of six years. Although the CR group consumed fewer calories -- averaging only about 1,800 per day -- they consumed at least 100 percent of the recommended daily amounts of protein and micronutrients. A second group of 28 study subjects was sedentary, and they ate a standard Western diet. A third group in the study ate a standard Western diet -- approximately 2,700 calories per day -- but also did endurance training. The researchers found reduced T3 only in the people on CR diets.
Echocardiograms showed that the hearts of people on calorie restriction were more elastic than those of age- and gender-matched control subjects. Their hearts were able to relax between beats in a way similar to the hearts of younger people.
Researchers at Washington University School of Medicine are getting ready to launch a 2-year study to look at the effects of calorie restriction. Later this year, they will begin recruiting volunteers between the ages of 25 and 45 who are willing to go on a CR diet for 24 months.