The nutritionally balanced diet, which resembles the Mediterranean diet, is based on strict and steady limiting of calorie intake. In animal models such a diet has been shown to increase lifespan by as much as 30 per cent.
"This is the first study to demonstrate that long-term calorie restriction with optimal nutrition has cardiac-specific effects that ameliorate age-associated declines in heart function," said lead researcher Luigi Fontana.
"Calorie restriction is associated with longevity only when it is coupled with optimal nutrition. On the other hand, calorie restriction coupled with malnutrition accelerates ageing and causes severe diseases," said Fontana.
The study, published in the Journal of the American College of Cardiology (Vol. 47, Issue 2, pp. 398-402), followed 25 volunteers aged 41-65 who had a daily intake of between 1400 and 2000 calories for over six years. Heart function, blood pressure and inflammatory markers were compared against 25 age- and gender-matched individuals who had a calorie intake of between 2000 to 3000, typical of a normal Western diet.
As a natural process in ageing our heart hardens and pumps less effectively. Ultrasound examinations of the volunteers in the study showed that their hearts were more elastic than the control group.
"Diastolic function declines in most people as they get older," said Fontana. "But in this study we found that diastolic function in calorie-restricted people resembled diastolic function in individuals about 15 years younger."
The blood pressure of the case group was also significantly lower (102/61 mmHg) than the control group eating the Western diet (131/83 mmHg), as were the presence of inflammatory markers, like C-reactive protein, tumour necrosis factor alpha (TNF-alpha), and transforming growth factor-beta1 (TGF-beta1).
Previous studies have shown that overweight and obese people have a low-grade chronic inflammatory state.
This led Fontana and his colleagues to hypothesise that: "this chronic inflammation causes chronic tissue damage and associated adaptative fibrosis that leads to premature and accelerated tissue and organ hardening."
In an accompanying editorial, Dr Gary Gerstenblith, from the Johns Hopkins Hospital in Baltimore, said: "The value of the study is that it points to possible mechanisms explaining how ageing occurs and, therefore, how it may be modified."
Dr Gerstenblith pointed out however that many people would be unable to successfully adapt to such a strict diet.
"It is important to note that the caloric-restriction subjects ate a healthful balanced diet with at least 100 percent of the recommended daily intake of each nutrient, providing approximately 1,671 kilocalories per day."
"The average diet was 23 per cent protein, 49 per cent complex carbohydrates, and 28 per cent fat, including 6 per cent saturated fat," reported Fontana.
The limitations of the study are acknowledged by the authors: "Because our study was not randomised, our cross-sectional study design does not allow us to assign causation, although the observed significant differences on the basis of cross-sectional data are an important first step in elucidating the effects of long-term caloric restriction in humans."
The calorie-restricted diet resembled the Mediterranean diet, rich in olive oil, vegetables, whole grains, fish and fruit. Previous population-based studies showed that eating a Mediterranean diet could prolong lifespan, while other studies have reported the diet reduces heart disease risk factors.