It s widely acknowledged that calorie restriction at least in animals can prolong life. According to a recent report in the journal Cell Metabolism, it is thought that in animals this effect may be mediated by a reduction in protein consumption. Dr. Valter D. Longo at the University of Southern California, along with colleagues from several institutions, sought to determine if there is a similar relationship between protein intake and risk of cancer, heart disease, diabetes or overall mortality in humans.
The investigators used data from the National Health and Nutrition Examination Survey (NHANES) to ascertain the food and protein intakes of approximately 6,400 adults aged 50 and over. Participants in the NHANES surveys report a 24-hour dietary intake. They consumed, on average, 1800 calories per day. Of those, 51 percent came from carbohydrates, 33 percent from fat, and 18 percent from protein 11 percent was from animal protein. People who reported an intake of 20 percent or more from protein were assigned to a high protein group; a moderate protein group consumed 10-19 percent of calories from protein, and a low protein group ate less than 10 percent of calories from protein.
The participants were followed for up to 18 years, during which time there was 40 percent overall mortality, 19 percent from cardiovascular disease, 10 percent from cancer and about 1 percent from diabetes.
When the investigators divided the participants into two age-related groups, they found that those between 50 and 65 years of age had a significantly increased risk of all-cause mortality by 74 percent, and over a 4-fold increased risk of mortality from cancer. Consumption of animal protein seemed to play a large role in these effects on mortality.
In a somewhat paradoxical twist, however, these associations were not found for individuals over 65 years old. Indeed, these older people in the high protein group had a 28 percent reduction in all-cause mortality, and a 60 percent reduction in cancer mortality. They also found some evidence that a low protein diet in the oldest group was detrimental, and suggested that a higher proportion of protein might be beneficial for those individuals.
ACSH s Dr. Ruth Kava had this comment This is a complex study with suggestions for dietary changes that could be important for health. However, it was a cross-sectional study (only one point in time), and the authors noted that their sample sizes in some groups were small. Thus, it must be replicated by independent investigators before changing advice about protein intake should be contemplated.