"Eating less, if it is a high-quality diet, will improve your health, delay aging, and increase your chance of living a long, healthy and happy life," said Luigi Fontana, M.D., Ph.D., from the Washington University School of Medicine in St. Louis, Missouri and the Italian National Institute of Health in Rome, Italy. "This is the first paper to show that long-term calorie restriction with optimal nutrition has cardiac-specific effects that ameliorate the age-associated decline in diastolic function in humans. In other words, this is the first report ever to show that calorie restriction with optimal nutrition may delay primary aging in human beings."
A number of studies have shown that animals can live longer when they eat fewer calories, but human study has been difficult. The caloric restriction model requires a strict diet regimen, both to keep the total number of calories low and to insure that participants consume the right balance of nutrients.
Rather than try to randomize volunteers to different diets and then hope that they will stick to them for years, the researchers, including first author Timothy E. Meyer, Ph.D., compared 25 people who already had been following caloric restriction for an average of six years (consuming about 1,400 to 2,000 calories per day) with 25 similar control subjects who were eating typical Western diets (about 2,000 to 3,000 calories per day).
Hearts tend to stiffen and pump less effectively as people get older, but ultrasound examinations showed that the hearts of the people on caloric restriction appeared more elastic than those of the control subjects; that is, the hearts relaxed between beats in a way that is similar to the hearts of younger people. In addition, several heart disease risk factors and inflammatory markers--blood pressure, C-reactive protein, tumor necrosis factor-alpha (TNF-á), and transforming growth factor-beta1 (TGF-â1)--were lower in the caloric restriction group than in the Western diet group.
Dr. Fontana, who designed and led the study, emphasized that caloric restriction does not mean simply eating less.
"Calorie restriction is associated with longevity only when is coupled with optimal nutrition. On the other hand, calorie restriction coupled with malnutrition accelerates aging and causes severe diseases. Therefore, eating half a hamburger, half a bag of French fries and half a can of soft drink is not healthy caloric restriction and is harmful," he said. "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 plus or minus 294 kilocalories per day. The average diet was 23 percent protein, 49 percent complex carbohydrates, and 28 percent fat, including 6 percent saturated fat. Daily salt intake was lower in the caloric-restriction group compared to the Western diet group."
Dr. Fontana said that the diets of people on caloric restriction resemble the traditional Mediterranean diet, which is based on a wide variety of vegetables, olive oil, beans, whole grains, fish and fruit. The diet avoids refined and processed foods, soft drinks, desserts, free sugars, white bread and white pasta.
While many people could adopt some of these diet practices, Dr. Fontana cautioned that anyone attempting to follow a strict caloric-restriction diet should have expert guidance, because of the risk of malnourishment if the diet does not include the right amounts of key nutrients.
The authors noted that the study design had some limitations.
"Because our study was not randomized, 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," they wrote.
The lower levels of C-reactive protein and other inflammatory cytokines may indicate that caloric restriction helps to reduce damage from chronic inflammation in the body.
"It is well known that overweight and obese people have a low-grade chronic inflammatory state. This is due to the fact that hypertrophic fat cells chronically produce inflammatory molecules that are released in the blood stream. This means that body tissues in overweight and obese subjects are chronically exposed to inflammatory stimuli. It is our hypothesis that this chronic inflammation causes chronic tissue damage and associated adaptative fibrosis that leads to premature and accelerated tissue and organ hardening," Dr. Fontana said.
Gary Gerstenblith, M.D., F.A.C.C., from the Johns Hopkins Hospital in Baltimore, Md. wrote in an editorial in the journal that the study is the first to describe the effects of calorie restriction on a well-recognized marker of cardiovascular aging in humans. However, he pointed out that it is unlikely that many people would be able to successfully adopt such a strict diet.
"The value of the study is that it points to possible mechanisms explaining how aging occurs and, therefore, how it may be modified. The authors,and the disciplined volunteers following the practice of caloric restriction are to be congratulated for their important contributions to this effort," Dr. Gerstenblith wrote.
Daniel E. Forman, M.D., F.A.C.C., from the Boston Medical Center, who was not connected with this study, said that the researchers have presented exciting data showing benefits of caloric restriction.
"These data provide insight into the impact of diet on intrinsic myocardial function. Our normal Western diet likely induces inflammatory peptides that bring about changes in ventricular histology and function, including higher collagen content and associated tissue stiffening. Nutritionally balanced caloric restriction may constitute a key means to modify these detrimental patterns and mitigate age-related morbidity and mortality," Dr. Forman said.